Below is a letter I sent to Castle Tech this afternoon. Any ideas on my issue?
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Hello, I have a Castle BEC and it fried immediately after install. I have used CC Becs before and have had them last for awhile. One is still in use and the one that just fried was a replacement for one that lasted a year or so.

Here's my set up: Ofna Lx1e 1/8th scale buggy with 4s lipo and a Hobbico CS-170 servo (high current draw 1/8th scale servo). I was running the Castle BEC at stock voltage output (verified at ~5v at plug before plugging it in). Input voltage was verified at 16.8v.

Here's where I wonder if I did something wrong. My esc has a capacitor pack from the factory soldered to it at the same place the leads to the battery pack are soldered. I soldered the leads from the CC BEC to the same spot. Could that capacitor have fried the CC BEC? If you need a picture to see the set up I can forward one along. If not the capacitors, is there anything else with the set up that may have caused the failure? Too much current draw?

Thanks for your time,

Scott

Most, if not all, car ESC's have caps across the + and - battery inputs. Some are internal inside the ESC case, others are external on leads like yours. It doesn't matter if you solder the BEC input at the same point as the caps, or at a different point on the battery input wires, or at the battery connector. In terms of the circuit it's all the same point. So that would not be the cause.

It's very possible that it was just a fluke occurrence, a bad component or connection in the BEC. But Castle should take care of it for you no problem.

I would have thought so too. I can really think of nothing wrong with the set up.

However I might just bite the bullet and snag an EZRun SC8 esc. If I plan on running 4s in the buggy then I probably should get a beefier esc.