Frigidaire on modified sine power

706jim · May 2017

I'm ready to retire my propane fridge and am purchasing a Frigidaire apartment size fridge/freezer to use at my camp. I have an old Trace DR1524 modified sine wave inverter that I plan to run it from. Local solar salesman has advised that the electronic control board might overheat from this source of power. Other devices that I have used in the past including satellite receivers, TV's, stereo systems and drill chargers have all worked fine with this inverter.

Running watts are about 140 with expected consumption of about 1kwhr/day.

Has anyone here had experiences with a similar setup? Is circuit board overheating been a problem?

Photowhit · May 2017

I suspect it has more to do with the quality of the fridge's electronics. When I was looking into using a MSW inverter to charge batteries for a battery power circular saw and drill (in 2000). I asked on a solar forum and was told it would burn up pretty much any battery charger. I had one person say they had good luck with Dewalts. I contacted Dewalt and got the 'right person'. They said that the newer model charger would be fine on a MSW inverter and it has been.

Back before there were inexpensive true sine wave inverters, I looked into the MSW made and it appears there are 'square wave inverters and stepped wave inverters. The stepped wave isn't as harsh as Square wave (or cheap modified that just hole at neutral for a bit) I think The DR is a pretty good stepped inverter, but I didn't research long, you might hunt a bit more.

The graph is a link to a page that describes the differences. I couldn't link the graphs so here's a link;
http://www.techlineinfo.com/things-to-keep-in-mind-before-buying-an-inverter/

inverter waveforms

Interestingly I found a link to our website, but I couldn't open it, even when I told Microsoft Edge to ignore the old certificate. I can reproduce the graph, and I'll give it the link perhaps it will open for someone with Chrome or Firefox;

I couldn't link the graph so here's a link;
https://forum.solar-electric.com/discussion/20912/which-inverter

I would think a good modified sine 'stepped' inverter would have less issues than a square wave or neutral paused MSW inverter.

jonr · May 2017

According to this, you should expect more heat, noise and power draw. But if you have an inverter with lots of steps, then I wouldn't worry at all.

http://www.eaton.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/pct_1604836.pdf

Raj174 · May 2017

This a link to a post where a MSW inverter apparently caused a problem with a fridge/freezer.
http://forum.solar-electric.com/discussion/comment/353427#Comment_353427

706jim · May 2017

Guys, thanks for the input. Of all of the apartment sized fridges I looked at only one owners manual stated that it "was not designed to be run from an inverter". So I think I will do this in two stages: I will purchase the fridge and haul it out to my island camp and see how it works on my present system. And keep the existing propane fridge there in case it won't run from the power source I have out there. If it works ok, the next step will be to bump up the array by 600 watts to approximately 1kw. This should be within the capabilities of my C40 at 24 volts. While I would love to get a pure sine inverter and MPPT charge controller, there are (always) other expenses that have to be tended to first.

And while it is certainly "old news" on this forum, I can't say enough good about the performance of my Trace DR 1524. That thing is bulletproof and has enough oomph to start a 1hp spa pump with heaven knows what sort of surge current.

Photowhit · May 2017

Less options for inexpensive inverters for 24 volt, but I'd bet the Exeltech 1100 watt would run it, and they come up on eBay from time to time at $2-300. If Exeltech still does $100 flat rate repairs on inverters, I'd roll the dice on one. Actually I did (at $180) and it's been working fine for my outdoor loads, regularly use 1200 (Weedeater) and 1300 (chain saw) watt loads on it. I can tell with the chainsaw when it starts clipping the wave, but I haven't shut down the inverter yet!

OffGrid+LovinIt · May 2017

I totally agree with the suggestion on using Exeltech inverters.

I purchased a XP1100-12v from our sponsor, for over 15 years ago, and it's still going strong.

I can't vouch for it running your refrigerator, but I do know it'll run a 750 watt Kenmore Microwave.....

I've since bought a few XP1100-24v's off of ebay and I've been very happy with them. Running 24/7

And the Exeltech's flat rate can't be beat !!! Great company.

I actually bought a MX7000-48 system, from a cell site, called the factory, dropped the system off, they modified it for lower idle current and checked the whole system out for < $300. (It's been sitting in storage, waiting for me to need 7kw since).

Again, they are a great company to deal with and their XP inverters are rock solid.

706jim · May 2017

1100 watts would be more than adequate for a 140 watt fridge even considering start-up surge. So the plan is to buy the fridge, try it on my DR 1524 and see if it works. There's a one year warranty in case it fails although this means a lot less when you are on an island and may have to truck a failed unit back into town.

