Analog volt and current panel meters.

[Marco Polo]

If you've watched Aussie50 on Youtube much, you've probably seen his DIY power display panel. It has several analog meters on it: Volts 0 to 300, current 0 to 20A, and current 0 to 50A. I believe it also includes an on/off switch and emergency shutoff button as well.

I want to build one but am unsure as to what type and quality of meters I should be getting.

Amazon has a bunch of them in the 10 to 20 dollar range. I'm sure they're "OK" but should I get something better?

The problem with other companies, e.g. Simpson Electric is that they omit pricing information from their websites. Nearly every company I've looked into omits price info. I completely hate this, it's stupid because the price will have a large impact on what I ultimately decide to purchase. But based on poking around a bit, it appears that meters a la Simpson are 75 to 100 dollars each. This is expensive but not ludicrously horrible or out of the question — there is a lot to be said, especially in the long run, for using higher-quality components.

On the other hand, I don't need extremely high accuracy. I just want to have some parameters on display so that I can avoid blowing up my variac and whatnot. My current variac is rated 5A and I have one in the mail right now that is rated 22A. Both 120VAC, but am considering adding a third variac, 240VAC, as well.

I think voltage 0 to 300, current 0 to 20A, and current 0 to 50A meters would be about right. But which ones (e.g. price/quality) do you guys recommend that I go with?

ETA: This might be good. They even set your meters in a nice little plate for mounting on the panel. And they include pricing!
Plate-mounted meters

45 dollars for a pair of meters nicely mounted like that? Hard to argue with it, what do you think?

 

[Cyparagon]

Why not the $6 meters on ebay? They're not mounted, but I'm not sure that's worth the extra $33+shipping.

 

[Benm]

That would depend on what you want really. The ones mounted with a faceplate are easy to install. If you need to fsck around with a dremel and drill for half a day to save $33 you are working below minimum wage.

If you still have to build the entire eclosure and proper holes in that you may be better off with loose meters from ebay.

One thing with current meters though: make sure they include the shunt! Some meters sold on ebay do not and you need to have one of a specific resistance to get a current reading. Often vendors will also sell shunts, but they could be an extra despite the listing saying something is a current meter and you expect it to include the shunt resistor.

 

[Marco Polo]

One thing with current meters though: make sure they include the shunt! Some meters sold on ebay do not and you need to have one of a specific resistance to get a current reading. Often vendors will also sell shunts, but they could be an extra despite the listing saying something is a current meter and you expect it to include the shunt resistor.

This is the part that confuses me. I thought an ammeter just has two terminals on the back and you run the current through the meter and that's that. I have no idea what to do with a shunt resistor, or how to tell which is the right one, or anything else to do with it. I've read about them but can't really make heads or tails of it.

 

[Chrisbee]

I'm sure Cyp or Benm can explain it better, but I believe you only have to use a shunt resistor to measure current, if the amperage that you're trying to measure is higher then what the meter can handle.

 

[Cyparagon]

An analog meter operates at several mA at most. Otherwise, the winding on the armature would be too large to respond effectively. Therefore, they will always be part of a current divider. A low-value resistor (aka shunt) forms the other part of this current divider. For low currents, say, <10A, this shunt is often internal to the meter. For higher currents, the shunt is external. Whether the meter requires an external shunt, and whether it is included are two things you need to clarify before purchasing.

If you need to fsck around with a dremel and drill for half a day to save $33 you are working below minimum wage.

Have you not heard of a hole saw? If you don't have one already, they're a whopping $10 for a whole set. Even if you only had a drill/dremel, the only way it would take you HALF A DAY to make 2 medium holes and 4 screw holes in a panel is if you had some sort of physical disability.

 

[Marco Polo]

The hole saw idea is a good one. No reason that the mounting hole for a square meter needs to be square, I just need the terminals accessible.

So I'm going to get cracking on putting my panel together! There is a theater department at Ohio U and I recycling-bin dived a nice plywood rectangle with one side covered in smooth black plastic and the other in some kind of black felt. Perfect. Budget is improving due to steady employment (finally!!!) so that's a lot nicer.

My mom also replaced her heat pump, and the guys left the old one at the house for too long. They left the 240 volt wire run too. Sorry for them but they lost out on that 100' or so of 10 AWG THHN 90°C black wire. Oh, and the 100' of the red, same kind. Oh, and the 100' of the green wire too. 10 AWG copper isn't cheap, I bet they weren't happy to find it gone but that's the price of poor customer service I suppose and now I have some nice heavy wire to use.

Thank you for all your kind advice! Figure 0-30A, 0-60A, 0-120V, and 0-300V analog meters (might as well overdo it), a master on/off, indicator neon, a couple terminal blocks, and probably will want a circuit breaker or fuse on there too. Anything else I'm missing? I'll update when I get something substantial done!

 

[Benm]

Mouting depens on both the meter and how you want it to be.

Some models are mounted protruding from the panel, in which case you can just make a big hole with a hole saw and some smaller ones for bolts to fix it from inside the case. If you want it recessed in the case however, things get more difficult as you need to cut out the rectangular outline.

It's also a matter of having access to the proper tools. Making a rectangular hole using a dremel is quite shitty, but with a proper saw it can be easy work.

 

[paul1598419]

I actually cut my teeth on those Simpson VOMs with the analog meters. I had no idea they were still for sale as they were not even up to the ability of an RCA Vacuum Tube Voltmeter. I bought the RCA when I got a little older for $150.00 which was big bucks back then. Man, that takes me back. I still don't see the advantage of a meter movement over an 7 segment display array.

 

[Benm]

It depends on the application really. If you measure current and your load is something variable, an analog meter may indicate that better. Think of load changes in the order of a second or so, where you can see what the needle is doing while a digital readout can be jumping around a bit randomly.

It's a fault turned into a feature really, analog meters just respond slowly, and so display a moving average to some degree. This could also be done digitally, but is not visually attractive on a number display. Obviously there are digitally controlled meter hands as well, such as speedometers in newer cars.

 

[Cyparagon]

analog meters just respond slowly

Not true at all. The refresh rate of a typical digital voltmeter is a few hertz at most. Analog meters update nearly instantly (as far as your eye is concerned). Really good voltmeters can update at 10+ hertz, but with numbers flashing by on a 7-segment display, they can't be read easily. Digits will just look like "8" if they're changing a lot. An analog meter doesn't do that, and will show peaks that a digital meter may miss. The downside is of course the accuracy.

 

[paul1598419]

That's true. If I need to see a load or voltage, current or anything else change I rely on my scope. It was made for that specific purpose. I use a meter to look at basically D.C. or static variables.

 

[Benm]

@Cyp, i guess i should have worded that a bit better. Digital meters often indeed have limited refresh rate, the problem is more that it's a momentary value that gets displayed rather than an average (unless it has some mechanism to do that).

Fast update speeds make digital displays unreadable indeed. If you use something like an arduino do display an analog input to an lcd at maximum speed the display is worse than if you delay purposely between updates.

Tip on that: just do a lot of analog reads in a row summing the result, this will give you a little bit more software resolution (1 bit for 4 samples added, 2 bits for 16 etc) as long as the signal has at least 1 (hardware) bit of noise.