Serious Discussion about modifying 120v AC minifridge to 12v DC

[debit.servus]

As many people have noticed, there is a huge price discrepancy between 120v minifridges and 12v minifridges that it's a crime. I believe it is possible and cost-effective; to convert a low-end 120v AC powered minifridge to a 12v DC powered minifridge, with the right knowlege, knowhow and skill. Maybe even possible and cost-effective to rotate the compressor 90 degrees so the minifridge can lay on it's back, and become a chest fridge for more efficiency.

A few things I know about fridges is the compressors fundamentally can't run on 12v so the 12v fridges have a buckboost converter to raise the voltage to 48 volts or so to power the compressor. Other electrical modifications and circuits are required to get the 120v AC fridge to run on 12v DC, an DC to AC transformer/inverter might be required if the compressor uses Alternating Current. The KENMORE minifridge in the bedroom transfers it's heat to the sides of the fridge, so the walls need breathing room. The low-end minifridges are built cheap so it's not a great idea to bang it around in a moving van.

This thread is a serious discussion about modifying a low-end 120v AC powered minifridge to a 12v DC powered minifridge, to avoid the conversion losses that come with using an inverter to power an 120v AC minifridge. Has anyone attempted or sucessfully converted a 120v AC fridge to a 12v DC fridge? For the electrical engineers in the house; please help us with the fundamentals, wiring diagrams (if someone has a 12v DC fridge sucessfully converted from 120v AC, a detailed schematic would mean the world to us), and most importantly cost-effectiveness.

 

[GotSmart]

In the mid 1980's, I built cryonics units.  The differences in all cooling unit prices come down to a few details.

1.  Quality of the shell and frame.  

2.  Quality of the compressor.

3.  Quality of the electronics.

4.  Mixture of gasses, and price of patented freon separators.   

5.  Quality of final build.

We could get a 20 CF space to cool to absolute 0.  (-273.15c or -459.67f in 5 minutes.  

These ran about $12,000 each at the time for a small unit. Double for a full size one.  

The plant could turn out about 15 a week.   24 people working 10 hour shifts.   

The conversion of a dorm fridge to a 12v mobile unit would cost a non commercial buyer quite a bit for the parts alone.  Plus you would need to be trained and licensed in freon handling. 

It is cheaper to either buy a good inverter, or a proper 12v unit. $500 on up.

 

[Konaexpress]

Coming from that world, my answer is really simple....don't do it.

John

 

[jimindenver]

I have seen Danfoss compressor kits on ebay or CL for $2-300. It wouldn't be more than a r&r fpr a perspn with the skills ans tools. Those tools cost more than a Engel.

 

[SternWake]

Yeah, I have no idea how to convert a 120Vac fridge to a 12vDC fridge. If it were cheap and easy to accomlish, then the 12v compressor models could not be priced where they are and actually sell. The fact that they do sell at these rather ridiculous prices, speaks volumes.

One thing about the 12v units is they are built for efficiency, with a large well ventilated condenser, thicker inuslation, and likely well matched electrical components in the compressor controller that do not waste much battery power as heat.

Whereas a 120Vac dorm fridge is all about the sticker price and wise marketing to get the uninformed human to think, 'for that price, how can I not buy it?' Something I call The 'harbor freight' effect. Built to bottom dollor standards, ie " heck just use the case as the condenser, baby needs a new diamond, and I need that executive bonus before we declare bankruptcy. Warranty? Hahhhahhaaaaaaaaa!

How many corners can be cut to sell a 120V dorm fridge for 120$ and everybody from manufacturer to marketer to shipper to retailer to profit off of it?

Trying to put edges back on those corners, will not be simple, easy, or cheap. I don't know how, nor would I expend the effort to do so, but I wish you luck in this endeavor.

One thing I notice, is many of your threads seem to have ground rules set out by you that doom them to failure, simply from the attitude your rules convey to the reader here. I have put you on Ignore, for this reason, but I don't always sign in when I read this site and still read some of your postings which simply rub me, and I suspect others, the wrong way.

Only Bob and the moderators get to make ground rules here, As far as I am concerned.
Speaking down to your elders will get you nowhere in this life.

Pretend if you have to, but I find you very abrasive.

 

[NickTheoBennett]

It really seems like you're trying to reinvent the wheel here, debit.servus.  