One way or the other, it will be a new experience to run my inverter 24/7 to keep the fridge going. I doubt that running the Trace in standby mode will work for this sort of appliance.

706jim · August 2017

Well, the fridge is here and running fine from my MSW inverter. The brand I ended up with was Insignia and it appears to be a direct clone of the Frigidaire I mentioned earlier. Price (in stainless steel) was $450 CDN which I figure is very reasonable. Current draw is around the 140 watt mark during cool-down and about 100 watts cycling. Also 0.3 watts on and off when the compressor is stopped which I would assume would be due to the electronics checking the temperature.
Hopefully, this information may help someone else out there contemplating the switch from propane to electric.

BB. · August 2017

Jim,

Is that Watts with some sort of Kill-a-Watt meter? Can you do a VA measurement too?

In general, if VA~Watts, even with a MSW inverter--Things are usually going pretty well. If VA>>Watts, then the motor (and other components) can have a higher chance of overheating.

PF = 1.0-0.95 -- Pretty much "perfect" power factor
PF > 0.80 -- Not Bad power factor
PF ~65-75% -- Start to worry about devices that may not like MSW wave form
PF ~50% -- "Cheap" devices (like CPFL lightning) with cheap ballasts

Note--Induction motors (and many variable AC loads) can have a wide range of Power Factor. At low loads, they can have "poor" power factor, and at high/rated loads, have pretty good power factor.

For things like lights and refrigerator compressors, they sort of have a "fixed" load and poor power factor can cause overheating (high current flow through wiring/field windings/electronic components/etc.).

Remember for heating, P=I^2 * R.... If you double the current (I), you get 4x the self heating effect.

-Bill

Note the above are my humble opinion from my experience. Your experience may vary--And Kill-a-Watt meters may not show "non-linear" power factor numbers accurately because of the non-sinusoidal wave forms of electronic power supplies and MSW inverters).

mike95490 · August 2017

Even if the fridge does run on mod-sine, it will be:

* self heating from losses in the motor

* running longer to cool the above losses
* drawing more power from the battery bank - extended running times

you should consider getting a pure sine inverter to run a fridge, but they do cost more $

mcgivor · August 2017

Take the time to measure tthe DC current to the inverter under load, with the refrigerator running, the power factor, including all other losses will be revealed, measuring on the AC side can give eronious results. Use a ratio, for example 24VDC to 120VAC is 5:1, so for 1A at 120VAC you should be drawing 5A at 24VDC, add in the self consumption of the inverter, including efficiency losses, you should be in the neighborhood of, for arguments sake, around 7A at 24VDC. With a modified sine wave inverter, the current would be higher than that of a pure sine wave, largely in part due to the losses in eddy currents, or waste caused by the squared off waveform. These eddy currents manifest as heat, unwanted heat, which could have detrimental effects on the longivity of the motor. So while it may work in the short term, the savings may result in costs, in the long term. Just opinions based on experience, YMMV and so forth.

706jim · August 2017

BB. said:

Jim,

Is that Watts with some sort of Kill-a-Watt meter? Can you do a VA measurement too?

In general, if VA~Watts, even with a MSW inverter--Things are usually going pretty well. If VA>>Watts, then the motor (and other components) can have a higher chance of overheating.

PF = 1.0-0.95 -- Pretty much "perfect" power factor
PF > 0.80 -- Not Bad power factor
PF ~65-75% -- Start to worry about devices that may not like MSW wave form
PF ~50% -- "Cheap" devices (like CPFL lightning) with cheap ballasts

Note--Induction motors (and many variable AC loads) can have a wide range of Power Factor. At low loads, they can have "poor" power factor, and at high/rated loads, have pretty good power factor.

For things like lights and refrigerator compressors, they sort of have a "fixed" load and poor power factor can cause overheating (high current flow through wiring/field windings/electronic components/etc.).

Remember for heating, P=I^2 * R.... If you double the current (I), you get 4x the self heating effect.

-Bill

Note the above are my humble opinion from my experience. Your experience may vary--And Kill-a-Watt meters may not show "non-linear" power factor numbers accurately because of the non-sinusoidal wave forms of electronic power supplies and MSW inverters).

Ok here are some numbers as measured with a Kill a watt EZ meter:

Watts range from about 100 to 115 as pressure builds. VA about 190
Amps 1.6 which is what fridge nameplate states.
Power factor starts off at 0.45 building to about 0.58 towards end of cycle.
Voltage about 118 Frequency (normally 60 Hz with no load) about 65 Hz varying slightly.

softdown · August 2017

It wasn't many years ago that propane refrigeration was "derigueur" for off gridders. We have recently come so far as a result of giant, low cost panels. Shoot....I run a full size refrigerator and two freezers. There are reasons for that...

