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What To Do w/250 ma AC Meter




 
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Author Topic: What To Do w/250 ma AC Meter  (Read 435 times)
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W9ZSL
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« on: July 15, 2019, 05:45:03 PM »

 Roll Eyes Dumb me. Misread the ad. Bought a Triplett 250 Milliamp Meter.  Unfortunately it's AC. Thought it was DC.  Tongue Now I don't quite know what to do with it! I was going to use it with a 1 KV, 250 ma supply; bridge rectifier. Is there a way to wire it into the secondary? Must be Monday.
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #1 on: July 15, 2019, 05:55:11 PM »

try it at DC, may work fine. Perhaps just needs a little calibration adjustment
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w4bfs
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« Reply #2 on: July 16, 2019, 08:59:15 AM »

Nico may have something .... custom meters can be most anything  Huh Huh .... rig up a series circuit of a battery, variable resistor, dmm set to measure current and the meter under test ....  start at 50 microAmps current and decrease resistance allowing more current to flow .... if this still gives garbage results, carefully remove the 3 (usually) screws that retain the movement in the case .... you may find an internal shunt resistance or much more rarely a rectifier, etc
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
W9ZSL
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« Reply #3 on: July 17, 2019, 01:35:14 PM »

I certainly would like to salvage it. It's brand-new, in the box complete with all the hardware.
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Opcom
Patrick J. / KD5OEI
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« Reply #4 on: July 22, 2019, 11:55:55 AM »

Monitor your workbench or variac output voltage by adding a step down transformer from 240V to 24V@1A, and put a 100 Ohm 10W resistor in series with the meter, and put that series combination across the 24V winding so 0-240V reads 0-240. There will always be some error but it works well, adjust the 100 Ohm resistor to calibrate it at the spot you care about most.

Monitor a filament voltage choosing a resistor that gives a reading in center scale. A 60 Ohm 3W unit for a 7.5V filament, to read '125'.

Use a 100:1 current transformer to measure 25 AC amps (as 0-250) on your work bench 120V variac or outlet. - best use!

change the scale where needed. Far from useless!
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