12V fridge

[kitestrings]

I googled this from a post I’d done back in 2014:

One of the first off-grid appliances that I ever bought was a Dometic refrigerator from an AE dealer (and there weren't many of them then) in ME named Peter Talmage, Talmage Engineering; nice fellow I'd gotten to know in my wind days.  It is 8 CF, like many RV units, but uses a Danfoss compressor instead of the less efficient, and more common "3-way" absorption units.

Anyhow, this frig is still with us.  It is now 30 years old.  Works like a champ.  A few years ago it acted a bit flakey and I thought it was going to die, so I tried contacting Dometic; still had the manual.  Well, they never made such a thing I was told fairly curtly, but I explain to a couple folks there that the thing said Dometic RM760 front and center.  And, I had their manual in my hand.

Eventually I spoke to a guy who'd been there too long I suspect.  He explained, that they were actually labeled by Dometic under a contract for Winnebago, but manufactured by a company called Novakool.  Sure enough I called Novakool out in BC, CA.  They shipped me a new controller and we were back in cold beer.  And, our off-grid home had a new-found Winnebago prestige  .



Jump ahead another ~7-8 years, and I figured our fridge had finally died.  It was making this high-pitched, straining squeal when it wanted to start.  I boosted the voltage a bit and it went away, but not for long.  After a quick search of just how expensive new ones had become, and how long you had to wait now… I pulled the thing out of it’s pocket.  I was hoping perhaps that it was just the controller.  Those are discontinued now too, but I guess you can get aftermarket ones.


I tried by-passing the thermostat, and was please to hear it roar to life again.  Well okay, it is more like the sound of a fish-tank aerator, but it was music to my ears.

I had a little trouble finding a replacement – not an exact match – but in the end I match the application (fridge, manual defrost), the capillary length (1200 mm), and roughly the temps stamped on the old one.


There’s a movie “Free Solo” about the young climber, Alex Honnold, who free climbed El Capitan.  At one point Alex and his love interest are searching for refrigerator for their new apartment.  Up until now he’s been living, eating, training in a van.  She likes the larger, thru the door water dispenser & ice models, he focuses on a modest ~10-12 CF, no-frills.  He explains that it is “perfectly adequate”.  It’s a running joke here, when one of us is cussing about the size of this thing, that it is “perfectly adequate”.

[kitestrings]

This was the original thermostat:


This is the thermostat we used:


The description reads:
Danfoss 077B6175

Product description
This is the Danfoss Thermostat Original Part Number 077B6175 [W5-30240]•: Type:077B6819•: Connection:4.8 mm•: Cap.tube length: 1500 mm•: Cold out:-18.5º:C•: Cold in:+4.5º:C•: Warm out:-5.5º:C•: Warm in: +4.5º:CSuitable for: HELKAMA 0610200

The capillary tube had a white "PE coating + shrinkable flex. tube 135 mm".  I'm not familiar enough with these things to know when/why they use that.  I might assume it is when it travels through a warmer space (near the evap coils), or where it might have incidental contact with energized parts?  Anyway it seems to work well, and I'M set maybe 1/3 of the way up the dial, so we have room to move a bit warmer , and much colder.

[DamonHD]

Interesting, thanks!

Damon

[Mary B]

I googled this from a post I’d done back in 2014:

One of the first off-grid appliances that I ever bought was a Dometic refrigerator from an AE dealer (and there weren't many of them then) in ME named Peter Talmage, Talmage Engineering; nice fellow I'd gotten to know in my wind days.  It is 8 CF, like many RV units, but uses a Danfoss compressor instead of the less efficient, and more common "3-way" absorption units.

Anyhow, this frig is still with us.  It is now 30 years old.  Works like a champ.  A few years ago it acted a bit flakey and I thought it was going to die, so I tried contacting Dometic; still had the manual.  Well, they never made such a thing I was told fairly curtly, but I explain to a couple folks there that the thing said Dometic RM760 front and center.  And, I had their manual in my hand.

