Does anyone know if I shouldn't use the bind slot to power my Transponder. It seems to work ok but wanted to check really

My transponder has been plugged into my bind slot and a fan plugged into aux on my 3100 receiver all summer and I haven't had any issues.

Cheers for that, I just needed a second opinion

The Auxiliary and Bind/Battery slots can be used in any matter, aside from their intended purpose

Nothing like that extra slot for power!! I use it all the time for my motor fan.

I learned something at the track yesterday. The slot in the receiver is limited to 6v (vice the entire capacity from the battery). A friend soldered my fan wires direct to the ESC. More volts=more capacity=more fan speed. Very cool.

And I still have that open slot again.

The receiver receives its power from the ESC and the ESC has a BEC circuit in it that drops the voltage to 5 or 6V depending on the brand. All the ports on a Rx have the same voltage.

If you need more volts then you need to bypass the ESC BEC and use an external BEC that is adjustable for output. The other choice is to solder onto the battery leads on the ESC and then you'll get the full battery voltage.