My power supply is 6x 12v 33ah lead acid batteries and load is 3x sabertooth 2x50HV motor drivers driving 6 wheelchair motors.
My question: the out put on the shunt is in mV and i need to get this in the 2.5V range for the axon II. Do i need a op amp or something to get this into the correct range?
It's not the best idea to use a shunt with such high currents.
If both sides of a Sabretooth can peak at 100A each, a 1mOhm
shunt will dissipate 40W (120W when all 6 motors start)
But considering the low percentage of the total, it may be bearable - just don't use a homemade shunt - it should be rated for the max. current it's likely to see and anything above 1mOhm will be bad (with 10mOhm you'd dissipate 1.2kW at start-up).
You cannot go that much lower either, if you want to be able to measure low draws with any kind of precision (and you'll be hard pressed to find a shunt that low anyway).
And yes, you'd need an op-amp following it - a rather specialized circuit , if you intend the shunt to go into the positive line, but want the output to be ground referenced for the A/D-C to read.
This is a typical case for a Hall effect current sensor and here is a couple of links (you still need them beefy enough to withstand the max. current).LEM
is a page on the LEM transducers as well (perhaps it has some further info).http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm
That said... You might wanna check the price on those monstershttp://parts.digikey.com/1/parts/1376224-sensor-current-200a-24v-uni-mod-apr-200-b10.html
Ouch - suddenly a short rod of konstantan or similar makes sense
And... If precision isn't too important, you could use some stainless steel welding rods and make a shunt yourself - will be hard to calibrate without a reference though.
If it's just for getting some initial measurements, consider if you can borrow a suitable Hall based (to measure DC) clamp meter somewhere.
I didn't watch the video, but forget anything as fragile as the shunt shown at the initial pic..