off grid refrigerator power

I am thinking about making the transition from propane to an electric refrigerator. A recent windfall of panels and extra money have me wanting to cut the ties with the propane distributor, even though it is  a relatively small monthly amount.

I started out good, bought a 2500 watt pure sine inverter, and have since come to find out that the 2500 watts does not apply to motors, and I need 5-7 times bigger inverter than the load.

Now I was told by the salesman the refrigerator motors only draw1-2 amps, just a couple hundred watts, so I figured my inverter could still handle that, but in looking around it is difficult to find the actual draw listed, and the one refrigerator I was looking at was listed as 6 amps , and a google search for normal amps for the compressor motor came up with 6 as well.
720 watts times 5 exceeds my 2500 watt inverter.

Is there any one with some actual experience, either running a refrigerator with an inverter, or  taking apart refrigerator motors that can tell me what's the real power draw I'm looking at.

Hi Bob,

Is yours a normal fridge, or a special one designed for solar? I dont know much about the solar ones, but do know they exist.

We have a large fridge that is just a year or two old. It is listed as running at 230 watts. When the compressor kicks on it definately takes more power. But less than the old fridge. The old fridge would make the lights flicker. The new one doesnt. All that being said that the exact model and such are going to run totally different. The best thing you can probably do when planning any alt power system is to get a kill-a-watt sensor off of amazon. Plug the fridge into the sensor and it will give you a constant readout of the used wattage. I believe it does amperage also.

$20 on amazon -
P3 P4400 Kill A Watt Electricity Usage Monitor https://www.amazon.com/dp/B00009MDBU/ref=cm_sw_r_cp_api_i_99UCCbVWWZQJM

Bryan C Aldeghi wrote:Hi Bob,

Is yours a normal fridge, or a special one designed for solar? I dont know much about the solar ones, but do know they exist.

We have a large fridge that is just a year or two old. It is listed as running at 230 watts. When the compressor kicks on it definately takes more power. But less than the old fridge. The old fridge would make the lights flicker. The new one doesnt. All that being said that the exact model and such are going to run totally different. The best thing you can probably do when planning any alt power system is to get a kill-a-watt sensor off of amazon. Plug the fridge into the sensor and it will give you a constant readout of the used wattage. I believe it does amperage also.

$20 on amazon -
P3 P4400 Kill A Watt Electricity Usage Monitor https://www.amazon.com/dp/B00009MDBU/ref=cm_sw_r_cp_api_i_99UCCbVWWZQJM

Yep, those meters are very helpful with finding what really eats your power. Before even thinking about some expensive PV system one should checkout what really sucks and replace it with something better, perhaps not electrical powered. Thus one might get away with a smaller (cheaper) PV system.

Thought I am not sure how well those meter can record/visualize the pretty short fraction of a second some motor begins turning and draws lots of power. I'd drop the manufacture of inverter* and fridge a note and ask.

*Some decent inverter should have some huge electrolytic capacitor inside to handle such situations.

I haven't bought it yet. But it will be a normal one

I have a smaller junk one outside and have been trying to understand the motor markings, and there is one marking-- LRA 6.3 which stands for Locked rotor amps

I had started to believe that might be the amp draw, but perhaps that is the surge when the motor first starts, then it levels off back to 2amps or so which would work with my inverter.

Perhaps that is why the listings I saw were 6-6.5 .  .

It's been difficult for me to track down the numbers looking at products on line.  For some reason they think if they put 15 amps on it that will be enough information, but evidently they are only reassuring people that a 15 amp circuit will work with the fridge.

Where did you find the running watts listed, I could only find the yearly watt usage

My running watts were listed on a tag inside the fridge. It was where they listed the UL rating, the size of the fridge in cubic feet and the manufscturer and manfucture date

When I was in the store, looking at all tags available with the salesman, neither of us could find the running watts, but he assured me the amp draw was between 1 and 2--seems he was probably right, but it would be nice if they would just label the blessed things.
Anyway, thanks

My daughter's bar fridge for her 50m2 house seems to draw 42W fairly constantly.

Ill take a pic when I get home. Maybe it will help locate the tags on the ones you are viewing

That's ok, this rabbit hole really is turning into an interesting education.  I looked up dc compressors on ebay thinking maybe I might be able to swap them out for the ac motor which would save me lots of money on complicated (expensive) electronics.

Then I found out they are fazing out r134a refrigerant ( relative of freon which the one I was looking at had) and it will be tough to find when it becomes totally illegal in 2020.!!!

So the DC compressors I'm looking at are all coming with the new isobutane refrigerant, and it appears I may be able to just get an older or broken refrigerator cheap, substitute a new compressor (looks to be about 200-300 $, and be current with the new coolant, and have a cheaper refrigerator and cheaper solar system.  many of the compressors I'm looking at are direct replacements for sun dancers--a very pricey unit.

