How to upgrade mini fridge question mark?

[Sir Dude]

Long story short: I got this Frigidaire Retro Mini Fridge that only holds 6 normal sized cans of soda, but is rather portable. I got it last year during a Black Friday sale and it's been pretty good to me... until the cooling fan died. I tore it apart and discovered it's made with some pretty simple components. I've always wanted to get into hobby electronics and I think this would be a good start. I don't want to just replace the fan, I want to upgrade the machine so it gets colder. Is there anyone who can help me, or at least point me to some good resources so I can learn by myself?

 

Long story long: This is a relatively simple machine. It's small, compact, lightweight, comes with a handle for easy carrying, and even has a port for a cigarette lighter in a car. This thing is made to run off of 12v car batteries, so again, a pretty simple machine. Here are the internal components themselves in their entirety:

 

The fridge contains 3 main things:

A 3cm square Peltier cooling unit (left)

An 8x8x2cm fan (upper center)

A circuit board with a whack ton of heatsinks and capacitors. (right)

 

I didn't know about Peltier cooling units when I opened this thing up, and I thought that little white square was black magic. Coincidentally enough, Linus Tech Tips uploaded a video where they used Peltier's to cool a PC, to some degree. Basically they move electrons from one side of the unit to the other. Moving the energy away from one side causes that side to get cold and the other side to get hot. While it's not great for large scale cooling, it's great for small scale applications like this. The fridge actually gets decently cold too. Of course, as you can see the Peltier unit is connected to a FAT heatsink (2 actually, the second isn't pictured but it's a solid 3.6x.3.6x2cm metal block and the unit is sandwiched between them) and on the other side of that heatsink is the fan, which of course points to the back of the fridge.

 

To my understanding, if I wanted to upgrade the cooling capacity of this fridge, I would need either a bigger or more powerful Peltier unit, or maybe give the current one more power, of course I would need a bigger fan to carry more heat, and then maybe remove something from the circuit board so that it can run more power (because the units themselves need more power, otherwise I'm just throttling everything and ruining the point). Again, that is MY understanding of what I would need to do to upgrade this thing, but I am NOT a professional, and I don't know much about electronics, especially custom stuff like this. That's why I turned to the forums. If I were to try and go at this, I'm thinking best case scenario I get no perceptible difference in temperature, most likely scenario I would brick the fridge and have to throw it out, worst case scenario I burn my house down. I want as much help as people are willing to give me because I wanna make sure I get this right.

[Bombastinator]

TLDNR:

This could get complicated and will require more than ripping pieces off.  I would suggest replacing the fan, but doing only that.  That bit should be pretty easy and result in success with minimum hair pulling.

Increasing cooling looks doable but it also looks like a rabbit hole.

 

Why:

this isn’t just electronics it’s thermodynamics.

Thermal issues:

Peltiers are DC.  They’re also very inefficient.

They have a hot side and a cold side.  The amount of cold they make is proportional to the amount of heat they make.  You make more cold you make more heat which you then have to get rid of.  The limitation of this device could be the capacity of the peltier, but it could also be the capacity of the heat radiator, which I think is the aluminum thing.  You make more voltage to the peltier you make more heat for the radiator to remove.  It may have to be modified to do that if it doesn’t have the capacity currently.  And that’s just the hot side.  The cold side may have issues too.  I don’t think that bit is pictured.
 

Power issues:

The leftmost component in the pic is probably the ac-dc unit. The PSU. It is capable of producing an unknown number of watts but is probably matched very closely to the wattage requirements of the cooler and fan, unless it’s an off the shelf part.  Even then it might still be.  A bigger or higher volted peltier will draw more watts and possibly blow it.

the lower middle board with only the solder points visible is going to be some sort of controller. Probably a voltage controller.  It’s got the on/off switch wired to it.  

 The case fan looks to be attached at the other side of the cooling plate and is a cheapass 120mm case fan.  It is wired from the other side of the aluminum plate and there are only two wires going to the peltier, so it follows that the fan is wired from the peltier.  It’s 12v DC though which implies your current peltier is 12v DC as well.

 

What you need to know:

Thermals: will the radiator be able to handle the additional heat?  Is the aluminum thing even the radiator?  If the aluminum thing is cold side what does the heat radiator look like.

do you even need a bigger peltier or can you just run more voltage through the one you’ve got?

what is that PSU actually capable of?  It looks awful custom but it might not be.  If it isn’t it might have additional capacity in it.

