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Ravi
01-30-2006, 08:27 AM
Hello everybody,
I am trying to bulid an AH meter with the Basic stamp 2. The specs of the shunt are 75mv-15KA. I·want the meter to work both ways (charge/discharge of the battery). Also I want the resolution of the meter to be 1AH. Do I use an ADC? I am not sure how the ADC would work when the polarity of the input is reversed. Would be grateful for any help. Thanks, Ravi·

stamptrol
01-30-2006, 08:56 AM
ravi,

Briefly, what you want to do is measure the amps several times per minute, say every 6 secs ( 0.1 mins or 0.001667 hours) and multiply amps times hours and increment the result and store.

Are you really going to go to 15000 amps? Must be a big honking battery and load. An a/d converter that is designed to use 'differential' signals rather that 'ground referenced' ones will let you sense current in both directions. With your shunt, the 75 mV will have to be amplified so at maximum DC current, the amplifier output will be about 5 volts or what ever the a/d is expecting.

As a thought, some clip-on style amp probes will work on DC and they put out a 0 - 1 v signal for use with a standard multimeter. Would really simplify the shunt arrangement by allowing you to put the clip-on around any convenient conductor.

Cheers

Ravi
01-30-2006, 07:49 PM
Thanks! Would it work if I used a 555 and measured the pulse width instead of an ADC?