Ammeter/ Volt meter adjustment
I installed a cheap meter to read volts and amps sometime ago along with a shunt. There are two pots on the meter one for volts and one for amps. The volts I set with my volt meter but the amps I can ...
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doughere wrote:My meter is powered from the chassis battery. Using your example should I be able to adjust the amp pot to read 72 amps if I read a 27 mv drop across the shunt?Gjac wrote:doughere wrote:Doug if I understand your post if I take a voltage reading between the two large nuts across the shunt(as shown in BFL's post)and trust my voltmeter I could adjust the amp pot to match that reading. Is that what you are saying?
Your shunt is a resistor. Your ammeter is actually a voltmeter reading the drop across your shunt. If you know the shunt's value (usually expressed as Amp to millivolt drop) you can read the voltage across the shunt and calculate the Amperage. My shunt is 50 Amp to 50 mV; so if the volt reading across the shunt is 35 mV, my meter should read 35 Amps. The most common shunts are designed for 50 or 100 mV at max current reading.
Doug
You say your shunt is 200 Amps for 75 mV. If you measure the voltage across the shunt with a GOOD voltmeter, you can calculate the current through the shunt. Divide the voltage (in mV) across your shunt by 75 mV, multiply that by 200 and you have your amperage.
If you measured 27 mV across your shunt, divide by 75 you get .36; multiply by 200, you get 72 Amps.
I don't know how your meter is powered, but you may not be able to read the voltage from your shunt, if you are using power from your battery system to run the meter. My meter had to have an isolated voltage converter to read correctly.
Doug
