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Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
i have thought of using a ballast for couple of days and after reading that a well built variac can withstand overcurrenting for a couple of minutes i have decided to put a detacated 30 amp breaker and use scroll to the almost bottom of the page and i think i am going to buy that and use that as a ballast. If i am having some heating problems i will submerge it in mineral oil.
Registered Member #1127
Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139
Do you have access to 240V 4-wire outlet? It would have you a tonne of headache by simply running a 2 by 2 set - series of MOTs - putting the primaries in series for 240V and then wiring the phases together. Really simple and will cut down on current draw! You'll pull at least 23A 240V - on 120V thats nearly 50A!!!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well most of my MOTs draw ~19A shorted from 230V mains, so this is nearly 80A for 4 MOTs from 230V OR 160A for 120V, unballasted. I realise that in Tesla coil, they don't run "shorted", but I think you'll be still drawing some 60-80A from 120V unballasted.
Registered Member #1127
Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139
That sounds like you have several larger cored industrial/commercial MOTs. I had several of those guys hanging around a few years ago and then I sold off my power supply to a physics prof at a local university. It was built from 4 MOTs and unballasted it could pull somewhere between 43.5 - 48 A @ 220/240V. Using MO caps on the secondary side helped considerably but I still needed a range outlet running 40 A. With smaller 600-700 watt MOTs - it was easy to run my system off of a single 30A socket - The max current pull was 25.5 A @ 240V. So not bad at all .... built for $45
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
in transformers the VA rating is the constant average power rating, so a mot supply of 4 1200VA mots can draw 40A@120vac continuously with no problem. that would be the normal operation in a microwave oven but when a arc is drawn a peak currents can easaly be 4 times grater. the impedance of an electric arc is much lower than a magnetron. if you put a metal object in a micro oven the efect is the same. if a arch was created continously and you had a 100A service your mots would self destruct after a time. if an arc is drawn for a moment you cuold easaly pop the braker with out a balast. usaly the arc length is praportional to the power you can suck from the wall. a large tesla does have defined impedance that may excied the limitations of the mots but could be run until the mots got hot. if you live in apartment a balast is advisable. good luck
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quad mot ballast help
