Melting loop key? SOLVED

i will try it when i get home. im gonna try one of the ones that i toasted and see if it works. its only slightly toasted. just how i like my bread mmmm

hmm, interesting :no_mouth:

very observant @lox897 is right, i was plagued by the same issues and, while the size of the loop increases inductance, i calculated it in a later post and it looked insignificant. cant remember if loop keys had a ± stamped on them … or an electron flow direction in the ++ or – loop key scenario?

fact is: i still havent understood my problem and i left out the loop key ultimately. besides melting keys i had large induced voltages that killed one of my vescs. you could see that in the bench test live monitor: revving up and the battery voltage plummets, stopping the motor and it skyrockets way beyond the battery voltage. my 2nd loop key didnt have that inductance problem, but it also got hot.

Hmm, maybe @Karmannghiagirl is right about the XT90s being directional. Which side of the key is your battery on, positive or negative? I just checked my loop key and I have the battery coming in on the negative side of the connector and the positive side going to the esc. It also looks like there might be some black carbon buildup inside the positive terminal of the key where the green capacitor or resistor is located. I’m only running this on 6s though, so maybe that’s why I haven’t had it burn up yet? You’re running 10s, right?

I place it in the positive wire. The battery sits on the negative side:


@Karmannghiagirl I just did a bit of research on it. It is a resistor.

It has to be a resistor. Putting a cap in makes no sense. It needs to limit the inrush current to stop the spark.


And now you have a scientific explanation… Jeez your good @lowGuido :joy:

Im gonna try this tomorrow thanks for the diagram

Im not sure and now im flooded with studying so I will let you know tomorrow and ill try to fix it :slight_smile:

and yes 10s

thinking about it that does make more sense :sweat_smile:

Ok, I thought it was a resistor. All this talk about melting loop keys and capacitors had me second guessing myself. If I’m not mistaken, once the connector is fully engaged, all the current flows around the resistor. But maybe the main connector isn’t engaging/connecting and forcing all or most of the current through the resistor? Not sure what else it could be unless there is massive current draw overloading the connector, but aren’t these rated for like 90 amps continuous?

And fwiw, my setup looks pretty much like @nowind except I’m using XT60s for the battery connections.

That is way too far fetched.

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That was @whitepony 's theory. He quickly realised that it wasn’t correct.

I had the very same problem and everbody told me: “it does not matter how you plug the loop key in”…

Well it did make an difference for me. Here is the thread and to conclude the problem i made the following picture:

To put it in a nutshell i made the following diagramm:

here you can see that the polarity of the XT-90S needs to be switched. Otherwise it melts like mine or yours.

I hope i could help.

PS: Before someone says that this is not the problem please test both wirings and report back :wink:


Great! So it must be a polarity issue then! Thanks for the shared wisdom.

I noticed you had yours set up as a break in a serial connection. I have one battery and I am putting my xt90s as a break in the positive lead. Which side in that situation would you believe gets the positive side of the xt90s? The live wire gets the + or the severed wire?

Actually i do not really know. I would guess that you connect the xt-90s positive with the positive battery cable and the xt-90s negative with the esc. Then it is like mine except two batteries and you put it in the positive wire. But i dont give you guarantee.

So, sounds like it’s a combination of incorrect connector configuration and higher voltage, like 10s or 12s?

I dont think the voltage matters… I think it was just the wrong polarity… EDIT: But i dont think you can use 100S with a XT-90S :wink:

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Switched polarity same results… I might just keep the regular xt90 and let it spark and I’ll swap it out ever few months