Battery load test...

[DeeGee]

Previous post reminds me that I want to see the current drain on my batteries - I have a meter marked in amps, but it needs a shunt as the meter is really voltage driven. Not sure (off the boat at the moment) what the meter f.s.d is, but probably about 125mV, so measuring up to say 25Amps would need a shunt of about 0.005ohms. Does anyone know where I can get such a thing? I HAVE thought of making one, but then I need to prat about more than I really want.

 

[pvb]

Almost all shunts...

Almost all commonly-available shunts are rated at 50mV. Best to check your meter first. Shunts are easily available from people like Merlin or Index.

 

[dick_james]

For extra low value resitors, try RS components

 

[William_H]

About the lowest common value of wire wound resistor is .1 ohm so 10 in paralell will give you .01 ohm producing 250 millivolts at 25 amps.

any more resitors would become cumbersome and expensive.

I have made a shunt for 200mv at 20 amps from a piece of stainless steel plate about 20 gauge I think. It is about 25 mm from bolt hole to bollt hole and about 3mm wide for about 80% of that distance.
It is of course necessary to calibrate the shunt if you make it, You only need say a 10 amp multimeter to be able to extraolate 25 amps with sufficient accuracy.
Of course you could make a more substantial shunt say 50 mm between holes and 6mm wide. good luck olewill

 

[bedouin]

Go to the RS website and search for "meter shunts" they do a range but they are rather expensive. To use them of course you will use your meter on a voltage range!

As a cheaper alternative you could try putting a short length of higher resistance material in the circuit and calibrate that - I wonder whether something like a stainless steel bolt might have the right sort of resistance.

 

[MichaelHomsany]

Very conviently, 10 AWG copper wire is almost exactly 0.001 ohms/foot. Excellent shunt source, esp. if you don't have a calculator to pull out handy.

Best regards,
Michael Homsany