Refrigerator induction motor: peak current draw

[Agent24]

Re: Refrigerator induction motor: peak current draw

I'd be more worried about the refrigerator being 30+ years old.

Being ancient might be a good thing, probably built better than the new stuff!
Our freezer is probably that old and shows no signs of stopping.

[eccerr0r]

Re: Refrigerator induction motor: peak current draw

Unsure if it's really 60W or not (this is overall, not compressor-on), it was a guesstimate based on the numbers for a high efficiency unit. I was only looking at full sized refrigerators for the heck of it.

If it's more than 60W, then the payoff for these high efficiency refrigerators will take more than 2 decades...

Still... run my old one into the ground.

Here is one webpage that seems to indicate there do exist 18 ft^3 refrigerators that only take 60W
https://www.efficiencyvermont.com/Fo...ic-Usage-Chart

[budm]

Re: Refrigerator induction motor: peak current draw

how big is this fridge that only consumes 60W.

[eccerr0r]

Re: Refrigerator induction motor: peak current draw

For the curious:

Say I want to get one off those 60W high efficiency refrigerators. It will cost $1000 or so. I measured my average power consumption (counting compressor-off time) to be around 120W. The savings is 60W.
At $1000 at the current power rate where I live, which is 11 cents per kWh, will buy 9090 kWh. This is 9.09 MWh = 378.75kW*days = 1037 Watt*years. Now the saving is 60W, so the payback is 1037/60=17 years.

17 years?!?!

Run it into the ground, then buy.

Then again these 60W refrigerators are easier to power with a small generator.

[eccerr0r]

Re: Refrigerator induction motor: peak current draw

It's more like 20 years old right now, saw a 1995 date somewhere. The refrigerator still works, I just wonder how small of a generator I should be able to get away with.

But of course I'm going to try to run this thing into the ground. The cost of a new refrigerator these days is way too high, the earnback period measures in decades if I calculate it correctly...

[delaware74b]

Re: Refrigerator induction motor: peak current draw

The ptc relay is used to switch from start to run windings after the compressor has reached a certain load level.

The run capacitor would have nothing to do with starting current, only efficiency while it's running.

I'd be more worried about the refrigerator being 30+ years old. Not trying to sound negative, but this refrigerator is really past its prime. I would leave it alone and be prepared for its 'retirement.'

[eccerr0r]

Re: Refrigerator induction motor: peak current draw

Yes it says "Run Capacitor" on the schematic along with the 'ptc relay'. I wonder if over the years these could go bad and thus require more power to start up, or will a dead unit just stop the compressor motor from running...

[delaware74b]

Re: Refrigerator induction motor: peak current draw

If the capacitor is a small rectangular box, it's used across the run winding and the neutral. It's main function is to help the refrigerator's efficiency.

If the capacitor is a round can, it's a start capacitor. I believe your refrigerator does not use this type of capacitor.

Can you post pics of the cap and compressor? The model info tag is usually inside the fresh food compartment.

[eccerr0r]

Re: Refrigerator induction motor: peak current draw

Hmm...This is a really old Montgomery Ward (that went out of business...) and not sure what model. It's a conventional freezer-on-top refrigerator. There is a schematic printed on the back and the compressor motor has three wires, and has a capacitor hooked up to it, so I thought it was a capacitive start induction motor. Sometimes I think that 180W number seems a bit low because I've seen on some generator sites that refrigerators use more than that when running, and much much more than that when starting up. But does Mr. Kill-a-Watt lie?

Unfortunately Mr. Kill-a-Watt can't tell me what the instantaneous power draw is upon startup. However one thing that I do worry about: Power factor. That 180W is "real" power not "apparent" and this could make a big difference for generators. Then again I don't recall the PF being less than 0.5, it was in the 0.7 range, which does increase current required a bit...

But hopefully if the generator can get over the startup hump, that PF detail should be minor...

[budm]

Re: Refrigerator induction motor: peak current draw




http://www05.abb.com/global/scot/scot234.nsf/veritydisplay/18cb6349632fe21583257861003d9507/$file/technical%20note%20tm008%20low.pdf


http://powertips-elec.blogspot.com/2...rents-and.html

[delaware74b]

Re: Refrigerator induction motor: peak current draw

Eccerror - I don't think 180 watts running is too bad for a refrigerator, especially one that's 6-10 years old. The compressor has a thermal start device (unless it's one of those %^$$ GE side by sides with a motherboard) that switches between the start and run windings. There is nothing you can do to reduce the start current. A 'hard start' kit will ruin most newer compressors.

IMO, for overall efficiency, keep the coils clean, keep the doors closed, keep it at least half full (both fresh food and freezer sections). Keeping it full will actually drop compressor run time due to thermal mass in the compartments.

BTW, what make and model refrigerator? Conventional top freezer, side by side, or french-door?

[RCA2000]

Re: Refrigerator induction motor: peak current draw

Most refrigerators I have seen do NOT use a starting capacitor. Usually either a split-phase motor, with a start relay--or a "PSC" motor--that uses a RUN capacitor and NO start relay. A FEW MIGHT use a start cap on that relay--but not real common.

If it draws 180 watts at run--I would say likely it would not exceed 800 or so watts to start. So, an 1KW continuous generator --or inverter-should suffice.

[eccerr0r]

I was wondering about my refrigerator: It's a fairly old model and according to Mr. Kill-a-Watt, I get around 180W when the compressor is on (without the 40W lamp and without the defrost heaters). This is about 1.5 amperes. Now I wonder what the typical startup power for such motor would be?
Do refrigerators average more like 3x or 10x peak startup power?

Now I wonder if there's a way to reduce the starting power for a small generator, I don't think I can put an NTC inrush resistor on it Maybe over the years the starting capacitor has degraded a bit? Would it affect starting power?

Maybe there's some other way to reduce inrush power?