Reading the comments of those who have forgotten more than I know, it seems like pure sine wave is worth it. The smaller, lighter "high frequency" pure sign wave inverters are quite affordable and many of us have been quite happy with the results.

BB. · August 2017

Yea--A power factor of ~0.50 is pretty bad for an induction motor. Lots of losses (eddy currents, I^2R heating losses, etc.) when running with an MSW inverter.

If you are happy with the operation of the refrigerator and it is not making a lot of noise (120 Hz vibration)--I cannot tell you that things will go bad in a year or two (i.e., need a new compressor, possibly new capacitor starting circuit, have to replace thermostat contacts, etc.)--See what happens. There are a lot of MSW off grid installations out there (more than PSW/TSW inverters?).

Hard to "up sell" the (sometimes) large increase in cost for a TSW inverter without meaningful data to backup an engineering supposition (i.e., MSW Inverter == Shorter compressor life). I.e., spend a ~$1,000 more for a TSW AC inverter driving a $300-$600 refrigerator.

-Bill

jonr · August 2017

There is something to be said for getting an inverter refrigerator - which should be more efficient and won't care about MSW power.

nickdearing88 · August 2017

jonr said:

There is something to be said for getting an inverter refrigerator - which should be more efficient and won't care about MSW power.

I just got my new LG LFXS24623S after much debate about the price tag. The house is still being finished so the unit's just up and running to keep drinks and sandwiches cold but I'd say I made a good decision. Very quiet also!

Haven't had a chance to measure startup and running current with the clamp meter yet but I can tell you it runs perfectly on my Samlex PSW 1500w inverter!

706jim · August 2017

BB. said:

Yea--A power factor of ~0.50 is pretty bad for an induction motor. Lots of losses (eddy currents, I^2R heating losses, etc.) when running with an MSW inverter.

If you are happy with the operation of the refrigerator and it is not making a lot of noise (120 Hz vibration)--I cannot tell you that things will go bad in a year or two (i.e., need a new compressor, possibly new capacitor starting circuit, have to replace thermostat contacts, etc.)--See what happens. There are a lot of MSW off grid installations out there (more than PSW/TSW inverters?).

Hard to "up sell" the (sometimes) large increase in cost for a TSW inverter without meaningful data to backup an engineering supposition (i.e., MSW Inverter == Shorter compressor life). I.e., spend a ~$1,000 more for a TSW AC inverter driving a $300-$600 refrigerator.

-Bill

The compressor runs quietly; no problem there. I had ordered a Samlex 600 watt sine wave inverter but accidentally got 12 volts instead of 24 so was unable to install it. However.......
The fridge now runs non stop so I'm guessing I fried something. It ran fine for about 48 hours. And the unit is at my island cottage meaning that I will likely have to lug it back into town (by boat) for warranty. FWIW, the manual makes no mention of inverter power although some other fridges did.

mcgivor · August 2017

@706jim said, The fridge now runs non stop so I'm guessing I fried something. It ran fine for about 48 hours. And the unit is at my island cottage meaning that I will likely have to lug it back into town (by boat) for warranty. FWIW, the manual makes no mention of inverter power although some other fridges did.

In that case, don't waste the truth on the warranty claim.

706jim · August 2017

mcgivor said:

@706jim said, The fridge now runs non stop so I'm guessing I fried something. It ran fine for about 48 hours. And the unit is at my island cottage meaning that I will likely have to lug it back into town (by boat) for warranty. FWIW, the manual makes no mention of inverter power although some other fridges did.

In that case, don't waste the truth on the warranty claim.

Duly noted!

Estragon · August 2017

I wonder if excess heat generated by the compressor motor is what makes it run constantly? Does it turn off if you turn the temp control to as warm as it goes?

706jim · August 2017

I boated out to my camp expecting the worst.
To my surprise the compressor was not running and temp about 38F inside. Fridge then started up and ran for nearly an hour and is now off. Possibly, the compressor is "weaker" and runs longer to make up for that fact. Based on the Kw-hr rating of 311/year, this would indicate about 850 watt-hours/day or at the rated 140 watts load about 6 hours running on average. I suppose I'll have a better feel for it once we run it at least a few more days. I'm just happy that nothing seems to be fried. And I agree that a small true sine inverter will be a good investment dedicated to just running this appliance. Unlike many others on this forum with large systems, there is no foreseeable need for a large amount of power. A 1000-1500 watt array should serve me nicely in this seasonal cottage.