What is the voltage controller actually capable of?

 

If these things are off the shelf parts they will have part numbers you can look up.

[mariushm]

At a particular amount of power going through the Peltier element, there's gonna be a temperature difference between one side and the other.

Giving higher voltage to the peltier element won't do much, you'll just risk damaging the elements.

You can install a better fan or add some metal heatsink on the peltier element to spread the heat. If you get the hot part cooler, in turn the other side of the element will be colder, as the temperature difference should remain about the same.

 

Anyway... the power supply is about to die on you, those two output capacitors seem swollen a bit, they should be replaced

 

If the fan is 12v, just replace it with more powerful fan.

 

[Bombastinator]

3 hours ago, mariushm said:

At a particular amount of power going through the Peltier element, there's gonna be a temperature difference between one side and the other.

Giving higher voltage to the peltier element won't do much, you'll just risk damaging the elements.

You can install a better fan or add some metal heatsink on the peltier element to spread the heat. If you get the hot part cooler, in turn the other side of the element will be colder, as the temperature difference should remain about the same.

 

Anyway... the power supply is about to die on you, those two output capacitors seem swollen a bit, they should be replaced

 

If the fan is 12v, just replace it with more powerful fan.

 

So peltiers do not vary cooling power by voltage?  I’m trying to recall the LTT video when they used one as a CPU cooler.  My memory was they varied the power a lot but it’s possible they were turning it on and off, rather than varying the voltage.  A PWM effectively.  If that is the case that center board is more complicated.  Still don’t know which side is hot and which side is cold.  I think the aluminum square is the hot side but I wouldn’t bet money on it.  If it is, the thing needs to be turned over to find out how complicated it is.  If it’s the cold side we need to see what the hot side stuff looks like because it’s not pictured.  It’s also possible that fan isn’t 12v.  Unlikely considering it’s form factor, but possible.  Voltage needs to be measured.

 

If the PWM Thing is correct and the aluminum bit is the hot side increasing cooling capacity on the hot side would lower temps on the cold side without doing anything to the electronics.  It would merely make the heat removal more efficient.

 

i can’t speak to the health of the PSU myself, but I concur that at least in the photo the capacitors seem to be tenting up which is bad. If they’re not dead flat they are going bad.

 

So possible new capacitors and a test of the voltage followed by a new fan nets you continued use at the same level.  Soldering, voltage testing, reading capacitor codes, buying parts.  Definitely a substantial intro project.

 
hot rodding the fridge:

If the aluminum is the hot side and the peltier is PWM, things do get simpler.  A more powerful fan might work but I don’t know if it can be attempted.  I simply lack knowledge there. Additional fins would work with an equivalent  fan but they have their own problems.  adding internal fins could mean aluminum soldering or tig welding.  Both are somewhat complex, though tig is arguably worse.  

 

advantages/disadvantages of solder:

Soldering equipment is a lot cheaper than tig equipment, but it’s still different than electrical soldering.

Aluminum does not solder using the same materials or temperatures as electrical soldering.  Also because of the type of oxides it make you often get one(1) shot at it.  If it doesn’t work the piece needs to have the oxides filed off before another attempt can be made.  I’ve seen people put the entire piece on a running gas stove and then using a torch.  

advantages disadvantages of tig:

Tig welding is a gas feed welding system requiring iirc argon as a gas sheathe.  Lots of money just for the equipment plus you have to learn how to use it. A 110v mig/tig welder can be had for a couple hundred bucks at a hardware store and then you need the gas.  The bright side though is knowing how to tig is potentially very useful for many things, and a mug/tig welder can be used on steel as well.  Welding is one of those “useful skills”.  A certification in it can mean permanant employment.

[Sir Dude]

Sorry for the late reply, but thank you both so much for the responses. Here's some answers to your questions:

1. The aluminum block on the left side is the hot side.

The fan doesn't directly bolt to the radiator, it bolts to the fridge's plastic casing, but it is otherwise directly behind the radiator.

Also, here's how the cooling units are put together:

From left to right: cooling fan (not pictured here), radiator, peltier, metal block mentioned in first post but wasn't pictured, metal casing of fridge unit. Also I should mention there was thermal paste between these components, but I've cleaned that off and I have a tube on standby for if and when I put it back together.

 

2. The fan is indeed a cheap "Brushless DC 12v fan" from a company called Yaheng. It's directly soldered to the control switch board, but that should be no problem to just cut and splice wires together.