You have a lot of ideas, and innovation is a beautiful thing, but sometimes the "normal" way to do something just makes the most sense from a financial perspective.

 

[Konaexpress]

And silver soldering is a PITA! You will blow through so much copper before you get the hang of it.

I vote for new if you can afford it or some kind of pick-n-pull if you can't.

John

 

[johnny b]

if it could be done cheaply and reliably then it would:

First, be all over you tube and the interweb.
Second, be on the TV show 'American Makers'.
Third, the Chinese would be selling Whynters for $200 instead of $500.

Of course the real answer is that it CAN be done, but the secret is locked away in that 'Vault'....you know, THAT Vault.  

 

[debit.servus]

As I said cost effectiveness is the most important thing here. Wasn't asking about adding those cut corners back to the 120v fridge, just modding the 120v AC fridge to run on 12v DC without an inverter. Keep it upright like it was designed to be, no refridgerant handeling required. If it costs more to wire a 120v AC powered fridge to become a 12v DC powered fridge than an ENGLE, it's not worth it.

What would it cost to convert a low-end 120v AC powered minifridge to a 12v DC powered minifridge, with nothing else done to it? How many parts and labor hours are we looking at for this theroretical fridge mod? Note that I put theoretical in the last sentence because it might not be practical.

 

[jimindenver]

I might be a bit rusty but I could R&R a compressor on a fridge or commercial refrigeration unit in 2-3 hours. I had all the tools, pump, gauges etc. at my disposal so there were no delays.

Of issue anymore is the Freon. It has changed over the years and so has the regulations. I'm not sure the average joe can buy more than a top up can for the car A/C. Old Freon is some pricy stuff too.

By the time you even buy the mini fridge to convert, a danfoss compressor kit and the new freon, you could have bought a Edgestar 12v or the like ready to go.

Possible, sure. Anything is. Practical or even equal in application, not really.

That does bring up a possible money maker. Freon is collected now, the older stuff is gold. All it takes is a pump, gauges and reclamation tank to do it. I know the dump near me has the fridges lined up on the side of the road in waiting to purged.

 

[bcbullet]

I might be a bit rusty but I could R&R a compressor on a fridge or commercial refrigeration unit in 2-3 hours. I had all the tools, pump, gauges etc. at my disposal so there were no delays.

Of issue anymore is the Freon. It has changed over the years and so has the regulations. I'm not sure the average joe can buy more than a top up can for the car A/C. Old Freon is some pricy stuff too.

By the time you even buy the mini fridge to convert, a danfoss compressor kit and the new freon, you could have bought a Edgestar 12v or the like ready to go.

Possible, sure. Anything is. Practical or even equal in application, not really.

That does bring up a possible money maker. Freon is collected now, the older stuff is gold. All it takes is a pump, gauges and reclamation tank to do it. I know the dump near me has the fridges lined up on the side of the road in waiting to purged.

You do know that R12 (Freon) production was banned for very good reason, right?

 

[Optimistic Paranoid]

As I said cost effectiveness is the most important thing here. Wasn't asking about adding those cut corners back to the 120v fridge, just modding the 120v AC fridge to run on 12v DC without an inverter. Keep it upright like it was designed to be, no refridgerant handeling required. If it costs more to wire a 120v AC powered fridge to become a 12v DC powered fridge than an ENGLE, it's not worth it.

What would it cost to convert a low-end 120v AC powered minifridge to a 12v DC powered minifridge, with nothing else done to it? How many parts and labor hours are we looking at for this theroretical fridge mod? Note that I put theoretical in the last sentence because it might not be practical.

Well, IF it were a case of an electric motor turning a compressor via a belt and pulleys, then it might be as simple as replacing the AC motor with a DC motor.

However, as far as I know, the modern fridges all have one piece motor compressors direct coupled together.  So you'd have to source a complete 12 volt motor compressor from somewhere, extract the Freon from the system, put the 12 volt compressor in and recharge it.

As far as somehow modding a 120 volt ac motor to run on 12 volts, consider this:

Say it needed 10 amps at 120 volts to run.  That's 1200 watts. To get 1200 watts at 12 volts, you'd need 100 amps of current.  I don't believe a motor whose armature was wound for 10 amps can take 100 amps without burning out.  (Numbers arbitrarily chosen to illustrate the point I'm trying to make.)

