1990 EZGO Solenoid Dead?

[Fallamaihn]

The cart has been behaving a bit strangely since I got it a few months ago. Power would unexpectedly cut out and then surge back. Sometimes it wouldn't move from a dead start if it was on a slight incline. Well today it won't move at all. I did some probing, and I think it's the solenoid.

I did a few measurements and found that with the accelerator pressed the small terminals are showing full battery voltage. That means it's kicked, right?

Any recommendations on a replacement unit? And should I replace the resistor and diode as well, or does it matter?

[JohnnieB]

Originally Posted by Fallamaihn

The cart has been behaving a bit strangely since I got it a few months ago. Power would unexpectedly cut out and then surge back. Sometimes it wouldn't move from a dead start if it was on a slight incline. Well today it won't move at all. I did some probing, and I think it's the solenoid.

I did a few measurements and found that with the accelerator pressed the small terminals are showing full battery voltage. That means it's kicked, right?

Any recommendations on a replacement unit? And should I replace the resistor and diode as well, or does it matter?

If you have battery voltage on BOTH of the solenoid's small terminals when pedal is pressed, the black wire to the B- terminal on the controller is bad.

That wire is highlighted inn green on attached schematic.

[Fallamaihn]

I measured the voltage across the two small terminals, and it was full battery voltage. Did I misunderstand the diagnostic? Should I be measuring voltage from these terminals to something else?

[JohnnieB]

Originally Posted by Fallamaihn

I measured the voltage across the two small terminals, and it was full battery voltage. Did I misunderstand the diagnostic? Should I be measuring voltage from these terminals to something else?

With golf carts, voltages are typically measured from the battery pack's main negative terminal (B-) unless otherwise specified, so have pack voltage on both small terminals would indicate all the switch contacts it had to go through to get there were closed and the solenoid coil was intact, but the coil wasn't being connected to B- to complete the circuit.

Since you measured from one small terminal to the other and got pack voltage, it could mean the solenoid coil was open, or it could mean the solenoid coil was good and the solenoid was working, or it could mean the solenoid coil was working but the contacts were mechanically jammed.

If the solenoid clicks when the pedal is pushed, check the voltage on the solenoid's controller side large terminal. If the is a resistor connected between the two large terminals, you'll get up to about 5V less than fully battery pack voltage before the pedal is pressed and full pack voltage after the pedal is press. (DVM referenced to B-)

[Fallamaihn]

OK, ran some more measurements. I'm getting full pack voltage on the solenoid large terminals when the pedal is pressed, and I am hearing the click. So that seems to indicate the solenoid is fine.

I measured the voltage at the controller and am getting nothing with the pedal pushed. That seems to indicate the voltage is being cutoff somewhere prior to that, maybe at the F&R switch?

I found a guide for checking continuity on the four posts of the F&R switch, but I'm finding that they are all open to each other when switched to either F or R. I don't think it's supposed to be like that, correct?

[georgia088]

Originally Posted by Fallamaihn

OK, ran some more measurements. I'm getting full pack voltage on the solenoid large terminals when the pedal is pressed, and I am hearing the click. So that seems to indicate the solenoid is fine.

I measured the voltage at the controller and am getting nothing with the pedal pushed. That seems to indicate the voltage is being cutoff somewhere prior to that, maybe at the F&R switch?

I found a guide for checking continuity on the four posts of the F&R switch, but I'm finding that they are all open to each other when switched to either F or R. I don't think it's supposed to be like that, correct?

Measure the voltage between the controller's B- and M- terminals.
Should read full battery pack voltage when pedal is pushed just far enough to make solenoid click.

If it doesn't something is not "connecting" in the high current circuit of the schematic JB provided. Possibly the F/R Switch. Or, It could be a throttle issue.

If it does read full battery pack voltage when pedal is pushed just far enough for solenoid to click, continue to read DVM as you press pedal to the floor. The voltage should drop from pack voltage to close to 0.

.

[JohnnieB]

A to D and B to C should both measure 0.4Ω or less in F
A to B and C to D should both measure 0.4Ω or less in R

[georgia088]

Jb: when the pedal is pressed and the voltage drops Between m- and b- from pack voltage to 0; is this the controllers way of completing the circuit to the motor and controlling or limiting the amps delivered? Bc the (+) is completed to the motor by the solenoid closing and f/r switch closing contacts.

[JohnnieB]

Originally Posted by georgia088

Jb: when the pedal is pressed and the voltage drops Between m- and b- from pack voltage to 0; is this the controllers way of completing the circuit to the motor and controlling or limiting the amps delivered? Bc the (+) is completed to the motor by the solenoid closing and f/r switch closing contacts.

The high current circuit (Batteries, heavy cables, F/R contacts, solenoid contacts, controller and motor) is a series circuit.
The speed control element (MOSFETs) is located between controller's B- and M- terminals.
When the throttle is at 0%, there is effectively a single open in the series circuit (between B- and M-) and no amp flow, so the entire battery pack voltage (whatever voltage the pack is at the time) is felt.

(If there is an open, or a high resistance, somewhere in the series circuit in addition to the turned off MOSFETs, than either no voltage or something less than full battery pack voltage will be measured between B- and M-.)

If full battery pack voltage is measured between B- and M-, as the pedal is pushed and the throttle increases towards 100%, amps begin flowing and voltage starts to be dropped across all the various resistances in the series circuit. When the throttle reaches 100%, there is effectively a short between B- and M-, so there is no voltage drop across the MOSFETs. (Technically, there is typically about 0.08V/100A of current flow through the MOSFETs when they are at 100% duty cycle)

[Fallamaihn]

Originally Posted by JohnnieB

A to D and B to C should both measure 0.4Ω or less in F
A to B and C to D should both measure 0.4Ω or less in R

What if they all measure 0 to each other when either in F or R?