Diode on main contactor

My 2007 rolling chassis didn’t come with a contactor. Scrounged one from a local golf cart dealer’s junk yard. When I pulled it off I didn’t see any external diode across the coil. Don’t see one on electrical diagrams from maintenance manual either. Is this the norm on GEMs, no diode?

It’s in the controller. Still a good idea to have one at the coil.

Aah, Thanks! Any thoughts how to spec one? Rev bias min voltage, amp capacity, etc ? Wiki shows a 1N5401 100v reverse, 3amp. Digikey sells on the each @ $0.54

Good Morning - new to forum but saw your recent post and thought I would add my 2 cents. My schematics (GEM 2008) are not on this computer so I could be off a bit, but if it is a spike suppression diode (some times called a “flyback” diode) it is designed to suppress reverse voltage spikes generated by the contactor’s coil when it DE-energizes. I think that contactor is driven off the low voltage (12 vdc) loop - so the reverse bias rating could be anything at least 3x the normal operating voltage. The current rating is the key - theoretically the current this diode must handle is limitless and can be instantaneously very high. The good news is that diode failure is usually a function of heat at the junction, so as long as the spike is of short duration - most anything will work.

The 1N5401 you reference should work fine.

I would take a look at the output of the 72 to 12 vdc converter with a scope to make sure its not throwing off some high voltage spikes that could blow the diode with a higher than rated reverse bias.

Sorry - don’t mean to be wordy. Just wondering how active/current this forum is - haven’t totally figured out the date codes on post.


Find a 400v diode. Common.
1n5404 or better.

Hi Larry,
Thanks for the reply. I think the main contactor is supplied with 72v. At least on the GEM Electrical schematic that I am looking at. 12v goes thru a fuse to key switch to charger interlock to a relay “switch key”. One set of contacts on said relay shows 72v (fused) finding its way to the main contactor coil… Any way I just tried the contactor with 24v and it does not pull in. It does with 48 volts.

My project was pretty much missing all electronics except battery charger (no batteries either). I have an AC motor and controller that I am patching in… so all the related stuff to the original GEM setup is pretty much not related to what I will end up with. I did think (after some contemplation) that putting in a main contactor is prudent. Even if it is a constant power draw (13 watts when supplied with 48v)

Dave, thanks for the 1n54o4 suggestion. Have not had time to put on this project the last few weeks but should now…

Stretch, looked at the drawings I have for the 2008. You are correct, Page 5-36 shows the main contactor coil is energized at 72 volts. That being the case, a diode could easily see 150 vdc spikes - I would put something rated at 400 vdc or more. (agree with Dave). Could not find a listing for 1N5404 but did see a 1N5406 600 v 3 amp which should do it.

Sounds like you’ve got an interesting project going. I don’t have my GEM in the shop yet so I don’t know what all I’m facing. If the motor is OK, will likely just keep it stock for now. If the motor is not serviceable - that will open a whole new can of worms.

Good luck,

By “in the shop” I hope you mean your own shop and not somebody’s retail shop. Sounds like you have the savvy to fix your own. This website is probably a pretty good user group to help you thru the parts you cant figure out on your own (for me too). My data plate is a 2007 e4. Just bought a couple of months ago. Hope to have road worthy in the next few weeks. I am new to GEMs.

I would say that most of what you have (motor, controller etc.) is usable in one form or another with application of insight from this website.

Good luck to you as well.

Will you be running a 48v system?
Only practical way to use a 48v contactor.
I have some new 12v economize contractors. They will be for sale after I get the specs on them.

My work shop - here on the funny farm!! I try to avoid commercial shops when ever possible. This is the rural south – electricity is still considered black magic for the most part. There are a few exceptions in and around Huntsville - but that’s all DOD - nothing to good or pricey for Uncle!!

I don’t know the complete history of this GEM, As best I can tell I bought it from the original, institutional owner with a very capable in house maintenance shop. it’s been in continuous service since new as part of a fleet of several. Hopefully it hasn’t suffered from too much redneck engineering!

Got to make some room for it in the shop - next few days. Once I get into it will let you know what I find.


Probably will run on a “72v” setup. I got the contactor out of an older gem. I dont have a bench power supply but have 48v at the ready and just thought I would try it. It seemed to actuate ok.

Sounds good. So far I have found the Gem pretty easy to work on compared to a regular golf cart. Easy to take apart at least… Easier than working on a Bonanza!

The good news about Bonanzas - the Beech engineers who designed them were some of the best, as were the Continental Engine guys. I’ve owned my 1949 model since 1972 and she is still going strong! Will likely out last me!!

Tell me about your AC conversion. Whose motor? Controller? Is the motor mounting face a NEMA standard - common on most golf carts or LSV differentials? If my motor is cooked, I would very likely consider an AC conversion - done it in a number of industrial applications but no golf carts or LSV’s. Did you look at Navitas? Batteries?

I have surplus ac induction motors, pmac motors.
Standard spline for Gem and golf carts.
Also matching Sevcon controllers.
What I don’t have is the time to get them working. :frowning:
$200 ac motors, $500 pmac, $500 Sevcon.
All unused.
I will pay for programming information if someone can get them working in a Gem.

Any spec sheets available - I’m new to this and I don’t know anything these products. Might as well be “moon pies”!

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What would you exactly need for programming information to get them working in a Gem? That pmac motor would fit nicely in the first gen Gems!

I obtained the sevcon programming sw and dongle.
I can communicate, and loaded the Pmac files into one of my controllers.
A Pmac motor is mounted in a test Golf cart.
Then ran out of time. All on hold until a batch of 800 batteries are tested and disposed.
My contact is in a similar situation. Mounted and ready to run. He tells me it only needs some fine tuning to run.
I have no idea what it will take to get a Gem running.
Anyone with Sevcon knowhow wants $100/hr and no promise of success.

If someone can convince me of a good chance of success, I will supply parts and programmer with deposit. Another license is nonrefundable $50.
Not doing me any good on the shelf.
The easiest test would be on a new Gem, as the sevcon is wired.
With a new controller and motor, it should not cause any damage.

I use eBay for the quick and easy. I see the 1N5404 can be purchased for .99 for (10) of them with free shipping…