MZJ-400S Solenoid failure

[otis30223]

I have a 1999 Txt 36v cart with stock controller and motor. Recently I had a issue where it would intermittently die. It would occur when the throttle was released then reapplied when stopping or slowing down. After much head scratching I finally isolated the issue to a solenoid that was barely 6 months old. It was replaced shortly after I installed a set of reversing contactors and was a MZJ-400S, which is supposed to be a quality solenoid. However, if you look at the photos you will see the contacts are badly burnt and one is partially melted. The only reason I’m posting this is to remind everyone that sometimes a part that is relatively new will fail, especially one made in China.

[JohnnieB]

Wow! That solenoid didn't last very long.

Do you have the proper value pre-charge resistor installed? Should be 250Ω for a 36V system.

The pre-charge resistor keeps the filter capacitors inside the controller charged up to within a few volts of the battery pack voltage so the solenoid contacts don't arc as much as the bounce to their closed position. For a MZJ-400, they bounce for about 3ms.

[otis30223]

Yes, 250 ohm resistor was installed when the solenoid was new. Only thing I can think of was misaligned contacts or poor materials. As most of the burning is on one side I can only speculate that the contacts were not mating properly on that side.

[JohnnieB]

The only other solenoid I've seen cut open was a stock (85A rated contacts) one from a stock 36V series cart that had about 10 years of use. One of the stationary contacts was eaten up more than the other on that also. The moveable contact was somehow allowed or caused to rotate and the damage was spread fairly evenly.

Here's a couple of pictures of it. The movable contact was flipped for the picture.

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I couldn't find a downloadable spec sheet for the MZJ-400S, but here is a bit of info on-line: https://www.nocoev.com/product/MZJ-400S.htm#gsc.tab=0

I wonder if the dual coil version (400S) is more prone to arcing than the single coil versions. like the 400A and 400D.

The MZJ-400 I've got has been running for 10 years so far, but like everything else, the manufacturers are continuously reducing the quality and raising the prices.

[Fairtax4me]

That is arc damage and can be caused by the solenoid opening or closing while there is current moving through the main circuit. If the controller is trying to tell the motor to run before the solenoid closes, or if the motor is still running when the solenoid opens, it can/will arc and burn the contacts. A burned contact will pretty quickly end up melting because of the reduced surface area causing high resistance.

Is the wiring to the solenoid still original? Has something been changed about the way the cart operates?
Normally I would say this could just be the wrong type of solenoid for the application, but I've seen quite a few failures of these solenoids mentioned on this forum, so it's probably a weakness in the design of the solenoid.
But you don't want to install a new solenoid (different brand, etc) and have the same problem with that one in 6 months, so you first need to make sure the cart is operating the way its supposed to, and not doing something to cause the solenoid to burn out.

[otis30223]

The wiring is original, the only change has been the replacement of the series switch with reversing contactors I ordered from Scottyb. It has the stock Curtis controller and motor. I have up graded the high current wiring with 4 gauge ones, other than that it is a pretty basic Txt 36v cart.

[PingEye3]

I have had a couple of failures of the MJZ400 bought from Amazon. Attached is a spec sheet for the MJZ400 when it had not been replaced with all those Chinese knockoffs. There are several certifications on the solenoid label in the picture on the pdf. Note the Blue text in upper left hand corner of the label which is one of the certification labels. The CCC is also one. Now look them up on Amazon or eBay and each one of them has a different mfg name in upper left hand corner and no original certification stamps. You won't find any documentation of this available for the Chinese KO's.

This is my opinion only. The link is an example of one of the KO's from Amazon, no certification labels at all, but looks like the real thing.

https://www.amazon.com/dp/B081CSZCZF...EEQ%5Erapha%5E

[JohnnieB]

Things like tweaking the pedal switch and plunger so the solenoid is activated before the throttle tells the controller to pass amps to the motor will help.

That is probably the reason for the plunger to be a specified distance outside the ITS sensor when the pedal is up and it looks like the specified distance is 3/64 greater for a series drive than it is for a sepex drive. (see attachments)

Reducing the throttle up ramp rate may help also. I've got my throttle rate percent as well as the linearity, speed and torque curves adjusted so I can takeoff from a standstill on grass without spinning the tires, which also limits the amps the motor can draw for the first moments and keeps the arcing down during the contact bounce period.

When the solenoid I have installed starts failing (they all do eventually) I'll probably go with a SW2200 with magnetic breakouts.

[ThreeCW]

Originally Posted by JohnnieB

When the solenoid I have installed starts failing (they all do eventually) I'll probably go with a SW2200 with magnetic breakouts.

I think you mean SW200 ... spec sheet attached for reference.
I actually like the idea of a sealed contactor ... I am currently using a Kilovac LEV200 500 amp Solenoid (spec sheet also attached).
Gigavac also is supposed to make a good contactor ... see attachment.
Replacing with a high quality electric vehicle contactor should be a once in a lifetime replacement vs a limited life of some of the knock off contactors.
Comparing the 10,000 cycle electrical life of the MZJ-400 to the Kilovac and Gigavac +100,000 switching cycles, it is easy to see how cost effective a premium solenoid can be.

[Sideways]

Following as I am on my 3rd MZJ-400S in 4yrs. I took both of the solenoids apart but never found anything obvious, neither solenoid was burnt or had a odor of being burnt either.