Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

+x

 

Sandy.Garrity - 1/8/2020

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

Hi Sandy,

I have a lot of experience with AGM batteries and to look after them properly you really need a decent sized hot rated alternator AND a 3 stage SMART regulator.
Your standard automotive alternator will not look after the batteries properly and motoring for long periods will kill the batteries, by keeping them at 14.4V for ever.
A 3-stage SMART regulator begins (1st stage) by sending maximum voltage to the alternator field which makes the alternator produce maximum current until the voltage reaches the absorption voltage (2nd stage), the regulator then holds the voltage at the absorption level and the current slowly drops as the batteries accept the charge. When the current reaches a predetermined level, or a set time, the regulator switches to float voltage (3rd stage) and maintains this until the regulator is switched off.
If you intend to use a standard automotive alternator then you must take out the inbuilt regulator and connect the field wires to a SMART 3 stage regulator.
The only issue with this, and it is an issue, is that AGM batteries have a high charge acceptance rate and the regulator will drive the alternator to full output until it reaches the absorption voltage (~14.6V). If the batteries are quite discharged this could take some time, and during this time the alternator will get very hot and eventually burn out. Therefore you need a hot rated or KKK alternator .
This is all in Calders book.
If you intend to spend a lot of money on good batteries you need to care for them or they will not last very long at all.
Cheers
Alan
S.V.Elyse

+x

 

Alan Leslie - 2/3/2020

+x

 

Sandy.Garrity - 1/8/2020

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

Hi Sandy,

I have a lot of experience with AGM batteries and to look after them properly you really need a decent sized hot rated alternator AND a 3 stage SMART regulator.
Your standard automotive alternator will not look after the batteries properly and motoring for long periods will kill the batteries, by keeping them at 14.4V for ever.
A 3-stage SMART regulator begins (1st stage) by sending maximum voltage to the alternator field which makes the alternator produce maximum current until the voltage reaches the absorption voltage (2nd stage), the regulator then holds the voltage at the absorption level and the current slowly drops as the batteries accept the charge. When the current reaches a predetermined level, or a set time, the regulator switches to float voltage (3rd stage) and maintains this until the regulator is switched off.
If you intend to use a standard automotive alternator then you must take out the inbuilt regulator and connect the field wires to a SMART 3 stage regulator.
The only issue with this, and it is an issue, is that AGM batteries have a high charge acceptance rate and the regulator will drive the alternator to full output until it reaches the absorption voltage (~14.6V). If the batteries are quite discharged this could take some time, and during this time the alternator will get very hot and eventually burn out. Therefore you need a hot rated or KKK alternator .
This is all in Calders book.
If you intend to spend a lot of money on good batteries you need to care for them or they will not last very long at all.
Cheers
Alan
S.V.Elyse

Hello Alan 

Thanks for the posting.

OK, there are a number of things I need to understand from it:

1. what is a decent sized hot rated alternator, it is not a term I've ever come across;
   
   
2. How long would you describe "motoring for long periods" is?

I consider my primary charging device is the Watt and Sea hydrogenerator,that has a three stage charging programme, and given your comments wonder is the alternator output should be routed through that?  I do not plan for motoring for long periods of time, perhaps 12 hours maximum after I have a sailing vessel not a motor vessel. 

Regards

Sandy

+x

 

Sandy.Garrity - 2/3/2020

+x

 

Alan Leslie - 2/3/2020

+x

 

Sandy.Garrity - 1/8/2020

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

Hi Sandy,

I have a lot of experience with AGM batteries and to look after them properly you really need a decent sized hot rated alternator AND a 3 stage SMART regulator.
Your standard automotive alternator will not look after the batteries properly and motoring for long periods will kill the batteries, by keeping them at 14.4V for ever.
A 3-stage SMART regulator begins (1st stage) by sending maximum voltage to the alternator field which makes the alternator produce maximum current until the voltage reaches the absorption voltage (2nd stage), the regulator then holds the voltage at the absorption level and the current slowly drops as the batteries accept the charge. When the current reaches a predetermined level, or a set time, the regulator switches to float voltage (3rd stage) and maintains this until the regulator is switched off.
If you intend to use a standard automotive alternator then you must take out the inbuilt regulator and connect the field wires to a SMART 3 stage regulator.
The only issue with this, and it is an issue, is that AGM batteries have a high charge acceptance rate and the regulator will drive the alternator to full output until it reaches the absorption voltage (~14.6V). If the batteries are quite discharged this could take some time, and during this time the alternator will get very hot and eventually burn out. Therefore you need a hot rated or KKK alternator .
This is all in Calders book.
If you intend to spend a lot of money on good batteries you need to care for them or they will not last very long at all.
Cheers
Alan
S.V.Elyse

Hello Alan 

Thanks for the posting.