The manufacture states that 4 hours of continuous running is normally needed to cool down a new fridge, so perhaps what I'm seeing is "normal" for this unit.

Estragon · August 2017

In a sense, the fridge may be "weaker". The compressor just moves heat from inside the fridge to outside. The compressor itself is likely not affected by the MSW, but the motor, generally packaged with/near the compressor, will likely be heating more. Depending on how and where the compressor disipates heat, the extra heat from the motor may also have to be overcome.

Good to know you don't have to lug the thing in for repair. My cabin is also water/ice access, and I know how much of a PITA that can be.

softdown · August 2017

Estragon said:

In a sense, the fridge may be "weaker". The compressor just moves heat from inside the fridge to outside. The compressor itself is likely not affected by the MSW, but the motor, generally packaged with/near the compressor, will likely be heating more. Depending on how and where the compressor disipates heat, the extra heat from the motor may also have to be overcome.

Good to know you don't have to lug the thing in for repair. My cabin is also water/ice access, and I know how much of a PITA that can be.

FWIW and more technically speaking.....refrigeration compressors are "removing energy". Heat is energy.

Speaking of which, I have to go look at my BP panels before they have absorbed too much energy.

mvas · August 2017

softdown said:

FWIW and more technically speaking.....refrigeration compressors are "removing energy". Heat is energy.

Speaking of which, I have to go look at my BP panels before they have absorbed too much energy.

FWIW and more technically speaking ... the refrigeration compressor does not "remove energy".

Actually, the refrigeration compressor adds energy to the refrigerant.
And that added energy comes from the motor.
The refrigeration compressor changes the refrigerant from a low pressure gas, into a high pressure gas = ADDED energy.

The evaporator coil transfers the heat energy from the inside air to the cold refrigerant.
The condenser coil transfers the heat energy from the hot refrigerant to the outside air.
I agree with @Estragon, the refrigerant transfers the heat from inside of the fridge, to outside the fridge, via the two coils.

Estragon · August 2017

Yup, and the net of the heating and cooling is an addition of energy to the fridge overall. If it wasn't, we could use the fridge to charge our batteries overnight

BB. · August 2017

And since virtually all home refrigerators use hermetically sealed compressors (motor+compressor in a sealed metal shell)--Any additional motor inefficiencies (waste heat) are added to the working gasses and moved outside ("compressed" via the pump) to the condenser.

http://www.brighthubengineering.com/hvac/52198-hermetically-sealed-refrigeration-compressors/

httpimgbhs4comFBEFBE0F8C47DD5BF0BAC5983831443F8FE6FE4B260_largejpg

-Bill

mvas · August 2017

And initially, the amount of energy transferred from inside to outside is GREATER THAN the energy ADDED by the compressor = COP > 1.

706jim · September 2017

So far, so good, fridge is running just fine. FWIW I believe it uses propane rather than freon for a refrigerant. Ironic since I just sold my propane fridge.

BB. · September 2017

Yea, propane (and similar) is not a bad refrigerant. And since there is only 1 lb or so in the system, a small leak is not usually a problem. Although, Freon (the bad Ozone Hole stuff...) was a replacement for flammable/dangerous refrigerants. Apparently, refrigerator fires are one of the most common type of home fires (electrical fires, not even a propane specific issue).

https://www.consumerreports.org/home-safety/how-appliances-catch-fire/

But even if the propane is a "concern", it appears that plastic backed refrigerators with highly flammable insulation are simply fire booms waiting to happen (yes, a UK tabloid. Link is probably not work safe due to sidebar content).

https://www.thesun.co.uk/news/3873812/hotpoint-fridge-freezer-fire-video-grenfell-tower/

The fire chief explained how the fridge-freezers start fires: "Once a spark ignites in the compressor which powers the freezer, it can be as little as 90 second before the whole kitchen is engulfed in flames.

"The foam used to insulate them is highly flammable and is the equivalent to having four gallons of petrol around your freezer.

"Once ignited it produces an intense heat three times that of a large bonfire."

He went on to describe the fires sparked by plastic-backed fridge-freezers as "some of the worst home fires we have had".

It comes as investigators also said that cladding and insulation that was attached to the outside of the building has failed all safety tests and cops were now looking at possible manslaughter charges.

This was a test of a similar fridge from the Grenfell (UK) Tower disaster. An Italian mfg. fridge (no longer sold).

Add to the above, cheap flammable cladding to the building exterior (with chimney space behind flammable aluminum+foam cladding), and it appears to be a disaster just waiting to happen (and one that has been occurring in one form or another for years).

-Bill

Frigidaire on modified sine power

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