Author Topic: New AGM Batteries not charging  (Read 239 times)

Hooligan

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New AGM Batteries not charging
« on: July 22, 2018, 10:25:07 AM »
 I have 3 new AGM batteries. 300 amp hours.  I have been using them for 4 months I am tied up to a slip and have them charging on shore power. 20 amp charger. They are going from 12.5 to 12.2 volts, mostly 12.2. In a matter minutes.  the only load is the fridge. approx. 5 amp.  This has been going on for three days. Does this sound normal? shouldn't they go up to 12.8? over night?

DeanA

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Re: New AGM Batteries not charging
« Reply #1 on: July 25, 2018, 12:26:20 AM »
Here's what comes to my mind but - hopefully some smarter folks then me out there will chime in.

Yes, should go to 12.8v but also frig is taking some of that power too so charging will be slower than without frig. Maybe put a DVM in series and measure what the frig is actually taking and with it off you can check on other power drain on those batteries.
Its worrisome that the batteries rapidly drop 0.3V after charging. Since it seems this has been an issue since 'day one', maybe you have a bad cell in a battery or a bad wiring connection.

Otherwise, for a day of use, if you have a 0.3V drop that's about 25% drop in charge state for those AGMs. For a 300aH bank that should be about 75aH. If your 5a frig is drawing power continuously over 24 hrs., that would be 120aH. If its on 2/3 of the time, that would about match your bank's draw down.



Maruska

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Re: New AGM Batteries not charging
« Reply #2 on: August 05, 2018, 08:04:16 AM »
Is the charger specifically design to charge AGM's? The charge rate and voltage curve for AGM's are different than traditional wet or Gel batteries. 

How are you measuring the voltage drop?  Many analog meters are just designed to be used as a reference.  I would agree a good digital meter perhaps would be the answer in itself.  An analog meter operating in the same range can often develop a worn spot in the gear train and you may be seeing just that when it hunts between the .5 and .2 volts.

Just a thought....
Dale
"Maruska"
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Hooligan

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Re: New AGM Batteries not charging
« Reply #3 on: August 11, 2018, 05:19:30 AM »
I want to thank everyone for their help. I found the problem. The charger was bad.