 

[LeeRevell]

It basically boils down  to "economic viability" and skill.  Some folks have the latter.  Most don't.   But usually conversions of appliances costs more than getting the correct unit to begin with.  Good 12V units don't have to be expensive if you don't need to stock a month's worth of stuff.

 

[johnny b]

As I said cost effectiveness is the most important thing here. Wasn't asking about adding those cut corners back to the 120v fridge, just modding the 120v AC fridge to run on 12v DC without an inverter. Keep it upright like it was designed to be, no refridgerant handeling required. If it costs more to wire a 120v AC powered fridge to become a 12v DC powered fridge than an ENGLE, it's not worth it.

What would it cost to convert a low-end 120v AC powered minifridge to a 12v DC powered minifridge, with nothing else done to it? How many parts and labor hours are we looking at for this theroretical fridge mod? Note that I put theoretical in the last sentence because it might not be practical.

OK a more serious answer this time. Your question has been answered in the posts prior to your second post.

If you're not going to change the voltage (ie inverter), then you have to change the compressor. In order to change the compressor, you need specialized tools, which are expensive, and you need at least 2-3 hours of labor.

So....ebay danfoss 12volt compressor kit $200-300. Labor.....let's go cheap and say $50/hr = $150.  $300 + $150 = $450 and that's without buying the specialty tools (or the refrigerant if what can be saved is not compatible or enough).

A Whynter 12vdc fridge can be had at Home Depot for $450-500....therefore the answer to your original question is NO....which you already knew by your use of the word theoretical in your 2nd post.

(All future replies will be back to the satire.....     )

 

[debit.servus]

Now that's the reason I haven't seen more than 1 or 2 successful home minifridge conversions to 12v, it isn't cost-effective.


"Well, IF it were a case of an electric motor turning a compressor via a belt and pulleys, then it might be as simple as replacing the AC motor with a DC motor." That might be cost effective, provided one can score a vintage & operational minifridge with that belt driven compressor arrangement. I didn't know that about todays fridge compressors being one piece compressors, I imagined the compressors could be taken apart and motors swapped without handeling refridgerant. it's cheaper to get the ready-to-go ENGEL/WHITHER/EDGESTAR 12v fridge.

 

[jimindenver]

You do know that R12 (Freon) production was banned for very good reason, right?

For the ozone layer.

That's why reclamation is done and why it is resold for ridiculous prices. People will pay a lot to keep their old Subzero going rather than spent 5-10 grand to replace it.

 

[highdesertranger]

on very old refers compressors where belt driven. a few years back R-12 was like the 4th most smuggled item behind illegal drugs, people, and cigarettes. highdesertranger

 

[debit.servus]

Looks like this thread has moved on from "cost-effectiveness of converting a 120v AC powered minifridge to a 12v DC powered minifridge". And moved onto "R-12 refridgerant gas". Do they still use R-12 in Mexico? If so one could go south of the border to get their system recharged legally with R-12.

I heard R-12 transfers heat better than the "ozone-friendly" refridgerants, which means it takes a larger compressor and more energy to transfer the same amount of heat with most newer refridgerants. Kind of hurts the envrioment seeing as it takes more energy to transfer the same amount of heat as R-12.

 

[ZoNiE]

I have a friend who did this in a GMC motorhome. Here are some links.

There is a lot of GMC relevance, and some topic wandering, but these guys have been screwing around with this for years... Lots of good insight.

http://www.gmcmhphotos.com/photos/refrigerator/p16527.html

https://groups.google.com/forum/#!s...ridge/gmcnet-archive/74JYFUjYX9E/YPn9bUeTycMJ

One thing, if you go this route, add at least an inch of polyiso or foam insulation around the fridge, and make sure the condenser coils have good airflow and venting. Heat extraction is key. Computer fans are your friend. It doesn't take much.

Somewhere in all of this is a thread about different model's efficiency...
https://groups.google.com/forum/#!s...ridge/gmcnet-archive/Q0S16DIapU0/T7ZGhgOwE0QJ

 

[ccbreder]

I would venture an educated guess. There are no successful conversions of a mini fridge to 12 volt operation that do not use a inverter to change 12 volts/DC to 120 volts/AC. Otherwise too impractical and too expensive.