93 Marathon has low torque

[49ford]

I got a 93 Marathon to fix up. I've put in new batteries and some good 6ga cables with all connections cleaned. I also cleaned the forward reverse switch.
The cart will run in forward and reverse, all micros working, main solenoid working, and nothing getting hot after running for awhile. It just has no bottom end, no low end torque. It will take off on level ground, but if it is angling uphill it will not move.
I'm on 4th charging cycle. It charges at 41V. It kicks off under 15 A. All batteries are 6.3 or 6.4V. Load tested all and are ok.
Should I be looking at the controller the motor? Or what?

[49ford]

Ok, today I tested the pot. It swings from 0 to 6000, supposed to be 5000, guessing its workable not perfect.
Checked voltage from Bat- to M-, on the click goes to full batt voltage, 37.4., ok.
Upon pushing thottle to floor it goes to 0 volt, ok.
Motor turning.
Voltage between M- and B+ is 0 pedal up and 36.4 pedal down.
Still looks good even though have 1 volt loss to motor. Correct?
Im guessing I'll have to pull the motor.
ANY SUGGESTIONS?

[JRaf]

You should check this thread:
http://www.buggiesgonewild.com/showthread.php?t=179336[/URL]
...and do all the tests recommended. (I'm having similar problems with a 93 Marathon.) There are questions you should be prepared to answer:
- New batteries? What kind of batteries and how new?
- What's SOC 12 hours after a charge?
- Do all the tests to make sure throttle and controller are opening fully and delivering full pack voltage.
- You stated that batteries passed load test. With an automobile load tester? I don't think that means much on high amperage golf cart batteries. You need to measure voltage (and amperage) under load (like when you're running up a hill and cart is slowing or stopping).
- Six gauge cables sound like the original cables and might be suspect. Most of the smart guys here will recommend something heavier.
- Very important: What kind of charger? A modern charger is "multi-stage" but amperage is meaningful as well. You should be charging with something that delivers north of 15 amps.

[49ford]

Ok, batteries. Mine are Energizer GC2, bought last week, labeled 9/21.
I've had a charger on them 4 times, but it shuts off after a short period, not like my other carts that seemed to take several hours.
Today I put an older charger with a non working timer on it. It charged up to 45 volts, started at 25A and drifted back in time to 2 or 3 A. It didn't fix the low torque problem. I'm leaving it on for 4 to 5 hrs this evening to try to get batteries conditioned I guess.
I also made a good set of 4gauge cables with copper ends. Looks good, didn't fix the low torque problem.

[JRaf]

I'm not an expert in any way but it seems like you still have to isolate the problem. Do all the tests that were in the other thread. and that are in the service manual. My observations:
- I'm not convinced you're getting a good charge. Your chargers sound a bit like mine, older, single stage, maybe not reliable.
- I don't think you've yet cleared the throttle, F/R switch, controller. You have to run a load test and see if the controller is delivering pack voltage as your running up a hill. Make sure the F/R switch is delivering full voltage as well. Are the big contacts in there delivering power? Do you have an ammeter? That can help.
- You should also measure continuity between the (isolated) motor poles and the case. If there's continuity, you should pull the motor, clean it, and maybe replace the brushes.
Honestly, I still haven't solved a similar problem, so take my advice with a grain of salt. I do think I have it down to the charger or the motor.

[bronsonj]

I don't think your new batteries are the problem. It's something else in the high current circuit. The high current circuit contains the motor, controller, solenoid, battery pack and all the big cables.

Your batteries are probably fine so check your cables, give them all a tug, should be tight and feel solid. This includes the ones that go to/from the motor and controller. They do go bad from corrosion or breakage. Just because they look fine doesn't mean they are fine. This is the cheapest item that I know of that could be causing your speed issue at this point. Another option is to check the voltage going into the controller when you mash the throttle. If the voltage into the controller matches matches the battery pack when you do this, then those cables are fine. The ones between motor and controller will still need to be checked separately.

When you put a heavy load on the pack the voltage should drop a few volts. But that is still your reference voltage. If you see further drops anywhere along the high current circuit before it gets to the controller that'll tell you there is a problem. If there's something that's stopping the amps from flowing you'll also see a drop in voltage and/or an increase in heat.

[49ford]

For the record, I have the cart going now. Here are my steps.
I took the motor in and had them cut, polish, segment the commutator, and put on growler. Installed and same problem.
I got a new controller from bay, then discovered I had a varistor blown upon taking the old one out. I ordered a 75v mov, installed it , and now the cart moves as it should. I suspect the varistor wasn't needed, but at this point I figured what the heck.
Final fix, controller.

[JRaf]

Thanks for posting! A lot people seem to be having similar problems.

[baymee]

What is the name of the 75v mov ?

[49ford]

It has no name. I just ordered one from debco.com. They are with ebayelectronics.
It wasn't the exact thing I had but I got tired of trying to buy from the Mouser site. It just seemed to make me mad instead of letting me purchase what I needed.