# Sevcon Controller Mass Failure?



## gerbear (Apr 23, 2012)

Hey all

Building an electric go-kart utilizing a Sevcon Millipak 4QPM controller with a Mars ME0708 PMDC motor. Long story short, whenever the key is switched closed the contactor closes briefly and the motor spins immediately until the fuse on the switch line connected to the B1 input (enable) blows. I'm afraid there is a short somewhere within the controller.

Here's the run down on what happened:
Originally I was able to power the controller with a contactor fault. I am running a 48v battery bank and using a 60V albright contactor which works fine for other ev karts using an Alltrax Axe 7234 controller. I was never able to get the contactor to close. For some reason the B8 input (line contactor) was reading a voltage of 38v which was connected to one of the terminals. The other terminal was connected to the B1 input (enable)/key switch line which is powered by the 48V bank. That leaves only a 10v drop across the contactor which is not enough to close it.

I decided to switch to a 24V contactor. Here's where things get weird. I flipped the switch and the controller turned on. 5 seconds later the contactor closes and the motor instantly starts turning and the key switch line fuse blows.

Since then whenever I flip the switch the motor spins for a brief moment before the key switch line fuse blows. The controller never lights up and I am afraid the controller is now damaged.

If anyone can give a recommendation on how I should go about testing for where this fault is please let me know.

Thanks
Gerry


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## MPaulHolmes (Feb 23, 2008)

I would check resistance from controller B+ to Phase1, then B+ to Phase 2, then B+ to phase 3 while the controller is off and not connected to anything. Then, check resistance from phase 1 to controller B-, phase2 to B-, and phase3 to B-. Each of those paths have a mosfet(s) or igbt(s) that should be causing near infinite resistance. If you see a near-zero resistance, or even just significantly smaller than infinity, a mosfet or igbt has failed, and their favorite way to fail is ON (conducting).


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## gerbear (Apr 23, 2012)

Given its for a dc permanent magnet I assume you meant m1 and m2 in which case the resistance across those two and b+/b- were in fact all short circuited. I believe I now own a $500 brick.


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## MPaulHolmes (Feb 23, 2008)

Oops, I thought it was for a permanent magnet synchronous motor. Yep, they can't be fixed. Maybe you could take it apart and put new ones in?


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## frodus (Apr 12, 2008)

The first time you hooked it up you used the wrong contactor coil voltage. The coil voltage of 60V is incorrect. The Millipak uses 24V for the contactor. If you used a 60V coil contactor, it MAY have blown the driver circuitry.

https://www.msu.edu/~tdc/play/electric/MillipaK%204QPM%20Manual%20V1.01%20(633T43801).pdf

How do you have it wired?

Take a look at the installation/wiring pages from the above PDF. Look at the connections for Connector B. You must have a direction wired (either B2 or B2) to ground, as well as FS1(B4) and Seat(B5) wired directly to -ve. Do you have one end of the contactor going to B8 and the other going to the keyswitch?


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## gerbear (Apr 23, 2012)

Yes I have one terminal of the 24V contactor connected to B+ and the other to pin B8. 

I believe you have a typo here "You must have a direction wired (either B2 or B2) to ground". Are you referencing the B2 forward switch? Initially that needs to be open on flipping the key switch (B1 pin) and then B2 is switched closed to engage forward drive.

For this setup I have been referencing the Millipak Manual as well as this thread which refers to a different millipak controller but shares many commonalities in the setup.
http://www.diyelectriccar.com/forums/showthread.php/sevcon-powerpak-and-d-d-motor-55062.html


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## frodus (Apr 12, 2008)

Not a typo, but it's unclear. You need to have a direction chosen, not upon closing the contactor, but before movement occurs.

Are B4 and B5 connected to ground?


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