Hello all,
I am building an isolation transformer/variac/dimbulb tester and want to monitor the input and output voltages and currents using separate cheap panel meters, but I'm finding this a surprisingly difficult task. The usual assortment of Chinese panel meters come in two and four wire variants with the former being powered off the voltage under test and the latter requiring a separate supply to power the meter circuitry thus leaving the meter free to measure the voltage without a built-in power supply loading it down. I prefer the four wire types because the test voltage can go down to zero volts while the two wire variants have a minimum voltage requirement of 20, 50, 60 or even 80 volts before they'll even start to read the test voltage reliably.
Two panel meters are envisioned, one for input to the variac, one for output, and both must measure voltage and current. For some reason there just aren't any in the usual Chinese vendor sites (including eBay and Amazon) that can measure AC voltage AND AC current AND go down to zero. However, numerous examples can measure DC voltages and currents down to zero, including this one. So my question is, how can I safely rectify and filter the AC line voltages going to these meters so I can use DC meters instead and still maintain reasonable accuracy? This is supposed to be an isolated AC power supply so emphasis is on the word 'safely'.
My enclosure space is limited, hence my combining volts and amps measurement into one meter. I'd also like to keep the parts count as low and not bulky as possible. Resolution should go down to single volts and milliamps, if possible. Also, I'm not looking for super accuracy. Just reliable, automatic monitoring of those voltages and currents whenever I turn the device on.
Thanks for your help!
I am building an isolation transformer/variac/dimbulb tester and want to monitor the input and output voltages and currents using separate cheap panel meters, but I'm finding this a surprisingly difficult task. The usual assortment of Chinese panel meters come in two and four wire variants with the former being powered off the voltage under test and the latter requiring a separate supply to power the meter circuitry thus leaving the meter free to measure the voltage without a built-in power supply loading it down. I prefer the four wire types because the test voltage can go down to zero volts while the two wire variants have a minimum voltage requirement of 20, 50, 60 or even 80 volts before they'll even start to read the test voltage reliably.
Two panel meters are envisioned, one for input to the variac, one for output, and both must measure voltage and current. For some reason there just aren't any in the usual Chinese vendor sites (including eBay and Amazon) that can measure AC voltage AND AC current AND go down to zero. However, numerous examples can measure DC voltages and currents down to zero, including this one. So my question is, how can I safely rectify and filter the AC line voltages going to these meters so I can use DC meters instead and still maintain reasonable accuracy? This is supposed to be an isolated AC power supply so emphasis is on the word 'safely'.
My enclosure space is limited, hence my combining volts and amps measurement into one meter. I'd also like to keep the parts count as low and not bulky as possible. Resolution should go down to single volts and milliamps, if possible. Also, I'm not looking for super accuracy. Just reliable, automatic monitoring of those voltages and currents whenever I turn the device on.
Thanks for your help!