Analog panel meter questions thread

[Marco Polo]

300V meter

Is that volt meter a direct-connect type, or does it need a current transformer? I'm honestly not sure. It's pretty clear when an ammeter needs a CT because it will say something like 200/5A on it, but I'm not sure about this meter. It looks like it should be direct-connect without any other parts needed, but I'm confused by the "CT" on the face plate.

Amazon is definitely good for getting these sorts of gauges but definitely buyer beware because the listings are often fairly vague!

 

[paul1598419]

I now see that this is for monitoring your line voltage. It looks like it is direct hook up from the description. Unlike a DC volt meter that uses a shunt, this is only made to monitor AC.

 

[lasersbee]

It looks like a normal 300VAC Voltmeter.
Seems you just hook it up to your AC supply that
is less than 300VAC.

@Paul...
IIRC a standard DC Voltmeter would not need a
shunt unless you want to measure current with
the voltmeter.

Jerry

 

[paul1598419]

Yes, I meant to say that, but I was in a hurry and it came out wrong. The shunt is necessary as the meter movement can't handle but very small currents. In the voltage setting, this is not a problem as the current sent through the movement is reflective of the the voltage and is not used to directly measure voltage.

 

[Marco Polo]

Are the 750-volt, 1kV, etc. higher voltage meters safe? It seems a bit dangerous to have 1000 volts going to a 10-dollar chinese panel meter. At the very least I would want to put fuses on the meter leads in case something shorts out.

I hope these questions aren't too silly. I can't find much information on the subject online. Quite a few catalogs and product listings, but nothing really basic or introductory.

 

[Benm]

As long as the case is made out of plastic safety should not be that much of a problem, at least from the perspective of not getting an elecric shock when touching the meter.

If it could shomehow short out is another matter and hard to tell. They may skimp on isolation distances quite badly, but isolating 1 kV is not that difficult either.

All these meters are internally current meters, the ones indicating voltage usually are a sensitive current meter with a series diode. One thing that can go wrong is using a resistor not rated for the voltage applied, such as a standard 0.25 watt, 10M resistor for a 1 kV meter. Those resistors are usually rated at 'only' 250 volts ac or 400 volts dc, though generally do not fail when taking up to a kV or so.

 

[paul1598419]

What do you need a 1 kV AC ammeter for? You certainly don't have access to that in your house, unless you plan on using a step up transformer.

 

[Benm]

I meant a voltmeter, which is internally an ammeter with a series resistor, but intented to display line voltage.

In european power systems there are 3 phases with 230 volts between phase and ground, resulting in about 400 volts between phases, or 460 volt when using 180 degree antiphase (very uncommon). In such an application using 1 kV panel meters is not that bad an idea.

If you want to indicate voltages between phases instead of between one single phase and neutral a 300V meter will not be sufficient in europe. A 500V model might be best suited, but if not available, a 1 kV one would work well.

 

[paul1598419]

^ I get that, but OP is in Ohio.

 

[Hemlock_Mike]

I put a small plastic analog meter into a PS
years ago. I had many Megs of resistor in line.
NO PROBLEM... The meter blew itself out of the
panel at 7,000 volts. It might work for you
HM

 

[Benm]

Euh yeah... i reckon that meter was not intended for use with 7 kV, right?

As for why these meters are sold: I guess the audience is not limited to the US, and the vast majority of the world actually uses 220-240 volts mains. 110-ish volts are mostly limited to the american continent, and even south america has numerous countries that use 220 volts.

 

[lasersbee]

I have a few items that are running on 220VAC here
in Canada...
I even have one that outputs 220VAC into my power
grid when I need it...

Jerry

 

[Benm]

I bet you do, but 'standard' mains voltage in canada is still 110 volts, right?

It seems to be less and less important since many switchmode supplies can operate from both, but here are always things that cannot. The only 110V country i've ever visited is mexico (and i've travelled anywhere from say albania to west-papua and most letters in between), and i had to bring a transformer to charge silly things like my toothbrush or shaver, everything else has universal supplies.

 

[lasersbee]

In Canada the mains power that comes into a house
is 3 phase 240VAC. All the standard wall receptacles
are wired 1 phase 120VAC.
The Stoves and Clothes Dryers are plugged into 240VAC
3 phase wall receptacles...

For quick low power 240VAC testing in the shop I use a
120VAC to 240VAC step up transformer.

But I know what you mean....:beer:

Jerry

 

[DashApple]

Are they actually three phases or are they split phase ?

I though over there it was single phase three wire with 230V between both phases and 120V between either phase and neutral

Three phase over here in the UK is 400V between any of the three phases and 230V between any of the three phases and neutral

 

[diachi]

Are they actually three phases or are they split phase ?

I though over there it was single phase three wire with 230V between both phases and 120V between either phase and neutral

Three phase over here in the UK is 400V between any of the three phases and 230V between any of the three phases and neutral

It is split phase here - 120V phase to neutral, 240V phase to phase. Often times you'll see one half of your outlets on one phase and the other half on the other phase, with appliances (stove, dryer) using both phases for 240V. Buddy of mine was running his wall mounted AC (external heat exchanger on balcony...) in his apartment by plugging one line into one outlet and the other into a different outlet on the other phase to get 240V.