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50A 0.1% Bench ammeter?

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Berni:
The problem with shunts at such high currents is that the P=R*I^2 gets really out of control, so you need really low resistances to not be dissipating an unreasonably high power as heat in the shunt resistor.

Even precision resistors tend to drift a bit with temperature, so that impacts your accuracy. At the same time the output voltage is tiny, making it difficult to measure properly. Then since it gets hot it also causes thermocouple voltages at the connections to the shunt, at the low shunt resistances you can easily get a thermocuple voltages equivalent to a few amps flowing trough the shunt. Okay but the whole shunt gets hot equally... well not really, the cables connecting it could be removing heat at different rates on each side, the contact resistance of the massive cable lugs might not be exactly the same on each side...etc.

This is why flux gate current transformers are so good. The wire passing trough the center can be made as thick as you need, allowing for potentially 1000s of Amps without getting too hot. If it gets hot it is no problem since the number of turns on a core is not temperature dependent. The winding ratio can be chosen so that you get a nice big signal in the 100s of mA on the output, making it easy to measure. It also does not suffer from thermocuple effects (since no part of this uses voltage, it is all currents) and so it means a transformer made for 1000A will still measure 1mA reliably.

PwrElectronics:
OK, looks like they used a LEM IT 1000-S/SP1.  That is a 1000A range unit and around $4k USD.  Overkill for the OP but smaller ones are available.  This one used a +/-15V supply and a precision load resistor.  The DAC unit in the tester measured the voltage on that resistor.

alm:
While I agree that current shunts don't scale well with current because the voltage scales linearly while dissipation scales quadratically, I think 50A should still be manageable: 1 mOhm would dissipate 2.5W and drop 50 mV.

Berni:
Yeah brand new these LEM current transformers are going to be insanely expensive.

But they are really easy to find for under 50 bucks a piece on ebay:
https://www.ebay.com/itm/334966674098?hash=item4dfd91d2b2:g:RiEAAOSwZvJkyVaf&amdata=enc%3AAQAIAAAAwBnESRXNfqPrwU4GSWNzyOvyc4VtTMLwEddKiDhdbG2TFvuwQlFfQFSbG%2Fgg8c1Jysha9j7VlKcAQiIWnffE9YmfHyeO7wtKRC1%2FrDirIoiDWFJW6gHKF0sMiYibbsMK5%2BbGLEVstPa16crxTG%2BhXEzHR3Y7aL0UTCynLoCusyV1p3pWWDoO%2BcED6fj1GbLvwZ32bxj1Vobs6UjBgvMBye9PWHxK0gvz7x5p7ZhGiFfcjpvHWUHDI5%2FePQufQJPnIw%3D%3D%7Ctkp%3ABk9SR56999fgYg

alm:
What load will your DUT tolerate? Shunts will be fairly resistive at lower frequencies, while a DCCT will be quite inductive. See this article about the LEM/Danfysik Ultrastab by TiN where his current source is getting unstable above 16A due to the inductive load.

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