Voltage drop across solenoid terminals

[matt_in_TX]

Newbie to the forum here. The short version is: I've got a voltage drop of about 4V across the large terminals of my solenoid (compared to the battery bank voltage) when the solenoid clicks (closes) and I don't know what the cause is.

Here are the details: I have a Yamaha G16E and everything electrical has been replaced with exception of the throttle sensor and the F/R switch. Almost exactly one year ago I replaced the controller (Alltrax SPM 400A), motor, solenoid, cables, and batteries are only about 2 years old. It's a 36V cart which I keep charged and the batteries read 38.2V resting.

This week, sporadically, the solenoid would click shut with the throttle but it would not move an inch. I'd pump the pedal and finally it would accelerate normally. I was able to replicate the problem in my shop while looking at the controller, and the trouble code that flashed was one green/two red, indicating "under voltage". That didn't make sense to me since the battery bank was measuring 38.2V with a digital multimeter.

I emailed Alltrax and they asked me to test between B+ and B- on the controller while the trouble code was flashing, and sure enough that showed 33.7V, for a drop of 4.7V between the line (in) side of the solenoid and the load (out) side of the solenoid. Worth mentioning, I guess, is that it's a year-old HD solenoid (I forget which brand), rated for 500A continuous/1000A peak. I have a 250ohm resistor across the main terminals and the supplied diode across the small terminals. The cart has probably seen less than 20 hours of use in the past year and every connection is clean and tight.

This doesn't make sense to me, and that's why I'm hoping someone can point me in the right direction. I guess the easy thing would be to replace the solenoid but minus the voltage drop, (mechanically) it is acting fine. Thank you in advance.

[cgtech]

Bad solenoids still click "normally" about 75% of the time.

[scottyb]

I have a customer who's solenoid is also exhibiting the same problem with an Alltrax SR control on 36v 400a solenoid. He sent me the solenoid and it tested good, I returned it and it was bad. Currently waiting for another solenoid to reach him. But I suspect the solenoid is not the problem but Alltrax insists it is?
I should know something more on this cart after a weekend, if you want to PM or email me about this after that, that's okay.