OK, there are a number of things I need to understand from it:

1. what is a decent sized hot rated alternator, it is not a term I've ever come across;
   
   
2. How long would you describe "motoring for long periods" is?

I consider my primary charging device is the Watt and Sea hydrogenerator,that has a three stage charging programme, and given your comments wonder is the alternator output should be routed through that?  I do not plan for motoring for long periods of time, perhaps 12 hours maximum after I have a sailing vessel not a motor vessel. 

Regards

Sandy

Hi Alan & Sandy,
Alan, well put and agree completely.
Sandy: Properly set up, you can motor forever with no fear of harming the battery bank.
The size of the alternator is dependent on many factors: what the engine can tolerate, battery bank size & type, room for large frame vs small frame, etc.
Alternator output should not be routed through the W&S. I suspect you were actually wondering if the regulator for the W&S could be used for the alternator and I very much suspect the answer is “no”. The alternator/engine/regulator charging system should stand alone.
Your questions are all good, but they are also so fundamental, that I believe you would be best served by hiring a consultant or finding an experienced cruiser who knows his/her charging systems and can walk you through what you have and what you want to change. I also suggest spending time reading and re-reading the relevant chapters in Calder.
Let us know how you get along.
My best, Dick Stevenson, s/v Alchemy

+x

 

Sandy.Garrity - 2/3/2020

+x

 

Alan Leslie - 2/3/2020

+x

 

Sandy.Garrity - 1/8/2020

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

Hi Sandy,

I have a lot of experience with AGM batteries and to look after them properly you really need a decent sized hot rated alternator AND a 3 stage SMART regulator.
Your standard automotive alternator will not look after the batteries properly and motoring for long periods will kill the batteries, by keeping them at 14.4V for ever.
A 3-stage SMART regulator begins (1st stage) by sending maximum voltage to the alternator field which makes the alternator produce maximum current until the voltage reaches the absorption voltage (2nd stage), the regulator then holds the voltage at the absorption level and the current slowly drops as the batteries accept the charge. When the current reaches a predetermined level, or a set time, the regulator switches to float voltage (3rd stage) and maintains this until the regulator is switched off.
If you intend to use a standard automotive alternator then you must take out the inbuilt regulator and connect the field wires to a SMART 3 stage regulator.
The only issue with this, and it is an issue, is that AGM batteries have a high charge acceptance rate and the regulator will drive the alternator to full output until it reaches the absorption voltage (~14.6V). If the batteries are quite discharged this could take some time, and during this time the alternator will get very hot and eventually burn out. Therefore you need a hot rated or KKK alternator .
This is all in Calders book.
If you intend to spend a lot of money on good batteries you need to care for them or they will not last very long at all.
Cheers
Alan
S.V.Elyse

Hello Alan 

Thanks for the posting.

OK, there are a number of things I need to understand from it:

1. what is a decent sized hot rated alternator, it is not a term I've ever come across;
   
   
2. How long would you describe "motoring for long periods" is?

I consider my primary charging device is the Watt and Sea hydrogenerator,that has a three stage charging programme, and given your comments wonder is the alternator output should be routed through that?  I do not plan for motoring for long periods of time, perhaps 12 hours maximum after I have a sailing vessel not a motor vessel. 

Regards

Sandy

Hello Sandy

Hot rated alternators are rated to put out their rated current continuously even when hot. They are also known as KKK alternators.
For example :
http://www.balmar.net/alternators/

Motoring for long periods in my opinion is more than 6 hours. If you motor like this regularly with an automotive alternator and its internal regulator you will considerably shorten the life of your deep cycle batteries.

