Reversed polarity – what would you do?

[Tiernan85]

Hi fellas,

I bought the PDB recently and today got everything soldered up. I resoldered the esc positive and negative wires also as I was replacing them with fresh stuff. On one esc I made the mistake of reversing the positive and negative. When I connected everything to power, I quickly noticed a small amount of smoke from the esc and unplugged the power. I’ve torn it all apart again and pulled the shrink wrap off the esc. The wrap was very partially melted to the positive lead. It appears that was what heated up and I can see there was some flux residue which I’m assuming is what caused the bit of smoke. I’ve resoldered everything correctly and stand alone tested the esc. It powers on and runs the motor perfectly fine.

My question now. Would you still run this esc? I’m going to give it a full battery cycle test to check for excessive temps or failures but it really does seem ok and there’s no burn marks on it anywhere. I would happily order a replacement esc but the potential month down time would really be painful. Just looking for opinions.

[rd]

Ok, I will go out on a limb here and tell you what I would do, and you can make your own decision. I am more careful with expensive fpv stuff than just flying with quads or tricopters. The truth is, they all crash. Being too conservative can lead to crashes and being too aggressive can lead to crashes. If I had your problem with a regular quad or tricopter, i would fly it.

That said you need tons of stuff to stay in this hobby. I have many extra esc’s of various sizes, i have so many props i have to organize and label by size and pitch. My kitchen looks like an experimental aviation lab.

[Michar]

absolutely NOT

[Tiernan85]

Appreciate the feedback.

Spares are a necessity yes, don’t know why I didn’t have one kicking around already. They’re on order now.

Well I have refitted it already. I’ve bench tested a pack through it on full power. This was with no load on the motor though. The esc did not get any warmer than normal(which is hardly at all). I will also bench test it with a prop on to give it a load and see how it fares.

If that is ok, I will take the chance it’s ok and fly it. Once the new esc arrives I will still replace it. Here’s to hoping I don’t regret it!

[Triffnix]

It is not the cable that got hot, but some protective circuit, or a component acting as protective circuit. Those circuits are designed to handle short spikes, making the device EMC-safe. They are not designed to handle a constant reverse current. This is why the magic smoke escaped.

You almost certainly damaged a component on the ESC. This can lead to unpredictable behavior. If the voltage regulator has been damaged, the ESC may brown-out at some point, and the copter will come tumbling out of the sky. If a FET has been damaged, you may lose power under load. Worst-case the FET bridge shorts out, and the battery catches fire.

There are more possibilities, each with a nasty failure mode. Of course, spectacular failures are a part of the hobby. So there is no reason why you should not fly your copter until the replacement ESC has arrived. Just do not fly over people. Or valuable objects.

[Tiernan85]

It was definitely the positive lead that got warm. I know this because even the boom had become a bit warm. And there was also a small amount of smoke from flux residue where I soldered to the board.

I don’t doubt that there’s possibly some damage. But I still think the smoke was from the flux residue heating up. I had checked the entire board and none of the components had burn or excessive heat marks. I’ve still to do the full test with the prop on and I will run it down to my normal cutoff range to ensure it doesn’t prematurely fail. And obviously once the replacement has arrived it will be swapped out.

If it does end in a crash. I’ll be sure it’s recorded 😀

[Author]

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