 

3. The fan is not wired to the peltier. It appears to be in the picture but the cords are zip-tied together and it made it look like the same wires.

 

4. Here's a better pic of that lower center board:

You can refer to the pic in the first post for the other side. There's nothing of note on the other side and you can see it pretty clearly so I didn't feel the need to take a pic of the other side, however I will go into more detail and attempt to map everything out upon request. I have no idea if this thing controls voltage. The most I can guess is maybe it limits power going somewhere because of that resistor on the left side underneath the wires but there's nothing else on it. You can see the cords connecting to the fan more clearly, the wires going off the left connect to the peltier, the port pictured in the top right is the plug for cigarette lighters in vehicles, and the wires going off to the right connect to the main circuit board/power supply.

 

5. Speaking of, here are some pics showing the power supply in more detail:

There is a URL on the back that leads to a Chinese website. I don't know if this is a custom power supply or not, but I could probably order a new one and just replace it. I don't know where or how but it does appear to have been burnt on that left side. And yes, those bottom two capacitors are indeed bowing out, and I didn't know that meant they were on their way out. It could be that there was a short somewhere and part of the board fried itself, now that I think about it.

 

Lastly:

-I don't have a way to measure voltage. Any recommendations?

-At one point Bombastinator said a bigger peltier might blow the power supply. I was thinking that a bigger peltier would need more power but not get it, so it would be throttled instead. That's why in the closing statement in my first post I mentioned ripping something off the power supply (most likely a resistor) to give it more power, but the bulk of my electrical engineering expertise comes from learning about car batteries and wiring in vehicles from an automotive class, so I don't have much to say about that.

-And Bombastinator also mentioned "PWM." I have no clue what that means.
 

@Bombastinator and @mariushm

[Bombastinator]

25 minutes ago, Sir Dude said:

Sorry for the late reply, but thank you both so much for the responses. Here's some answers to your questions:

1. The aluminum block on the left side is the hot side.

The fan doesn't directly bolt to the radiator, it bolts to the fridge's plastic casing, but it is otherwise directly behind the radiator.

Also, here's how the cooling units are put together:

From left to right: cooling fan (not pictured here), radiator, peltier, metal block mentioned in first post but wasn't pictured, metal casing of fridge unit. Also I should mention there was thermal paste between these components, but I've cleaned that off and I have a tube on standby for if and when I put it back together.

 

2. The fan is indeed a cheap "Brushless DC 12v fan" from a company called Yaheng. It's directly soldered to the control switch board, but that should be no problem to just cut and splice wires together.

 

3. The fan is not wired to the peltier. It appears to be in the picture but the cords are zip-tied together and it made it look like the same wires.

 

4. Here's a better pic of that lower center board:

You can refer to the pic in the first post for the other side. There's nothing of note on the other side and you can see it pretty clearly so I didn't feel the need to take a pic of the other side, however I will go into more detail and attempt to map everything out upon request. I have no idea if this thing controls voltage. The most I can guess is maybe it limits power going somewhere because of that resistor on the left side underneath the wires but there's nothing else on it. You can see the cords connecting to the fan more clearly, the wires going off the left connect to the peltier, the port pictured in the top right is the plug for cigarette lighters in vehicles, and the wires going off to the right connect to the main circuit board/power supply.

 

5. Speaking of, here are some pics showing the power supply in more detail:

There is a URL on the back that leads to a Chinese website. I don't know if this is a custom power supply or not, but I could probably order a new one and just replace it. I don't know where or how but it does appear to have been burnt on that left side. And yes, those bottom two capacitors are indeed bowing out, and I didn't know that meant they were on their way out. It could be that there was a short somewhere and part of the board fried itself, now that I think about it.

 

Lastly:

-I don't have a way to measure voltage. Any recommendations?

-At one point Bombastinator said a bigger peltier might blow the power supply. I was thinking that a bigger peltier would need more power but not get it, so it would be throttled instead. That's why in the closing statement in my first post I mentioned ripping something off the power supply (most likely a resistor) to give it more power, but the bulk of my electrical engineering expertise comes from learning about car batteries and wiring in vehicles from an automotive class, so I don't have much to say about that.

-And Bombastinator also mentioned "PWM." I have no clue what that means.
 

@Bombastinator and @mariushm

Re: hot side

That’s a better radiator than I was hoping for.  It’s still not great, but improving it would require either replacement or aluminum work.  The fan sits on top of it I assume, leaving some space.  It looks like a 140mm fan would fit giving better hot side cooling.

