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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Any better way to measure HV other than 1.1cm spark = 10kv? Also, how do you measure milliamps at that high potential?
I've just been measuring the current draw from my transformer and figuring out what should come out of the secondary based on transformer ratio. IE; if i want 1ma at 75kv, I'll put a 75watt lightbulb in series with the transformer primary.
But there must be a better way to measure mA and Kv at 60hz.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
For current (it would measure short circuit current, not loaded) you can put a resistor in parallel with the output, provided it is a short circuit safe supply. Then you read the voltage across it, and use Ohm's law to calculate the current.
Like GBD said, just use a resistive divider to measure voltage. Depending on the voltage, and the available current (or rather, how much load the output can take before it drops the voltage too much to get and accurate reading), you can figure out what resistors will be best. I used 2.2Mohm and 220Kohm to measure my 2400v 10ma transformer, so i got 1 volt per 10 volts from it. I used a 100 ohm 1/4 watt resistor to measure the current.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Grenadier wrote ... Any better way to measure HV other than 1.1cm spark = 10kv?
That's a pretty poor way, because it's so sensitive to the electrode shapes. See According to my old CRC, the length of spark gap for 10 kV is 0.27 cm (between 2.5-cm balls), 0.32 cm (between 25-cm balls), and 0.85 cm between needle points. For 50 kV the spark gap lengths are 2.0, 1.66, and 5.20 cm.
If you are measuring DC, get a standard high-voltage divider probe used in TV service. For AC, the dividers need more attention because resistance and capacitance ratios must match. Search this forum for hints.
Grenadier wrote ... Also, how do you measure milliamps at that high potential?
Put a milliammeter in series. In many small x-ray machines, with a center-tapped secondary, the ground connection of one half-secondary passes through a meter.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
If you a way to simply measure mA at high voltage use this trick:
Find 2 #49 bulbs-- 0.06 amp lamps. Connect one in series with the high voltage terminal. Connect the other in series with a battery and a DC milliamp meter. Compare brilliancies (carefully)
Also works great for RF. Years ago Sylvania actually made a 2 filament buld to do just this.
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measuring high voltage.
