Alternator overcharging AGM

[IanCC]

I think there are 11 different options for battery type. So i don't think there are any problems with it. You can't choose them fir the starter battery, you are reliant on the alternator regulator.

 

[[70521]]

Hope you don't mind me posting as I am a raggy, but with a very similar battery bank with AGMs. 70 AH starter, 390 AH domestic and 100 AH winch. The engine is smaller at 18 HP and the alternator is rated at 100 Amps. My shore power is set to AGM.

During the summer of 2021 I had to motor for 48 hours on passage from Plymouth to Ramsgate with no problem whatsoever. I also had a number of other long passages either motoring or motor sailing. When motoring my instrumentation is showing 14.4 V and anything between 40 and 2 amps of power being delivered to the battery bank.

So far I'm delighted with the AGMs

 

[Scarron]

ScarronI/IanCC, can the Sterling thingy hold a voltage down so it does not overcharge when on float? And can it sense when to go to float?
(I don't understand why there is not plenty of equipment to do this. Both shore power chargers and solar PV take a higher voltage and make it palatable for charging/floating battery banks.}

If you have a look at the instructions on Sterling’s website it says you can change between 9 different charging profiles ( including 2 different AGM options). And yes they do float charge.

I haven’t used one but it looks useful for a twin engined boat because you can combine the outputs of both alternators to 4 stage charge the house batteries whilst trickle charging the starting battery.

 

[ss2016]

Scarron, thanks for your input. I called Sterling today and as I thought it can up the voltage but not drop it they say by more than .5V, and that is not enough. The problem stems from Volvo, their high o/p and no external regulation.
Sandy, your input is interesting. From what you are saying you must be overcharging AGM batteries. But the question no one I have spoken to touches is how much overcharging causes damage. I have done about 100 hours this season. For some of that time the batteries would have been taking needed charge. So perhaps 80 hours over charged. Is 80 hours in a year significant to AGM ....or not?

 

[IanCC]

I think i might be tempted to have another word with sterling. When i talked to them they said that starter battery was held at 13v. So presumably not being charged above that by their gadget which might get around your problem. It isn't sophisticated charging for the start battery but i don't think it needs it. The small solar panel does the float. Least ways this is how i plan to do it. It seems to me the thing to do is talk to the battery manufacturers. There are AGMs and AGMs. My reading around the subject, particularly nigel calder, suggests that one of the principal causes of agm failure is not charging back to 100% often enough. When you read the fine print of some agm batteries they say needs to be back to 100% every day. I see me going red flash starter agm and lead acid domestic at present with sterling gadget.

 

[BartW]

BartW , your change to Gels is interesting. I have often wondered why the marine industry has never gone that way but never looked into it.

neither have I,
in UK there appears to be an adoration of AGM batt's, that I don't experience here in Benelux
Gel has a longer service life compared to AGM, (data from Victron)
and price is similar or less (for the Gell's)

 

[Scarron]

I called Sterling today and as I thought it can up the voltage but not drop it they say by more than .5V, and that is not enough. The problem stems from Volvo, their high o/p and no external regulation.

If you haven't yet bought your AGM batteries then you should consider a different technology that will accept the higher charge voltage put out by the Volvo alternator.

I use Calcium sealed lead acid batteries which charge at a higher voltage and require no maintenance. I have been using the Numax CXV range for a while Numax Leisure Batteries - Leisure Batteries The first pair I fitted lasted 10 years and I replaced like for like a couple of years ago. Last year I fitted four in another boat and plan to add another couple soon to increase my domestic bank capacity.

I think they are a really good price per AH and give acceptable performance, change them every 5 years - its quite easy to spend too much on marvellous new battery technologies,

Lithium being a case in point, the potential weight saving is irrelevant in a Mobo, I reckon my battery bank is around 0.5% of the overall boat mass and if I want more capacity then I'll just chuck a couple more in the bank.