[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: The "second pig" ballast: Questions.

Original poster: BunnyKiller <bunikllr@xxxxxxx>

Hey Arron...

a quick lesson in core physics in laymen terms...


ok.. you have a core that is "complete" no cuts no gaps.... when a coil of wire is wrapped around one of the "legs" ( we are considering an inductor here) and voltage applied ( AC) , the magnetic flux in the core changes direction with each change of the AC sine wave. Since the magnetic flux is moving in one direction and then the AC sinewave changes direction at peaks, the magnetizing force of the coil must reduce the existing flux flow in the core and make it start running in the opposite direction. This takes power to do so, ( this power to do it is taken from the source and thus limits the power to the item being driven, in our case the hi volt xfmr) .
If you apply a gap ( air gap) to the inductor, you now have less "magnetic" material available, when the same voltage is applied to the coil on the inductor, the amount of magnetic flux produced in the core is reduced ( due to the gap) soooo now you need less energy from the coil to reduce ( reverse) the magnetic flux flow in the inductor. Now you have more power available to the item being run on the other end of the inductor.... ( the word is reluctance)

so in a general rule of thumb situation, the bigger the core center, the more magnetic flux it can handle without saturating... ( a core can handle only so much manetic flux and then after that it doesnt resist the AC flux changes and it basically goes into hyperdrive pretty much like no inductor present at all)

the tighter the gap on the core the less power is available to the transformer.... widen the gap and you get more current to the xfmr

as far as winding numbers... you really arent looking for current capacity for a minimum of turns you want to have volts per turn safety factor... in general about 1- 2 volts per turn max... so a 240 V system should have about 150 - 200 turns.

also... the wire on the inductor should be rated amp wise to be equal to or greater than what the maximum current you plan to use with the hi volt xfmr.... since the wire will be all tightly wound around the core, the cooling capacities will be diminished and the wire will become warm.... best bet is to go at least 25% better than your maximum needs.... if you are planning on driving a piggie 10KVA or better
look at a single #6, or double # 8 or triple # 10 THHN


hope this helped


Scot D





So, a quick physics lesson on why the air gap is so
critical would be interesting (at least to me).  My
mental model of an inductor is obviously
over-simplified.