Help please: Controller problems after replacing batteries in a 36v melex

[kryten_007]

I am a new member... and stumped with an electrical problem on my Melex cart! Can new batteries break a controller? Or is it possible that a controller could still run at a lower voltage if it was/is defective?

Here's the background:

I have a Melex 512 (yes, I know it's not the main-stream and rather old) and I have been running it for quite some time with batteries that were holding less and less charge... clearly, they were on their last leg... anyway, a short while ago it also had a "dead" spot in the throttle so I followed the threads here and found it to be a defective pot... went to my local electrical store and replaced the pot and viola... I was running again.

So thrilled with the first repair, I went out and forked out the bucks for new batteries, (since I got it working "normally" again...) but now it won't run at all... UNLESS I change the battery config to 24 volts. At first, I thought I just had a battery with a bad cell so I figured I would remove them a pair at a time to speed up troubleshooting, but when I removed the first pair the cart started moving again. Doesn't matter which pair I take out, so long as it's 24v configuration I can run.

Any ideas why my cart will run at 24v but not at 36? Is there any adjustments I can make to the controller?

From what I can tell it's a Curtis 1204 or 1205 (not sure which is which) and I haven't pulled the controller from the cart to get the serial/model number.

Any assistance or ideas are greatly appreciated! I don't have a ton of $$ to just replace everything and it sucks that I already dumped a ton into the new batteries only to find I have a new problem.

[roady89]

May sound dumb but are you SURE they are 6 volt batts? (it has happened before)

[kryten_007]

Yes, definitely 6v (Trojan T105's).

[kryten_007]

Finally figured it out...

Turns out the resistor/diode in the throttle was bad making the ground float... thus getting about 20v at the 0-5k ohm pot input at the controller when the batteries were at full charge which I guess was putting the controller in the high-speed-disable at startup.

That's why it worked when the voltage was lower and not with the new batteries.

Took forever to figure out, but if anyone else is in the same situation, check all the items in the pot box and not just the items that are "obviously" bad