Dimitri, I've built a rather complete battery monitoring system for my
sailboat. I used a standard shunt (50 millivolt, 100 amp), amplified the
voltage up to + or - 2 volts, then fed it to a  MAX186 A/D converter, which
is connected to a PIC.

The shunt in my case goes in the -ve battery lead, as this makes life a bit
easier. I used an external A/D that can handle bipolar input voltages. This
one I had on hand - it is an 8 channel, 12 bit converter - I also needed
the 12 bit resolution.

I originally tried a "absolute value" circuit, right out of "The Art of
Electronics", to convert the + or- 2 volts into a positive only voltage,
and a comparator to detect +ve or -ve. This worked fine, but I eventually
went to the external A/D as I had one on hand, and I wanted the higher
resolution.

The shunt I used was from Blue Seas Systems (they have a web site, and any
boating supply place should have their stuff.


At 03:48 PM 2/12/2004 -0500, you wrote:
>Hello everyone,
>  I think about measuring current in car.
>  The problem I see - current is big enough and impulses
>  may go really high and measure voltage drop on resistor I see chalenging.
>  Another thing I'd like to have -
>  indication of current direction to or from battery.
>  Anybody has any thoughts? Current transformator, Hall sensor (??)
>  anything else?
>Thanks.
>Dmitriy Fitisov.
>
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Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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