Why do I keep burning out XT90s connectors?

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Jun 12, 2017
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I have a 52V (14s2p) battery with an XT90s (anti-spark) connector that I've been using on a BBS02 for awhile with no problems. I recently started a new build with a TSDZ2. I hooked up the battery and did a test of the new motor with an existing bullet-to-XT90 cable I already had (made it for my BBS02), and there were no problems. Then I cut off the factory bullet connectors from the new motor, soldered on the new ones (the old ones were not the length I wanted, and bad quality). Then I made a new bullet-to-XT90 cable.

I hooked that up and, and when I did, immediately burnt out the resistor in the XT90s connector on the battery. I figured maybe I plugged it in too slow, which resulted in current flowing through the resistor for too long, so I made a XT90s female to XT90 male adaptor and plugged that onto the existing XT90s connector on the battery (the one with the burnt resistor now). I plugged that into the motor, and the resistor in the *new* connector immediately burnt. That time I had made sure to plug it in swiftly and smoothly.

What's going on? Why am I burning out the resistors? Could it be a problem in the new cables I made somehow? I've confirmed (many times) that the polarity is correct. The anti-spark connectors are a little pricey and I only have a few of them so I don't want to keep burning them out with random experiments. Thanks!
 
Ron Paul's Blimp said:
What's going on? Why am I burning out the resistors?
The obvious answer would be that for some reason (misconnection, heat from the soldering warping the body, some new torque on the connector) the contact isn't making completely and all the current flows through the precharge resistor forever.

I'd take your assembly and connect it while looking at it with an ohmmeter. Verify that the resistance goes to zero very quickly. (Note you only have to disconnect one side to do this.)
 
Not sure if this would work for you, but I put one of these on the hot wire of the Andersen to XT jumper I made, to connect my battery to controller. I switch it off before connecting/disconnecting the battery.
https://www.homedepot.com/p/GE-Q-line-50-Amp-1-in-Single-Pole-Circuit-Breaker-THQL1150/100167462?MERCH=REC-_-PIPHorizontal2_rr-_-300224018-_-100167462-_-N
 
billvon said:
The obvious answer would be that for some reason (misconnection, heat from the soldering warping the body, some new torque on the connector) the contact isn't making completely and all the current flows through the precharge resistor forever.

I'd take your assembly and connect it while looking at it with an ohmmeter. Verify that the resistance goes to zero very quickly. (Note you only have to disconnect one side to do this.)

Thanks for the idea. I did this and I can't find a problem with the cable. The resistor gets shorted out and resistance falls to 0.01ish ohms with around 2-4mm of travel left in the plug. By the time there's only 3mm of travel left, it's solidly 0.01ish ohms. The cable I've been using for a year or so on my BBS02 tested the same.

Could a kink or broken conductors somewhere else in the cabling do this somehow?

E-HP said:
Not sure if this would work for you, but I put one of these on the hot wire of the Andersen to XT jumper I made, to connect my battery to controller. I switch it off before connecting/disconnecting the battery.
https://www.homedepot.com/p/GE-Q-line-50-Amp-1-in-Single-Pole-Circuit-Breaker-THQL1150/100167462?MERCH=REC-_-PIPHorizontal2_rr-_-300224018-_-100167462-_-N

That might be a good stopgap, thank you. I still want to figure out what the heck's going on though.
 
Wellllll I'm a huge dumbass. I gave up and decided to redo everything from scratch for lack of better ideas. When I took the new bullet connectors I'd put on the motor off, I found I had in fact gotten the polarity wrong. :oops: I don't know if that could blow the anti-spark resistor but it sure can't help. Hopefully the controller isn't toast :(
 
Maybe you purchased counterfeit XT90's

I like the XT90's and I bought a bunch from HobbyKing, havent had an issue. Only issue now for me is they use FedEx so Canadians get ripped off, but I could be wrong, as Duties have to be paid.

I have melted 4mm bullets with housings, taped together. I am lucky I caught it in time.

Wrong polarity would easily melt the the connectors. But you'd hear and see sparks.
I did that once on my hksunwin controller, but I realized what I did, luckily the controller survived.
 
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