So maybe a can of foam to add some insulation, a new compressor, a little work and I'll have a 2000$ refrigerator.

In case these pics are helpful to anybody:

This is kind of funny, the label says 3 amps but according to that,  the formula (a times v= w) says that should be 345 watts, not 230

what did kill a watt  say it was?

Mike Homest wrote:

Bryan C Aldeghi wrote:Hi Bob,

Is yours a normal fridge, or a special one designed for solar? I dont know much about the solar ones, but do know they exist.

We have a large fridge that is just a year or two old. It is listed as running at 230 watts. When the compressor kicks on it definately takes more power. But less than the old fridge. The old fridge would make the lights flicker. The new one doesnt. All that being said that the exact model and such are going to run totally different. The best thing you can probably do when planning any alt power system is to get a kill-a-watt sensor off of amazon. Plug the fridge into the sensor and it will give you a constant readout of the used wattage. I believe it does amperage also.

$20 on amazon -
P3 P4400 Kill A Watt Electricity Usage Monitor https://www.amazon.com/dp/B00009MDBU/ref=cm_sw_r_cp_api_i_99UCCbVWWZQJM

Yep, those meters are very helpful with finding what really eats your power. Before even thinking about some expensive PV system one should checkout what really sucks and replace it with something better, perhaps not electrical powered. Thus one might get away with a smaller (cheaper) PV system.

Thought I am not sure how well those meter can record/visualize the pretty short fraction of a second some motor begins turning and draws lots of power. I'd drop the manufacture of inverter* and fridge a note and ask.

*Some decent inverter should have some huge electrolytic capacitor inside to handle such situations.

It will show you the surge, it will also show min max.

Bob, 5-7 times surge is not always going to be the law. I key people in to have the meter and use it at the store when shopping so you can exclude the ones that will not work out. Usually the current rating is max.

Our danby under counter fridge draws 65-75w running and 125 or so on startup per the inverter watt meter.

bob day wrote:I haven't bought it yet. But it will be a normal one

I have a smaller junk one outside and have been trying to understand the motor markings, and there is one marking-- LRA 6.3 which stands for Locked rotor amps

I had started to believe that might be the amp draw, but perhaps that is the surge when the motor first starts, then it levels off back to 2amps or so which would work with my inverter.

Perhaps that is why the listings I saw were 6-6.5 .  .

It's been difficult for me to track down the numbers looking at products on line.  For some reason they think if they put 15 amps on it that will be enough information, but evidently they are only reassuring people that a 15 amp circuit will work with the fridge.

Where did you find the running watts listed, I could only find the yearly watt usage

Absolutely correct on LRA. Now, stop worrying and chil that beer, or kombucha or whatever! ;)

And snip, unplug or place on a switch that defroster wire unless you have battery/solar capacity for it.

Oops, you guys are way out typing me!..... the butane refrigerant may be a great thing and a danfoss( nasa) type compressor found in the sun danzer and sunfrost, stecca, etc are long term reliable, quiet and effficient.

thanks  Frank,

I'm fairly well focused on figuring out the installation of a dc, r600a compressor in an older AC freon type refrigerator.

I'm still searching for the utube video that tells me how to do it  :-)

it doesn't make sense to not at least try and figure it out with so much at stake. maybe I should start a new post investigating the knowledge base on Permies.

frank li wrote:
Bob, 5-7 times surge is not always going to be the law. I key people in to have the meter and use it at the store when shopping so you can exclude the ones that will not work out. Usually the current rating is max.

This is exactly what I did too. The meter was the make or break for each refrigerator before I even looked at it any further. Nice to have a non-biased 'friend' along that you can trust!

For what its worth, we have a 1500watt inverter that runs a standard size refrigerator. Takes about 120 watts on average when running. Not sure of the surge but it handles the load no problem.
About 90% of the time, its the only thing that's using power so there is hardly any competition for total load on the inveter.

bob day wrote:thanks  Frank,

I'm fairly well focused on figuring out the installation of a dc, r600a compressor in an older AC freon type refrigerator.

I'm still searching for the utube video that tells me how to do it  :-)

it doesn't make sense to not at least try and figure it out with so much at stake. maybe I should start a new post investigating the knowledge base on Permies.

The knowledge base at permies is second to none for the sheer volume and variety of esoterica......its why i come  here!

There are absolutely genius people on here and some who simply possess knowledge and experience a genius may never know.

I hqve made my share of quick fire egg on my face, but generally if you poll and trol (fishing) you will likely find it.

