Having run nitro RC for a while, i thought i would buy an xmod to run around the house. Knowing nothing about electronics, its been standard in that department till today. After looking into how to do it, I decided to add another cell, and bought a holder for a AA which because of its design will also fit a AAA nicely.
It is wired as per a diagram i found on this forum, cut the wire joining the 2 stock cell holders, and fitted it in between them. I checked to make sure that it would run without the 5'th cell in place to make sure it was wired correctly, and all was well. I fitted the 5'th AAA and ran it woithout any problems, then wondered how it would go with a 5'th AA. Everything was fine till I turned it off at the switch with all 5 cells still in place (4 AAA +1 AA) at which point smoke started coming out of the front of the xmod

I think I pulled the 5'th cell in time as it still works normaly, as far as i can tell, but im not sure why it started smoking now .. is mixing AA + AAA a big !!NO!! ?, or is my wiring messed up ? or something else ?
Please excuse my noob questions, but we all gotta start somewhere.