I agree with Dick re the Watt and Sea regulator. The rule is that every charging source should have its own regulator.
I also agree with Dick that the best you can do is to
1. Study Calder diligently
2. Find an experienced cruiser with a proper charging system and have him/her walk you through it.
I would happily do it, but I am in Australia and Elyse is in New Zealand.

Good luck

Alan
S.V. Elyse

+x

 

Alan Leslie - 2/4/2020

+x

 

Sandy.Garrity - 2/3/2020

+x

 

Alan Leslie - 2/3/2020

+x

 

Sandy.Garrity - 1/8/2020

+x

 

Dick - 1/6/2020

+x

 

Sandy.Garrity - 1/5/2020

+x

 

Dick - 1/5/2020

+x

 

Sandy.Garrity - 1/5/2020

Hello 

I am in the planning stage of rewiring the boat and have decided to move from lead acid batteries to AGM.  On reading around the subject I understand that they should be charged at between 14.6 and 14.8 volts. The place I use for my alternators are not experienced in AGM batteries and the battery supplier just sells them.
Does anybody have any practical experience of charging AGMs with an alternator?  If so what voltage are you using.

Thanks

Sandy

Hi Sandy,
It may be a more complex change than you anticipate: I hope not. In any case, AGMs will likely be a far more efficient and effective battery for any boat that is off the grid with some degree of regularity. To start, the voltage level you stated is for a specific battery temperature and batteries vary widely in temperature and the optimal voltage level also changes with temperature making a battery voltage goal a moving target. (AGMs and Gels are prone to damage if charging voltage is not well-managed.)
A few considerations:
Rewiring is probable wise when shifting to AGMs.
The simple answer is that an alternator can easily charge AGMs if it uses an external regulator of the “smart” variety that allows charging profiles to fit the AGMs requirements.
AGMs are not all built alike, so check the manufacturer’s recommendations for charging profiles and match it to the regulator.
AGMs accept a much higher amperage and many alternators are not up to the task and will burn out. Similarly, ensure that cabling is able to handle the increased amperage and that your OCP (over current protection) is designed to up to date standards. Then there is a review to ensure the belt(s) powering the alternator are up the task of the increased load on the alternator and that the loads do not ask too much of the PTO (power take off) of your propulsion engine. I consider the propulsion engine “mission critical” so I shy away from asking too much of its ancillary duties for worry of compromising its main function.
For many, the upgrade you are considering leads to a complete upgrade of the whole charging system of the boat.
Much of the above can be mitigated by a good regulator. Balmar (among other manufacturers) makes one where amperage can be limited and where the regulator can monitor battery temperature as well as alternator temperature; both are wise safety options. But to get the most out of your AGMs, it is better to have the whole charging system upgraded.
Having good consult is important and you say there is none where you are. This is a complicated area where significant damage to components and/or fire might occur inadvertently. By far the best series of articles on the care and feeding of AGMs is on the Attainable Adventure Cruising web site (https://www.morganscloud.com/). Visiting this site will entail a ~~$20 fee, but any sailor will benefit far beyond the $20 very quickly.
Another alternative is to find a professional marine electrical engineer (in the US I would insist on ABYC certification) and ask him/her to consult from a distance and possible pay for a visit at the end to “sign off” on the changes or take the boat to him/her early the next season.
I am sure I missed important elements: please feel free to come back with questions/comments/thoughts.
My best, Dick Stevenson, s/v Alchemy

Hello Dick 

Thanks for the posting, thankfully I have a friend who is a university lecturer in electrical engineering who I can talk this over with. As yet I've not found anybody who really knows the answer.   My primary consideration is if I was to motor for a long period of time that this would cause damage to the batteries.   Later in 2020 I am fitting a Watt and Sea for my long distance power requirements. 

