converting AC refrigerator using r134 a to DC using r600a

I wanted to get this topic started, since this could potentially help lots of people off grid with similar issues.

item 1 It is much more efficient and less costly to run a dc motor with a dc supply current.
item 2   dc refrigerators are very pricey
item  3 the current refrigerant used in conventional fridges is being changed over to a non freon replacement. this r600a is isopropane isobutane based, and actually is a more efficient refrigerant than  r134a

item 4 they sell dc compressors   compressor that I think can be swapped out with an older freon unit.

item 5, with a little clever labor and at a very low cost we can have both a recycled fridge, a new more efficient fridge, a lower cost fridge, and a more environmentally friendly fridge


or at least that is my goal, anyone with hvac  or appliance repair background is especially invited to join this discussion, but all comments welcome

I contacted the seller of that compressor, and was reading the instructions also, and he says I can't just change the compressor and use the r600a in an r134a system. But in my preliminary research it looked like people were doing it,  So even though I have used Ebay sellers as a source of information I may have to look a little farther to find out for sure. sellers now are all about the feedback, and he may be reluctant to give any advice about changing the coolant profile.

I think he was saying however that he did sell dc  compressors that handled r134a, so at least that changeover would be possible  The main reason to change the coolant is because the r600 has a better profile to work as a refrigerant and is more efficient. but just getting a fridge that runs on dc would at least eliminate the inverter from the operation. next step though is going to be actually finding a used refrigerator as the seller wanted to know the make and model of the compressor in the fridge so he could replace it exactly.

again, all suggestions welcome , thanks

Bob,
I was just researching this myself. I saw a video on someone using a DC chest freezer, and I couldn't help wonder how that was accomplished. Some coffee, Google, and a half an hour later I was informed that I may not order a new compressor for one of our chest freezers. Something about it not being in the budget right now... BUT, I could do it. It is possible.
While there may be individuals doing a direct conversion to R600a, I'm inclined to advise against it unless it is a unit already using it and the conversion is just the compressor. I'm not familiar enough with r600a to know what the pressure bands are for it, but generally speaking the components of the freezer/refrigerator are configured for that specific gas. If others are retrofitting a system using r134a to r600a, it would appear that it is possible. Not sure I'd do it and I am curious about the efficiency and lifespan of the equipment if it's using a different gas than it was designed for.

Personally I'd switch compressors and use the existing gas. Get chummy with someone who can recover the gas, swap the compressor out, then have them recharge the system.

I don't know enough jargon, and I can't remember the exact name for the property, maybe it's the heat of conversion (from liquid to gas. or maybe gas to liquid, and the pressure needed is less,  but the general  gist is that r600 is more efficient, whatever, so the same watts makes more btus. Since i don't yet have a fridge to convert I have lots of flexibility in what I get- if I'm willing to wait for the right one to come along.

Evidently it is possible to just do the ac to dc conversion and keep the same refrigerant without missing a beat, but I got the idea, right or wrong, that I could do the whole thing with the more efficient refrigerant and the ac to dc conversion. the r600 is isobutane or isopropane or some such combination -flammable and it definitely needs its own compressor, but once done  then I'm right up to speed. otherwise I may be farting around with a half assed conversion now, and changing it out  again in another couple years. Why buy into a technology that's being abandoned? just getting r134 is going to be a special process in a couple years, and the price will just keep going up on any recharge or repair that might be needed.  plus the r600 is totally ozone friendly.

If you're buying a refrigerator, there will be lots of sales of old stock around 2020

Agreed. Hopefully the research will show converting r134a devices to r600a is possible, "easy", and beneficial.

Yes I've spent some time tonight searching, have a possible appliance repairman to consult for 6$, but he's not online right now.

I'm thinking if the pressure is lower and the gas is cooler what can go wrong?

Don't answer that.

