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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
yes Klugesmith all of what you said is true but at power, in my experience above about 500Hz-1kHz power becomes difficult if not imposible to push through.
Laminated iron transformer cores aren't limited to mains frequencies. They've been used for about 100 years between vacuum-tube amplifiers and loudspeakers. And are found in galvanically-isolated microphone inputs on professional audio boards. And in 56K modems (remember them?). The laminations for audio transformers are commonly thinner than those for mains transformers. Eddy current core loss is a linear process (does not introduce distortion). Hysteresis loss is present in ferrites as well as steel cores.
As mentioned previously, the OP talks about a MOSFET but shows none in schematic.
Replace the BJT with a MOSFET and you've got the idea ;)
EDIT: Since I'm in need of an old unrectified flyback, I grabbed this on eBay which should suit my needs well. I have plenty of spooky capacitor-ridden DC flybacks but they're pretty fussy with regards to the primary pins sparking over and require careful discharging after every use.
As for this iron cored mystery transformer, I'll have to play around driving it with a 60 Hz 12V output from a stepdown line transformer and work from there. Any precautions to take? Resistors, fuses etc. I've never driven any HV transformers off line frequency before.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Iron core audio output transformers for tube amps are capable of operating from about 50-15000 HZ with one modification, the core has an air gap to prevent the DC from saturating it.
If you want to drive your transformer with transistors, configure it. as a class B amp using 2 drivers and feed it through a capacitor.
Getting 500 Hz and beyond to drive such a transformer is possible as long as is it is NOT a square wave.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
You should be fine just hooking it straight up, the step down transformer will limit your current input. You can add some line conditioning circuitry but that isn't needed to get it going. Just be careful, the reason line current is so dangerous is that it is the same frequency as your heart. This means a little current can send you into fibrillation. Aka death.
Insulate all line voltage connections and wires and you should be alright.
You should be fine just hooking it straight up, the step down transformer will limit your current input. You can add some line conditioning circuitry but that isn't needed to get it going. Just be careful, the reason line current is so dangerous is that it is the same frequency as your heart. This means a little current can send you into fibrillation. Aka death.
Insulate all line voltage connections and wires and you should be alright.
Yeah that's what freaks me out :P With the high-freq flybacks the worst you can really get is an RF burn.
On hand I have a 12VAC 1.5 A power supply/transformer thats powering my keyboard speakers. Perhaps I'll try that in a while.
That sounds like it would be perfect for experimenting with your HV transformer, not too much current but enough to do something.
Success! 12VAC in at 60Hz produced a very nice ~10kV thick orange arc. I'm sure it could take 24V in without a problem. This thing will be perfect for a Jacobs ladder!
Good to hear you got it running! Make sure you post picture of whatever you do with it!
Seeing as your transformer is only rated for 1.5A you might want to take an amperage measurement... or at least feel if it's getting hot after runs.
Yeah, herein lies the problem. It was drawing 2.5 A at idle and about 3.5 A when arcing. The stepdown transformer was pretty warm but the HV transformer was cool to the touch.
When I run this thing at 24VAC, how much current draw should I expect? 5A? 7A? I'll need a huge stepdown transformer
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
dwarnecke11 wrote ... Yeah, herein lies the problem. It was drawing 2.5 A at idle and about 3.5 A when arcing. The stepdown transformer was pretty warm but the HV transformer was cool to the touch.
When I run this thing at 24VAC, how much current draw should I expect? 5A? 7A? I'll need a huge stepdown transformer
Huge is a relative term.
Back to your question: That depends on whether this transformer moves into saturation between 12V and 24V. At any given frequency, the transformer has a maximum input voltage that it will take without saturation. Saturation is not a "brick wall" that springs into effect at some sharply defined threshold voltage. And it does not depend on how much current you are drawing on the output.
Since you are already able to measure your AC primary current: a conservative approach is to increase input voltage in small steps and watch for a nonlinear increase in input current. Or go straight to 24V, with an on/off switch so you can apply the voltage for just a second. Maybe you can't find a 24V 10A transformer at the hardware store, but you can find 12V lighting transformers and put 2 in series.
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Mystery HV Transformer and Frequency Troubles
