Testing & Replacing Your Solenoid

I'd been carting around town a while back, and pulled into my driveway and stopped in the carport. As always, I plugged in the charger and went in the house. The next day I unplugged the charger, climbed in the cart and turned on the key, and pushed the pedal to the floor. And nothing happened. It didn't move... it didn't even make a noise.

I tested all six, 6-volt batteries (I have a 36-volt system) and they all clocked in at between six and seven volts. I then put the meter probes on the battery series endpoints, and hit over the 36-volt level. At that point I had a pretty good feeling that the problem wasn't with the batteries, so I then looked to the solenoid. It's not all that uncommon for a solenoid to go out, and they're relatively easy to test.

I should say up front that I first found the solenoid test procedure on the D&D Motor Systems webpage, and it contains a ton of of information on solenoids. I believe in giving credit where credit is due!

Anyway, let's talk about golf cart solenoids, many of which have four connections: two small posts, and two large posts. Inside the case of the solenoid is a steel plunger with a thick plate on one end, surrounded by a coil of thin wire wrapped many times. When a small amount of current from the battery flows across the thin wires connected to the two small posts, the magnetic field created by the coil throws the steel plunger and plate into two large posts and the plate conduct the high current needed to power the starter (in a gas cart) or the motor (in an electric cart). Basically, think of the solenoid as a switch - like a light switch on the wall. When you manually turn on the wall switch, electricity flows to the light bulb. On a golf cart,
the voltage flowing between the two small posts "turns on" the solenoid and allows the current to flow between the large posts and on to the motor.

Keep in mind that your solenoid may look different depending on your cart, but this is a top view of the solenoid on my EZ-GO TXT. It's the same one shown in the angle shot above, it's just that it's mounted with the black end with the posts facing up. To get started, I always take a photo with my phone so that I'll be able to reference it when hooking things back up. That done, I next disconnect one of the wires from the battery series. I usually take off the wire between batteries three and four on the other side of the cart. You're going to be working in a tight space with your tools, and definitely don't want to have electricity arcing everywhere because your battery series is live.

1. With all the prep work done, let's get serious. Remove the screws and disconnect the cables from the two large posts. As you do, wrap the cable ends in electrical tape as you disconnect them. In my opinion, you can never be "too safe," so please take precautions. Once that's done, reconnect the wire from the battery series that you disconnected above (in my case, between batteries three and four). Be careful, because you have current to the solenoid through the smaller posts. Get out your voltmeter, and it's time to begin. Make sure that the ignition key is off, and that your golf cart directional switch is in the neutral position. Set the voltmeter to measure ohms, and put a probe on each large post. There shouldn't be a reading at this point.

2. Next put the golf cart directional switch to forward, turn on the key, and press the acceleration pedal. There should be an audible "click" from the solenoid. If you hear it, continue to step #3. If not, go to step #4.

3. You're here because you heard a click from the solenoid in the last step. With your voltmeter still set for ohms, put a probe on each large post again, and repeat step 2. The reading should be in the range of 0.0 to 0.4 ohms. If it's higher than that, then the solenoid has faulty contacts and you're going to need to replace it, so go to step #5. Otherwise, the problem is somewhere else, not in the solenoid. Re-connect everything and keep troubleshooting.

4. You're here because you did not hear a click from the solenoid in step #2. Set your voltmeter to measure DC volts (200 scale), and this time put a probe on each of the small posts, and repeat step 2. If the meter indicates full battery voltage for your cart, but there is still no click, the coil inside the unit is faulty, and you're going to need to replace the solenoid, so go to step #5. If the meter remains at zero, the problem is somewhere else, not in the solenoid. Re-connect everything and keep troubleshooting.

5. If you must replace the solenoid, go online and do a web search for one for your golf cart make, model, and voltage. For example, in my case I was looking for one for an EZ-GO TXT 36-volt system. There should be a photo of it online, and compare it to the one in your cart to make sure that it's the same one. Most places have a turnaround time of only a few days from ordering. Once you have the new one in hand, it's simply a matter of disconnecting a wire between two of the batteries in the series to break up the flow of electricity, and then moving the wires from the old one to the corresponding posts on the new one. Once that's done, reconnect the battery wire that you removed, and you should be good to go. Congrats - you've diagnosed and replaced your solenoid!

NOTE: On mine, which is in the photo above, you'll notice a resistor connected between the two small posts, and a diode connected between the two large posts. I put these back when installing the new solenoid, but had no idea what they were used for. Yours may or not have them. After a little research, here's what I found...

The 250 Ohm Resistor is used on 1989-current EZ-GO Electric Vehicles without DCS (Drive Control System) controllers. This wire resists the flow of electric current and helps to control the amount of current in a circuit, thus protecting the device from overload and damage.
This resistor, typically seen across the two big posts of the solenoid, pre-charges the filter capacitors in the electronic speed controller. This pre-charge minimizes the voltage across the solenoid to reduce arcing on the contacts as they close. The resistor can be connected either way, it is not directional.
Closing the contactor without a pre-charge resistor causes arcing on the contact surface and they can become pitted. Plain copper contacts experience the worst pitting and wear because that cannot tolerate peak inrush currents. Excessive pitting over time causes the contacts to weld together or not make a good contact. The pre-charge circuit draws little or no power. Its purpose is to maintain the capacitors within the controller at the battery pack voltage so that when the contactor closes, no arcing occurs. Resistor value is determined by battery pack voltage.

A diode is a protection device across the solenoid and in general, is a one-way gate for electricity. When the accelerator pedal is let up, the current stops, and the magnetic field collapses causing a “voltage spike” or “fly-back voltage” that can damage the controller. This voltage can exceed 150V. The diode safely dissipates this energy and protects the controller from sustaining damage thereof. Vehicles with ITS (Inductive Throttle Sensor) throttle inputs have been known to jump or “shutter” from solenoid spikes when a diode is not used.
This is the small diode that mounts between the two small terminals of the solenoid on electric golf carts with an electronic speed controller. Note the thin gray band on one end of the diode. The side with the band connects to the micro switch that turns the solenoid on and off (battery side). If it is connected backwards it will blow out the diode. To test the diode, disconnect one end from the solenoid and connect an ohm meter to each end of the diode. There should be a partial ohm reading in one direction and no reading in the other direction. Any other results indicate a bad diode.

Happy carting,
The Psychic

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