### Author Topic: Tools to measure ~10,000v  (Read 1579 times)

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#### ejecta

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##### Tools to measure ~10,000v
« on: June 03, 2016, 12:59:58 pm »
Hello folks,

I'm working on a little project here on the farm; it's going to be based on an old dynamo that once regulated "should" be putting out a stable 10,000 volts. Current (AC) involved should be less than 1/4 an amp (in theory - aware of the danger of HV/HC projects).

However, I'm looking for a way to measure this. Is the ebay/aliexpress analog "42L6-V" 12kV panel meter for \$26 going to be the easiest/cheapest way or is it possible to hack together / adjust an existing meter. Is it possible to use an ammeter and a known load to mathematically work out volts? Other ideas more than welcome.

I'm handy but new to electronics theory - but happy to fiddle and learn to build a better (or cheaper) measurement device if possible.

#### alsetalokin4017

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##### Re: Tools to measure ~10,000v
« Reply #1 on: June 03, 2016, 01:31:19 pm »
Your dynamo can put out a quarter of an amp at 10 kV? You are in "kill you dead quick" territory there, not even one mistake is allowed.

From looking at the Ebay listing for that meter, its construction and the fact that it says "10kV/230V" makes me think it's not really capable of handling 10kV directly. I could be wrong but I'm not willing to bet your life on it.

You probably need something like a BK Precision HV DMM probe,  PR 28A, which sells for around 70-80 dollars US.

The easiest person to fool is yourself. -- Richard Feynman

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#### ejecta

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##### Re: Tools to measure ~10,000v
« Reply #2 on: June 03, 2016, 01:46:54 pm »
Your dynamo can put out a quarter of an amp at 10 kV? You are in "kill you dead quick" territory there, not even one mistake is allowed.

Yep, she's an old girl from a massive hunk of equipment.

Indeed, however it's kill you dead if you touch it / make an error territory rather than machinery on the farm that can kill you even if you're doing everything perfect so the hobby it seems "safer" than the day job. Having previously built a spot welder from a microwave oven transformer I do however have a healthy respect (and fear) of tinkering with electronics & power.

From looking at the Ebay listing for that meter, its construction and the fact that it says "10kV/230V" makes me think it's not really capable of handling 10kV directly. I could be wrong but I'm not willing to bet your life on it.

You probably need something like a BK Precision HV DMM probe,  PR 28A, which sells for around 70-80 dollars US.

I also noted the vague voltage rating of 10kv/230v and 10kv/110v on the two "brands" of that model, I certainly wouldn't be touching the thing when it was live believe me. Thank you for the tip regarding the BK DMM I shall have a looksee at it.

#### uncle_bob

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##### Re: Tools to measure ~10,000v
« Reply #3 on: June 03, 2016, 03:01:51 pm »
Hi

One very real caution here:

You are looking at AC and not DC. A gizmo rated at 10KV AC is not the same as a 10KV DC gizmo. You have a 1.414 factor between the two and in this case it matters. For a 10KV AC circuit, the isolation at DC needs to be 14 KV.

Since somebody could get killed .... an error on the "high side" is probably worth the extra couple of bucks.

What's in a high voltage probe:

If you take a hammer to the thing, you will find a high voltage resistor. It's calculated to work with the input impedance of a specific meter to scale the voltage. Put the "wrong" impedance on the other side and you get the wrong number. For instance, a 10 Meg input impedance used to be pretty common. A 10 KV to 100V probe needs a 100:1 step down. One way to do this is just to put a 10M x 100 = 1 Gig ohm resistor in the probe. Net result = you may have a meter, you may have a probe, if they don't match up ... watch out.  Also be really careful of the red wire out of the probe.

Bob

#### jitter

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##### Re: Tools to measure ~10,000v
« Reply #4 on: June 03, 2016, 08:11:19 pm »
From looking at the Ebay listing for that meter, its construction and the fact that it says "10kV/230V" makes me think it's not really capable of handling 10kV directly. I could be wrong but I'm not willing to bet your life on it.

I'm thinking the same. My guess is that it needs to be connected through a transformer and that the 10kV/100V rating means that the transformer takes the 10 kV down to 100 V to get a 10 kV reading on the instrument.

Edit: yeah, here's a panel meter with a bit more info. The kV models need to be connected to a transformer.

« Last Edit: June 03, 2016, 08:41:47 pm by jitter »

#### N2IXK

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##### Re: Tools to measure ~10,000v
« Reply #5 on: June 04, 2016, 02:50:22 am »
Yes, switchboard instruments like that require devices called potential transformers to drop the high voltage down to safer levels.  In your case, a transformer with a 10 KV primary, and a 100V secondary. This way, only the safer low voltage is brought into the meter enclosure, with the transformer located remotely near the HV supply.

https://en.wikipedia.org/wiki/Instrument_transformer
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