Cheers
Sandy

Hi Sandy,
Where is your boat located?
Electrical systems on a boat follow all the same laws that they do on land, but many a well-educated electrical engineer can make significant errors if he/she is not well versed in unique marine considerations.
Motoring for long periods is perfectly acceptable if the regulator adjusts the float voltage to the correct level for battery chemistry (in this case the manufacturer’s recommended float voltage for their AGMs) matched to the temperature of the battery. The regulator has to be a “smart” or “multi-stage” regulator that is programable and will set the charging profile for AGMs where the voltage will vary according to whether it is delivering “bulk”, “absorption” or “float” levels of charge.
In fact, AGMs are recommended to be fully charged with regularity (every couple of weeks if I remember correctly) as opposed to other batteries (flooded and gels) where regular full charging is not really an issue. This is a concern for those who spend longer periods at anchor and away from shore power and who tend to not motor long distances.
You really can get this area seriously and dangerously wrong if this vessel charging system is not well understood. I do not have my library at hand (others readers please help), but I suspect one excellent source might be Nigel Calder’s “Boat Owners Mechanical and Electric Manual”.
I would read his chapters closely, as well as his excellent wiring recommendations as I know you are in the process of re-wiring as well.
My best, Dick Stevenson, s/v Alchemy

Hello Dick

Thanks for the reply.  I an currently based in Plymouth, UK.

Caldwell is a fantastic book and really useful when addressing specific questions.

So far, it nor anybody else can answer the question, but further research indicated that AGM require a "float" charge delivered at 13.8 volts so any good alternator should be able to deliver that.  My primary power generation source on long trips will be the Watt and Sea and I can programme their converter to any charging regime I want.  The big worry was that I needed to motor for more than 12 hours and end up damaging the batteries.  Looking at the float charge that does not appear to be an issue. 

I'll keep everybody updated with the system once I've built it and start using it.

Cheers

Sandy

Hi Sandy,

I have a lot of experience with AGM batteries and to look after them properly you really need a decent sized hot rated alternator AND a 3 stage SMART regulator.
Your standard automotive alternator will not look after the batteries properly and motoring for long periods will kill the batteries, by keeping them at 14.4V for ever.
A 3-stage SMART regulator begins (1st stage) by sending maximum voltage to the alternator field which makes the alternator produce maximum current until the voltage reaches the absorption voltage (2nd stage), the regulator then holds the voltage at the absorption level and the current slowly drops as the batteries accept the charge. When the current reaches a predetermined level, or a set time, the regulator switches to float voltage (3rd stage) and maintains this until the regulator is switched off.
If you intend to use a standard automotive alternator then you must take out the inbuilt regulator and connect the field wires to a SMART 3 stage regulator.
The only issue with this, and it is an issue, is that AGM batteries have a high charge acceptance rate and the regulator will drive the alternator to full output until it reaches the absorption voltage (~14.6V). If the batteries are quite discharged this could take some time, and during this time the alternator will get very hot and eventually burn out. Therefore you need a hot rated or KKK alternator .
This is all in Calders book.
If you intend to spend a lot of money on good batteries you need to care for them or they will not last very long at all.
Cheers
Alan
S.V.Elyse

Hello Alan 

Thanks for the posting.

OK, there are a number of things I need to understand from it:

1. what is a decent sized hot rated alternator, it is not a term I've ever come across;
   
   
2. How long would you describe "motoring for long periods" is?

I consider my primary charging device is the Watt and Sea hydrogenerator,that has a three stage charging programme, and given your comments wonder is the alternator output should be routed through that?  I do not plan for motoring for long periods of time, perhaps 12 hours maximum after I have a sailing vessel not a motor vessel. 

Regards

Sandy

Hello Sandy

Hot rated alternators are rated to put out their rated current continuously even when hot. They are also known as KKK alternators.
For example :
http://www.balmar.net/alternators/

Motoring for long periods in my opinion is more than 6 hours. If you motor like this regularly with an automotive alternator and its internal regulator you will considerably shorten the life of your deep cycle batteries.

I agree with Dick re the Watt and Sea regulator. The rule is that every charging source should have its own regulator.
I also agree with Dick that the best you can do is to
1. Study Calder diligently
2. Find an experienced cruiser with a proper charging system and have him/her walk you through it.
I would happily do it, but I am in Australia and Elyse is in New Zealand.

Good luck

Alan
S.V. Elyse

Hello Alan

Thanks for the reply.  The more I study this the more confusing it gets and have come to the conclusion that there is no right answer. 
Modern motor vehicles use AGM all the time and don't appear to suffer.  My engine hours last year were 20, so I don't see this as being a major issue.  I see the engine as an auxiliary to the sails and it is usually used for getting in and our of harbour.

Regards
Sandy