FET Heat sink shorting with ESC

[Horshu]

This one's more of an informational post than anything else. I've got one of Zero's texalium chassis plus the full run of GPM aluminum parts. Additionally, I have a Dean's flex antenna, requiring a custom-drilled #4 screw drilled in the rear deck plate. Ever since I first built the chassis, I've been having electrical issues with the car. Sometimes, I'd put the antenna on, and it would heat up quite a bit (killed a board this way before). Even more often, I'd feel the FET heatsink get even hotter, with *smoke* coming out! With the battery heat sinks on, it's hard to take batteries off very fast, so I built a quick-connect harness. Over time, I found a few gotchas that were causing my problems:
1. Antenna short -> RS antenna lead's wire coating is pathetically fragile. On one board, it got nicked screwing the rear deck plate screws in, exposing a small bit of wire. I'm trying different wires for antenna leads (hopefully superflex will work, but if that fails, I've got the Dean's antenna lead I can cut up)
2. The other day, my board started flaking out a lot...range issues. Now, I'm in paranoia mode due to trying out the superflex antenna lead (AtomicMods faq says the RS antenna wire is tuned for these frequencies, so he does not say you can use superflex like this), but I had already run chassis-less range tests that worked fine. Turns out two problems were going on:
a) Battery springs were compressed on one side of the harness, so a battery was getting jostled loose.
b) Battery's solder points were shorting against the motor heat sink posts. IF YOU HAVE GPM PARTS, CHECK FOR THIS!!! I fixed by painting some liquid rubber on the solder points.
3) Found the lingering cause of the super-hot FET heat sink finally (this has shown up on 3 or 4 separate boards). Basically, I have everything tightened down so much that some leads on the ESC (likely battery leads) were cutting through the heat sink insulation, shorting the power against the aluminum. The smoke was coming from the cooking insulation. Two things that could be causing this, I think: First, too much tightening of the ESC screws, but they are going into plastic, so I doubt it. Second, I am likely overtightening the battery holders. I'm thinking of cutting some new standoffs so that there is no space between rear deck plate, battery holder screwholes, and standoff so that it can't be overtightened. I'm also shaving down some leads on the board to dull and shorten them

All in all, even though I'm fixing various electrical issues that have been lingering without blowing any more boards (knock on wood), it is still pretty nervewracking to know that at any point, there's the possibility that the board is going to run the risk of frying. Which leads me to another piece of advice if you've got custom chassis/metal suspension parts -> separate your battery from the battery lead with a quick connector (I'm using rubber-dipped Dean's connectors) in case you need to pull power in a jam (and trust me, that heat sink, if shorted, will heat up VERY hot and VERY fast.

Ouch!!!!!!!!!!!!!!!!

Good info there H, all that aluminum means conductivity issues. Good luck and keep us posted............

[Horshu]

So far, it's been very stable with the rubberized insulating sheet and ground-down board contacts. My range is still flaking out, though (antenna lead is 18 gauge superflex), which may be due to interference from the motor lead directly under it, or maybe it merely needs to be tuned for that kind of lead (I put screwholes for the tuning pots on all my ESC covers). I'm still checking the heat sink temp religiously after swapping on boards, but so far, it looks like I've whittled the electronics problems down to just the range, which is nice because that doesn't involve any shorting parts pouring smoke out of my car (my lead is fully insulated down to the board) I've got to make damn sure I don't have any more shorts before I put my lithium harness on this thing (got an NML SSv3 on the way that doesn't get run until this thing is fully stable) for the final round of platform stability tests.
All this has ultimately led me to start a case study document of XMODS modification. It isn't an end-all-be-all for all kinds of optimizations, but just takes my vehicle, which is close to being as modded out as possible without changing the form, and describes, in detail, the benefits and caveats to an all-aluminum, tuned suspension, modular electronics system, covering stuff down to things like optimal axle spacing on individual wheels and protecting from electrical shorts.