Amper hour meter

At $10 for a shunt I should think the wise move would be to purchase. I did not realize they were so cheap.
Just wondering. What would the shunts be made from?
Constantan wire has much lower temp. co. eff.
It available here

**broken link removed**

and you would need 41.66cm of it to make a 0.01 Ohm resistor (drops one Volt at 100 Amps).
and I just realize thats 100 Watts!
The purchased shunts look better by the minute...................

BTW the PIC I am going to use does not need the Analogue to Digital converter to be 'programmed'.. It contains an alalogue to digital converter on the chip (in hardware).

AmperMan

The wire you linked to at 100 amps or even close to 100 amps would glow red for a very brief moment. You would have to be very fast to see it before it was toast. It is close to AWG 14 in a US standard and SWG 16 has a diameter of about 1.291 mm so how much current do you think it can handle? You are talking a current of about 100 amps. You need to understand ampacity ratings of wire. This is why when you mentioned the use of nichrome wire I said it was better suited for a toaster than making a current shunt.

Since the shunt is a resistor which operates in a varying ambient temperature environment and
generates heat whenever current flows through it, we must design the shunt resistance portion
with a special metal alloy which has, essentially, a constant resistance value through its operating
range. In addition to using a precision resistance alloy with a negligible temperature coefficient of
resistance, the alloy must have a low resistivity in order to keep the self-heating to a minimum,
and it must also have a low thermal E.M.F. against copper. A special shunt manganin alloy meets
all these criteria, therefore, all our shunts are designed using this special alloy.

Click to expand...

The above quote was taken from here.

Manganin alloy is an alloy pretty common in the manufacture of shunts. Other alloys can also be used. For measuring DC currents including in excess of 1,000 amps the use of a shunt is an economical and practical way to do it. The obvious downside is the need to amplify accurately the mv signal from the shunt and accurately scale it proportionally to the actual current. Additionally as I mentioned earlier if you plan to monitor 100 amps for weeks or any extended period I suggest using a shunt rated at maybe 150 amps. That is purely my opinion.

Ron

100 amp shunt (1 milliohm) will dissipate 10 watts at 100 amps. A 500 amp shunt (0.01 milliohm) will dissipate 25 watts at 500 amps. Both get pretty hot at full current.

They don't rate full current for a continuous duty cycle. 100 amp shunts are good for 50 to 75 amp continous. 500 amp shunts are good for 300 to 400 amp continuous. They take full amp rating for 3 or 4 minutes only.