Xct400 pds solenoid diode burnt up

[Tbirddipp]

I have a 2001(pre) EZGO PDS cart. I just bought the XCT400 PDS controller off of ScottyB and installed it. Rode it around the house a few times and just brought it up to our camp site. I rode it around some with no problems then took it out one more time and smelled something burning. I lifted the seat and smoke came out. I found that the diode that goes on the solenoid was smoked and the wire was melted off of the one side of it. I know it was installed correctly.*ScottyB told me to post this problem here to see if anyone could figure out why this could have happened.

[scottyb]

Just to be clear we are talking about the Regen Diode on the large posts.
I have never heard of this happening when the diode is installed correctly.
Can you check to see if the red end of the diode was connected to the + post that shares the battery side cable on the solenoid?

[Tbirddipp]

Yes that's correct scotty. Now the cart won't move at all with this diode burnt up.

[scottyb]

Remove the burnt diode and see if the cart runs.

The diode may be collateral damage from some other problem?

[JohnnieB]

What was the cart doing in the minutes prior to the burning smell be noticed?

IE: Going downhill with regen braking or coming to a stop with regen braking?

When the diode is installed correctly (banded end connected to the large terminal with the high current cable from the main B+ terminal on the battery pack attached to it) the only way to get the diode to conduct is having the controller side terminal more positive than the battery side terminal and that only occurs during regen braking.

If the solenoid contacts open for any reason during regen braking, then all the regen current will try to pass through the diode. It is only a 6A diode and the regen braking current can be 10 or 20 times that, or more, depending on what the Max Regen Braking Current slider is set to in the XCT.

If for some reason the solenoid contacts aren't making good contact, (have excessive resistance) a portion of the regen braking current will pass through the diode even when the contacts are closed. That portion of the regen current might exceed the ratings of the diode enough to burn it out.

The controller ought to work with or without the regen diode installed.

[scottyb]

I have not seen this problem before. Since the cart ran good for several test rides I suspect something changed. I wonder if there could be a short in the field wires

[JohnnieB]

I'm sure the blown diode was collateral damage, as was suggested in post#4.

I'm about 99.999% sure the diode was blown because the solenoid contacts were not making contact during regen braking since the only time the controller side high current cable is more positive than the battery side high current cable is during regen braking.

I'm not sure why the solenoid contact were open during regen braking. It could be a solenoid failure, or it could be a controller failure, or it could be the loss of any of the control voltages that will keep the controller from energizing the solenoid, or keeping the solenoid energized, during regen braking.

The text on the package the diode comes in states that the solenoid will deactivate if the keyswitch is turned off during regen braking. Losing the voltage on J1 Pins 4 or 5, or the voltages to/from the Run/Tow switch will do the same thing.

This is speculation, but I suspect there was a momentary loss of one of the critical voltages and the solenoid deactivated during regen braking. The diode tried to do its job and pass the regen braking voltage/amps to the battery pack, but the diode being used wasn't large enough for the task.

[Tbirddipp]

What happened was I got on the cart and went to back up and I heard a clunk but thought it was just the suspension. I was on flat ground the whole time. After I backed up I started going forwards and smelled a burning smell. I stopped and lifted the seat and saw smoke come out. I tried to move the cart and it wouldn't go anymore. I found the diode burned up and the controller is no longer powering up.

I'm going to call altrax tomorrow too troubleshoot it with a meter.
Hey scotty, are you going to send me a new diode for this since the old one is melted in half?