Eventually I spoke to a guy who'd been there too long I suspect.  He explained, that they were actually labeled by Dometic under a contract for Winnebago, but manufactured by a company called Novakool.  Sure enough I called Novakool out in BC, CA.  They shipped me a new controller and we were back in cold beer.  And, our off-grid home had a new-found Winnebago prestige  .
(Attachment Link)
(Attachment Link)

Jump ahead another ~7-8 years, and I figured our fridge had finally died.  It was making this high-pitched, straining squeal when it wanted to start.  I boosted the voltage a bit and it went away, but not for long.  After a quick search of just how expensive new ones had become, and how long you had to wait now… I pulled the thing out of it’s pocket.  I was hoping perhaps that it was just the controller.  Those are discontinued now too, but I guess you can get aftermarket ones.
(Attachment Link)

I tried by-passing the thermostat, and was please to hear it roar to life again.  Well okay, it is more like the sound of a fish-tank aerator, but it was music to my ears.

I had a little trouble finding a replacement – not an exact match – but in the end I match the application (fridge, manual defrost), the capillary length (1200 mm), and roughly the temps stamped on the old one.
(Attachment Link)

There’s a movie “Free Solo” about the young climber, Alex Honnold, who free climbed El Capitan.  At one point Alex and his love interest are searching for refrigerator for their new apartment.  Up until now he’s been living, eating, training in a van.  She likes the larger, thru the door water dispenser & ice models, he focuses on a modest ~10-12 CF, no-frills.  He explains that it is “perfectly adequate”.  It’s a running joke here, when one of us is cussing about the size of this thing, that it is “perfectly adequate”.
(Attachment Link)

We used to cram 12 + people in a 35 foot camper and manage to feed them all for a week out of a fridge that size. Of course all beverages were kept in coolers under the camper, dad had built a locking box under the front to hold coolers, fishing gear, life jackets, wet clothing had a space to hang and dry if it was rainy. Beer alone for 12 adults for a week at the lake takes a LOT of space LOL

[bigrockcandymountain]

"Perfectly adequate" I like that line.  The line in our house is, "people raised kids in tipis you know"

Our fridge is just an energy efficient, plain, bare bones frigidaire.  It is about 13 cu ft and with a family of 5 it is fine.  It is a good thing christmas is in the winter though.  When 20 people show up for a few days it doesn't quite cut it. 

My mom has a fridge in her house plugged in in 1958 and still going strong.  To my knowledge it has never had any parts replaced.

[Mary B]

Those porch fridges come in handy LOL been there done that!

[kitestrings]

That's a colorful image MaryB.

We now have a small, 6 CF freezer in the basement.  It is a German made unit, made by the solar company Stecca.  It also uses a Danfoss compressor, but runs on 24VDC.  The basement stays at or near ~15 degC (55 F), and it is top loading, so it is pretty efficient.  We store a lot of packaged drinks and nonparishable's down there.

Most of the time the fridge is adequate.  When it is problematic is usually just if we host a larger family gather, holiday.  One Thanksgiving we decided it would be a good idea to just throw the leftover turkey in the back of Mary's Volvo.  Apparently that smell appeals to other mammals.  I thought I'd never get the mice out of her hvac ducting.  Go figure.

[westerly]

what a timely post - I just got a 12v rv fridge that was discarded - without the controller. The controllers can be found on ebay but are rather pricey just to see if all else works (has the desirable danfoss brand compressor). Had never before delved too deeply into the actual powering of a 12v compressor until now, only to find it is a 3 wire bldc motor. So now I have a $14 ebay "bldc controller 36v" being ordered from overseas. I will either utilize the existing thermostat or use an arduino to configure a new control panel that can set temp, display temp, do gradual startup, monitor low input voltage, control fan etc. It's good to hear yours lasted so long.

