Yet Another Charger Question

[93yellowclubcar]

I don't visit this side of the forum with questions much, but today I have one. My 87 3 wheel resistor cart is in great shape, but the charger worries me. Today I plugged the cart in at 37.9 volts and turned the charger on. Now, 5.5 hours later it is still going at 5 amps, seems it always does this, and I've never actually seen this charger shut off except when it makes its full circle and shuts off after 12 hours - just doesn't seem right to me, what in the charger could keep it from kicking off?

IMG_20140626_182731_734.jpg

Thanks in advance!!

[93yellowclubcar]

Checked it just now and was still sitting on 5 amps, batteries boiling pretty good too. I unplugged it, checked the pack voltage about 2 minutes after doing so and it was 41.9 volts. I'll check the batteries tomorrow after they've rested, maybe it really needs that long to get full charge, just doesn't seem right to me when compared to my Club Cars...

[JohnnieB]

Sounds like you might have some battery issues or the charger might have a bad diode or capacitor.

The On-Charge voltage has to climb into the 44 - 46 volt range for that charger to turn off automatically. Otherwise, it will run until the timer times out at 12 hours.

The batteries gassing vigorously means that the cells have reached, or exceeded, about 2.35VPC (42.5V for a 36V pack). Are all 18 cells bubbling about the same?

Measure the pack and the individual battery On-Charge voltage while the charger is pumping out about 5A. Each battery's On-Charge voltage should be very close to 1/6 the pack voltage.

-----------
Also, what does the ammeter climb to when charger is first plugged in?
It should go to about 18A-20A and then start tapering off as On-Charge voltage climbs.

[93yellowclubcar]

This was a long time in answering, but today I finally got the chance to really monitor these batteries while on charge. The charger is putting out a steady 7-8 amps, started at 20 and declined within a couple hours down to there. Batteries are at 44.8 volts, all batteries read 7.4-7.5 volts. It's only been on for about 4 hours, but the batteries were near full charge to begin with. I'll continue to monitor the thing until it (hopefully) shuts off. Should it not shut down, what should I check?

[93yellowclubcar]

Charger now has been on just over 8 hours, putting out 6 amps. Batteries at 45.0 volts and four read 7.5 volts, two read 7.4 volts toggling to 7.5. Batteries making bubbling noise, but not aggressively and not boiling over. Normal operation? I have always wondered because I've never seen the charger kick itself off.

[JohnnieB]

The charger's control board is supposed to shut off the charger when the battery pack's On-charge voltage climbs into the 44V to 46V range and your pack voltage is reaching 45V, but the control board in your charger may be looking for a voltage closer to 46V, so it cannot be said that the control board isn't shutting off properly until the On-charge voltage actually exceeds 46V.

Even then, we do not know the exact cutoff voltage programmed into a Green-face Total Charge 36V battery charger. It could be higher than the generic rule of thumb of 44V to 46V.

The Trojan battery charge profile (attached) recommends the On-charge voltage reach at least 2.45VPC (Volts per Cell)m but not exceed 2.79VPC, which is from 44.1V to 50.2V for a 36V battery pack, so your aren't exceeding the max recommended On-charge voltage.

You stated the charger starts out at about 20A, so the diodes are most likely good and the AC output voltage from the transformer feeding the diodes may be in specs. Basically the battery charging portion of the charger appears to be working correctly, but needs some testing to prove it one way or the other.

The charger's on/off switch (control board) may or may not be working correctly, also.

The batteries are not responding normally. With 6A of charging current flowing through them, the On-charge voltage ought to be climbing past the 45V they are sitting at.

-----------
There may be more than one issue.

1. You stated you've never seen this charge shut off automatically, so the relay on the control board may have been bypassed.

Does the transformer hum when the charger is plugged into AC power without being plugged into cart?
If so, the relay is bypassed.

2. The batteries, which you said were close to being fully charged, have been on charge for 8 hours and the On-charge voltage is only 45V.

Either the battery plates are too sulfated to take a full charge or the charger's max output voltage is lower than it ought to be.

--------------
Attached is how to check for proper AC voltage out of the transformer with the transformer leads disconnected from the diodes.

[yurtle]

Could excess resistance in the charging circuit - plug, Radsak, charging cables, and battery cables dirty - cause this? Coffee hasn't kicked in, but I would think voltage drop would prevent the batteries from seeing the full charger output.

[JohnnieB]

Originally Posted by yurtle

Could excess resistance in the charging circuit - plug, Radsak, charging cables, and battery cables dirty - cause this? Coffee hasn't kicked in, but I would think voltage drop would prevent the batteries from seeing the full charger output.

The green-face TC senses the pack voltage between the heatsink and ammeter, so excessive resistances in the areas mentioned would cause a premature cut-off.

You are correct that excessive resistance in the charging loop would keep the batteries from see the full voltage being put out by the charger, but by the same token, that would reduce the current flow and the charger starts out at about 20A, which is more or less normal.

There could be some excessive resistance between the heatsink and ammeter and the control board causing the control board to sense a voltage lower than the pack voltage, thereby increasing the cut-off point, but the reported individual battery voltages are fairly consistent with the reported pack voltage, which appears to be too low for having been on charge for ~8 hours.

This is just guessing, but I suspect the relay in the charger is bypassed and the batteries are on their last legs. But I might be wrong.

[93yellowclubcar]

The relay isn't bypassed (I don't think anyhow) because when I plug it in there is no hum and it only starts to hum once I have plugged it into the cart and turn the knob to start.

About an hour ago the batteries were at a hair over 39 volts. I hooked up the meter and drove around, the lowest I ever saw them get was 34 volts up a steep hill. Cruising WOT on flat ground saw 36-36.5 volts most all the time. After a short rest from the run, the pack voltage was at 38.4 volts.

I hooked up a crowsfoot plug and am charging it now with a CC charger I know is good. In theory, if it runs, declines in amperage as normal, and shuts off, then I have a charger issue. If it runs forever and the batteries don't climb to nearer 46 volts, then I know the batteries are an issue (highly likely). As for corrosion, all connections on the cart, specifically in the charging loop, are clean and tight.

Thanks for all the help so far! With your help I know I'll get to the bottom of this.

[93yellowclubcar]

On-charge voltage is 45.3 and rising, CC Accupower is at 6 amps and dropping. Now THAT seems normal (to me). Batteries are still probably getting weak, but looks like I'll be tearing into the EZGO charger and doing some testing, as soon as I see what goes on with this charge cycle.

Thoughts? I'd appreciate any guidance, chargers are not my strong suit.