I think I know the answer--the refrigerator could catch fire or blow up and burn down the house

Easy stopped being a descriptor for this process as soon as I saw the brazing torch on one of the videos. I'll settle for "possible" with   someone to install the compressor for a reasonable rate

Bingo, we have lift off--sorry for mixing metaphors

paper describing changeover from134a to r600a

Long and short of it is I need to change compressor, and disable the automatic defrost which probably wouldn't be an issue since I'm also changing the control box and such to dc

here's an exerpt

2.1 The refrigerator
The case study refrigerator investigated in this study was originally manufactured to use 145g of R134a as refrigerant. The specifications are summarized in Table 1. A schematic of the refrigeration cycle is shown in Figure 1. When the experiment was finished using R134a, the system was vacuumed. Then, the compressor was changed to a HC type one. Finally, the refrigerator was charged with 50g of R600a which was previously found to be the optimum charge for the system

Bob ; An Apple for you ! This is an excellent idea! I like it!  Please keep experimenting, this could be a big breakthrough for off griders!  

bob day wrote:

Easy stopped being a descriptor for this process as soon as I saw the brazing torch on one of the videos. I'll settle for "possible" with   someone to install the compressor for a reasonable rate

Fortunately for me, brazing and welding are in my "easy" wheelhouse. One key on that is making sure you use the correct brazing rod for the job, then place the system under vacuum and verify no leaks. Of course leaving it to someone who does it for a living is a good idea.

I could not get to that article, they wanted me to log in to something and give access to my contacts. I came across this article that was free to download. Could be similar if not the same. Very interesting.  
Once I get my powerwall operational I'm going to have to dig into this a little more and I'll be keeping my eye out for a cheap to free freezer that I can retrofit.

Since r600a is flammable, the procedure for refilling is a flush with nitorgen, then vacuum then refill.

I saw one guy who had salvaged a fridge compressor from the side of the road, he filled it with ordinary propane and got it to work. I'm not sure if it was an r 600 compressor or not, even though they're rare here the rest of the world has been using that coolant for some time.

I find that DC fridge compressors are quite expensive… and am wondering if an AC compressor could be used with some tricks…

Yes, the r600a  doesn't care which current runs the motor, more important to match the cooling capacity of the compressor to the refrigerator. Note that r600a does a little better job at cooling than the freon, but likely not enough to under size it.

My first post shows a link to an ebay dc compressor that is 249$,  I have been trying to figure out the capacity of this compressor , my best guess is at least 11 cu ft, probably 17. But I could be wrong and it could be much more or even less. If anyone knows more about watts and btus and how they relate to cu ft of a refrigerator, please comment. It is described as a replacement for a sun dancer, but they don't mention a specific model. I have seen sun dancers at 9 cu ft, but I'm guessing they make more than one model.

If you contact the seller on ebay with your specific compressor model /capacity, he may be able to help you size it.

I don't yet have a refrigerator, so until then I don't really know what to ask

Bob how big of a fridge do you want to end up with? It seems like the r600 limit is more to do with the total volume in the fridge reflected in the total amount of r600a used in the appliance. I'm attaching a paper that refers to the north american limit of 57 grams of r600a in appliances where in europe its 150 grams... I've been looking into chest freezers and mini fridges most of which are r600a powered. up to 11cu ft for fridges and 7cu ft for freezers it seems easy then they disappear... Interestingly enough they are mostly using the manual thermostats which is another plus for off grid as there is no inverter loss issues with the electronic thermostat loads. I know the whole point is to go DC but if you can get an off the shelf ac with r600 for a comparable price to just the dc compressor and the fridge tech to do the work with no inverter losses... Just a thought.
Cheers,  David

https://www.danby.com/products/apartment-size-refrigerators/dar110a1wdd/

freezer with mechanical thermostat, the led I would disable or the transformer feeding it anyways.
https://www.danby.com/products/freezers/dcf038a3sdb/

Article...
http://hydrocarbons21.com/articles/8018/are_home_fridges_in_u_s_turning_toward_hydrocarbons_

I just found this post.
In another life I did a little refrigeration.  Here’s my two cents.

Propane has great refrigeration properties but is flammable and possibly explosive when in a compressed area.   This is why they use other refrigeration gases.

