Re: Quick & Dirty Current Shunt

Tim Wescott wrote:
Problem: I need to measure up to 30 amps (50 would be nice), I've spent my discretionary budget for the upcoming month, and all I have are 10A meters.

What's a good quick & dirty current shunt? There's no dead heaters on site -- would it make sense to hack a bit of FR-4 to just the right length & width to develop 50mV at 50A (while dissipating 2.5W, of course)? Or should I find the right length of copper wire to do this?


Open a meter. Many have a tap on the shunt that gets moved during initial "calibration". It can sometimes be moved. But don't blast it with 30A for too long, and if there's a fuse this won't work.

Other option: Thick piece of copper on the outside. Measure current with a source that can generate 5-10A, sans extra copper. Hook up copper in parallel and measure in brief bursts. Enough copper thickness so the indicated current shows lower than your desired ratio and safe handling is maintained. Between bursts file into it a little here and there until the indicated current has gone up to 1/3rd (or 1/5th in case a 50A full scales is desired) of the initial value.

To get rid of (most of) the tempco you could drop this into a water bucket. Of course only for GND-side shunts that are _not_ connected to mains in any way ;-)

However, in general it's better to just have one big fat outside shunt and run the meter in voltage mode.

--
Regards, Joerg

http://www.analogconsultants.com/

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