Products > Test Equipment
Measuring 100A DC current
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Martin72:

--- Quote from: gaminn on June 07, 2024, 07:58:37 am ---Hopefully I will be able to screw in some banana sockets (and they will not melt...) instead of that 8-32 screws to make my measurements easier.

--- End quote ---
Banana sockets are not designed for such high currents, which is why most power supplies that deliver 20A and more also have regular terminals.
At higher currents, contact resistances can no longer be neglected.
I really hope that if you “drive” currents over 10A, you no longer do this with normal banana cables...

Psi:
A little 10x/50x/100x gain current sense amp IC and a good quality precision current-sense resistor, or array of them, is how i would do this.
You need some gain to keep the resistor power loss manageable at 100A
The current sense amps output 0-5V.  So with some careful selection of the right resistors you can make the output match current.
1V = 100A for example.
coppice:

--- Quote from: gaminn on June 07, 2024, 09:08:59 am ---
--- Quote from: tooki on June 07, 2024, 08:40:16 am ---If you really care about accuracy, do you really think you should be buying from AliExpress?

--- End quote ---

That's why I expect 0.2% accuracy from 0.1% Chinese shunt.

--- End quote ---
The problem isn't with China, its with AliExpress. It could be E-Bay or any other unregulated source, and your chances of good results are just as bad. Get things through a well regulated supply chain from a Chinese maker and they will most likely perform to spec.
coppice:

--- Quote from: ArdWar on June 07, 2024, 10:17:51 am ---I don't think even the best reputed shunt manufacturers offer 0.2% accuracy, much less 0.1%.

It's current shunt, if you need accuracy you're expected to calibrate out for gain errors. The sought after qualities here is usually the temperature coefficient instead.

--- End quote ---
For 99% of uses a high accuracy shunt makes no sense, as its cheaper to get a shunt with a great temperature coefficient, and calibrate out its errors. However, there are certainly 0.1% accuracy shunts on the market.
trobbins:
Both those meters have the same 1yr 100mV range accuracy, and only have a 3Adc current range (the Keithley seems much better spec).  You could compare both those meters at say 50-100mV to get some confidence that they haven't strayed far from their original accuracy, but be mindful that unless you keep the meters on full-time and keep them close to 23C ambient, the meter may have a significant tolerance itself, and especially for readings well below 100mV FS from the shunt.

Even with the +/-0.25% shunt, your uncertainty could still exceed 1% when used with your meters if you don't take some effort to cross-check your meters, and importantly use a fan on the shunt to keep its temp rise as low as practical (even at 50-60A where the accuracy of the meter gets worse).  But I think that is the best and easiest path to take.

Martin72, I think the comment about banana plugs was for the voltage sensing connection to the voltmeter - perhaps look at the link to the 0.1% shunt, and to the Murata 0.25% shunt for context.
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