The Shop > Electronics & IC Programing
DIY Ampermeter
DavidA:
How about this 'rugged' approach to meter construction.
50 Micro amp to 10 amp conversion. :zap:
Dave
one_rod:
Can I ask for a little explanation here?
I'm guessing that the copper windings are acting as a shunt.
If so how do you get away with using an ammeter as the indicator. Should it not be a microvoltmeter?
At work we use shunted DC ammeters that read up to 10,000 amps. Although the meters are scaled in kA they are actually reading the voltage generated across the shunt.
Or (quite likely) am I just missing something simple. :scratch:
Second and fairly obvious question: The apparatus next to the ammeter. Parallel, separated plates, insulated spacers and a coffee jar lid.
Home made wet cell? Z.F.M.? Electoplating set up?
Come on, don't tease.
one_rod.
picclock:
@ one_rod
Ammeters are just coils of wire wound on a spring loaded bobbin placed in a magnetic field. Just cos it says ammeter doesn't make it any different to a voltmeter.
The wire coil has resistance, and if you supply the correct voltage it will behave as a voltmeter ~ for low current designs typically around 50mV will give full scale deflection - so a 50mV meter. So now its a 50 uA ammeter and a 50mv voltmeter. If you want to get more technical, when measuring current the meter drops some voltage, this is called the voltage burden of the meter. If you put a resister in series with the meter you would increase the voltage burden for measuring current, or you could start calling it a voltmeter :smart:
However, IMHO, best way for making a shunt is to use studding. Connect the meter via wire and solder tags with nuts to a section of the studding. Connect current source to ends of studding. Adjust separation distance of tags until calibration is achieved. This gives two chunky screw on terminals at the ends and simple calibration. As a guess I'd say M3 studding for 10A. When done reduce length of studding to separation distance + 10% for future calibration. This will give minimum voltage burden.
:offtopic: Really impressed with your welded Halloween sculpture, very very impressive - I think you may have missed your vocation :med:
Best Regards
picclock
Rob.Wilson:
Whats It for David :scratch:
Rob :D
DavidA:
One_rod,
As picclock says, All analogue voltmeters only really measure current. So they are actually ampmeters with the volt markings simply a convenience; saves you calculating voltage from Ohm's law.
I made up this 'device' as part of a 10 Amp supply circuit to run my experimental HHO cell. The thing on the right is the plate assembly used in the test. Fits in a coffee jar. To calibrate the meter I placed a normal multimeter (on the 10 Amp range) in series, increased the load until I got 5 Amp on the multimeter then adjusted the tap position on the coil to give me half scale deflection on the Micro ampmeter.. It does it's job. Also allows me to sample the current for use in computer data logging.
The voltage drop with bare copper wire is very small so the coil doesn't even get warm.
Dave.
Rob,
Does that help ?
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