As far as I know R600a isn’t flammable that’s why it’s being used also safer for the environment as past refrigeration gases.  

Ammonia is also a great refrigeration gas.  But is very toxic, in the event of a leak.  It’s used a lot in commercial ice rinks and so on.    Also used in rv industry because for the gas to change state propane dc or ac was used to heat it to continue the cycle.

Most refrigeration gases or excellent for refrigeration and safe if possible leak for personal health or fire in the house.  That’s why there used.  The big problem comes with disposal and accidental leaks leading to ozone depletion.   That’s why manufacturers or always looking for and researching new refrigeration gases.

In order to replace refrigeration gas in a fridge you need to do the following.

Drain old refrigeration and capture it.
Vacuum the system down and hold a vacuum for 24 hours to prove the system has no leak and free of contamination.  
Recharge system with new refrigeration.

So you need
Silver Soder and torch to install a access valve
Scale to weight refrigerant
Gauges to monitor the system under a vac
Vacuum pump
Two cylinders old and new refrigerant

In a nut shell this is how it’s done.

Hope this helps with your project.  
I’m intrigued about retrofitting dc compressors sounds like it a great idea.

Just so you know a refrigeration system to work properly has to have 0 contamination.  The compressor is a sealed unit and sits in a oil bath any moisture will contaminate the oil and the compressor will fail.

You seem to know quite a lot about refrigeration in general, and I wish you lived closer to help with this project.  I sort of stalled a bit on this as I have so many other irons in the fire and my current propane fired fridge is relatively economical all things considered- but still it is using fossil fuel and I still make a trip to town every three weeks to refill a tank, so there is some room for improvement.

One thing you neglected, is the new compressor necessary for the conversion of refrigerants, and i'm not sure the new refrigerant isn't flammable, in fact I have seen utube videos where the guy is repairing one and doesn't bother with saving the old refrigerant, and as he is using his brazing torch he sets the leaking refrigerant on fire--just a little flame slowly coming out the end of a tube. Oh, and in your step by step, you neglected the nitrogen flush before the final vacuum and filling with refrigerant.

I did see one utube vid  where a guy took a junk refrigeration unit and just filled it with straight propane (this must have been a unit already using the r600a) and it seemed to work just fine--of course the video didn't show how long it ran or if it might have blown up two days later.

The fact that the refrigerant is flammable was the excuse used for not already converting refrigerators in this country. The main explosion risk might be a leak in a closed space where the gas could mix with oxygen.

It is funny however that you posted here today, just a couple hours ago I saw a new (used) refrigerator where I took my lunch break that was sitting out in the middle of the space, plugged in and running as if it was being tested, and it made me think to keep an eye on it in case it might be available for the conversion, it is about the right size, close by, and i should be able to research the compressor I would need to buy before I actually bought a used fridge.

Anyway, I do still have this project  open  on my mental computer, I'm just not actively researching or acting on it right now. I'll have more time in a month or so.

Yah it’s been awhile since I have changed a compressor. Lol!  Forgot a couple steps.  Don’t hold it against me.

I very sure all refrigeration is safe, fire and explosion wise.  I could be wrong but when I was dealing with it this was the case.  I don’t think any manufacturer will allow any refrigerant in a unit inside a house.

Yes you can very well use propane no problem.  It’s just the fact you got a system that’s flammable or possibly explosive.  I would not have that in my house.  The properties of propane is what make it such a good refrigerant.

It all has to do with the temps that’s certain gas boils and condense at.  I don’t have my old book in front of me for the certain temps but that’s why Propane works it’s certain boiling and condensing temps match what’s needed in a refrigerator.

Mankind is always in search for the perfect refrigerant.  I think it still hasn’t been found but we’re getting there.

I hear yah on projects I’m in the same boat never bored and there’s always something more interesting to do!

If I remember also if we didn’t know how much refrigerant needed in a system we would fill until the system started to frost on the condenser line I believe.  If my memory serves me correct.

