SR48400 and HD Solenoid Troubles

[JakeJones8]

Lastly, should mention I pulled off the resistor and did an Ohm test with my voltmeter and got 250ohm which is what is stamped on the precharge resistor so I believe that part is good. Can’t figure out why I’m losing 9.8v across the two big terminals??

[JohnnieB]

Originally Posted by JakeJones8

Lastly, should mention I pulled off the resistor and did an Ohm test with my voltmeter and got 250ohm which is what is stamped on the precharge resistor so I believe that part is good. Can’t figure out why I’m losing 9.8v across the two big terminals??

Did you measure the voltage on the solenoid's battery side large terminal while the pedal was on floor and the controller side large terminal had 28.3V on it? Unless you did that, there is no proof that the 9.8V voltage loss is between the two big terminals.

Also, I asked for the voltage between B- and M- when pedal was pushed just far enough to make solenoid click, NOT with pedal up or pedal down. What I am looking for is the voltage with solenoid contacts closed and the controller powered up, but 0% throttle so the motor isn't drawing any amps.

In addition, the battery pack voltage might be dropping, so verify pack voltage after each reading with the same conditions used for that reading.



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Since the KSI voltage appears to be the higher one, measuring it at the solenoid's coil terminal with the red wires ought to be okay.

[JakeJones8]

Originally Posted by JohnnieB

Did you measure the voltage on the solenoid's battery side large terminal while the pedal was on floor and the controller side large terminal had 28.3V on it? Unless you did that, there is no proof that the 9.8V voltage loss is between the two big terminals.

Yes, did it again after I saw this just to double check.
Cart on no pedal
38.0v at battery terminals
38.0v at battery side of the solenoid
37.1v at controller side of the solenoid

Cart on WITH pedal 100%
38.0v at battery terminals
38.0v at battery side of the solenoid
27.7v at controller side of the solenoid
While the pedal was pushed 100% I moved the positive contact of my voltmeter around and got the above results all within seconds of each other. Looks like 10.3v loss today?

Originally Posted by JohnnieB

Also, I asked for the voltage between B- and M- when pedal was pushed just far enough to make solenoid click, NOT with pedal up or pedal down. What I am looking for is the voltage with solenoid contacts closed and the controller powered up, but 0% throttle so the motor isn't drawing any amps.

My apologies, I misread your request. Just re-did this test and stopped the pedal the second the solenoid clicked (0% throttle).
Cart on, solenoid click, 0% throttle
38.0v at battery terminals
37.1v at B- and M- before I started pushing the pedal
37.1v at B- and M- once solenoid clicked and was held at 0% throttle

Out of curiosity (and maybe this is where you are going with this...) shouldn't the controller side of the solenoid go back UP to full pack voltage once the solenoid has clicked until the throttle starts going past 0%? This is how my other cart seems to work.

Thanks for all your help!

[JohnnieB]

Series drives are a bit difficult to troubleshoot since the controller isn't powered up until the solenoid is energized and more so with when a SR controller is used because the controller can be configured to complete the solenoid energizing sequence. More correctly, the stock and aftermarket controllers used in EZGO series drives are powered up when B+ is applied to the solenoid coil. With a stock controller, the other side of the solenoid is connected to B- all the time while the SR only connects B- to the coil after it is powered up.

When the solenoid is energized (contacts closed), both the battery side and controller side large terminals ought to have exactly the same voltage on them. If they are not the same, there is some unwanted resistance between the contacts.

If there is a precharge resistor installed between the large terminals, there is typically 3V to 5V less on the controller side large terminal. The purpose of the precharge resistor is to keep the filter capacitors inside the controller charged so the solenoid contacts don't arc as much when the bounce to a close when the solenoid energizes. The filter capacitors have a safety network to discharge them once power is removed, so the amps flow though the precharge resistor that causes the 3V to 5V voltage drop is effectively the amp rate the filter capacitors are constantly being discharged at.

The electronic "valve" (MOSFETs) that controls how many amps the motor is allowed to draw are located between the B- and M- terminals. At 0% throttle there is an open between the B- and M- terminals and it being the only open that is supposed to be in the series high current loop, the full battery pack voltage ought to be measured between them. If the is less than full battery pack voltage between them, there is an undesired open or excessive resistance in the high current loop.

At 100% throttle, the MOSFETs are effectively a short, or close to it, so only a volt or so should be measured between B- and M-. (Controllers typically drop about 1V +/- 0.5V between B- and M- at WOT)

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Cart on, solenoid click, 0% throttle
38.0v at battery terminals
37.1v at B- and M- before I started pushing the pedal This ought to be lower.
37.1v at B- and M- once solenoid clicked and was held at 0% throttleThis ought to be 38.0V


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Try attaching black test lead to solenoid's battery side large terminal and red lead to controller side large terminal.

What is voltage before solenoid clicks?

What is voltage after solenoid clicks and 0% throttle?

[JakeJones8]

Originally Posted by JohnnieB

Try attaching black test lead to solenoid's battery side large terminal and red lead to controller side large terminal.

What is voltage before solenoid clicks?

What is voltage after solenoid clicks and 0% throttle?

Voltage before Solenoid clicks = -.947v
Voltage after solenoid click at 0% throttle = -.942v

Question - If I were to swap out the HD solenoid with the old stock solenoid I just took off to see if it fixes the problem, would it hurt anything? The HD Solenoid is 200amp but I do not know what the old one is rated at. Trying to isolate parts of the cart to find the issue... Scotty suggested I called Alltrax so I am about to do that now.

[JohnnieB]

The stock solenoid is only rated at 85A, but should get cart running if the 200A solenoid isn't working right and dropping 9/10 of a volt before and after it clicks doesn't sound like it is in good health. If it doesn't have the optional dust cover, something may have climbed into to it and is keeping the contacts from making good contact.

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let us know what Alltrax says.

[JakeJones8]

I spoke with Will at Alltrax. He said what it boils down to is if the solenoid is clicking, then the issue is B+ is getting 5v less than KSI (in my case 9.3v less). He said B+ should never drop more than a volt or two below KSI and because B+ is getting its power supply from the solenoid, the solenoid is bad. To test this, he had me take a 4gauge wire and bridge the two big terminals together on the solenoid (Jump It) and see if the cart will move forward/backward which it did. Will mentioned he has seen both the SW180 and MZJ400 die right out of the box so it doesn't surprise him at all that it is new. Contacted Scotty and a replacement was put in the mail same day!

1) Thank you Johnnie for your many responses and help! I know series carts can be a pain in the butt to troubleshoot but couldn't have figured it out without your suggestions and tests.

2) For anyone reading this thread, always buy your parts through ScottyB at cartsunlimited. Best customer service hands down.

[JohnnieB]

Thanks for the feedback.