If even more is wanted, Depending on the amount of space available a top down style cpu cooler might be put in its place.  Some of them are quite cheap.  Measurements would be needed.  It’s a lousy cheaply built cooler but it’s a very wide one.  Might have to spend real change to get something with better TDP.  I’m not sure.

 

re:cold side

is it just that one highly corroded screw touching the peltier?  If so that’s the weak point, but it also looks like it’s the thing that varies temperature.  If it is it is set specifically for some reason. Possibly to prevent possible freezing. Improving the hot side may do nothing then. You might get better cooling by simply replacing or eliminating the screw.  Possibly way too much, even without a bigger fan.  If that is the cold connection it bothers me.

 

re: switch

Useful info.  It does mean that you may want a two wire rather than 3 or 4 wire fan, though it may not matter.  The switch either is the fan controller or there is none.  I’m not sure what the differences in operation between the fan types are.  I know they work differently though. Lack of fan knowledge on my end.

 

re: PSU

@mariushm mentioned possibly degrading capacitors.  Top pic says no, middle pic says yes bottom pic says maybe.  I say NFC.  I bow to @mariushm’s opinion on the matter.

[mariushm]

You can measure voltages with a digital multimeter, even the cheapest one will be suitable for your needs.

Here's an example of a cheap and ok one, it's heavily discounted now so it's only ~6$: Extech MN25 MiniTec Digital MultiMeter

You twist to DC voltage on the setting you think it's higher than the voltage in circuit, and you measure.

For example, the meter above has setting for 20v and 200v and 600v ... I'd put it on 200v and measure. If the voltage is lower than 20v, I can switch to the 20v range to get a higher precision (more decimals).

 

No need to replace the power supply just because those capacitors are going bad. And no, they're probably going bad due to heat in that area of the circuit and just the capacitors being of bad quality from the factory, unable to handle heat. 

You can buy quality capacitors and replace them yourself, if you have a soldering iron around.

Here's an example of good high quality capacitors you could use and will last years: https://www.digikey.com/short/p1ttfh

Any result from the filtered list above will work.

 

Same site has fans you could buy to replace that cheap fan. I don't see the label but I saw you wrote 8x8x2.

The standard fans are 80x80x25mm , not 20mm (2cm), but Digikey has 20mm fans as well if you really mean. I think you mean 25mm (or 1" more or less, 25.4mm)

Here's a list of 80x80 x 20/25/25.2/25.4mm fans, powered by 12v : https://www.digikey.com/short/p1tt24

You can further filter by bearing type, by amount of airflow and so on.

I'd suggest avoiding the sleeve bearing ones (cheapest) and to get something with a bit more airflow, as you can always set that switch to lower rpm (the switch simply puts that resistor on the board in series with the fan, reducing the voltage going to fan, so the fan spins slower)

For example, I'd suggest: https://www.digikey.com/product-detail/en/sanyo-denki-america-inc/9A0812G401/1688-1334-ND/6192050

It has 3 wires, but the third (yellow) is just a rpm sensor, you can cut it or just tape over the end (so it won't touch anything) and leave it disconnected.

If you don't want to spend that much, this will do: https://www.digikey.com/product-detail/en/sunon-fans/MF80251V1-1000U-A99/259-1804-ND/6198742

 

[mariushm]

and just in case you're curious, here's a description of the psu "building blocks"

 

On the bottom, there's most likely a controller chip and a voltage reference and a few other tiny components... basically the voltage reference always outputs a fixed voltage, like let's say 2.5v - the output voltage comes to the controller chip through that black component on the right side of the transformer (optocoupler), controller chip compares voltage with the reference voltage and if it's too low, it increases the number of pulses, if it's too high it lowers number of pulses. That's PWM (pulse width modulation).

In theory you could modify the voltage reference to fool the controller into outputting a higher voltage than 12v or whatever is there, but it's risky, and there's not much room - you could probably safely get it up to 14v or so. There are other limitations in the design of the psu that are harder to go around. For peltier elements. it's not enough of a voltage variation to make it worth the hassle.

 

[Sir Dude]

Oh, this is so helpful!

 

@Bombastinator Re: Cold side
The radiator bolts directly to the metal block, and the metal block bolts directly to the back of the fridge. The screw does not control anything electronically, it's just corroded because of condensation on the back end, and there are 2 screws, not just the one. The only switch on the entire unit is the power switch. It only has 2 positions, and they are labeled "Off" and "Cold", not even "On."

