Mechanical Refrigerator Thermostat? Simple? Cheap?

[MEXICOWANDERER]

I just Inherited a Peltier refrigerator. OEM control is bad, and I just spent 2 hours in frustration looking for a remote probe totally mechanical thermostat on the web. The gizmo IMO would be useless as a battery powered cooler but with a power supply it might work OK. Clad with 6" of insulation it might do OK with battery.

But a thermostat eludes me except on marine sites where a doorstop costs $199.95 on sale.

[MEXICOWANDERER]

Boy, you guys got me nailed to the peg 🙂

The Peltier wafer tested out to 1.3k? so, endgame.

Chop, unscrew, pry, twist, cut, later -

I've got some impressive heatsinks for TO220 devices, and a couple of killer aluminum heat sinks. The chill sink is AN INCH THICK with serrated fins and a 12 volt fan. The heat sink is twice as large and an even larger fan.

Found out the 10 watt 12 volt LED's I purchased are being 50% overdriven at 12.03 volts. Methinks the easiest way to get around this is to simply spring for an 8 amp PWM LED dimmer. See what that baby will do with 6 ten watt devices connected to it. I still have the willies about attaching the devices with adhesive heat sink compound. Anyone familiar with that stuff versus straight zinc oxide compound? Screwing means finding a 4-40 tap and appropriate drill. And 4-40 screws.

Yeah I agree Peltier is like a bicycle spoke playing card flapper - makes for little more than impolite conversation.

Why can't I live on top of a natural gas field and find a nice Worthington natural gas engine and Kato generator laying around? Oh well, free heat sinks are better than a kick in the butt.

Anyone have a c-h-e-a-p source of regulated (switched) 120 volt dongles? Seems like my Brady wire marker is demanding 3.1 amperes at 9.0 vdc and an LM7800-9 ain't gonna cut the mustard. Sucker eats batteries like a six-year-old gobbles M&M's. Six AA's at a shot. You don't want to know what Brady asks for a power supply. Wasn't there a line of TO3 regulators that was higher current?

[Chris_Bryant]

I always wanted to stack peltier devices and use the heat in an absorption unit.

[marcsbigfoot20b]

You can always double stack plates to get ~-70 ambient, but you need one real nice heat sink and fan, and your power doubles. Of course then you would have more capacity and could have less than 100% duty cycle.

[pianotuna]

Hi,

Given that temperature is simply not going to be more than about 20 C below the ambient, why not just forget the thermostat and let it run flat out all the time?

[MrWizard]

or add them to the material is using on his lighting project

[Gdetrailer]

MrWizard wrote:
Peltier coolers with cut off

Single unit with cut off $14

Yeah, they AREN'T worth much or expensive.. plus they guzzle a lot of energy.

Folks think that regular home fridges are not for boondocking, these types would require a field of solar panels if you scaled it up to a real actual usable fridge size..

On the other hand, folks who are into overclocking their PCs might have some interest in these devices, but on the used market Mex might get $5 for the one he has..

I'm thinking Mex is better off selling the heatsink and cooling fins for the aluminum, a better use of the materials.

[LittleBill]

click

[MrWizard]

Peltier coolers with cut off

Single unit with cut off $14

[Gdetrailer]

Peltier devices don't like hard on/off switching, for longest "life" pwm controls are the better choice.

With that said.. to simply make it "work" you could use ANY thermostat which would be usable for your home A/C Heating system provided they will operate at fridge temps (34F-40F) degrees (remote mount the sensor inside the cooler)AND provided you use a high current 12V relay between the T-stat and Peltier.

Keep in mind, Peltier devices are #1 EXTREMELY power hungry for the minimal amount of "cooling" they will give.. That cooler is going to easily draw 5A-8A at 12V (up to 96W)

#2 only cool about 30F - 40F degrees BELOW AMBIENT temps for a single stack.. That means if your air temp is 70F the cooling temp would be 30F - 40F, if your air temp is 90F you will get 50F - 60F which is entirely too hot for safe refrigeration..

Some folks however are undaunted by these draw backs and use them anyway..

Here is a "spec sheet" Peltier Spec Sheet

By the way, that Peltier "should" have a high temp thermal cutout wired in series.. That cutout may be bad which would cause the same symptoms of not cooling..

Additionally the outside fan may have failed, taking out the device in the process.

Personally (especially in your case) I would pull the heat sinks and cooling fins off the Peltier device and scrap the cooler... Just too much of a power hog and very little cooling power especially at high ambient temps.

[MEXICOWANDERER]

I've got lots of 9V LM voltage regulators. But not a danged single RV refrigerator control. My searches obviously took me to every doggone online refrigeration site except the "correct" one. Mexican reefers seem to use all line voltage thermostats. I'm going to connect the critter through a regulated power supply tonight and see how far down unregulated operation temperature droops. Do a few Delta T measurements to see just how lousy the insulation really is.

It's original incarnation was as a Kenmore. I am asssssssuming the Peltier device is still fully functional. Will find out tonight.

[MrWizard]

mexi
did you check RV parts
the old Norcold and Dometic fridges used mechanical thermostats
would something like that work

what about a cheap digital A/C thermostat, like you mount on the wall, uses 12v ? or maybe a 9v battery