Easy and Inexpensive DVM conversion to Read HIGHER AMP's

Next time you need to measure Amps try using your DVM (Digital Volt Meter). Very easy, set your meter on the lowest mV scale you have and put a shunt resistor across the leads. Done properly this can expand you DMV mV scale to read any amperage you need.

Briefly here's what goes on..

Assuming you have a DVM that has say has a 100 mV scale and you want to measure 100 A (DC) consider the following: In essence you would like to have a full scale reading of 100 mV (.1 Volts) while measuring 100 A ... so... Ohms law tells us that R (resistance in ohms) = E (volts) / I (current in amps) ... so... R=.1/100 = .001 ohm resistor. This tells us that if we put a .001 ohm resistor in PARALLEL with our meter leads we've transform our mV scale into a 100 A scale. Note, you may need to do some experimentation to get the meter calibrated but that's reasonable easy.

Same math applies if you have a DVM that has a 200 mV scale and you only need to measure say 50 A. The shunt resistor you will need in this case is ... R = .2/50 = .004 ohms.

The actual shunt resistor is nothing more then a short length of #12 or #14 house wire. In this example the shunt is approximately 1.8" of # 14 wire... Very easy to do and VERY, VERY easy on the pocketbook.

Good luck

Ron

PS: I failed to mention this setup needs to be in series with you battery ...