You see each system has a sort of a metering device and depending on what refrigerant that device was designed for mixing refrigerant caused the system to act different.  

Another step I missed was replacing the desiccant dryer lol!

It’s all starting to come back know.

I had pretty much decided this is only a partial do it myself, I can research and get everything in place, then give the parts to a refrigeration guy to swap out compressors, then I'll do the electrical modifications

Any updates on compressor change.  Converting a frig from AC to DC, the compressor (and interior lighting) is changed.  Can a 600a refrigerator be powered by a 134a compressor?  The frig piping is sized for 600a but how about the compressor?  How about the lubricant...are the the same?  It seems a compressor compresses.   Thank you.

I finally gave up on finding a used refrigerator to convert. I know there are likely a million of them somewhere, and I had asked to be notified when an installer/sales guy might find one with a bad compressor, but otherwise in good shape, but after a year of waiting nothing. Anyway, long story short I bought 8 -100 AH batteries, a 6000 watt inverter and a regular ac refrigerator relatively small-14 cu ft-. with the plan of running it mostly during the day while the solar panels were producing  and turning it off or down overnight without opening doors so it used as little battery power as possible.  One thing and another and a stupid mistake blew a protection circuit in the brand new fridge and I have yet to repair it. New fridges don't just have a reset button, rather a complicated relay with computer chips so the supplemental system and operation has yet to be fully vetted.  My 3000 watt inverter on my 12v  house system could run it (before the stupid mistake), but the batteries dropped to 10v while it was on, so whether this will work is still a big question (I think this one is about 600w also) . and the conversion idea is still in my mind if this system fails.

When I was contacting dealers for the alternate refrigerant compressors I was told they needed to know the details/ model of the refrigerator I was converting and got the idea that it wasn't  so much limited by size or wattage, just a question of matching them up.

I found the original dc -isopropene compressors on ebay, but likely there are many other sources

The benefit of dc over ac is the fact that dc can easily, using electronics and computer chips be converted to simulate three phase ac.
The pulse widths and amplitudes can be adjusted on the fly to produce an optimal load match for the desired output.
you can't just connect one of these modern "dc motors" to a battery and have it work.
Charging an existing compressor with a different refrigerant than it is made for in general is a disaster and potentially dangerous.
The compressor must compress the refrigerant into a liquid state from a gas state and the temperatures and pressures at which this occurs vary wildly from refrigerant to refrigerant.
Also the seals in compressors are chosen such that the refrigerant they are made for doesn't dissolve them.
The best I ever achieved in my home brew heat pumps was using R22 in a compressor made for r12. that was 40 years ago before the ozone scare.
The only reason I got away with it was because my evaporator and condenser temperatures were very low in my application.

I think this is a very worthy challenge, but I advise a little education on the principles of refrigeration before even proceeding.

I read somewhere that someone almost got hit by a flying refrigerator door that blew off a modified fridge.

You have evidently missed important details of my posts and are responding to things I didn't actually say. If you are actually interested in this process a more thorough rereading will likely answer your questions/comments

Hey Roger

I followed my own advice and reread all the posts, and it's true all the information is there, but I see now the specific query. funny, I thought you were talking about electrical amps of the compressor,600a, which makes no sense,  but you were talking about mixing and matching different refrigerants with compressors. And the answer is compressors are pretty specific, especially in the difference between freon and propane based refrigerants. At this point I don't know if tubing sizes between compressor and rest of the refrigerator need   adaptors or not, but that is a minor thing. At the middle of this thread there are links to the paper I found and other links to articles describing the conversion and general theory.

Like J McKravits pointed out the compressor determines the refrigerant. One will not work with the other.