 

Re: Radiator

I don't know it's going to be to replace the radiator. A quick Google search for things like "10cmx10cm aluminum radiator" mostly brought up water cooling radiators or small replacement heat sinks that go on motherboards. I'm gonna have to look more into that.

 

@mariushm Re: Fan

I made sure to measure everything with a small measuring stick I have and the fan is 20mm thick. I could just buy a better quality same sized fan, but that would kinda defeat the purpose of upgrading this thing. I'm gonna have to modify the back cover anyway if I wanted something larger so I'll just do that and see what I can come up with.

 

Re: Capacitors

They are definitely bulging out and I will make sure those get replaced. I just saw that they're both labeled 25v, so I really should get that multimeter before trying anything.

 

Re: Fan Resistor

There is no fan speed controller, so if I'm understanding this correctly if I wanted the fan to spin faster I would have to rip that resistor out (and bridge the connection, of course), right? And then if it's spinning too fast I could put a different resistor in, yeah?

[Bombastinator]

Re: cold side

Ok.  That’s less disconcerting, perhaps som stainless screws then. Maybe a high grade thermal paste.  I’ve had really good luck with the industrial diamond powder filled stuff.  It’s pricey but it’s the next best thing to liquid metal and it lasts orders of magnitude longer.  There isn’t much way to increase efficiency other than that that I can see.

 

re: radiator

merely upsizing the fan may be enough.  That 10cmx10cm thing worries me though.  that would be 100mm.  A 120mm fan shouldn’t fit on a 100mm square.  Something is off.   It’s possible the fan is 92mm.  If that’s the case they do make 100mm fans.  They’re more expensive though.  To replace the heat sink a full on computer cpu top down cooler would be needed and they tend to not be cheap. A noctua nh-l9i would be a classic if incorrectly sized and overpriced example.

 

Re: multimeter

dont buy an analog one.  Get digital.  The analog ones have a tendency to blow out.  The digital ones don’t.

[mariushm]

@Sir Dude

 

I think you have a switch which lets you select between two fan speeds: low and high speed.

My guess is the resistor by the slide switch is always in series with the fan, but when the switch is on the high speed position, the switch creates a short between the leads of the resistor, practically removing it from the circuit:

 

in the low position, the switch creates a connection between pin 1 and 2, and since the 1 is not connected to anything, nothing happens. The resistor is in the circuit, so the fan spins at lower speed, because it gets lower voltage.

In the high position, the switch creates a short between 1 and 2, so now the current goes through the path of least resistance, which is the switch (basically 0 ohm)... so now the resistor is as if it's not there.

 

Anyway, this is a very crude way of limiting the speed of a fan because the value of the resistor will be different depending on the power consumption of the fan. For example, a fan that needs 12v 0.15A and a fan that needs 12v 0.5A would not be reduced at the same percentage of maximum speed if you use the same resistor value.

 

I can show you very simple circuits which would allow you to adjust fan speed with very fine control, and with parts that cost you around 1-2$.

 

Anyway, to the topic of fan, the reason i asked about 20mm vs 25mm was because I assumed you want the whole thing to look nice, to put the back panel back in position and maybe there's no room to install a bigger fan or a thicker fan.

If you can, by all means, go with a 92mm or 120mm fan, or go with 38mm fans.

You can reset the filters in that link I gave you and choose bigger thickness if you want to.

 

As for the heatsink. I doubt you're really gonna make much of a difference by changing the heatsink, but if you really want to, the same website I gave you has heatsinks of all shapes and sizes.

Here's heatsinks that are at least 80mm in one dimension :

 

1.  https://www.digikey.com/short/p1q8dp

 

Examples:

80x80: https://www.digikey.com/product-detail/en/wakefield-vette/SKV808012-AL/345-2039-ND/10108376

90x90: https://www.digikey.com/product-detail/en/wakefield-vette/SKV909010-AL/345-2041-ND/10108378

80x80 copper: https://www.digikey.com/product-detail/en/wakefield-vette/SKV808012-CU/345-2038-ND/10108375

94x94 : https://www.digikey.com/product-detail/en/advanced-thermal-solutions-inc/ATS-57003-C1-R0/ATS1360-ND/1285074

 

90x90 (requires blower fan, to blow through the fins) : https://www.digikey.com/product-detail/en/delta-electronics/DHS-B9090-11A/603-1749-ND/3621528