How to wire a voltmeter?

Original poster here:
Thanks to everyone who chimed in. Lots of good discussion, ideas and advice. Like I said, I was just bored and looking for project ideas.

For now, I'll just stick with the plug in meter I have and that I used in our previous trailer.

When our new trailer arrives, I'll robably do it right and install a hardwired Progressive Industries unit with the remote display option.

Resistance i.e. voltage drop "should be" almost non-existent in an RV chassis AC voltage system. This excludes the pedestal connector wire and plug. And ideally that too should also be tiny. There is no reason on the face of the earth to suffer alternating current voltage drop within a rig. Of course all circuits should be periodically tested. I test receptacles with an 1,875 watt heater, and roof air connections with a voltmeter, starting the unit on high head pressure.

It doesn't matter much where, as the available voltage will be pretty much the same anywhere on the system, dependent on load and resistance of wiring and connections. I measure at a convenient interior circuit, rather than at the power cord, because I expect that wiring problems raising resistance, if any, will be mostly before or in the junction box, rather than on branch circuits.

The issue here may be one of presentation as well as function.

I've three or four 4-lead AC voltmeters. All are LED lit segment.

Red D.C. Positive (dimmable)
Black D.C. Negative
Alternate Color 1, connect to AC line or neutral for 120vac
Alternate Color 2, connect to AC line 2 for 240, neutral for 120 vac monitoring.

I do not like the quality of the A.C. line connections on any of the meters I have purchased. I soldered 18-gauge silicone wire, yellow and blue for the high voltage connections.

I also smeared dielectric silicone grease on the exposed PC board, then clamped a PVC hobby box covering the meter rear.

The 12 VDC LED wires exit the box 180 degrees opposite the 120 VAC leads to prevent possible inductance AC to DC. I still have quite a bit of 20 gauge twin wire with a drain wrap that I connect to chassis negative.

Hope this helps-

Meters that measure 120 VAC only, will likely have 2 leads. Sometimes 3.

Be aware that any connections to your 120vac power must be in an approved electrical box by code.

Plugin Voltmeter, Polarity light both plugged into a 3-way adapter.. Done.. Everything one would need in one glance.


D.E. Bishop: He's trying to keep it simple by not worrying about copper losses others were pointing out. Without giant loads running the voltage is the same anywhere

2oldman wrote:

Big Katuna wrote:
Not true. Copper has losses that increase with load and that drops voltage.Add in a bad connection and you can measure 120 at the pedestal and 108 at the AC compressor.Turn everything off and the voltage will rise to 120.

You're getting off track. OP is talking about a voltmeter installation inside the coach, not at the pedestal. Nor are we talking about whether it's 120..or any other specific number.

The voltage reading inside won't be exactly the same everywhere, but it's certainly close enough for any voltmeter. If the ac is on, and the voltage at the coach is 108, it will measure 108 at any outlet in the coach. That's the point I'm trying to impress to the OP...for practical purposes it doesn't really matter where he connects it.

OK?

X2 on 2oldman's comment. This ain't rocket science and it ain't the ISS, it's a RV.

RoyB wrote:
Wiring in a PANEL TYPE 120VAC meter will require wiring inside conduit or protected type wiring to prevent anything from from touching the terminals etc...

You just can't run a couple of tapped cables out of your Power Distribution Panel and stick on the terminals of the Panel Meter sticking through a hole in the wall all out in the open... 120VAC Items should be mounted inside small enclosures all protected. Otherwise someone will get hurt or you may burn your trailer down...

Have to follow safe wiring techniques when dealing with 120VAC items...

Should be plenty of info on the internet on how to wire up 120VAC items...

If you are not into this you should get a professional licensed type person to do this for you... The fact you are asking these questions indicates you may be out of your knowledge base here.

Just saying....

Roy Ken

I hope folks understand what you have presented here. Simply put, running those skinny wires to a non-listed meter is a recipe for disaster.

I installed an outlet where it can be seen and plugged in a meter.

wa8yxm wrote:
Depending on the meter it will have 2,3 or 4 leads

K.I.S.S.

Go to your favorite RV store and get the plug-in meters they offer.
I have one for 120 VAC.
I have another for 12 VDC.

Both are plenty accurate enough for what I need to see, that is that the gen is really up to speed and has the proper output and whether or not the 12 V system is charging or discharging and a rough estimate of it's SOC.