I don't think it's necessary to be an expert, but at least read through the papers detailing the conversion, and have the literature available for whoever does the actual project.

bob day wrote:I finally gave up on finding a used refrigerator to convert. I know there are likely a million of them somewhere, and I had asked to be notified when an installer/sales guy might find one with a bad compressor, but otherwise in good shape, but after a year of waiting nothing. Anyway, long story short I bought 8 -100 AH batteries, a 6000 watt inverter and a regular ac refrigerator relatively small-14 cu ft-. with the plan of running it mostly during the day while the solar panels were producing  and turning it off or down overnight without opening doors so it used as little battery power as possible.  One thing and another and a stupid mistake blew a protection circuit in the brand new fridge and I have yet to repair it. New fridges don't just have a reset button, rather a complicated relay with computer chips so the supplemental system and operation has yet to be fully vetted.  My 3000 watt inverter on my 12v  house system could run it (before the stupid mistake), but the batteries dropped to 10v while it was on, so whether this will work is still a big question (I think this one is about 600w also) . and the conversion idea is still in my mind if this system fails.

When I was contacting dealers for the alternate refrigerant compressors I was told they needed to know the details/ model of the refrigerator I was converting and got the idea that it wasn't  so much limited by size or wattage, just a question of matching them up.

I found the original dc -isopropene compressors on ebay, but likely there are many other sources

Bob what fridge did you use was it new and was it energy star rated? 600 running watts is huge is that aeasured value? my current fridge runs about 140 watts. I've had the least issues with bare bones models with good energy ratings. Finally the inverter was full sine? I'm always interested to know who has problems and with what models...
Cheers,. David

I never did the conversion--yet-- At this point I don't feel like tearing apart a brand new refrigerator.  Yes, it was energy star rated, which is why the tremendous energy draw surprised me so much. The salesman had talked about it drawing 300 watts and I didn't double check him so I'm still trying to figure the whole thing out-the label says 6.5 amps at full load- more like7- 800 watts, about three times what I was told it would be.

I'm hoping the new batteries will carry the full load better and the actual running load will drop after the box cools down, but i have to get it running first so I can try this new electrical system. If everything  works ok then I won't fix what isn't broken. if not, the conversion may still be on the table. but likely not for a while.

This is really a project for the winter, so I will run my tests with this refrigerator through the summer and any alterations will have to wait.
















i

bob day wrote:I never did the conversion--yet-- At this point I don't feel like tearing apart a brand new refrigerator.  Yes, it was energy star rated, which is why the tremendous energy draw surprised me so much. The salesman had talked about it drawing 300 watts and I didn't double check him so I'm still trying to figure the whole thing out-the label says 6.5 amps at full load- more like7- 800 watts, about three times what I was told it would be.

I'm hoping the new batteries will carry the full load better and the actual running load will drop after the box cools down, but i have to get it running first so I can try this new electrical system. If everything  works ok then I won't fix what isn't broken. if not, the conversion may still be on the table. but likely not for a while.

This is really a project for the winter, so I will run my tests with this refrigerator through the summer and any alterations will have to wait.
















i

hmm .. sounds like the defrost cycle is kicking in. It generally lasts for about 2 minutes at start up then shuts down and you just have compressor draw which is lower. I have seen where the sleep mode on the inverter can do weird things to the fridge circuit board. Modern fridges have a small transformer on them which powers up, brings the inverter out of sleep mode,  then the transformer cycles down causing a loop with the inverter, eventually the board or the inverter fry  If your inverter has the option turn off the sleep mode function.
Cheers, David

Wow David, sounds like you know your way around these complicated modern appliances.

That tragic mistake I spoke of that caused this beautiful refrigerator (whirlpool) to stop working was plugging it into a 220 volt inverter- yes, it's a 110 volt -I'll skip the song and dance that led to this tragic error, but I believe it fried the start relay So I have been focusing on replacing that and the capacitor associated with it. That's all I really know to do, so if you have any suggestions I'd love to hear them

bob day wrote:Wow David, sounds like you know your way around these complicated modern appliances.

That tragic mistake I spoke of that caused this beautiful refrigerator (whirlpool) to stop working was plugging it into a 220 volt inverter- yes, it's a 110 volt -I'll skip the song and dance that led to this tragic error, but I believe it fried the start relay So I have been focusing on replacing that and the capacitor associated with it. That's all I really know to do, so if you have any suggestions I'd love to hear them

Nice! The relay would be a good place to start. Hopefully it ended there.
Good luck on your winter project.

