# Reduce 1kV pulse to 12v

Discussion in 'The Projects Forum' started by GammaRay, Jun 14, 2012.

1. ### GammaRay Thread Starter New Member

Jun 11, 2012
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I'm searching for a method to reduce a 1kV pulse @ 1 Hz (+/-) down to 12 volts. The 1kV pulse is provided by a spark gap connected to a HV source. Conversion efficiency is my goal. I will be appreciative of some helpful guidance.

2. ### MrCarlos Senior Member

Jan 2, 2010
400
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Could you use a resistive voltage divider?

1000/12 = 83.33.
100 and 1,200 MOhms. connected in series.

regards

3. ### Ron H AAC Fanatic!

Apr 14, 2005
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High ohmic resistors are generally expensive. How much load can your source tolerate?
Also, keep in mind that resistors have voltage ratings based on breakdown, so if you want to use inexpensive ones, you might have to use a few in series.
What are you really trying to do?

4. ### wayneh Expert

Sep 9, 2010
16,102
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A spark gap doesn't produce pulses, the HV source does. A gap may produce a spark if fed a high enough voltage.

As asked, what are you really trying to do? Are you trying to charge a battery with a magneto?

Otherwise, the most efficient solution is to unplug your HV source and plug in a 12v wall SMPS. Done.

5. ### GammaRay Thread Starter New Member

Jun 11, 2012
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Okay, here is more detail. I've inherited a Zamboni Dry-pile electrostatic battery. It outputs about 1kV in the microamp range. No telling how old this thing is, but it still works. A google of the Zamboni battery leads one to believe it can operate for decades with a very light load. I connected a 1kV spark gap (a gas spark arrestor) to the Zamboni and it causes a spark to jump the arrestor at about 1Hz, slower if there is low humidity. I am interested in an efficient method to step down the 1kV spark to around 12 volts. That is my reason for making this post on this Forum. From there, the 12 volts will be used to pulse charge a small cap that will trigger an SCR when X voltage is reached and dump the cap's accumulated charge into a small load, such as LEDs or audio buzzer. I am aware this will only provide occassional-intermittent operation of the load, if it is even possible at all. Why am I doing this? For fun, but mainly to see if it can be done.

6. ### wayneh Expert

Sep 9, 2010
16,102
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That's probably going to be the challenge - to not leak the power away faster than it's being produced. Cool project, thanks for writing up the details.

So your pile is essentially a high voltage, ultra-low current battery. You want a circuit that will allow power to be slowly captured from the battery and then self-trigger itself to do something fun, however often it can, given the power available from the pile.

One temporary simplification would be to use a timer that's not powered by the pile, maybe a wind-up clock of some kind that could trigger the circuit once every 3 hours or whatever. This would free you from having to design an ultra-low power clock right away and let you focus on the power storage challenge.

7. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
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How about paralleling the battery with a high voltage capacitor, and putting a step down transformer in series with the spark gap?
The capacitor will slow down the pulse rate, but it will be able to deliver more current. You can put your load circuit on the secondary of the transformer.

8. ### wayneh Expert

Sep 9, 2010
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I was thinking of that also, but I thought leakage might exceed the battery's output, which might be down in the nanoamps range. Maybe the key here is to identify a suitable capacitor. You might have to put some in series to get enough voltage.

9. ### GammaRay Thread Starter New Member

Jun 11, 2012
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I like the step-down transformer approach and would like to try it. I need, and kindly request, guidance on exacty which transformer part# to purchase in order to accomplish the 1kV to 12v step-down. Once I know that, I'll build the circuit and let you know how it goes. I am all ears, this should be fun.

10. ### wayneh Expert

Sep 9, 2010
16,102
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The problem with a transformer is that it's an AC device; nothing happens except when the current through it changes. You're battery makes a constant and tiny current. You do get a sudden current burst when it's finally able to jump the spark gap, though, so maybe the transformer will allow capturing a bit of that. It will give you more current at a lower voltage, and reasonably efficiently.

You'll want reduce the spark gap to a voltage that the transformer can survive, unless you can find an old TV flyback transformer that can handle high voltage without arcing.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
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There are pulse transformers being manufactured that might work. He needs a transformer with a turns ratio of ≈1000:1. Most are designed to convert a low voltage pulse to a high voltage, but you should be able to turn them around. A current transformer might also work (in reverse), but I suspect that the secondary inductance (was primary) might be too low.

12. ### THE_RB AAC Fanatic!

Feb 11, 2008
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The 1kV he said at the sparkgap is a pretty trivial voltage, most hobby-wound pulse transformers would probably handle 1kV input without any special treatment.

You can buy a \$5 potcore (the type that has a separate plastic bobbin which has 2 divisions) and wind some turns on it, that would allow for adjusting the number of turns to try to get some usable power out.

13. ### Stoney New Member

Jun 7, 2012
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try and old coil from a car.
unlikely to get 12v out though.
will be a nice low impedance though, you could feed that into a second small transformer to step up to something suitable.

Apr 14, 2005
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15. ### wayneh Expert

Sep 9, 2010
16,102
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Interesting. That looks exactly like one of the 4 sections of the transformer in the starter/igniter of my grill. It uses just one AA battery and generates big sparks at about 2Hz.

16. ### GammaRay Thread Starter New Member

Jun 11, 2012
17
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I like the idea of trying a HV pulse transformer, so I've spent several hours this morning researching pulse transformers to try and make an informed decision on which one to purchase.

I realize this forum is not to be used as a crutch, but rather a place to share legitimate information and ideas. However, without a background specifically in pulse transformers, I must admit selecting the right one is proving to be a challenge for me.

Rather than my spending good money and wasted time on a wild guess, I kindly ask if anyone can suggest which pulse transformer part # for me to purchase. Once I have that info, I have everything else covered and can try this approach.

Respectfully

17. ### THE_RB AAC Fanatic!

Feb 11, 2008
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1kV is so low that you are unlikely to need any specialised type of winding.

18. ### wayneh Expert

Sep 9, 2010
16,102
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I had to go read about copper wire but RB's point appears to be true, especially if 1kV is truly the upper bound.

OP, how well do you know that the peak voltage is 1kV? And, are you sure you want 12v output (what are you powering)?

I ask because the transformer output will be the input divided by the turns ratio. The better you know in and out, the better you can specify the turns ratio.

19. ### GammaRay Thread Starter New Member

Jun 11, 2012
17
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The spark jumps a new Epoc 1kV gas-filled arrestor. Assuming Epoc manufacturing tolerances are decent, I'm pretty comfortable that the 1kV figure is accurate. Admittedly, 12 volts output is a figure I pulled out of the hat because it gives more than ample headroom for any small load I may want to power, but I'm not married to 12 volts, I could settle for less v if it opens up a more accessable solution.

20. ### Ron H AAC Fanatic!

Apr 14, 2005
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I agree.
I think it will be difficult to find a ready-made pulse transformer that will work, and I am no expert on pulse transformers.