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Solar and Generator Back Up

Solar Power and Back Up Generator

We realised from day one we would need a back up generator for those dark days. And so purchased a Hyundai 5 kw diesel plant from Trade Tested.

It is nominally a 4.5 kw output, 5 kw for brief periods. Pretty simple little plant, and not expensive. It runs well, but we had a problem getting much more than 2.0 to 2.5 kw out of it, and we noticed that the two solar panel inverters would shut down. Also the output would fluctuate by as much as 1.5kw. So a bit of a double whammy. Lower than expected output, and we lost whatever the panels were otherwise supplying. Occasionally the panels would supply, but when that happened the generator was only putting out 1 to 1.5kw. The generator is coupled directly to the battery inverter through a 20 amp plug, and there is also two standard 10amp  3 pin plugs as well. So I plugged a 2 kw load directly into the 3 pin generator socket. We could hear the plant load up, but no excessive smoke, so not overloaded. And the panel inverters came back on line, and the gen set output to the system went back up to around 2.5 kw. Which is where I had the battery inverter input set to. But turn the extra load off, and it all went pear shaped again. So not at all satisfactory

How Our System Works

Head Scratching

More or less through trial and error I found that under no load the gen set was running at around 55 hertz, but with a full load this would drop to around 47 hz, and none of the 3 inverters liked this at all. The generator, as I said was not expensive, and I guess you get what you pay for. What was happening was the mechanical governors were doing a very poor job of controlling the engine speed to give the standard 50hz. Not a problem normally, but not at all suitable for synchronising with  our inverters.

Partial Solution

The governors are mechanical & spring controlled, and there was no way to adjust the spring tension, so hence the difficulty in keeping to 50hz. So after a bit of experimentation and finally putting a throttle to adjust an override spring I set up on the on the governors we now have a gen set synchronising well. This allows the output to reach 4kw as I’ve upped the inverter input load to 17.5 amps. I don’t really understand the technicalities of synchronisation, but from what I have read getting the frequency (hz) is the secret. l I do have to adjust the “throttle” as the load comes on, but it is noticeable that when the gen set is running at 50hz, the frequency and output is very stable, almost as if the gen set and inverter get into lock step.

“Final Solution”

I have found online electronic governor controls. Not all that expensive. One sort relies on a magnet built into the flywheel which the machine reads the revolutions per minute off and then activates a stepper motor which is attached to the fuel rack. A second type reads the frequency directly, thus controlling the engine speed that way.