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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Im having trouble finding a large enough variac for my coil, and from what i read, they are not totally necessary.
I have been working on coil specs from people using 120v mains power and i thought if their power supply would run at say 3000w, then i would only need 1500w to run the same powered coil since our mains is 240v.
Now ive been told that my coil could run at up to 20A so this may be a problem, since i thought i would only need 6A at the wall and i managed to score an 8A variac.
perhaps i can do without the variac and just adjust the breakout from the midi controller instead?
I was going to use voltage doubled mains output from a variac that would let me get up to 270vac from the overwind on the variac itself, so the bus voltage would be somewhere around 680v.
The other problem is i may need to wire in a 20A outlet in my garage, but ill worry about that later i guess.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
Years ago, I had a big problem with my TC popping the circuit breaker (120VAC@15A). I would have to cut the primary current by -something like- 40%...?
Then, I connected a power factor correction capacitor bank to the primary connection of the neon sign transformers (a lot of 15kV 30mA and 60mA all in phase-corrected parallel), and the breaker remained intact...never tripped again from that point on. The primary needle Ammeter (20Aac) no longer slapped a peg again either!
I don't recall the total current at 15kVAC, but I got hot 4' sparks. I remember one run, where the air must have gotten highly ionized and sparks of over 4' reached out like an arm and hand with fingers, as if attempting to grip my head! FREAKY!
The thing is stored in the corner of my shop, as the huge grounding system must have worn out--did wonders for the lawn in that area, though.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it. Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hazmatt_(The Underdog) wrote ...
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it. Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
I found a cheap GR variac on Ebay for $20, but cost $200 in shipping to New Zealand, considering small 2A chinese Variacs cost that here i figured out it was a bargin, 8A may do it, are you running on 240v or 110v mains?
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday. It's been on the back-burner for a long time, just got the box 4 months ago.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
Hazmatt_(The Underdog) wrote ...
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
...as for those cheap orange Chinese variacs--BEWARE!! I was recently zapped really, really, really, hard when I touched the orange thing. I think this was not noticed before since, this time, I was barefoot on the floor. The AC outlet tester (the variac had an ac outlet on it) reported HOT AND GROUND REVERSED!!!! I verified this with a meter--this was indeed the case! BTW, this was the first time I saw this particular error. Also, I saw a youtube video reporting that this (exactly what happened to me) was a possibility in the guy's 10A model. He reported that his particular variac design, IIRC, used 'careless' earth grounding techniques, focusing mainly on the HOT wiring. I am going to check the internal wiring.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hazmatt_(The Underdog) wrote ...
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday. It's been on the back-burner for a long time, just got the box 4 months ago.
Well i guess i should be able to push 10A through my 8A rated variac if thats the case, this is probably the most my unit will handle unless i het a higher rated power outlet installed.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Mads Barnkob wrote ...
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
OK thats good to know, it hums a bit as it is without a load!
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How cruical is a VARIAC?
