Full charging of AGMs

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oldbilbo asked Mar 20, '19

Full charging of AGMs

Hello. I'm asked to use this facility by posting a q.

In a complete 'lecky refit on a 40 y.o. modest sailboat, I'm fitting 3 groups of AGM batteries - start, port domestics, and s'board domestics. These can be linked. All Optima BlueTops, with a RedTop for starting. The new Beta 14 engine has a 75A 'nominal' alternator with fixed, internally-regulated output voltage. This is nominally 14.4V and the AGMs need 14.7V for full recharge.

I've fitted a Victron ArgoFET 100/3, believing that will do the charging biz. for each battery group... but only so far. I plan to fit some PV panels, for use in 'topping up' when the boat is unattended, and I understand I should fit PV controllers which can/will provide the additional higher Float voltage.

Is this right, and what controller(s) should I fit for this purpose?

AGM Battery

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Answer 1 · 2019-03-20T04:11:54Z

John Rushworth answered · Mar 20, 2019 at 04:11 AM

You can try the calculator here https://www.victronenergy.com/solar-charge-controllers You can enter non Victron panels too and also download the VictronConnect app from your App Store. It has a demo mode you can experiment with and alter battery settings. I’ve no experience of the Argo FET.

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oldbilbo commented · Mar 25, 2019 at 08:09 AM

I note from a 'Related Question' that the Victron MPPT manual suggests use of preset 3 for spiral-wound AGM batteries - which, being Optima, mine are - to produce a required nominal voltage of 14.7V ( 29.4/2 ), unmodified for 'temperate' temperatures.

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Answer 2 · 2021-04-10T18:16:45Z

Fra answered · Apr 10, 2021 at 06:16 PM

It is not true thath an agm battery need 14.7 v to be charged. It charged completly also with 14.4v or 14.2 or 13.8v...depend on time of charging.

If is possiblle , it is always better to prefer the lowest voltage and the largest time, to avoid tomuch gassification...

14.7 or more is good only to fast charging after a deep cycle of discharging.

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neoneddy commented · Apr 15, 2021 at 02:01 PM

The only way I know to test that idea is to do a capacity test. I'm running into this very thing and I'm finding mine are not at the capacity I thought they would be. Now I'm having to try and recondition them. I do agree depth of discharge can inform your method of charging, but I can't see 13.8 being too useful unless it's 100 degrees F out.

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