Refrigerator start surge

Re: Refridgerator start surge

Oh My! I hope you're ready for this! lol
After explaining it a few times I made it easy on myself - - saved it so all I had to do now was copy and paste.
"Converting a freezer to fridge
Each of the half doz I've modified was done slightly differently. First off, you have to have a good understanding and ability with electrical etc. I'm not aware of anyone else having done this, but obviously it can be done.
First off, the original equipment varistor starter must be removed and replaced with a relay controlled by a timer of some sort, to apply power to the start winding for a short time. This time has been different for each unit I've modified. The first ones were timed by a simple resistor/capacitor delaying the action of the relay. The last one uses a 555 timer IC and that works much better as a timer. Second, a start capacitor must be wired in series with the start winding. The value of that capacitor is VERY critical. Too big and the inverter is overloaded and shuts down, too small a value and the motor won't start. Each of the ones I did required a different value capacitor, as each motor was different. The values ranged from I think 200 MFD (was a few years ago), a;; the way down to 66 MFD if I remember right. I'm lucky I have a friend operating a motor repair business, and he loans me several different values, allowing me to try each to see which one works best. If the units were operating on grid, or a bigger inverter, the cap size wouldn't be so critical, but the TS-300 is being pushed to it's very limit with every start, resulting in a VERY fine line between getting the compressor up and running, and shutting down on overload.
But you're not done yet! Each and every unit I've done, normally draws so much current on startup, even with these modifications, that the inverter shuts down before the compressor gets up to speed. The next step just barely takes care of that. You must use a transformer of some sort, I use autotransformers, rated for roughly 100 VA, that will drop the voltage from the inverter by roughly 10%, and in doing so, increase the available current to the motor by that same rough 10%. This is just enough, with all the other modifications, to get the motor up to speed, but as soon as it is up to speed, the starter relay must be timed exactly to kick out the start winding, and at the same time, switch over a DPDT relay which takes the transformer out of the circuit, and connect the now running motor, directly to the TS-300. It's not going to be easy, will take some frigging around and trial and error to get it working right, but it can be done, as I've said, I've already done it at east 6 times.
Of course it goes without saying, that all these mods will void your warranty , and of course the CSA or UL approval. Hahaha
But for me, it's perfect. Have had two freezers and a converted fridge running with these mods, all on TS-300 for 5 years now. No, they don't all run at once! The fridge had priority, so when it wants to run, it powers a relay that disconnects the other two units. When it's not running, the freezer in the basement is next, then finally, if neither of the first two are running, the freezer in the outside shop has it's chance. The "fridge" only runs an average of 5 minutes per hour, so there's lots of time for the other two.
So there you go. That's the best I can describe it. Like I said, you'll have to be proficient in electrical and have access to all the things you need.
To be perfectly honest, it would be a whole lot easier for you to just use a larger inverter, capable of starting and of course running your fridge, and have the thermostat control the on/off of the inverter so it's not running when it's not needed."
To be perfectly honest, it's far easier to get a bigger inverter than to struggle with all the above.
Wayne

Re: Refrigerator start surge

Joe94 wrote: »

My plan was to get a Supco RC0410 and see if that softens the start surge enough.

I've tried both the Supco URC0810 and the URC0410 on my small chest freezer and neither lowers the start surge enough. Both do lower the power draw by 3-5 watts when the freezer is running though - I think because it replaces the varistor starter with an electronic unit.

Re: Refrigerator start surge

My rough guess as to start current reduction is:

lower voltage - 15-20%
autotransformer - another 15%
PF correction - 75%

Re: Refrigerator start surge

Expect single phase motor (and transformer) starting currents to go even higher - it's a side effect of greater efficiency. Permanent magnet/inverter driven motors are a good solution.

An online UPS running off of another inverter means that you double the losses. Running it directly from existing batteries is fine, but it's the same thing as adding another, bigger inverter.

Looks like the ICM803 hard start device works by adding PF correcting capacitance during start and then switches it out. Certainly an easy device to add.