agm batteries

[Pops]

I need to replace my house and starting batteries, one group 24, one 27 (old batteries, taking a trip). Every thing that I read shifts me closer to agm batteries. The one concern that I have, and am not finding much info on is alternator requirements. My H27 has a 1GM10 yanmar diesel (I am assuming the alternator is stock). People say that because agm batteries will accept huge amounts of charge quickly they can severely overheat and destroy the alternator as it tries to feed this intense hunger for ions. What they don't make clear is what type of bank they are charging. They don't say if it one house battery or a 10 battery rack in a trawler engine room. Can anyone help me out with this.

 

[Ed Schenck]

My gel cell batteries were eight years old when I switched to AGMs. And for the same reason, a long trip. Maintenance free is great. I never heard that about AGMs though. I have a smart 3-stage regulator so have not really had to worry about the alternator. But a Google finds a blog discussing your point. They are writing about a 400 amp-hour bank though. Needs more investigating I think.

 

[Steve Dion]

I would assume that you have a 35 amp alternator on your 1GM engine. I had the same setup on my H'31 which had 2 G-31 (110 amp) Gels and there was never an issue with the alternator.

The AGM batteries are a lot more foregiving than the Gels and I don't think you would have an issue with having 2 batteries in your house bank with that alternator.

 

[Don S/V ILLusion]

People say that because agm batteries will accept huge amounts of charge quickly they can severely overheat and destroy the alternator as it tries to feed this intense hunger for ions. .

Half correct. AGMs can accept a higher rate of charge but that's the end of the story. Batteries don't "draw" power from a charging source. The charging source "pushes" current into the batteries. You alt will only produce whatever it's capacity is regardless of the load as nothing sucks current from it so the alt would never overheat as a result of feeding any battery.

A collateral issue is that the cost of AGMs is usually valued in it/their ability to accept a higher charge rate from a larger alternator so if your alt is small, that somewhat defeats the purpose in using AGMs unless you are only interested in the no maintenance aspect. Give everything on a boat requiring maintenance, this one shouldn't be that onerous.

 

[Bill Roosa]

AGM/GEL/wet cell charging voltages

Didn't I read somewhere that AGM and Gel have different charging voltages than wet cell batteries? That would requrie a reset of the regulator to keep form over/undercharging them.

 

[Pops]

Re: AGM/GEL/wet cell charging voltages

"A collateral issue is that the cost of AGMs is usually valued in it/their ability to accept a higher charge rate from a larger alternator so if your alt is small, that somewhat defeats the purpose in using AGMs unless you are only interested in the no maintenance aspect. Give everything on a boat requiring maintenance, this one shouldn't be that onerous." Good point Don.

 

[Pops]

Re: AGM/GEL/wet cell charging voltages

End of story. Bought 2 really nice lead/acid batteries. Thanks Guys.