Can a Shunt Go Bad?

The necessity of zeroing is more acute in handheld measuring devices -- hence manually triggered null (pressing a button). Twisting millivolt wires will reduce error in this circuit. And keep all forms of magnetic flux away from the meter the millivolt wires and the shunt.

From the school of red-faced hard knocks :)

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That seems to have worked, Mex. :B

It’s back to displaying -0.0 with just the Trimetric meter drawing power from the battery.

I assume that since the minus sign is lit, it just doesn’t have enough digits to display the tiny bit of current being used by the Trimetric itself.



Thanks for all the help.

:):)

This is an attempt to null the millivolt zero BFL13 :)

No need to to solder a clothespin will work to hold black and white wires for a few seconds.

My "guess' is they didn't put a "zeroing" circuit inside the meter. And this may be the way they calibrate to zero. Like a DMM with zero ohms. Pure guesswork.

Since doing this is free and easy it's worth a try.

DANGER WILL ROBINSON

Just make sure a dropped millivolt pair of wires cannot gain potential of > 50 mv somehow shorting across voltage potentials. It would tale 2 shorts one pos the other neg to do this. This is why I recommended a wooden clothespin.

Take an image beforehand th eliminate the irritating and slightly embarrassing reversing of millivolt wire reconnection.

Hope this works for you!

If all three are together, you can't measure across the shunt.

Thanks Mex, I’ll give all of your suggestions a try.

Just to make sure I understand the re-zero process, I need to pull the fuse to the meter, then remove the three wires (two black and one white) from the shunt and hook them together. I’ll solder the ring terminals to the wires first, and use a nut and bolt to connect them.

Then, touch those three wires to the negative battery post? That’s the only way the meter is going to be repowered it seems to me. Or should I repower the meter through some temporary leads?

Thanks for the extra help.

:):)

Turn off meter

Disconnect millivolt wires.

Connect millivolt wires together but not with the fingers. Keep mv wires isolated from any power wires when doing this

Repower meter for a moment

Shut power off to meter

Reconnect millivolt wires to shunt

Some meters will rest but you need to empower the meter with shunt wires disassociated from voltage but connected together. I have several non loop powered 100 and 50 mv digital meters that can be zeroed this way.

What time2roll said. The shunt is disconnected so the non-issue is that the meter is slightly off cal but still within spec per boondocker.

I have one of the cheap-cheap meters that can be calibrated to zero. Surely the expensive one can be calibrated also.

Even if it can't, your within spec.

The shunt is just a calibrated high amp resistor. Yes the shunt can go bad if it is overheated and the material changes resistance. And if shorted the shunt can open like a fuse. (don't ask how I know)

As for the reading you posted while shunt is disconnected... not a shunt issue.

You have a decent shunt. Look at the bridge and see silver-solder to the blocks.

I use Caig De-Oxit D-100 to eliminate resistance between the block and the millivolt wire terminals which BTW ahould be soldered not just pinched on.

Millivolt wire leads to the monitor should NOT be paralleled with other wires.

Millivolt lead wires to the monitor should be twisted around each other 2x - inch to null stray inductance.

I am so fussy about millivolt wire integrity I silver soldered them to the shunt blocks on my big bank. Aircraft 20/2 shielded wire and yes, the wires are twisted inside the braided tinned sheathing and teflon cover. I used a Bernz-o-Matic pencil tip torch to solder the wire to the block. Five aluminum hemostats to keep the bridges cooler.

But do try the De-Oxit D-100 it keeps everything honest in my measuring stuff.