[kitestrings]

I think ours is considered a brushless, electronically commutated motor.  Most of the later ones are 12 or 24V; ours is not.

I had jumped ahead to research controllers, initially thinking that to be our problem, here are few things I found that might be of help to you:

These folks sell an aftermarket controller that is compatible with the Danfoss:

Here is a link to their catalog: HMP Online Catalog (hollandmarine.com) (the part is on page 298, #3033).

This was a video I found looking at controllers, diagnostics:

https://www.youtube.com/watch?v=wETaZHf0amI

This was some generic information I found on Danfoss thermostats:

https://assets.danfoss.com/documents/97788/AD300657221431en-GB0101.pdf

There also are some pretty low cost temp display units that will monitor a remote probe, and allow a for a programmed relay contact closure.  I was considering this, but then you have to have power to it, and consider how reliable it might be compared to a mechanical unit.

Good luck, and do post how it goes.  ~ks

[westerly]

thanks, I'll have a look. Yes there are temp controllers that I might consider too, though a big selling point of the newer danfoss controllers appears to be a soft start feature (which I hope to do by mimicking the speed pot on the ordered bldc motor driver board). I'm paying for that cheap price with 40-65 days of shipping though!

[kitestrings]

Well, I was too hasty, and should know at my age to never gloat…

The thermostat I installed quit working after just a few days.  I initially thought it had outright failed; open contact… but, more on that idea to follow.

The fridge itself was fine, but I was back to a jumper and manual intervention.  This time, I took a little more time to research the right fit.  Ultimately, ordered this one, a Danfoss 077B7001:



All good now, but I was curious about the first one.  Dug it out of the trash and sitting at room temperature, I noticed that it again had -0- ohms, closed contacts, as we’d expect.  I popped it in the freezer, and to my surprise the contacts opened after just a few minutes.  Looking at the two (7001 new vs. 6175 my first replacement) here’s how they compare:


On the original thermostat, aside from needing 1,200 mm long (min.) capillary, which ruled out a few choices, the uncoated tube mounts directly against the evaporator plate.  The first replacement (6175) has a fixed cut-in of 4.5C degs (40.1 F)… that’s kind of warm, huh?  I think once the temperatures stabilized, and condensation turned to frost on the evaporator plate, we were probably always below the cut-in.  I might of moved the probe off the surface, but oh well, it is done and working good now.

I temporarily moved the outdoor sensor of our indoor/outdoor thermostat into the fridge for a few days to fine tune the setting, and joked that I had no idea what the outside temperatures were, but what I did know… was that the fridge was ideal for cooling beer.

[Mary B]

I have temp probes in every fridge and freezer ad a remote readout on my desk! If a freezer goes down an alarm goes off... Lacrosse WS-09

[kitestrings]

Thx for the tip.  I'd considered one like these, but they are a bit pricey; some lower cost on Amazon:
https://www.go2marine.com/Product-Guides/MFR/Frigoboat/Which%20Thermostat%20Should%20I%20Use%207_02_12.pdf

I like the mechanical unit, I can always hear it click in/out, but a remote like you've suggested for the freezer in the basement would be an worth considering.  Thx again.

[SparWeb]

Great story!

Starts with a tragedy (fridge failure) passes through despair (excel spreadsheet) and comes out victorious (cold beer).

For the epilogue, I have one of these:
https://www.amazon.ca/110-220V-Temperature-Controller-Electric-Thermostat/dp/B07HQM3K1G

[kitestrings]

Well, we got another year out of it.  This spring the fridge stopped starting, for no apparent reason.  It only happened once or thrice.  What I discovered was if I shut it off, and gave it a good wiggle & shove - yes, like slapping the old TV - and then turned it back on it would resume the effort.  I didn't know how much longer I could expect this to work, and I didn't want to put another $370 (Can., after-market) into a controller that might work on something this old.

A new one was about 23-25 weeks out.  We decided to get a new one coming, and hope this one would make it that long. 