Long story short, fridge is working- I think, using a 24 volt system with new batteries it's draining them slowly--overcast day here, and I'm planning to wait till tomorrow for a fuller test, so far it's just a half hour test, one of the keys was the suggestion it did a two minute defrost when it first started, and I noticed it almost didn't seem like the compressor was running at first, but it was making sort of a humming sound. I noticed the battery drain wasn't terrible, so I just waited and after a couple minutes I did feel some cooling and after a half hour or so it's definitely getting cold

So the next tests will just be if it keeps running, and how much does it take from the bats to keep it running. If all that works, then there will be no conversion in the near future, unless I stumble onto  a good refrigerator with a bad compressor.

Thanks to everybody for starting up this thread again. it got me off my butt and gave me some new info to use.

The last test I had to do that seems to have it running was swapping the black capacitor that came with the new relay for the grey cap that was with the old one, that and waiting patiently for it to cycle from defrost and start cooling again. So I don't actually know if the capacitor made a difference, or if it was just being patient to wait for the cooling

Is there a way to keep it from defrosting ?

Quick update. The new regular electric fridge is doing fine, looks like it will be viable with the batteries and solar panels dedicated to it.
The batteries are reading at 26 plus all day with occasional ventures into the 27 range, and most of the day it was running, bringing the box down to temperature.

I'm not going to disable the propane fridge right away, but I have started to transfer some of the stuff. Most important will be how well the freezer holds temperature overnight with the fridge switched off. I expect partial sunlight days will also give me vital information about battery status,

These details may not be as relevant to this conversion thread,  but since I broached that topic earlier explaining my lack of work on the conversion I though it good to keep everything up to date. Assuming the tests on this "normal" 110 v ac fridge continue to be good it will be a long time -hopefully- before I have to deal with this again--unless a used fridge falls into my lap, then I might not be able to resist the temptation.

By the way, even though the maximum load spelled out 6.5 amps, it looks like most of the run time was working at about 1.6 amps @ 120 v, closer to 200 watts, which was what I expected.

bob day wrote:Quick update. The new regular electric fridge is doing fine, looks like it will be viable with the batteries and solar panels dedicated to it.
The batteries are reading at 26 plus all day with occasional ventures into the 27 range, and most of the day it was running, bringing the box down to temperature.

I'm not going to disable the propane fridge right away, but I have started to transfer some of the stuff. Most important will be how well the freezer holds temperature overnight with the fridge switched off. I expect partial sunlight days will also give me vital information about battery status,

These details may not be as relevant to this conversion thread,  but since I broached that topic earlier explaining my lack of work on the conversion I though it good to keep everything up to date. Assuming the tests on this "normal" 110 v ac fridge continue to be good it will be a long time -hopefully- before I have to deal with this again--unless a used fridge falls into my lap, then I might not be able to resist the temptation.

By the way, even though the maximum load spelled out 6.5 amps, it looks like most of the run time was working at about 1.6 amps @ 120 v, closer to 200 watts, which was what I expected.

Always good to hear the follow up on these threads. Have you put a kill a watt on the fridge yet? Measuring it once it reaches temperature over a few days is always good to do. Over a week even better as that will work in the short defrost cycles. 200 watts with roughly a 10 percent duty cycle is about right ..
Cheers, enjoy. David

Hi David, I don't actually have a kill a watt, you're  right about getting more precise specs on the performance over time would help me plan it out better. The good performance today was encouraging, lets see how it works on a cloudy day. With these simple lead acid batteries I really want to minimize the drain to  prolong the life. So far I haven't really done any discharge cycles, but I can only wonder how long that can last.

Thanks for all the info and great ideas, they've helped a lot

The batteries can sure pull a lot of the efficiency out of a system.
Who is it that is running their 12 volt freezer directly off a panel?
They have a utube channel.