Strange charging behavior, 1993 marathon

[Squeazel]

Hi,
New member here- I just bought a used marathon with the series controller complete with a total charge iii charger. The batteries are in unknown condition but they looked new and unused, just discharged. I brought them all up to 6 volts with a 12 v charger, then hooked them to the total charge. After about 10 hours, the charger shut off, as expected, and the batteries showed 6.3 volts after resting for 10 hours. Great! I was expecting to have to buy new batteries, but I lucked out, it seems.

Anyway, the funny behavior is that the charger showed 20 amps for most of the cycle, and shut down still showing 15 amps. I think. I wasn’t there for the shut down. But I measured the pack voltage at 43.8 v at a time shortly before the shutdown, so the shutdown voltage and current are approximately correct. But every other charger and cart I’ve ever dealt with would start at 20 amps, slowly decrease to less than 5 amps, then shut down.

My question is this: What’s that mean? High charging current? Is it the battery type or the fact that it happened in a hot Texas garage or are the batteries damaged? Or is the total charge broken?

A couple of other factoids: the open circuit voltages from the transformer were right in the correct ranges and the capacitor measured 19 microfarads. All the wires in the cart were cleaned and reinstalled with dielectric grease, so the connections are all good.

Thanks for your help-

[JohnnieB]

If the batteries sit in a discharged state for a significant length of time, the plates are badly sulfated and it may take several charge cycles to get them to charge normally, if they every charge normally again.

With a ferroresonant transformer type charger, such as the TC-III, the amp flow is determined by the on-charge voltage of the battery pack being charged. Normally, that tracks the attached charge profile if the charger's boost capacitor is matched with the ferroresonant transformer.

If you get 55VAC to 65VAC from the transformer secondary with not capacitor attached and 83VAC to 97VAC with capacitor attached, the charger ought to be good.

Just keep using and charging the batteries and they might start acting normally.

[Squeazel]

Thank you, JohnnyB! That's exactly the sort of thing I wanted to know. From the curve, it looks like I'm never getting down to the 1-3% range of current, it's more like 6% or greater. The charger seems to be doing what it should; its voltages are good (62 VAC and 92 VAC respectively) and it shuts off at around 44-45 volts. So the batteries are probably damaged from sitting around long enough to self-discharge and sulfate up. But they seem to be pretty healthy now, so I'll just run them up and down a few cycles and see if the charging curve gets any better, like you suggest.

My fingers are crossed! Now I just need to replace the solenoid (it was bad). Then see if the controller is OK. Then see if the motor is OK. One thing at a time, eh?

[JohnnieB]

Those are normal voltages for a working TC-III.

No need to intentionally run the batteries down more than normal usage does, but doing some back-to-back charges may help them regain some of their capacity. BY back-to-back, I mean initiate a new charge cycle without discharging batteries any.

The batteries that were in my cart when I got it would only charge to 85% SoC and I would start new charge cycles two or three times a day even when I didn't move the cart. I got them taking a 95% charge in a few weeks and close to 100% in a few months of adding a few back-to-back charges every week.

Might not work out as well for you, but it'll most likely help some.

[cgtech]

I think He's otherwise saying "whack your batteries" with a few repeated charges. In-between uses, unplug & replug the charger. Charge them obsessively a few times, even if you didn't drive it. Especially if you didn't drive it. Unplug it's charge port and hit it again. Like 5 times of this! They could probably use a good "whack"! Even though the battery manufacturer may not agree, I truly think a "once a year discharge test" is good for them occasionally, draw them down (to 20% as the industry standard tester does) & fully charge them. The battery manufacturer stats may disagree, but, I have seen again & again that the second discharge test always results in a better score than the first one (unless the batteries are totally garbage the first time).

[Squeazel]

OK, the batteries are up to 80% according to the measured voltage after resting for 12 hours. This is very good. Whacking them helped- but I haven't discharged them significantly yet- only driven the cart around the block a few times. The batteries charge at 20 amps, then the current drops to about 10 amps before the charger shuts off, so we're heading in the right direction!

After replacing the solenoid, the cart would drive forward and reverse, so it seems everything is fine. It's slow, though, maybe only 13 or 14 MPH top speed. I guess that's not unusual.

Thanks for your help!

[Timberwolflt]

13 is slow... 14 is fast...lol

Every stock EZGO I’ve had has run 13.5 mph... I’ve always assumed that was their target speed by design

How long it takes to get to that speed is the question... I have one with brand new batteries that seems to be a bit slow getting up to that speed

[Squeazel]

I owe everybody who's following this thread a follow-up:

I think the major factor is that one of the terminals in the cart wasn't making good contact to the plug. It had melted the plastic around the socket, and the connector contact wasn't protruding fully- it was melted about 1/4 inch back, and sometimes wouldn't even allow the charger to start. I fiddled with it to make the contact better, and after that the charger would drop to 5 amps before shutting off. I'll be replacing the socket when the new part arrives this week.

My speculation is that the batteries were never getting a full charge because the resistance of the bad contact allowed the voltage of the charger to get higher than it should have, shutting off the charger prematurely.

SO, if you have this problem- that the charger doesn't drop to 2-5 amps before shutting down- then check your contact resistance by checking the voltage drop between the charger and the battery terminal- it should be millivolts. Mine was about a volt. That volt at 20 amps means that the contact was dissipating 20 watts! No wonder the plastic was melting!