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converting AC refrigerator using r134 a to DC using r600a

 
pollinator
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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
 
bob day
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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
 
pollinator
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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.
 
bob day
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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
 
Caleb Mayfield
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Agreed. Hopefully the research will show converting r134a devices to r600a is possible, "easy", and beneficial.
 
bob day
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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



 
bob day
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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
 
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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!  
 
Caleb Mayfield
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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.
 
bob day
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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.


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


 
bob day
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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.

 
Byron Gagne
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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.



 
bob day
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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
 
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