Discussion in 'General Electronics Discussion' started by MadMechanic, Jul 12, 2013.

48
0
Aug 28, 2012
Hello All,

I am looking into making a homemade shunt resistor from copper wire to measure high amperage with a digital multimeter. I have found that (Meter operating voltage) / (max meter amperage) = meter resistance in ohms. and (Meter resistance) / (Ohms/ft. copper) = Shunt wire length in feet.

The question is...if meter is rated 10A un-fused...and I am going to be measuring up to 30A, should I calculate the (max meter amperage) as 10A or 30A ? Has anyone built their own shunt before?

2. ### duke37

5,364
772
Jan 9, 2011
Doing it your way puts the meter at risk. A better way would be to measure the voltage across the shunt. Four point connection can be used, the current is put through the entire shunt and the voltage is measured inside the end connections. This would give a better measurement but you should realise that the resistance of copper varies with temperature. Constantan would be better for the resistor.

3. ### Y2KEDDIE

259
15
Sep 23, 2012
I’ve built crude shunts for analog meters, typically milliamp ranged. I would find a carbon resistor a little smaller in value and then file a notch in the resistor while connected in circuit until the meter reads the correct value, then seal with a little dab of fingernail polish.

As Duke says, measuring voltage with your digital is safer. Similarly you can make a crude shunt out of copper. I would start with a piece 1/2" wide 3" long, 1/16 thk. Drill and tap 2 holes on each end, 4 holes total. Connect your digital on the 200 mV range across the two innermost ( holes) connection points. Then connect your 30A circuit with the two outer most points. As you reduce the cross section of the copper strip its resistance will increase. You will end up with a narrow channel in the middle maybe 1" long 1/8 "wide. Depending on how much material you cut away you can make the meter read 1mV per amp ,or 10 mV per amp.
This is a crude trial and error method. If you take too much material away you have to start over.

Last edited: Jul 12, 2013
4. ### shrtrnd

3,827
523
Jan 15, 2010
Trivia, I've done what Y2KEDDIE is talking about many times also.
Just remember. you can only do that with a full carbon composition resistor.
(Not a carbon film, or wire-wound resistor).
Just my 2-cents worth.

5. ### GonzoEngineer

321
2
Dec 2, 2011
I have a bunch of shunts at work, what value are you looking for.

I will gladly gift one to you rather than having them just gather dust.

You can order a small box shipping label on line from USPS, and mail it to me and I
will send you a shunt. I will check to see what values I have and get back to you shortly!

OK! I found a half dozen Yokogawa 50A current shunts. Type # 2215

It already has the four connections you need, and is mounted on a Phenolic base.

Looks to be made of Beryllium Copper (I think).

If you PM me an address I will go ahead and send you a couple of them UPS on Monday if you want them.

You can reimburse me for the shipping later.....my rates would probably be about 10-15 bucks to SC.

Let me know if you want them.

Last edited: Jul 12, 2013
rupe01 likes this.
6. ### GonzoEngineer

321
2
Dec 2, 2011
If the OP had checked his PM's, he would have had two of these by now.

Oh well...I tried to help.

rupe01 likes this.