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aj54552 asked

IP65 12V/25A charger - rising current in float

Hello, I have the Blue Smart IP65 12V / 25A charger which I use to charge my boat's batteries. I have 2 x 100Ah AGMs as house batteries and 1 x 62Ah AGM starter battery, connected via relay when charging.

Charging proceeds normally in absorption phase (High mode, around 14,8V with temp compensation), current decreases until it switches to float. In float, voltage is 14,0V and still about 2 amps going in, seems normal. However current rises steadily in float phase. I disconnected the charger when I noticed after a couple of hours float that current had risen to about 17 amps and house batteries were getting warm. Float voltage was still 14,0V.

Could this be a problem in the charger? Or is it definitely caused by damaged batteries? The batteries still work OK, and charging seems normal until beginning of float phase so that's a bit confusing.

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pwfarnell answered ·

14.0V appears to be too high for AGM float, reduce your float voltage, you are forcing current through and you are ending up with resistive heating. As the batteries warm up, the resistance reduces and the current increases. 14.8V also looks to be too high for absorption, you are pushing your batteries hard. When my 700Ah of AGM go to float at 13.6V the current is 1.4A, equivalent to 0.4A for 200Ah. As to are your batteries damaged, Hard to tell, reduce your voltages and see how they perform. If float current and temperature still increase then timebfor new ones.

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aj54552 avatar image aj54552 commented ·
Thank you for the input. I will try by tweaking the voltages. I'm still not totally convinced that too high voltage is the main culprit, battery manufacturer recommends 14.8V for absorption, 13.8V for float. Also the problems can be seen only during the lower float voltage, 14.8V absorption performs as expected without heating and with decreasing current. I would expect a smart charger like this could detect that something's wrong when float current increases that much and stop the charging or something.. Anyway, I'll try as suggested and see what happens!
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kevgermany avatar image kevgermany ♦♦ aj54552 commented ·
If you apply loads to the batteries during float the current will and should rise.

The system has no way of detecting what the cause of a current increase is. It also has no way of knowing if you have set the charging parameters correctly.

A charger like this works solely on the battery voltage, maintaining the set voltage. If the battery is drawing an excessive current at float voltage, good chance it's damaged.

In general AGM absorption is 14.4V

Float 13.6/7V.


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aj54552 avatar image aj54552 kevgermany ♦♦ commented ·
Thanks, understood, of course it doesn't know why more current goes through. The problem has to be in the batteries it seems. That is still strange for two reasons; battery manufacturer recommends these higher voltages which I have used, and the current doesn't increase yet in the higher absorption voltage, only in float. Anyway, I'll continue with the lower volts as suggested and see what happens. Thank you!
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pwfarnell avatar image pwfarnell aj54552 commented ·
During absorption the batteries are not full so the energy is converted into chemical reaction recharging the batteries. Once they are full the energy can no longer go into chemical reaction so it ends up as heat. If you left the battery on absorption after it was full then you would see this effect of warm up and current would increase.
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