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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I am building a quarter shrinker. I plan on using an analog voltmeter to measure the charge on the capacitor. The meter I plan on using is an old Weston 2500 volt meter. It has a resistance of 85 ohms and a full-scale current draw of 1 ma. I want to set it up to measure a maximum of 25 KV. To do this I am using a multiplier resistor of 25M ohms. The resistor is a Caddock HV resistor rated for 30 KV and 15 watts.
I see some applications that use a voltage divider using 3 resistors: the meter internal resistance, another resistor in parallel with the meter resistance, and the multiplier resistor. Is this really necessary? I plan on using a voltage divider using only 2 resistors: the meter resistance and the multiplier resistor.
I am also wondering if I should ground the meter terminal without the multiplier resistor to earth to avoid the possibility of the meter floating up to an excessively high voltage.
The entire quarter shrinker will be completely isolated from the mains except during charging. After the final charge voltage has been reached, the charging connections to the capacitor will be physically disconnected.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
since your mesureing the charge voltage you will need a lower divider resistor add a varistor or transorb and a small capacitance like .1uf in parallel with it. the lower resisitance will be your meter resistance in parallel with your chosen resistance. remember that your coin crusher is ferly dangerouse and your meter should not be near your person and just where you can see it. maby there should be a lexan shield between you and your device. please treat with respect and use a crowbar or proper shorting stick with your caps, it could be deadly
Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
Patrick wrote ...
MRMILSTAR wrote ...
I plan on using a voltage divider using only 2 resistors: the meter resistance and the multiplier resistor.
dont do it. ill explain when i get home from work.
follow up: are you using the meter movement or the whole meter ?
I measured the resistance of the meter as 85 ohms with my Fluke multimeter. I'm not sure what you mean my "the whole meter" or "just the meter movement". This is not a multimeter. It is a Weston stand-alone dedicated panel-mount voltmeter. It has a full-scale reading of 2500 volts with a factory-specified external multiplier resistor. I don't know what the factory-specified external multiplier resistor is. I assume it is 2.5M ohms. With the factory-specified multiplier resistor, the sensitivity is specified as 1000 ohms/volt on the face plate. I am not using the factory-specified multiplier resistor. I am using my own Caddock external multiplier resistor value of 25M ohms.
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Measuring HV using an analog voltmeter
