[MTBikerTim]

Originally Posted by BrianG

OK, here's where it gets a little tricky if you have a hard time understanding what's going on. It IS ok to hook the UBEC across both battery packs (as a whole) IF the whole battery voltage of both packs combined is less/equal to the UBEC max input of 25v.

I'll explain the reasoning of the "Don't do this" sections:

• The Castle UBEC is only rated up to 25v, so 6s is the max battery you can use. Castle's picture shows dual 6s packs, for a 12s total pack, which would be far higher than the UBEC can take. That's why they say to hook the UBEC positive lead to the "bridge" wire of the pack Y adaptor (the UBEC will see only the voltage from a single 6s pack).
  
  
• Just about all UBECs (Castle included) do NOT isolate the ground wire from the battery pack ground. So, if you hook the UBEC negative lead to the pack "bridge" wire, you are making the UBEC ground "float" at half the pack voltage. So, if the main battery ground is tied to the UBEC output ground ANYWHERE else in your setup, you WILL fry a wire, the UBEC, receiver, servos or any combination of these. Even if you ensure this is not the case, it is always best practice not to do this.

I hope that made sense...

Dang, 83gt beat me to it. I type too slow and talk too much.

Your info was still quite informative brian. I couldn't work out why the second setup wouldn't work but of course what you said makes perfect sense. Personally for a 12s setuo I wouldn't be using a bec that couldn't take the full voltage. That could lead to a over worked pack fairly easily couldn't it.