Modified Hobbico Voltmeter for higher load?

[Edgar Perez]

Anybody have modified the Hobbico expanded scale voltmeter MkII so that it test the baterries at a higher load , say 1amp, instead of the ~200mah?

Thanks,
Edgar

[Gary Warner]

I modified one that's a bit older (the original one I think).

There is a dropping resistor (shunt) used to set the current. I added a larger resistor and a switch to drop my current to 100ma (handlaunch receiver battery pack).

Though the exact value of the resistor used can vary a bit for assorted circuit designs, the basics on the resistor value needed for any given current is as follows:

voltage / current = resistor value

Example: 5 volts / 1 amp = 5 ohms

I used: 5 volts / .1 (100ma) = 50 ohms

If the meter is set to about 200ma (.2 amps) then I'd be looking for the large resistor that's about (5/.2=25) 25 ohms in value. Once you have identified this shunt resistor, simply replace it with the 5 ohm size resistor.

NOTE: Wattage will need to be increased for the new resistor. Wattage is voltage x current (5 x 1 = 5 watts). You should be able to use a resistor in the 2 to 3 watt range since the load (I assume) is only for a short period of time. If the load is applied for longer (say, more than 10 seconds) I'd use the correct calculated wattage resistor.

Gary
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[Edgar Perez]

Thanks!