I Finally Overdid It

Now what?

In tinkering with my grid tie project, I discovered a fridge and a freezer were not on the main power system, so I moved them. I estimate that moved about 75 kwh more monthly load onto the main solar system. Everything was fine. Then I added air conditioning in the Solar Shed’s Man Cave and control room. That did it. Things started happening…or not.

With all three refrigerators running, the dishwasher washing, the two a/c units running and then the wife decides to nuke a cup of coffee or I fire up the chop saw in the shop. The lights go out. About 3 seconds later they are back on and I realize I have hit the capacity of my main inverter. Had I gone with the original plan of using a mini-split a/c, it probably would have been ok. But I didn’t. It wasn’t ok. I could schedule my activities and sequence the power consumption, but no way that will happen with my wife. It all has to work when she wants it, so it is time to get busy.

A big transformer under the hood is important. I need to get some big transistors in there, too. I’ll turn off the power, first.
Don’t do this on the coffee table, unless it is the one in your Man Cave or She Shed.

I moved the big saw off the shed’s power system and plugged into my solar boat, which also runs the air compressor. Now I can finish building more shelves in the Solar Shed. What else can I do? I could pull an inverter off of one of the golf cars and run the a/c on that, but that’s still not a good solution. Nope, gonna have to replace or upgrade the inverter.

warning label
Use caution if you work on your own stuff. It can bite you!

In case you have not yet taken the solar plunge, the inverter, the box that takes DC from the battery and sends AC to the house, is one of the big ticket items in the system. I built my SunKing 5548 from odds and ends and I have had for some time the module I need to swap out to upgrade to 10kw. The transformer is already good for 12kw. I had hoped to build a new 10kw out of an industrial battery charger, but in the end, the transformer there is good for only 4800 watts. Nope, I’ll have to upgrade the 5548. The problem here is that the case is cramped and some really large and awkward cables are involved. I’ll have to fabricate a new backing plate and then shoehorn everything in, trying not to break anything. All the work will have to happen by flashlight because the lights will be out, right? And it is too heavy to move. Seriously, two people can barely pick this beast up.

Original inverter installation went badly. The dents hammered out nicely. Note the dirt floor and boat in background. This was before the Man Cave was built.
Two ratchet strap winches got it safely in place with just one person.

You probably didn’t build your inverter, so you might have an advantage. Some inverters can be run in parallel with each other. This is sometimes referred to as “stacking.” Aside from doubling your power, stacking also provides redundancy, in case one inverter fails. If an inverter breaks, you can still continue while parts are on order or the inverter is in the shop. No, you won’t be able to nuke coffee when the dishwasher and both a/c units are running, but you won’t be sitting in the dark. When choosing the hardware for your new off-grid system, consider an inverter with stacking of expansion capabilities for the future. Sun Electronics has them!

Stacked inverters
Our friend Daryl, in Texas, stacks THREE big inverters. Everything’s bigger in Texas.

–Neal