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Naio's avatar
Naio
Explorer II
Jul 05, 2016

'Nother dorky charger question

After struggling for weeks on the road with a funky charging setup I arrived at a mail drop and picked up my new ebay 24v charger for my ice machine.

Fool that I am, I did not check the soc on the 2 12v batteries before hooking up the new charger. I was excited to test it! But I canvtell you that they were at similar but not the same soc, and maybe around 12.5v.

Should I run the charger till it shuts off, or will that overcharge one battery?

I can top off as needed with my hokey 12v setup later tonight, but would love to get some aH in the batteries before then, using this new charger.

PS: After being plugged in for a while, I read 26.97 across the two batteries. That seems low for charger output... but is about the same per battery as I was getting on my other (12v) charger. I have not yet had a chance to compare my meter's readings with another voltmeter, so everything is speculative, but it gives plausible readings when I am checking soc.

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  • Naio's avatar
    Naio
    Explorer II
    Jul 06, 2016
    Alright, that test is over and I've got 2 more questions for you smarty-pantses :).

    Charger did not shut off. Pos wire read 3.85 amps and neg (on the other battery, of course) reads 1.72. I unplugged it after checking amps.

    Question 1: Why are are pos and negs amps different?

    Question 2: I see people here talking all the time about how many amps their batteries will take at a given voltage, as a measure of soc. If my batteries are taking this many amps, does that mean they are not really fully charged? (And, if so, how did my prev set of batteries get all swollen?)
  • Naio's avatar
    Naio
    Explorer II
    Jul 06, 2016
    Well, hmm. Ebay charger still running.

    I unplugged it and put a 12v load (little air compressor) on one battery at a time, to try to get a surefire voltage reading. The first said 13.24. The second said 13.30, but I left it on for 15 seconds or so to see if it would change and it went down to 13.24.

    These are MK gel cells and normally read about 13.13 when full.

    I put the charger back on because I want to see if it will shut off pretty soon or if it is planning to charge my batteries till they explode. It's only 4amp max, so I figure it can't do a lot of damage in 15 minutes.

    I really gotta get a second voltmeter to check this new one against.

    Anyway, the batteries do seem to be about the same now, even if I am not sure WHAT value they share.

    (I did have a charger go bad in such a way once that it charged my then-agms until they swelled up like they were pregnant. It is a thing.)
  • 2oldman's avatar
    2oldman
    Explorer II
    Jul 05, 2016
    In my case I was tapping 12v off 2 of a set of 8 series batteries. I was warned not to do that, I did it, and lo and behold that set of 2 was always lower in voltage. So I put them on a 12v charger to bring them back.
  • time2roll's avatar
    time2roll
    Nomad
    Jul 05, 2016
    At that voltage it is easy. If they were sharing 30 volts one might get equalized. If you always use them and charge them in series they should be fine.
  • 2oldman's avatar
    2oldman
    Explorer II
    Jul 05, 2016
    They may balance out, but series batteries (at least mine) were never very good at that.
  • Naio's avatar
    Naio
    Explorer II
    Jul 05, 2016
    smkettner, that was a brilliant idea! I'd checked them while charging, after about 45 mins, and they were at 13.52 and 13.24, approx. Now, after over an hour, they are 13.54 and 13.51. So it looks like they are balancing out?

    They are pulling 2.5amps for the pair, so not floating but maybe pretty close to full. If this ebay charger is good ;)
  • time2roll's avatar
    time2roll
    Nomad
    Jul 05, 2016
    I would run it as is. What is the voltage of each battery while charging?

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