Re: Quick & Dirty Current Shunt

On Mon, 30 Mar 2009 13:00:58 -0700, Joerg wrote:

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.

My plan was one big outside shunt and measure millivolts, yes.

Maybe I'll just start measuring the resistance of some of my lengths of
wire.

--
http://www.wescottdesign.com
.

Relevant Pages

  • Re: Quick & Dirty Current Shunt
    ... Or should I find the right length of copper wire to do this? ... Many have a tap on the shunt that gets moved during initial "calibration". ... Enough copper thickness so the indicated current shows lower than your desired ratio and safe handling is maintained. ... in general it's better to just have one big fat outside shunt and run the meter in voltage mode. ...
    (sci.electronics.design)
  • Re: Current measurement
    ... troubleshooting I would say the roll your own shunt and a cheap meter ... A copper shunt looks like a good idea until you look at copper's ... used to make inexpensive RTDs (resistance temperature devices). ... I keep a 100 amp and a 500 amp shunt in my tool box all the time. ...
    (rec.outdoors.rv-travel)
  • Re: tubes Vs fets, ohmmeter schematics
    ... voltage of say 9V across the DUT, ... 100MegOhm FS = 100K Ohms shunt ... The 1M shunt would make the meter have about 800k of input resistance, ...
    (rec.audio.tubes)
  • Re: Current measurement
    ... A copper shunt looks like a good idea until you look at copper's ... used to make inexpensive RTDs (resistance temperature devices). ... I keep a 100 amp and a 500 amp shunt in my tool box all the time. ... also have a DC clamp-on meter or two but when I really need the right ...
    (rec.outdoors.rv-travel)
  • Re: what size shunt do I need?
    ... I have a 70A alternator and 220AH house battery capacity. ... "you need a 50mv, 70A shunt", where do I get one? ... If you have a meter calibrated for full scale at 50A to use with a 50A, ... Navy, can do this calibration, and does, even on matched 50mv units. ...
    (rec.boats.electronics)