1997 EZGO 36 volt Series just clicks

Punahou808

1997 Ezgo 36 volt Series just clicks. Will not spin wheels at all. Did a lot of testing with the DVOM but finally just threw a bunch of parts at it. I have another EZGO that does work so I just parted it out. Things I know.
Batteries good. 6 months old. Each around 6.3 volts. All tied together about 38.7 volts. I changed out controller, F&R switch, solenoid, inductive coil. No change. I tested the motor according to a chart I found on this website with a 12 volt booster pack and motor tested good. I used a test light to check the connections between each battery(because sometimes DVOMs show voltage where there is little current) and no problems. What am I missing here??? It's like the power just drops to nothing like I have a bad connection that won't allow enough current to get through but I cant figure out where. Any suggestions?Thanks

BGW

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mgray70

Check the pack voltage when you try make the cart move. I had one one time where all the voltages were good till the solenoid clicks then it bottomed out. Ended up being a bad battery under load. You can also check each battery individual under load to find the bad one if that is the case.

JohnnieB

Connect your DVM between the B- and M- terminals on the controller.

Push the pedal just far enough to get the solenoid to click and you ought to get FULL (38.7V) battery pack voltage .

If you don't, you have a bad cable, connection or contact in the high current circuit. (Highlighted in attached schematic)

If you do get full pack voltage, re-connect your DVM between the M- and B+ terminals on the controller and slowly push the pedal to the floor. (For safety, put cart on jackstands)

The voltage should start at zero when the solenoid first clicks and then smoothly increase to full pack voltage as the pedal is pressed.

If it doesn't, and pack voltage remains at about 38.7V, either the throttle (ITS) or the controller is bad.

Attached Images

Wiring Diagram - Series- No A2 -Hi-Current traced.JPG (57.9 KB, 0 views)

Punahou808

Thanks for your replies mgray70 and JohnnieB. I ran all the tests suggested and discovered that the cable that runs from the solenoid to B+ was the problem. I was confused with the voltage readings from the battery pack versus the controller. It was the combination of the 3 tests that did it. One further question for you guys. Is there any sites or information that explains what the controller actually does and how it does it? I feel that this kind of info helps in diagnostics and without it the tests seem meaningless. Thanks again for the help!

JohnnieB

The two attachments explains how controller works pretty well.

In a nutshell, a controller limits the amount of current the motor is allowed to draw by adjusting the % duty cycle of the PWM (Pulse Width Modulated) DC output.

The MOSFETs are turned fully on and fully off about 18,000 per second and how long they stay on during each pulse vs how long they stay off is the % duty cycle.

The voltage actually being applied to the motor is either full battery pack voltage when the MOSETs are turned on, or 0V when they are turned off, but what you read on your voltmeter is the average voltage applied.

The MOSFETs are located between the B- and M- terminals on the controller, so when there isn't a throttle signal telling them to be turned on, there should be an open between B- and M- and if the high current circuit external to the controller is intact, you should measure full pack voltage. Then, as the pedal is pressed and the duty cycle of the PWM increases, the voltage between B- and M- should decrease to zero.

Measuring from M- to B+ puts the MOSFETs between B- on the battery pack and B+ on the battery pack through all the external components in the high current circuit, so you measure 0V when the MOSFETs are not being told to turn on and the voltage increases to full battery pack voltage as the pedal is pushed and the duty cycle increases towards 100%.

Basically, a DC speed controller used in series drive golf carts is the electronic equivalent of a rheostat.

Attached Images

	Curtis 1204 block diagram.JPG (55.5 KB, 0 views)
	PWM waveshape at motor.JPG (70.4 KB, 0 views)

Punahou808

Thanks JohnnieB. I have to admit that its a little over my head. Would it be safe to say that the controller is pulsing a bunch of tiny super fast super strong relays (MOSFETS) controlling the current to the motor without using very much current. Why the strange voltage reading on the motor side of the solenoid? Ex. pack voltage 38.4 volts and B+ 37.6 volts

JohnnieB

18kHz isn't very fast, but viewing MOSFETs as relays (electrically actuated mechanical switches) isn't a bad analogy.

The two large terminals on the solenoid are typically identified as the battery side and the controller side. When the solenoid contacts are open, you will usually have a voltage about 3V to 5V lower on the controller side than on the battery side due the the pre-charge resistor connected between the two terminals. When the solenoid contacts are closed, the voltage on both terminals ought to be identical.

The purpose of the pre-charge resistor is to keep the filter capacitors inside the controller charged so the solenoid contacts don't arc as much as they close.

DaveTM

When I was a young lad, I was attempting to explain to a good looking young woman with a completely filled out shirt, what a MOSFET was. I think even today you can actually see her handprint in the side of my face.

Punahou808

I am used to working with mechanical relays so I was comfortable with that description. I am in the dark on the physics involved on MOSFETs but I understand a small current being used to control a large current as in relays. The filter capacitors was also something I was wondering about. I noticed the controller held a small charge even after the cart was off and I read the controller had to be discharged for safe removal. Thanks JohnnieB.
DaveTM. If your not married already, you got to work on those pick up lines.

DaveTM

Married 35+ years. Way to many to count. Pick up lines? My only pick up lines are one's I try to use to get out of picking up "stuff" in the garage, yard, living room, or any place (which is everyplace) I don't want to pick up an inatimat object.