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m4rsu asked

Hydrogenerator damaged AGM?

Hi,

we have a hydrogenerator at the boat (12V system) which is charging 4x 100 Ah Victron Super Cycle AGMs.

Unfortunately the batteries (one year old) are now down in their capacity, one significantly more than the other three. Was tested by an electrican with CCA battery test.

This seemed to happen out of nothing from one day to another. Before that we had the hydrogen running for five days continuously.

I now discovered that the charger of it only has a lithium charging algorithm and charges with 14,4 Volts all the time. Without any absorption or float state.

Could this had damaged the batteries that badly?

Best regards, looking forward to your responses

battery chargingAGM Battery
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4 Answers
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pwfarnell answered ·

You will have overcharged your batteries and damaged them, AGM batteries are sensitive to overcharging. They have very little fluid in the battery and continuous overcharging can dry them out as the water is vented as gas. In a bank of AGMs such as these if you overcharge them by not dropping to float when they are full they start to overheat which also causes damage. But this does.not happen uniformly, one battery will get slightly hotter and the hotter battery reduces it resistance so it takes more of the charging current and gets hotter still and more damaged than the others. I have seen AGM battery banks that are full but left.on absorption charge at 14.5V getting warmer and the current increasing despite them being full. Once they are close to full they must be dropped to float.

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Alexandra avatar image Alexandra ♦ commented ·
Yes, aka excessive bulk charging.
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m4rsu avatar image
m4rsu answered ·

Thank you very much, that really helps. Interesting is the statement of the manufacturer, they can’t believe that their product would damage any batteries and still claim that their only available lithium algorithm is good for lithium, agm and flooded batteries.

A little bit off topic now: I have to set the absorption time (at least it has absorption and float time…) for the solar charger manually. I set it to 3 hours. It also gets the temperature of the batteries and should drop the voltage before overheating. Is this a safe setting or better use one of smart solar chargers with automatic absorption time but without temperature sensor?

We’re sailing in the Mediterranean, so temperature is a big thing.

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pwfarnell avatar image pwfarnell commented ·

Temperature compensation is good to have. Absorption time is always hard to quantify with solar as the time required can vary depending on the power produced. 3 hours is probably a good compromise. I have a Victron Smartshunt, smart solar and Cerbo GX so I use DVCC to share the charge current from the shunt to the solar and use tail current to end charge which is much better than fixed or adaptive absorption.

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JohnC avatar image
JohnC answered ·

@M4RSU

4x low resistance batteries in parallel, Hmm.. Similar has been reported before, and in these threads I had a bit to say, against some resistance. See it as you will, but ignore it at your peril.

https://community.victronenergy.com/questions/173977/victron-super-cycle-agm-sizzle-and-smoke.html?childToView=273162#answer-273162

https://community.victronenergy.com/questions/95629/agm-super-cycle-overheating-problem.html?childToView=273133#answer-273133

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m4rsu avatar image m4rsu commented ·

Thanks for the links. I read the threads…

I ordered some temperature sensors to monitor all of the four batteries.

We will see what the future brings

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m4rsu avatar image
m4rsu answered ·

After reading about the quite sensitive behaviour of this AGMs, what do you guys think about charging with a standard alternator of an old Volvo Penta Diesel? It charges the batteries directly with 14.2 V. Same thing as with the hydrogen but slower?

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kevgermany avatar image kevgermany ♦♦ commented ·
Yes
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