Originally Posted by BrianG

@Aragon: I see what you are saying. However, a coil can deliver more voltage than what was put into it if the magnetic field is allowed to collapse faster than it was built up. Take any coil, apply a 9v battery on it, and then remove the battery. Depending on the coil rating (in milli-henries), a voltage MUCH MUCH higher can be generated. This is how the cow fences I've seen operate. Applied to R/C; depending on how fast you brake, the field can collapse faster than it was built up and can generate higher voltages than the battery.