Fridges are much more efficient then they used to be. You should top out at less then 1 kW Hr per day for a full sized fridge with freezer. The dc fridges are really expensive put the money into more panels and buy an efficient ac unit. My 19cu ft with bottom freezer and the defrost line still hooked up runs at 890 watt hours per day with two kids discovering the joys of opening and staring into the fridge. When it starts up there isn't even a flicker unlike the pump and it settles in at 160 watts when running. Your new inverter should have a surge rating to cover momentary start loads like fridges. If watt hours are that precious a chest freezer modified with a refrigerator thermostat will greatly reduce watts consumed.
Cheers,  David

We've been off grid for nine years now and started off with the most efficient "regular" refrigerator we could afford at the time. Due the constant cycling of the auto defrost, especially at night, it put a strain on our system. We finally made the switch to a converted chest freezer and boy has that made a difference! I no longer cringe when I hear the fridge kick on! We've discovered we need to be more creative with organizing the space and there's some condensation that needs to be taken care of now and then but our veggies do seem to last a lot longer in there!

cheers! rob

I agreed with you David until I found out I might be able to get the efficiency of a new fangled solar fridge without paying for it-- but you likely didn't really follow my posts.

long and short, r134a, the freon you likely have in your fridge is obsolete, by 2020 it will be illegal to make the refrigerant and repairs will depend on recycling refrigerant or finding some one with a stockpile. Or you might do what I'm planning to do,

R600a is the replacement, a hydrocarbon, isobutane and or isopropane, it has better coolant characteristics so the same watts produce more cool, and the new compressor that uses the new r600a  only costs about 250$ with a DC motor, a replacement that fits the sun dancer units selling for 1.200 for a small one.

The plan is to recycle a refrig with a bad compressor, perhaps add a little insulation or a door seal, and plug directly into my 24 volt battery bank. waste not want not. :-)

Yes I saw the reply to Frank after I typed mine in. It's a good plan. You will want to use a mechanical thermostat retrofit due to the dc current on the compressor unless you plan on powering the control board that currently runs most ac fridges and using its compressor trigger  to run a relay for the new compressor. Hmm if it's a fridge/freezer combo you might have to keep the fan that pushes cold from the freezer to the fridge... an interesting project to get the gears turning.  be sure to post lots about it!!!

Sailors have dealt with refrigeration vs. power draw for many years. "In the Beginning" the compressor was driven by a belt off the engine; technology has moved toward all-electric low voltage systems. Researching their solutions should be directly applicable to your situation. Cruising sailors favor reliability, also. When last I was studying it there were at least half dozen good DIY books on the topic; I expect there are at least that many now. Replacing the fridge is a common issue with old boats and there will be discussions ongoing on all the cruising sites.

Designs usually revolved around very well insulated boxes with top access (as opposed to swing-open door(s)). They used cold plates which the compressor froze down once or twice a day and the cold mass kept the fridge at low temperatures. That may have changed somewhat with new technology, but top access remains easily the best aids to efficiency when one factors in actually using the thing. The best equipment sold is very pricey. However, cruisers are one of the cheapest breeds out there and much of the discussion revolves around how to roll your own.

Motors draw startup current which can be 3-5 times the normal operating current. The high draw usually lasts about 1 second with the highest current being drawn in the first 200 milliseconds. IOW, the high draw lasts a very short time and most electrical systems and sources can provide and tolerate high draws for short periods. LRA gives a very worst case reading of a motor's draw.


Regards,
Rufus

Thanks David, some of the compressors come with a new control board.

Right now I'm in the research phase, This morning I was planning to just forget it all and keep the propane fridge for a while, then I cycled through thinking I would go ahead with the AC fridge, and  just this afternoon started to understand some of the finer points of the issue, with many bits and pieces still unknown. There's also a fan  down there with the compressor that may need to be replaced, They make lots of little dc fans though, so it's likely not beyond  a solution.

It does piss me off though that they would run out the clock on the efficiency thing, insisting on making the same old units until the very last minute. And yes I will  start a new post right now and see who else might have some helpful information to move this all forward.

I picked up this digital thermometer at Amazon and connected a used chest fridge I picked up for $25 from a coworker. The thermometer lets you set a temp and a +/- range from that, and when the temp gets above that threshold it provides power to the cooling outlet, and if it gets below the threshold power is sent to the heating outlet. I then plugged my freezer into the cooling outlet, and plugged it all into my kill-a-watt meter to compare power use.

Running the freezer normally (in the garage, mild temps outside in the 70-80 range so maybe low 80s inside it) for 2 days and it used about 880 watt hours each day with a target temp of 0F. Plugging in to the thermometer and setting that to 35F +/- 2F so it starts cooling once it hits 37, and power use over 4 days dropped to 232 watt hours per day. I only opened the lid once and pulled nothing out either time, so the numbers would be a little higher with normal use rechilling items pulled out for a bit. So perhaps 0.25Kwh per day, when used as just a fridge and not a freezer.