Brendan Moran wrote:

> Most current sense resistors that I have seen have been 1ohm or
> 0.1ohm.  Those were only for low current applications, however.  For
> the currents you are mentioning, that would require a carefully
> calibrated piece of wire. There are other ways of handling this kind
> of current, however.


Here's a (related) idea, get a small 12v relay
etc, unwind the coil, and replace it with a few
thick turns of enameled wire. The main current
only goes through this coil, which is efficient
as it has close to zero resistance.

When current exceeds 10A, 20A, 100A etc the
relay contacts will open, giving a signal to your
PIC etc. Obviously the contacts only carry the
signal, not the main current.

I know some commercial circuit breakers use a
similar magnetic system, I just never thought of
unwinding and rewinding a common relay before.
-Roman

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