Here's the new one:


It was a pretty good fit.  I just had to narrow the drawer height by ~1/2".  Seems to work well.  This one is solely vented through the front grill, which means there is condensor fan.  The fan is noisy compared to the old unit, but we did get some modest increase in size.  This one is 9.1 CF with the freezer on the bottom.  Basically we gain the ~3-4" of depth where the other unit had the evaporator coils on the back (and convective cooling).  It was pricey, but I guess if it lasts anywhere near as long as the other one - well yes, I'll be dead 

The old one, I'm not sure... I might try keeping beer cold in the shop for as long as an occasional shake and bump seems to work.

~ks

[MattM]

Maybe you can use your uber electrical skills to kick off a high-frequency vibrating stimulus to the motor that shuts off after a few seconds.  Sort of automating the kick.

[kitestrings]

I like it Matt.  Maybe a Rube Goldberg design with a hard-toed boot 

Well, here's Murphy's Law: I don't believe it stopped only once after I ordered the fridge.  I think we can say the thermostat is good.  When I have a chance, I'm going to try to determine if it is the controller or the compressor.  If it is just the controller, there may be an option to fix or replace it.  If it is the compressor, I think we call it a good run, and look to recycle and dispose.  Gotta be pushing 40-years with this thing.  Good run either regardless...

[Bruce S]

After reading about the it "needing a good kick" reminds me of our washer. The drain pump would just stop, I found that if I gave it a good "smack".
I ordered a replacement pump, then being the curious person I am, found a flat spot (actually burnt looking) on the motor windings, my guess is that it would hit that spot and not have enough oomph to get past it until a good whack moved it along.

I agree , if it's the compressor (after reading the "fix"  I think it is), salute it with a good beverage and recycle.

Cheers
Bruce S

[tanner0441]

Hi

I spent a couple of years working in the R&D Dept of an air con company on computer room AC. we occasionally had to fit things called hard start kits. From memory a big capacitor which would start the compressor up if the pressures hadn't quite equalised. Don't know if they do them for domestic fridges but it might be worth a look.

The electronic thermostat recently went on my fridge freezer I priced a replacement, £57 so I turned up the miser button and ordered a cheap Chinese thermostat with the standard 10k NPT thermister as a sensor and programable set point. OK the display read 2 degrees high but the dead band was only 2 degrees and it was £3 and had a 10A relay on board so i used it to control an extension lead.

Worked for months like that. Weve just replaced a couple of weeks ago and the new one is displaying all the signs of a low gas charge, hey ho you can't win.

Brian

[OperaHouse]

My fridge has been giving me trouble with hot starts which is controlled by my microprocessor. Last year I was playing around with restart delays and shortly after that the computer died.  This year I'm over 5 years on the car battery that runs it and capacity has dropped quite a bit.  So
 it can die on startup. It runs on a MSW inverter which everyone says you shouldn't do.  Necessity is the mother of invention. For years I had the idea of changing the duty cycle of the wave, but everything worked and i didn't bother. Did some experimenting and found that many of these inverters extend on times to compensate for lower voltage at high load. The opposite you want to do with a motor.  I installed an ONTIME limiter so on times dropped from 4.8ms to 4.0ms and the control circuity couldn't extend the times.  Startup current went from 120A to about 60A.  Power consumption of fridge also dropped about 9W.

[Mary B]

Best practice on a compressor is 5 minutes off for pressure bleed down. All the commercial beer brewing temp controllers have gone to that to prevent hot starts that are very hard on the compressor.

[OperaHouse]

I need a bit longer for battery recovery in cloudy weather. It doesn't take much charging to make old batteries seem fully charged based on voltage. This is what happens when you are playing around and the music stops.

The real story here is I have reduced srart up current down to a reasonable value in the 60A range so using a 100AH lipo is possible.  Not comfortable with a short term surge to 120A even if they claim it could take it for a short burst.