How to mesure negative voltage with a positive device

These are probably what he is looking at:

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I have seen them before. Very minimalist. Regulator, trim pot, and a microprocessor doing all the adc and display. Definitely no AC capability.

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Reply to
David Eather
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Like I give a fat flying f*ck about you, or your posts, much less your retarded filter edit announcements.

Reply to
Long Hair

And it doesn't have to be analog either. I have a VM very similar to the OP's and another one combined with an ammeter.

I also monitor my house mains voltage with an AC VM using the same principle, semi-permanently fitted on the wall. It has separate inputs for power and signal but I just wire the two together.

Reply to
Pimpom

While I agree that the above connection will work properly, What happens if your 12v supply measures incorrectly? Now what do 'you' think? Measure a known good 12V, then measure your unknown.

Mikek

Reply to
amdx

Show me where, and I will show you someone else doing it first and insulting me. They get it right back in their face.

"Egomaniac"? Yeah, right.... sure bub.

Reply to
Long Hair

But you're AlwaysWrong and everyone knows it.

Forget the ego part.

Reply to
krw

ritto:

e only two wires one positive and one negative, they use it for self poweri ng and measurement.

mine are like this one

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res however mine are 3v to 100v (99.9v exactly)

Reply to
Juri Fossaroli

And that is exactly what is required, so just do it! Positive terminal to GND, negative terminal to -12V, and the whole thing is powered from the -12 and displays "12.0".

Reply to
Rob

You are one of the biggest offenders in the group.

Your capacity to make a valid assessment of or about anything rests firmly at nil compared to any real man.

Reply to
Long Hair

We're talking about the same thing, only differently. You're thinking in terms of GND and line. The OP didn't mention GND, only positive and negative. If he flips the leads, that will connect the +ve terminal to the -ve input.

Reply to
Pimpom

That is one clue. It requires a minimum of 3 volts to operate, so that is also the minimum reading. (referring to 'yours').

Reply to
Long Hair

Yep... That is how a 'full floating supply' works.

Reply to
Long Hair

But you're AlwaysWrong. Always.

But you're always wrong, AlwaysWrong.

Reply to
krw

Then why do you write that it won't do?

Those $2 electronic voltmeters that you get from Ebay/Aliexpress often have 3 leads: GND +supply and +measurement_input.

When you want to use them to measure a powersupply output (5-30V) you just connect the +supply to the +measurement_input and you are left with 2 leads. Apparently his meter already came wired with 2 leads.

Those 2 leads are connected to the voltage to be measured: GND to the relatively negative and +/+ to the relatively positive.

It does not matter what the actual GND is so this meter can measure

-12V supplies just as well as +12V supplies. Only it will not display a minus sign when measuring the -12V supply.

In fact, just like an oldfashioned analog meter. It will only draw a little more current. To measure voltages without drawing current to supply the device at the same time, you can use the separate

+measurement_input but it will not work when measuring negative voltages.
Reply to
Rob

Because reversing the connections - connecting a positive source to the negative input wire - will not work and may even damage the product.

It seems you're still thinking in terms of GND reference. The issue is not which lead is GND. GND did not enter into the picture until you brought it up (maybe someone else did too - I don't remember). The question was simply how the meter should be connected.

The correct answer, as I said before, is to connect the positive lead to the positive source, and the negative lead to the negative source. That's *not* flipping the leads.

But the OP's meter doesn't. I think it's safe to say that few, if any, here have perused AliExpress listings of those meters more thoroughly than I have and I know about the many variants, but we're talking about the OPs's meter which has TWO wires.

I explained all of the above in my first post.

Reply to
Pimpom

Turn it upside-down;IOW connect it properly and ignore the sign.

Reply to
Robert Baer

You are an imbecile.

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Reply to
Pomegranate Bastard

You know better. The term for AlwaysWrong is "Nymbecile".

Reply to
krw

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