Battery charger always runs 12 hours

[JohnnieB]

Originally Posted by holotc

Thanks JohnnieB & rabbitreborn

It's been several hours since I removed the charger and checked the voltage (got 34v at that time). I am now getting 39.6v across all batteries. Sounds about right

Either I misread the meter the first time, didn't have the probes tight against the posts, or the voltage has gone up. We all mess up occasionally

I checked across each battery adding one battery each time as rabbitreborn recomended. I get 6.7v, 13.2v, 20v, 27v, 33v,39.6v. My math tells me that your battery voltages are 6.7, 6.5, 6.8, 7.0, 6.0 & 6.6 respectively. The 6.0 is only a 50% charge, so it is probably bad? Also the pack is imbalanced and if you've been hitting it with 12 hr. charges, it ought to be pretty well equalized. (Variations between batteries should by 0.15V or less)

If these are the reading I should get 3-4 hours after removing the charger (with no cart use), is the problem pointing to the charger? IF is the key word here. With the one battery only getting to 6.0V, the pack probably isn't reaching charger cutoff voltage even though the pack voltage is close to what would be expected after some rest time.

I suspect you've got at least one bad battery.

To check if your charger does in fact, turn off automatically when it sees the cutoff voltage, unplug it from the cart while charging. You ought to hear the relay drop out, or put a voltmeter across the primary of the transformer to see if AC is removed. (Technical info - The output voltage of the ferroresonant transformer is saturation limited by the load, so it climbs to max when the load (cart battery) is removed and that will shut off the charger if the control board is working.)

[GreshamCA]

If you have a 6 volt charger, charge that low battery by itself. Let it sit over night and then check the voltage. If it drops back down to 6 volts over night then replace that battery with a good one of close to the same vintage.

[rabbitreborn]

How far are you from a legitimate repair shop? Can you get the cart there? At my shop I charge $55 to do a battery discharge test. From the readings you have supplied I agree with JohnnieB that the one battery SEEMS to be bad.

The only real way to know for sure though would be to do a discharge test. You can have them do a rapid test by charging the cart overnight yourself and trailering it to them. The full discharge test on a good set of batteries would take 1.5 hours, however on your set I am betting that in under an hour you will have a positive result of a bad battery.

There is an alternative to this if you don't have a decent cart repair shop around. It's somewhat dangerous so I usually don't reccommend it. You COULD run the pack down til the cart is barely moving. Then find a wall to brace the front end against. Remove the seat. put your tester leads on each individual battery and briefly step on the gas. Have someone nearby that can record the voltages as you call them out. Again this test is dangerous since the cart is in a volitile state. The batteries are at their lowest point and you are putting maximum amp draw against them. One loose wire and you can melt a post, or worse yet, explode a battery (and with the seat off, that would NOT be a good thing). Use this testing method at your OWN RISK and only as a LAST RESORT.

[JohnnieB]

I was out mowing some rough ground on a riding lawnmower and the few brain cells I have remaining got bouncing around and it occurred to me, I might be barking up the wrong tree.

In post#7 holotc said all the batteries read between 6.6 and 6.8. If those are correct, the batteries ought to be good.
In post#10, he gave an incremental list of voltages starting with the most negative battery in the chain. Those readings were batteries plus connections, rather than batteries alone.
If the reading in post#7 are correct, than the voltages in #10 point to the cables/connections rather than the batteries.

Before doing anything drastic, try this.

Put the cart on charge and measure directly across each of the five heavy interconnecting cables. Go from lead battery post to the lead (Pb) battery post rather than the studs. That way you are measuring, cables, terminal lugs and binding posts. Push the pointed tips of your DVM leads hard enough to dimple the lead (Pb) so you get good contact.
Each reading should be ZERO, or darn close to it. (Technical info - Each amp of current flow from charger will produce a 1 Milli-volt voltage drop across each Milli-ohm of resistance. Any voltage at all across these cables is bad. For example: 2Ga cable is something like 0.156 Milli-ohm per foot, so you'd need about 6 feet of cable to get a 1mv reading and the interconnecting cables on a battery pact aren't that long.)

I'm not saying the battery isn't bad, or that the cables are. It is just that reaching cutoff voltage for the charger is a dynamic condition while measuring the incremental voltages was more or less a static one. If the voltage drop across the cables is zero, then its time to take a hard look at the batteries.

Good luck,
John