RV, Generator & House Power Meter

Our new generator doesn't have a power meter on it so I want to understand how much power certain items are consuming so we can better understand how to manage the load when using it.

During the winter we lost power for a couple of days and decided during the last outage that I need to get a generator and a transfer switch put in place so we can have power during the outages.

We are going to use the same generator for camping and last year when desert camping at 4000 ft our previous generator couldn't cut it. Our new one has more output but I still want to see how things work at home and when in the harsher conditions when camping.

Of course you can buy a prebuilt one but they are kind of expensive so I figured I would just built it myself.

The box and wire and connectors, I got at Home Depot, just including these items for completeness.

Tools wise, Drill press, hole saw, wire cutters, screwdrivers, ruler, files, Dremel tool.

The way I wired the meter up isn't correct by any electrical standards. I assumed #8 wire was correct for 120v 30 amps, no idea if a plastic box is correct either. Just putting it out there.

So to get the box ready I need to do a couple of things.

1. Cut the holes for the connectors so the wire can come in and exit.
2. Cut the rectangle hole on the lid of the box so I can mount the meter.

Note - Measure twice, then again, then cut once.

So I decided that the wire would enter at the bottom of one side of the box at the bottom and exit on the other side at near top of the box. I figured this would give me some additional space to work with.

For the lid, I carefully measured where I needed to cut on the lid of the box for the meter. Then I hole sawed part of the opening, then used a Dremel tool to cut the rest - then I used a file for the final fit. It fit perfect but was a little tilted. (Better than needing a new lid or having to glue a new top on the lid and do it again.

So the way I wired it was to NOT cut the wire in half. The idea is to have the three wires exposed so that I can put the current pickup around one of the wires and get access to two of the wires so they can power the watt meter.

So I carefully removed the rubber outside casing of the wire with a razor blade. Taking care not to cut into the rubber casing of the three wires. Before I did that I had to slide the wire through one of the connectors, into the box then out of the box. I wanted to measure how much casing I needed to remove. To much and I'm going to have exposed wire outside of the box, which no one wants.

Once cut, I did a test fit in the box to make sure the current meter pick would fit with the wires inside the box. I also fitted the watt meter into the cover and put the cover on to make sure the wires weren't pressing against the meter.

Now the hack part - using either a X-acto or razor blade, I cut a small ring around the white and black wire just exposing a little bit of the copper. I stripped the two power leads from the watt meter and soldered the ends. Then I wrapped them around the black and then the white wire (doesn't matter to the meter which is which, wrapped them tight and then taped over the connection tight.

Wiring the watt meter is pretty straight forward - except I wired it backward the first time- Two of the wires from the pickup go into the watt meter, the other two - 120v go to the other connections. I tinned all of the wires going into the meter because I think it makes for a stronger connection when screwed into the meter. Not shown here - the wires into the meter will be taped down to the meter just incase any of them try to get lose and cause a short/fire/issue.

Plugs on both ends of the L50-30 plugs, one to each end of the meter. The L50-30R (female) is what is on the generator, so I have a L50-30P on one of the cables to plug into the generator. On the other I added a L50-30R that will either connect (via another adapter) to my transfer switch in the house or the cable that comes from our camper trailer.

WARNING - make sure - with a meter and visually that the wires on one plug match the wires on the other plug. I.e. ground on one plug goes to ground on the other, white to white, black to black.

Testing - Lets not blow any breakers...

I hooked up the meter between the generator, to the adapter and on to the extension cord to my transfer switch.

I have a multi-story house and there is a 50 amp sub panel for the main floor, the transfer switch is used for this sub panel. The generator can do 30 amps at 120v the sub panel is 50 amps 220v. I can't run everything (the oven is 220v) but it will run enough to be comfortable when the power is out.

So I fired it up and did a quick test. Meter came on, show 120v 0 usage since I hadn't switch the transfer switch. Switch over, generator revs changed, saw a load on the meter. Switched things back to all city power

Now I figured I had to do some type of calibration to see if the meter is even in the ball park with what its reading.

I have a Sense meter hooked up in my house and decided to test with two items - A 4ft LED light and the microwave in the kitchen. Opened up the Sense app, got a baseline and then fired up the the microwave. I did this a couple of times and collected the data. Then I got a baseline again - and turned on the 4ft LED light. Got base line numbers before every test.

SENSE METER

Microwave

1,365 off

2,249 on

Microwave - 884w

LED light

383 off

415 on

LED light total 32W

Then I did the same test again with the generator powering the house.

My Generator Watt Meter's Readings

Generator running, nothing connected 124 v

Microwave

Base line 123 v 6.7A 844 watts

microwave 1.73kw 121V 15.2A

Microwave 884W

4ft LED strip

On generator Baseline 155w 1.75A

led light 175w 1.98A 

LED 20watts

Results -

Well it works. Will test this a couple more times with different items and loads so I can have more data to average. I supposed I could just buy a AC current meter as a 3rd measurement device but for now I don't want to spend the money.

So it works, no blown breakers or magic smoke. Turns out the watt meter was the cheapest part of the project. Cost me over $100 bucks by the time I added everything up and the meter was like $16 bucks.

While I don't like the extra adapter cord between the meter and the load, I can't really do anything about it. The plug on the transfer switch is different than the plug from the trailer.

I'll probably pick up a spare watt meter. It seems pretty fragile and the meter is going to spend some part of its life in the cargo area of the trailer.

Good luck if you try this - be careful!