1990 EZGO Marathon 36V "No Go"

[mh29803]

I got an old cart for $200, the guy said it just stopped when they were climbing trails and "giving it hell".

I work on heavy equipment and aerial lifts, so I am fimiliar with most electrical stuff...this cart is killing me tho!

I have installed new parts as follows:
1. solenoid
2. micro-switches
3. batteries
4. ignition switch
5. motor

-I have tested potentiometer, it ohms 0-5k.
-All wiring connections are clean and tight.
-Battery pack total voltage is correct.
-FNR switch has clean contacts and seems OK.


Heres the problem, when pedal is depressed (F or R) the S1 and S2 wires at the motor get VERY HOT and axle tries to spin VERRRYYYY SLOW. Also, all four wires on FNR switch get VERY VERY HOT. I have checked versus STICKY schematics and all is correct. I have a feeling the Controller has failed, and I cant find a solid way to test it.

I am at a loss, any help will be great! Thanks in advance!

[JohnnieB]

The control element in the controller is a dozen or so MOSFETs connected in parallel between the B- and M- bus terminals on controller.
If they failed open, the motor wouldn't try to turn and the cables wouldn't get hot.
If they failed shorted, the motor would run like a bat out of Hades the instant the solenoid clicked and the cables wouldn't get much, if any hotter than they normally would at WOT.

I suspect you've got some abnormal mechanical drag someplace. (Brakes, bearings, bird nest in differential)
But, I might be wrong.

You can check out controller by jacking up rear wheels (Put on jack stands)
Attache DVM between B- and M- bus terminals on controller.
Press throttle pedal until solenoid first clicks.
Voltage should be full battery pack voltage (38.2V is what a fully charged 36V pack should read)
Slowly press pedal to floor.
Voltage between B- and M- should smoothly decrease to near zero.
(The voltage drop across the MOSFETs is up to about 0.5V per 100A of current flow through them)

If you get that, the controller is doing its job.