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Registered Member #662
Joined: Sat Apr 21 2007, 06:58PM
Location:
Posts: 32
I want to run a low voltage step down transformer (12V) in reverse. If I don't have any current limiting, the transformer starts to smoke this way. Would it work if I used a 100 watt light bulb or something similar for current limiting?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That doesn't work. if you try and shove more voltage into a transformer than it's rated for, it just saturates and starts to smoke. If you want high voltage, you need a high voltage transformer.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Mr.Cake probably thinks he can run transformers in reverse, but I think he is a doofus. You may get a peak voltage a good deal higher than normal before saturation, but it's not anything like a good or efficient way to run a transformer. Notice that he says it needs a big power resistor that gets very hot.
Registered Member #354
Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55
I have simulated using spice and with 220V at 12V side you have 900V at the other side. I have injected square pulses of 100ns width every 1us (10% duty) over a 900 ohm load (900Wpeak, 100W average). Then at primary power consumption was 145W I am not expertise in transformers, but if you inject x18 times the voltaje, you must do it at 1/18 duty in order to not saturate
The only problem is you would be over breakdown voltage of isolation coating, not only smoke but could have a big exploding transformer. Good fireworks!
Registered Member #546
Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239
Brock, I built that exact power supply.
It doesn't work.
What it _DOES_ do is charge the capacitor to ~1500v and then the core saturates and the thing goes into meltdown mode with the ballast resistor, burning a hole in the plastic table you work on.
then you think "what didn't work" and you pick it up and get bit by said capacitor. And you get upset and throw the whole thing against a wall.
and then you go to the surplus store and buy a $10 HeNe power supply brick.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Just to give this sad thread some slightly constructive input, you can run a transformer at a higher voltage than it is rated for if you increase the frequency at the same time. Since I doubt you have access to the components required to build a proper inverter, I suggest you try the self-oscillating relay trick. Sam Barros has some info about this on his page, he used it to get a few kV from a small wall-wart transformer.
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High voltage power supply
