High Voltage Bias for DIY Electrostatics - diyAudio
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Old 25th September 2001, 08:17 PM   #1
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I have built a pair of electrostatics using Sanders' book. I'm having trouble building the permanent high voltage power supply. Right now I'm using a professional, loaned power supply which costs about $2K more than I'm willing to spend.
I plan on using a step up transformer (400-500Volts) and using capacitors and diodes to retify/multiply the voltage up to 3KV DC. The plans are all laid out in Sanders' book, but I cannot find a step up transformer that is sufficiently cheap. The bias draws almost no current, so power is not a problem. So, can anyone help me find a cheap (<$30) transformer that steps the voltage up to 400-500 Volts (given 110V at 60hz, of course). The current rating can be less than 10mA.
Thank you very much.
-Dan
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Old 25th September 2001, 08:30 PM   #2
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Dan,
Try finding a transformer such as the ones used to light neon signs. Mucho voltage, minimum bucks...especially if you can locate one used, i.e. a junked sign.

Grey
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Old 25th September 2001, 08:57 PM   #3
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Hi Dan,
Contact Barry Waldron at the "ESL Information Exchange". He sells the hard to find items to complete an ESL project. Has assembled bias supplys for 45$, but would probably sell you just the transformer for much less. Hope this helps. http://www.jps.net/eslinfo/catalog.htm
William

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Old 25th September 2001, 10:29 PM   #4
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Thanks for replying, folks.
I have seen Barry's bias supply, but I'd like to try and build my own, and perhaps save some money. If it looks like it will be too expensive then I will swallow my pride and order a bias supply.
I'll check up on the neon signs though. I plan on using a scavenged variac to control the final voltage of the bias. Neon transformers seem like the most viable option.
-Dan
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Old 26th September 2001, 09:07 AM   #5
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Try hooking up a regular step-down transformer backwards. this is a very inexpensive way to use it as a step-up instead. The voltage ratio will be the same. Just be careful not to step up too far!!! The transformer should be hi-pot tested to a voltage well above what you intend for the output voltage.

Then, use your voltage multiplier to take it up to the level you need... Easy as pie!
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Old 26th September 2001, 10:30 AM   #6
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You could try here:

http://www.surplussales.com/Transfor...vLvTrmain.html

Jake
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Old 26th September 2001, 05:38 PM   #7
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After looking at some neon sign transformers, I ran across an obvious problem. How do I rectify 3-4KV in a way that is not cost-prohibitive? 1KV Diodes are no problem. Can I just put four of them in series, or do I have to worry about possible manufacturing differences in the diodes?

hifiZen, I've tried hooking up a transformer backwards. As I turned up the voltage on my variac the output did not climb linearly, and then I noticed smoke rising from the transformer. Obviously, it wasn't rated to take such high voltages. Finding a tranformer that is hi-pot tested above 500V is my problem. Do you know where I could get a cheap one?

Jake, thank you very much for this site. $19 doesn't seem like too much to ask for a 440Volt Transformer. I may just buy it and be on my way.
Thanks again folks.
-Dan
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Old 29th September 2001, 04:31 AM   #8
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Dan,
No, I hadn't forgotten you, just been busy.
Yes, diodes can be run in series. You will need to run resistors in parallel with each one to ensure even division of the voltage. The rule of thumb for the resistance is to multiply the PIV of the diode by 500 ohms, i.e. for 1000PIV, use a 500k resistor.
It's also a good idea to run a small cap (~.01uF will do) in parallel with the diode and resistor pair.
Be very sure that you allow *plenty* of PIV for whatever rectifier scheme you decide to use. Diodes, resistors, and small caps are cheap. An out of control power supply could be very expensive, indeed.

Grey
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Old 8th October 2001, 08:53 PM   #9
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After looking at my options I decided to do what seemed like the cheapest and simplist. I bought a couple of step down transformers off of Ebay and plan on using them backwards, as step up transformers. The model is Hammond 160H24, at http://www.hammondmfg.com/160.htm . I used a suicide cord and plugged it into the wall to see what would happen. It began to violently buzz and smoke. I am almost positive that there was no cross connections in my wiring. I did not have anything hooked up to the output, as I was about to measure the voltage across the leads. Is there anything obvious that I did to deserve such a fate? Should I have had a load across the output? The specs of the transformer say that it has been hipot tested at 2000V, which is well above the 440 that I was expecting. Any input on this is welcome.
Thank goodness I bought more than I needed.
-Dan
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Old 8th October 2001, 09:53 PM   #10
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Just thinking out loud (or at least in type), maybe you should've had a load across that sucker. Just imagining the primary by itself, its essentially a wire shorting the suicide cord. The built up EM field isnt being drained into the secondaries to dissipate energy. Perhaps this is what destroyed your transformer.
Then again, something doesnt sound quite right about this diagnosis, so I think I've just successfully talked out of my ***. But you do have several more of those things. Maybe we should try sticking a fuse in series with the suicide cord (making it a safety cord) and then putting one of our scavenged power resistors across the secondaries (in series, I assume you're running.). If you dont want to risk one of your heatsunk 2ohm power resistors, we can use that resitor bank that i ripped out of that power supply. Thats my input, anyway.
- Jonathan
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