General ESC Theory Discussion

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.

Do you have more info on this? Or a better explanation? :)

[BrianG]

Originally Posted by Aragon

Do you have more info on this? Or a better explanation? :)

You can do a Google search on inductor formulas, inductive kickback, back-EMF, etc to find all kinds of information about this phenomenon.

When you apply a voltage to a coil, a magnetic field will build up over time. The time it takes for the coil to magnetically saturate depends on the coil rating (henry value), core type (air vs iron), winding resistance, and voltage supplied. This built-up field is actually "storing" a charge, somewhat like a capacitor does. When you remove the battery from the coil, the field collapses instantly generating a voltage higher than the one applied because the collapse is quicker than the build-up. This voltage generated is opposite in polarity than the one applied because of the direction of the magnetic field motion cutting the coil windings. Incidentally, many times in circuits that energize a relay, you'll see a diode placed across the coil in reverse polarity, which shunts the back-EMF generated by the relay coil to prevent the V spike from damaging connected circuitry.