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how do you measure HV? Answered

what's the best way to measure High voltage (I think my output is somewhere between 10kv and 50 kv)? Is there a formula for the spark length and humidity (I can measure humidity)? I need to buy an appropriate capacitor for my tesla coil, my initial HV is from an ignition coil.

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FelixSP (author)2012-08-08

Maybe a static DC Voltmeter?
http://www.celnav.de/hv/staticvoltmeter.jpg

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gmoon (author)2008-07-22

Voltage divider? For instance, if the input voltage is 50KV, a 10M and 100K divider would give you an output of about 500V (495.5V).

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tazerboy (author)gmoon2012-08-03

Are you sure? I got 4950 volts

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steveastrouk (author)tazerboy2012-08-03

Yep. special high voltage resistors are used

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forgesmith (author)2008-07-23

How do I measure HV?

Well if my hand jerks back it's about 5kV, if my arm jumps back and it stings that's about 9kV, if I completely jump backwards and wonder what happened that's at least 15kV, if I get awake slightly singed and find myself up on the roof then...

What? Oh, you want to know how you can measure it! Never mind then.

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guyfrom7up (author)2008-07-22

I have an oscilloscope, but how would I use it in this situation? I think a voltage divider would be bad in this situation cause dont resistors fail at a certain voltage

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gmoon (author)guyfrom7up2008-07-22

If it's just DC, then a VOM / divider will work fine. You can use a scope, but you'd need a high voltage probe. Which is what? A voltage divider.

It's current that will cause resistor failure. If the scope or VOM is high impedance, where does the current have to go?

Of course, if you're nervous then a VOM is a lot cheaper to replace....

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NachoMahma (author)gmoon2008-07-22

. ROFLMAO. Do GMTA or what? We even used the same page, just at diff URLs!

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gmoon (author)NachoMahma2008-07-22

Oh man, you're right... just a minute or two apart. LOL for sure!

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guyfrom7up (author)gmoon2008-07-22

llol anyways the voltage divider didn't work, my multimeter went beserk, flickering random numbers (I think 1900 was displayed a lot), but I don't know...

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gmoon (author)guyfrom7up2008-07-22

Even on the AC setting? What kinda frequencies are talkin' about?

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guyfrom7up (author)gmoon2008-07-22

ohhhh ac settings, I'll try that soon Oh, and is there an answer to that diode question? Cause if its ac then I'll have to rectify it, and a couple lower voltage diodes are cheaper

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gmoon (author)guyfrom7up2008-07-22
Did you really fry the VOM? And the driver. Wow. Ouch.

I'm gonna "punt" on the diode question...even though there are lots of HV diode boards (multi diode) listed for sale, and most have the "balancing" resistors (so they must be series.) See what other tesla builders use, and do the same.

But I can't resist adding this video:

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guyfrom7up (author)gmoon2008-07-22

well, I'm a bit mad about the VOM, but it just gives me an excuse to get a newer better one. My driver was just a simple 555 timer that wasn't properly protected, I'm going to build a new one that is heavily protected. I'm going to see if I can just get one HV diode

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gmoon (author)guyfrom7up2008-07-22

If you were expecting a continuous 50KV from the ignition coil, you could have big voltage spikes when starting/stopping the 555....

might have something to with the demise of both...

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gmoon (author)gmoon2008-07-22

I hope it wasn't bad advice I gave...

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NachoMahma (author)guyfrom7up2008-07-22

. You need a high-voltage probe (AKA a well insulated voltage divider). Google h-v p

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guyfrom7up (author)2008-07-22

well, my multimeter and my ignition coil driver is busted, time to go get/make new and better ones.

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Tool Using Animal (author)2008-07-22

If I remember correctly, the general figure used is one megavolt per meter for air at STP.

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user

according to your volt de graff instructable it's 3 megavolts per meter... which one is right?

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user

THREEmillion is the right number, sorry.

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Gjdj3 (author)2008-07-22

I'm not sure... as Cameron said, an Oscilloscope might be the best option if you can get around the price.

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gmoon (author)Gjdj32008-07-22

A 'scope is useful if you need to see the "shape" of an AC signal. A cheap VOM works fine for typical sine wave AC or normal DC voltage. It's a "scale" issue...

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CameronSS (author)2008-07-22

For a precise/accurate measurement, I believe that an oscilloscope is the instrument of choice. They can get pretty expensive, though, if you don't already have one-check local universities' electronics labs.

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