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Re: [TCML] Measuring Voltage?



Hey Neal...

Sounds like the resistor ( that usually accompanies the meter) is missing. Sometimes there is a resistor inside the case of the meter and an additional resistor is required to "match" the voltage to the meter reading ( fine tunes the meter to the real voltage). Since you were getting about 100KV on approximately 250V, there is probably an internal resistor.... thus you need another resistor to reduce the voltage going to the meters coil. In most cases there is a tiny bit of text below the needle that states the full swing current ( F.S. 250mA for example) using Ohms Law you can figure out the needed resistor value for the range of the meter and voltage applied.

If I remember this correctly it goes something like this....

you have a 100,000 volt meter and the FS is at 250mA... divide 100000 by .250 and you get 4 megaohms.

Not knowing the FS for your meter and the value of the internal resistor, I can only guess at the needed resistor would be close to 5 megaohms... You will most likely need a high voltage resistor to avoid arcing at the upper end of the range of voltage...

Scot D



Neal Namowicz wrote:

I wanted to ask if whether or not the primary, or secondary, voltages can be measured with a meter. Here's what I did, and I don't know if my meter is that far off, or if there is something else affecting the readings that I'm not aware of. I have an old KV meter from an x-ray machine with a range of 40kv to 140kv dc. I attached a couple hv diodes to the meter and attached it to the secondary electrodes on a bi-pole coil. The needle was pegged almost immediately when I started to apply power. Then I switched it over to the output on the transformer (9kv, 30ma nst).  With the variac at about 1/4 power, the meter was registering 100kv. Not what I expected.

So I have a couple questions here; first, why is the primary voltage reading so high with this meter? I'm thinking that the meter is showing the voltage rise due to resonance, perhaps? If that's the case, is there any way to accurately measure the voltage? I'm actually more interested in knowing secondary output. How can one go about measuring, even "guesstimating" the approximate output on a coil? I'd like to have a somewhat more accurate answer for people when they ask what the voltage is of the arcs. Can my bi-pole coil be putting out more than 140ish kv at such low power? Thanks in advance for your help with this!

Neal N. _______________________________________________
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