Alternator overcharging AGM

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ss2016

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I recently bought a boat with a Volvo d6-400 with a 150amp alternator. I would like to use it with AGM batteries. 100AH for the starter, 100AH for the bow thruster & winch, and 3*100AH for the domestic bank. Volvo say the alternator outputs +- 14.4V though I measure this at 14.77 and after an Argodiode splitter 14.45V. AGM batteries require a typical float voltage of 13.8V at the upper end I understand.
Volvo say its policy is NOT to give out documentation regarding the alternator and admit it is not good for AGM batteries. Beyond that they are extremely unhelpful. The boat builder is at a loss as to how to wire things up for AGM and agrees Volvo are unhelpful. The alternator is internally regulated.
So my question is this, and I can not believe I am the first with this issue. Apart from buying a Balmar alternator and controler how can I practically use this alternator with AGM, without drastically shortening their life?
Some practical advice would be most welcome.

PS I presume the domestic bank would be relatively happy since when the engine is on there is a draw on the batteries, radio, chartplotter, autopilot and possibly a fridge. I have not checked the voltage when underway yet at the domestic bank. The starter and bow thruster battery will recharge very quickly though and be overcharging very soon. On shore power the charger is designed to recognise AGM.
 
I’m interested why you would want to change to AGM. More punch power per weight of battery, yes, but to what advantage considering the unconventional charging requirements.
Just a passing interest really and keen to learn.
 
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Two main reasons:
i) 'wet' batteries should only be discharged to about 70% so for a 100AH battery you have 30AH usable. For an AGM battery the figure is about 50% so 50AH usable.
Ii) their life is roughly twice as long, or more.
Iii) Fully charged they will happily sit for 3+ months without attention or significant discharge.
Iv) Higher starting current.
That's 4!
 
Farmer Piles, that's fine as long as you always remain tied to the dock, if intelligent it will switch to float, but what do you do when you leave the dock for a few days?
 
Our boat has agm batteries and they are charged by the alternator on a standard Mercury outboard.

I wonder if there is some setting on the motor that you change to set them to agm or other types.
 
tbh, having read all the shock horror web stories I find myself with 5 years on the same AGM house batteries and they still seem absolutely fine despite my desire to replace them with LiFePO4. That may be because although I dont use shore power the batteries are tendered to via solar panels and a good MPPT controller. Either way my personal experience is "no worries" and yes the internet still screams Boob! at me. C'est la vie
 
I have charged AGM’s via a standard van type alternator for many years with no issues. The last pair lasted 9 years. I do use a victron multiplus charger when plugged into shoreline.
 
I have just changed back to standard wet acid batteries from AGMs.
I set my Mastervolt charger to the AGM setting 0 no setting for the alternators so I left them alone.
Yes, I think the AGMs did last a little longer than the flooded cell ones but not an appreciable difference.
When I came to replace them this year, AGMs were nearly twice the price so I switched back to flooded cells (and set the switch on the charger back as well).

So, was it that I wasn't able to set the alternators - I don't know.
I am now considering batteries as consumables and changing them every 2 or 3 years.
This time, I was able to get some Varta J2s at a good price so I will probably be using them from now on.
 
I believe AGM's require a higher charging voltage? In any case could you not use a high power single phase rectifier diode to drop 0.7v? 150A ones are available and not expensive around £20. Available on Amazon, EBay etc.

Your choice but I'm no AGM fan, they don't handle under or over charging abuse and not able to dissipate plate heating effects as good as SLA if using high wattage inverters. I don't agree with the statement that flooded batteries should only be discharged to 70%. Who wrote that?
I'd sooner put extra money into higher quality Enhanced Flooded (EFB) batteries with low internal resistance and plenty of lead in them.
Battery FAQ
 
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ss2016 said:
Two main reasons:
i) 'wet' batteries should only be discharged to about 70% so for a 100AH battery you have 30AH usable. For an AGM battery the figure is about 50% so 50AH usable.
Ii) their life is roughly twice as long, or more.
Iii) Fully charged they will happily sit for 3+ months without attention or significant discharge.
Iv) Higher starting current.
That's 4!
Click to expand...

for all those reasons I have changed to gel batt's,
6y ago in the Karnic, battery's ran flat a few times, but are still ok to use !
1 y ago in the Canados, looking good so far
over the years we have very good expereince with Gel (Victron) , in the Mobile Broadcast Vans that we build in my business
 
Julians, as I said at the beginning "Volvo say its policy is NOT to give out documentation regarding the alternator and admit [in fact state] it is not good for AGM batteries." The reason is the output is too high for AGM float.

Limecc, if you look at Exide's DOD curves for their own batteries they claim AGM will last at least twice as long for the same DOD. There are many papers supporting that. I think the issue with them is overcharging at float. What I do not understand is how abrupt this issue is. In a year I have had the engine on for 93 hours. the longest single occasion being 10hours. Some of this time the battery is being charged the rest it would be being overcharged. What I wonder is how much overcharging is significant to the life of AGM? Wet batteries just blow off gas.
Your idea to use a diode to drop the voltage when on float is a nice theoretical one but AGM neeeds a high voltage to get up to 100%
The point about 50%AGM and 70%'wet' is everywhere if you google it. It is not a hard and fast number but it is around the point where the cycle life begins to drop dramatically. Look at Exide's curves. Here is one reference. AGM vs Lead Acid Batteries: 12 Differences + 9 FAQs

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.

What I am left wondering about is what I said above. "What I wonder is how much overcharging is significant to the life of AGM?"
 
I understand AGM's have been overhyped, oversold and consistently underdeliver. At any rate from what I've been reading they are being superseded by the EFB technology already mentioned. Major car manufacturers are onboard. Here's what I thought a good article that explains things well:
http://www.aandncaravanservices.co.uk/battery-technology.php

"Together 'Dry Out' and Corrosion accounted for the premature destruction of 92% of all AGM/Gel batteries.

That is 92% of ALL AGM/Gel batteries never reached their claimed cycle life because of premature failure from corrosion or loss of fluid"
 
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Limecc, I meant to say in my previous post I know nothing of EFB. Thanks for the idea which I will research. Steve.
 
ss2016 said:
Julians, as I said at the beginning "Volvo say its policy is NOT to give out documentation regarding the alternator and admit [in fact state] it is not good for AGM batteries." The reason is the output is too high for AGM float.

Limecc, if you look at Exide's DOD curves for their own batteries they claim AGM will last at least twice as long for the same DOD. There are many papers supporting that. I think the issue with them is overcharging at float. What I do not understand is how abrupt this issue is. In a year I have had the engine on for 93 hours. the longest single occasion being 10hours. Some of this time the battery is being charged the rest it would be being overcharged. What I wonder is how much overcharging is significant to the life of AGM? Wet batteries just blow off gas.
Your idea to use a diode to drop the voltage when on float is a nice theoretical one but AGM neeeds a high voltage to get up to 100%
The point about 50%AGM and 70%'wet' is everywhere if you google it. It is not a hard and fast number but it is around the point where the cycle life begins to drop dramatically. Look at Exide's curves. Here is one reference. AGM vs Lead Acid Batteries: 12 Differences + 9 FAQs

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.

What I am left wondering about is what I said above. "What I wonder is how much overcharging is significant to the life of AGM?"
Click to expand...
IIRC, my Mastervolt charger has a DIP Switch setting for AGM/Gels so I think you would have the same alternator issue with Gels.
 
It won't change anything for the starter battery. It will still be the alternator regulator that is in control. The sterling gadget just senses the voltage on the starter battery to keep it above 13v.
 
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.}
 
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