Anonymous Gerbil

For those that don't know, I live in Texas. Same Texas that spent the better part of a week in the deep freeze last winter. We were lucky in that we had intermittent power -- hour on, hour off, or there about -- for four days. Many around us had much less on time, some had none. This was at a time when the temperature outside was in the low single digits. We made it through with little damage, but it got me thinking more seriously about getting a generator. Costco had a tri-fuel Firman generator that I had my eye on before the deep freeze and going without stable power for the better part of a week made me look even harder. However, while not terribly expensive for what it was, it was still a good chuck of money for something I'll likely never use.

Fast forward to August and Hurricane Ida. I was down on the gulf coast, moving the boat (that's a story for another day) and right before coming home, I was at my Aunt and Uncle's house after the storm. They had no electricity and were running off a generator -- the same Firman model I had been looking at. It was doing well enough that they were able to run their downstairs central AC units, as well as an upstairs window unit. I bought one a couple weeks after I got home.

The generator has a built in meter that shows voltage, frequency, and hours. It doesn't have an ammeter. This seems like an oversight, but when I thought about it, I realize that it is more likely due to the average person not being able to interpret the display than for something like cost. The generator is a 240V/120V system. It has two 120V phases that when combined, give you 240V, like a normal house setup. A 240V device pulls equal current from both phases. A 120V device pulls current from one of the two phases. How would you display the current draw to the average person? If you have two 120V devices pulling the same current from both 120V phases, you can't tell the difference between that and a 240V device pulling the same current.

Still, I wanted ammeters, so I could monitor the overall load on the generator and make sure I was not overloading it. I'm running it off natural gas, so my output will be significantly lower than running on gasoline. Plus, I'm a nerd, and more information is always cool, especially when it involves LEDs. I picked up a couple of V/A displays off of Amazon.
They are rated to 50-500V and 0-100A. They aren't horribly precise, +/-2V and +/-2A, but entirely sufficient for this purpose. These meters only read real power, not apparent power. There are plenty of displays that will do real, apparent, power factor, and other stuff. However, I have limited space on the panel of the generator and need to be able to monitor both phases. I have to fit everything in this space.
The two display will just fit in the blank space.

Cool project. Interested in seeing how it turns out.

Before I went drilling into the panel, I wanted to make sure there wasn't anything behind the blank spot...
And there wasn't. Clear to drill... I want this to look reasonably decent, so I spent a good bit of time figuring out where the centers should be. Not the cleanest markup, but since I was the one marking it and drilling it, I could make it work. Really, I should have done it a second time.
I really need to get a proper center punch, but I was able to make do here. The metal of the panel is pretty thin and soft, so a sharp rap against a pick, with a hammer, did a reasonable job.
I should also note that the panel has a plastic overlay, with all the printing on it, that is stuck on the metal panel.

First hole drilled. I used a step bit to do the drilling.
Second hole... you can see where the plastic overlay pulled and stretched when I drilled it.
After a bit of clean up, it looks better. Still a little rough, but its just the overlay. The actual metal panel is good and clean.

Time for a test fit. To be fair, I had to open up on of the holes a little, vertically, to get the nice alignment.
Rear side of the mounting.

With the mechanical parts done, time to address the electrical bits.

First up, mount the current transformers, one on each phase. The transformers were installed on the output of the main breaker.
The power to the meters, and also the voltage input are just screw terminals on the meters. I took the voltages from the from the output side of the main breaker as well. I used the screw terminals on the input side of the switch that turns on/off the 120V outlets on the panel. Just an easy place to screw down the wires. Hot wire from each phase was fed to one side of the meter input.
The neutral line feeds the other side of the voltage input for the meters. I tapped the neutral from the 120V socket on the panel. It happened to be similar to household sockets where it has a screw terminal as well little holes you can insert wires into. Unfortunately, I didn't have any white wire to use for the neutral line. Had to use yellow. If I ever pull the panel apart again, I'll replace it with proper, white wire.

Buttoned everything back up and time to test it with power. No magic smoke! As noted, the meters are +/-2V, so some difference between them and the built in meter is to be expected.
Time to load things up. Heat guns and hair dryers are really good for basing generator testing as they are almost entirely resistive loads and so won't do anything really weird to a generator. Starting with my heat gun on a low setting.

Now we put a bigger load. The is the heat gun on high. Because this is a resistive load, this is all real power.

As a final test, I grabbed a hair dryer to load up the second phase.
Everything looked good and at least reasonably accurate. I had testing both my heat gun and the hair dryer with a Kill-A-Watt. The added meters were pretty close.

Time to test with real loads. I connected the generator to the house and powered things up. I left the AC units off, but turned both blowers on, as they would be when running the furnaces. I also turned on all the lights we would normally use, as well as ceiling fans. Both fridges, as well as the deep freeze were also on. This represents a normal, high load for the house under a winter time, generator situation.
As a last check, I turned off any unnecessary lights. HVAC blowers were still on. I also suspect one of the fridge/freezer compressors was still running. This is a more normal load under a generator situation.

All-in-all, it took me a bit over an hour to install the new meters. Definitely a success, and helpful if I ever have to run off the generator. I would like a set of smarter meters that can show power factor as well. Unfortunately, they are much larger and I'd have to figure out where to install them. I'd want three, one for each phase and one for neutral. The reason for putting one on the neutral would be to get the power factor there as well. The two 120V phases can have different power factors, as can the 240V feed. Three meters would let me see everything going one. That's a project for a future day though. For now, the generator is a bit better than when I bought it.

--SS