It sounds like what you have MIGHT be configured as a voltage meter intended to be used in conjunction with a current shunt. Do you have an ohmmeter? Measure the resistance of the meter and see what you get. If it is high, then it is probably a voltmeter. If it is low, then it is probably an ammeter. Then, if you can, measure the current flowing out from your batteries when you connect them to the meter. That will let us determine if it will be easy to do what you want. By using suitable external components, it should be doable.

Good morning all. I appreciate everyone's help. I have a digital ohmeter, one that my father in law gave me, but don't know how to use it in regards to testing this particular meter. But if someone were to help me out then sure I could measure it, like out to set it up and where to put the dial. The one I have is a commercial electric. And yes I have the probes. And to Kermit2 I have not tried to open it up but will see if it will open up today.

 

Guys, she wants to use a DC meter with an AC circuit. We can't discuss a diode-resistor-cap solution as that would be mains-direct. That limits discussion to batteries, which the TS doesn't want to bother with, or a transformer/SMPS.

It is worth knowing what current is required to move the needle. Cranking more than, say, 1A through it would be wasteful and a heat risk.

So you are saying that is someone wanted to know how to make an AC voltmeter similar to the what is part of their analog VOM that we couldn't discuss it?

 

I don't make or enforce the rules but that is my interpretation. If the project isn't isolated from the mains, no dice. I could be totally wrong. It's only sort-of a "power supply".

 

Good morning all. I appreciate everyone's help. I have a digital ohmeter, one that my father in law gave me, but don't know how to use it in regards to testing this particular meter. But if someone were to help me out then sure I could measure it, like out to set it up and where to put the dial. The one I have is a commercial electric. And yes I have the probes. And to Kermit2 I have not tried to open it up but will see if it will open up today.

There are plenty of tutorials online about how to make voltage, current, and resistance measurements with a digital VOM. What you want to first do is just measure the resistance of the meter by connecting your probes directly between the meter and the VOM (using the 'COM' and 'VΩmA' inputs) with the VOM set for a resistance measurement (the lower left green arc of your meter). Use whatever scale gives you the most significant reading. Do that much and let us know what you get.

 

Thanks wbahn. I appreciate it! I did what you said. With the meter set at 200. I took a couple readings. I got readings from 6 to 9 with 8 holding strong for the last couple.

 

Thanks wbahn. I appreciate it! I did what you said. With the meter set at 200. I took a couple readings. I got readings from 6 to 9 with 8 holding strong for the last couple.

So that would indicate that it is an 8Ω coil. That would only ask about 375 mA or so from a pair of AA batteries.

The next test you might make would be to put your VOM on the 200mA scale and then just use one AA battery and put the meter, the battery, and your VOM in series and report what the both the VOM and the panel meter read.

Do you have any resistors available that are in the, say, 5Ω to 20Ω range?

 

So that would indicate that it is an 8Ω coil. That would only ask about 375 mA or so from a pair of AA batteries.

The next test you might make would be to put your VOM on the 200mA scale and then just use one AA battery and put the meter, the battery, and your VOM in series and report what the both the VOM and the panel meter read.

Do you have any resistors available that are in the, say, 5Ω to 20Ω range?

Ok I did the test. With one lead connected to VOM, then to the positive side of one AA battery and the meter set at 200m with the red lead in the 10ADC port and the black in the COM port the VOM jumped to the first hash mark which I'm assuming is 10 and the meter stayed at 00.0. So im not sure if I did it right. And then with the nothing else changed, and just because I was curious, I moved the dial to 10A and the numbers in meter ranged from 4.50 to 5.20 and the VOM needle moved to 10. I also did an experiment yesterday, again because I was curious. I hooked up a 2 wire lamp wire to a polarized plug and a candelabra socket with a nightlight bulb. Neutral wire right to the socket and the VOM connected in the series on the hot wire...nothing showed up on the VOM but the bulb lit up. And no I don't have any resistors. I can get some no problem. Which would you suggest, the 5 or 20, or should I get a couple different ones.

 

Did the prior resistance measurement read 8Ω or 0.8Ω?

 

It measured .8 ohms before but I then measured it again today to be sure and it now it gave me a reading of 1.3 to 1.8. The meter with nothing going through was at a starting point of -1 and I used all the readings at the 200 setting. I found the the manual that came with it and I'm thinking for the first tests I may have had the black probe in the adc and red in the com. The manual said to put them the other way. So with them correctly positioned I got the higher reading.

 

Okay, there is a big difference between 8 (as mentioned in Post #25), and 0.8 (Post #29). With 0.8A I would expect something on the order of 2A to flow from a single AA battery, so that is roughly consistent with what you saw. It might also have blown the fuse in your VOM because it so greatly exceeded the 200mA max (it's probably a o.5A or 1A fuse, the 10A side is probably not fused, which is why it uses a different jack). That was why I had you do the first measurement -- to see what the max current would be from 2AA batteries and with 8Ω that would have been 375mA which exceeded your highest fused range on your VOM, which is why I had you only use a single AA battery. But with 0.8Ω, it's an entirely different story.

So check the fuse (the manual should show you how, and replace it if necessary).

I'm still a bit surprised that the meter resistance is that high. I would expect it to be on the order of 0.01Ω or so. But your VOM isn't going to be very accurate down at those resistances.

For what you are trying to do, you are going to have a hard time getting a significant deflection of the meter due to the bulb current. A 120W bulb will only draw about 1A of AC current from a 120V outlet. You are needing a few amps to get significant deflection of this meter (since it is intended for 60A scale applications). If you had a meter that was more responsive (i.e., the full scale was something more like 1A to 10A), then you could put a diode in series with it to rectify the current.


The top diode is the one you need. The bottom diode is optional. You want diodes that are rated for at least 200V PIV (peak inverse voltage) and are rated to carry several amps (a 1A rating is enough provided you never short the bulb -- but if you short the bulb you have other problems and should blow a house breaker and other components in the lamp probably aren't intended to carry the 15A or 20A it will take to do so either. You can get suitable diodes, such as the 10A04, for under a dollar from DigiKey and if you have a Radio Shack nearby they might actually still stock something suitable.

I don't think you will get much of a needle deflection with the meter you have. Yes, you could put in a circuit that steps down the voltage and ups the current in order to drive the meter, but I would recommend against it.

Changing gears, I'm a bit concerned that you are working with electrical appliances without having much of a basic knowledge of electric circuits and how to make measurements on them. Make no mistake, you are doing something that can be dangerous -- deadly so. I strongly recommend that you take the time to learn some of the basics before you go much further -- I think you've been luckier than you have a right to expect up to this point.

 

I'm going to take your advice and just use this piece as a decoration. It would have been neat to get it to work in conjunction with my design but oh well. It was worth a shot. And I appreciate your input and concern. I'm more familiar with electric with regards to household repairs and upgrades. It's the converting with small electronics that I'm unsure of because of not working with them until recently.