3
\$\begingroup\$

My old multimeter, with all through hole components had an accident (I was measuring current on the 10A unfused range and then decided to check the voltage of the a lead acid battery) with one large carbon resistor glowing and melting and another through hold low value 1 Watt component suffering failure. Everything works apart from current measurement.

Can anyone identify this resistor (I cannot measure it as it has fused). enter image description here

I have checked various sources and this value doesn't appear in any of the E... series. I think that the colors are blue silver white and gold and suspect that is is a sub 1 Ohm value part as it was used as a shunt for < 0.5 Amp measurements but I have never seen a dark green resistor before (I think that this would be early 90's vintage).

\$\endgroup\$
10
  • 4
    \$\begingroup\$ Are you sure it even is a resistor? In any case, if its part of a range switching mechanism you might be able to work out its value by reverse engineering parts of the schematic and comparing. If you suspect its a shunt, you can put a decade/pot in place and run a current through it and adjust until the meter shows the right values. \$\endgroup\$
    – PlasmaHH
    Commented Mar 20, 2017 at 10:28
  • 1
    \$\begingroup\$ I'd be surprised if anyone can give much insight from the image. Find the service manual for your multimeter. Chances increases the older it is. \$\endgroup\$
    – pipe
    Commented Mar 20, 2017 at 10:37
  • \$\begingroup\$ I was thinking that it was an indcutor, but the markings didn't match any chokes/indcutor markings either. The second band is silver and the last gold. Silver should not be in the second position if gold is in the last. I cannot get any value for the component as a choke nor resistor. \$\endgroup\$
    – user142731
    Commented Mar 20, 2017 at 10:53
  • \$\begingroup\$ Hard to tell, but could it be brown-orange-silver-blue, that is 0,13 Ohm with 0,25% tolerance? \$\endgroup\$ Commented Mar 20, 2017 at 11:26
  • \$\begingroup\$ What is the country of origin of this device? \$\endgroup\$ Commented Mar 20, 2017 at 11:42

2 Answers 2

3
\$\begingroup\$

Replace it with a resistor you have that is closest to 0.1Ω

Or try 13.6" of 24 gauge wire.

Take a 100mA current reading and see how close the it is to the actual current. Ballpark will do, just want to know the magnitude.

From there it's just simple arithmetic.

Is the current 10x? Or 1x.

If you need to buy a resistor, try a 0.01Ω and a 0.1Ω Tolerance is up to you, smaller is always better.

The first band is likely brown because a 1 makes sense for a current sense resistor value.

The second may be silver where most of it has flaked off.

So my guess is 0.01Ω

0.01Ω is the most common resistor in that range so would be the most likely value for a current sense resistor.

\$\endgroup\$
1
\$\begingroup\$

How about 0.19Ω 0.25% ?

Yes I agree

Brown White Silver (space)  Blue
  1     9    x0.01          0.25%

thus 19x0.01 =0.19 Ω

enter image description here

schematic

simulate this circuit – Schematic created using CircuitLab

Hard to tell from component without schematic, but I would expect 1A limit. 10A would need a much larger >=5W part.

\$\endgroup\$
2
  • 1
    \$\begingroup\$ Generally, I'd agree. But what on earth would something else than a resistor do in the "business end" of a multimeter? A MOV, TVS or fuse perhaps, but I've never seen those in a resistor package. \$\endgroup\$
    – Oskar Skog
    Commented Jul 30, 2017 at 7:46
  • \$\begingroup\$ i agree ..... now that I see multimeter \$\endgroup\$ Commented Jul 30, 2017 at 14:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.