Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Upgrading 12v peltier based refrigerator

rado28

Newbie level 3
Joined
May 28, 2020
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
34
hello,

firstplan is simple. take some standard 12v refrigerator based on peltier cooling to have the box and upgrade it to lowest target temperature possible, until it makes sense to get small food freezer.

lets start with this example
https://www.amazon.com/K-Box-Electr...coding=UTF8&psc=1&refRID=3VNW3BS7VVDV5E7CGYQ0

based on my basics about peltier i plan to achieve this general target by simple adding more peltiers. if serial or paralel, or serial stacked. thats the first question. question - A

another question - B, how to achieve this target most effectively (least ammount of power needed from my small offgrid solar/battery power source? lets count with 2000w/day + 500w/night for 24 hrs cycle.

to achieve this i plan to order/build some water cooling and coldest place to get rid of heat. either
1 - hot water to standard radiator and fan (unknown size)
2 - closed water circuit with cooling in 200 litres barel of 10C water
3 - opened water circuit from the barel to peltier

could we get to some sizing? what peltiers, how many, what cooling sizes, pumps capacity, fan...? is there a way to have it counted first, or just try-fail approach?
 

wwfeldman

Advanced Member level 2
Joined
Jan 25, 2019
Messages
651
Helped
162
Reputation
324
Reaction score
155
Trophy points
43
Activity points
4,742
start with the small food freezer and let the peltier effect refrigerator go.

the freezer will be more efficient and will freeze stuff that isn't frozen
the peltier device becomes less efficient as the temperature difference rises.

since it is natural for the energy to move from hot things to cold things,
as the cool side gets cooler, the energy moves to the cool side.

you have to cool the hot side
it draws a lot of power, and will likely use your entire solar or battery source.

it is not likley that adding more peltier devices will significantly reduce the
lower temperature.

see https://en.wikipedia.org/wiki/Thermoelectric_cooling

and see the purchaser/user comments
https://www.amazon.com/K-Box-Electr...coding=UTF8&psc=1&refRID=3VNW3BS7VVDV5E7CGYQ0
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
6,722
Helped
1,981
Reputation
3,966
Reaction score
1,799
Trophy points
1,393
Location
USA
Activity points
53,908
You can get higher delta-T with a series Peltier stack
but you need geometrically increasing size (like a 4X
supporting a 1X) to get equal delta-T per stage. And
you need a -lot- of cooling, both raw airflow and heat
sink surface area.

I'd think about a mini-fridge (or freezer, but if you
remove the shroud about the little freezer section
and add insulation, you can get it to be like a mini
freezer). Put some closed cell foam sheet on the
inside walls. Run it off a 12V inverter.
 

rado28

Newbie level 3
Joined
May 28, 2020
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
34
it is not likley that adding more peltier devices will significantly reduce the
lower temperature.
could u explain, pls? how is that possible, that if i add more peltiers, more energy, more heatpumping it will not do much?
 

wwfeldman

Advanced Member level 2
Joined
Jan 25, 2019
Messages
651
Helped
162
Reputation
324
Reaction score
155
Trophy points
43
Activity points
4,742
it goes back to what dick_freebird said
"... but you need geometrically increasing size..."

one device will cool to a certain point
at that point, the cooling ability will be balanced by the tendency
of the energy to flow from the hot side to the cool side

adding a second device will cool things faster, but not to a lower temperature.
the thickness of the peltier device, the heat conductivity (material) of the peltier device,
etc will determine the maximum differential temperature
 

rado28

Newbie level 3
Joined
May 28, 2020
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
34
ahaa.... so i should better go for stronger tec, than more tecs. right?
 

schmitt trigger

Advanced Member level 5
Joined
Apr 17, 2013
Messages
2,627
Helped
837
Reputation
1,678
Reaction score
816
Trophy points
1,393
Activity points
17,631
The laws of diminishing returns quickly reach you when using Peltier devices.

They are significantly less efficient than compressor based refrigeration.

I have seen DC powered fridges, for use in boats and vans. Those would be your best bet for the very limited power available.
 

rado28

Newbie level 3
Joined
May 28, 2020
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
34
i cant find 12vdc compressor for a reasonable price, not even comparable to peltiers setup. could you recmnd?
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
6,722
Helped
1,981
Reputation
3,966
Reaction score
1,799
Trophy points
1,393
Location
USA
Activity points
53,908
Inverters are pretty cheap, one that will run the
refrigerator should cost well less than the
refrigerator. And useful for other things as well
if your 12V power source supports.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
46,788
Helped
13,893
Reputation
28,034
Reaction score
12,524
Trophy points
1,393
Location
Bochum, Germany
Activity points
273,037
Suggest to read this old Melcor application note that gives a good overview of peltier operation. Melcor is now Lairdthermal.com, the classical CP peltier device series is still continued.

According to the AN, you can expect 10 - 15 K delta T for forced air convection. Having this on both sides of the peltier, as in popular refrigerator boxes doesn't leave more than 20 - 30 K maximal ambient to box internal temperature difference for a single stage peltier. Multi stage is only applicable for very low cooling power due to the said low COP (Coefficient of performance) of peltier devices.

If "food freezer" targets to -18°C - give it up.

- - - Updated - - -

Mobile compressor freezers are e.g. offered by Dometic https://www.dometic.com/en-gb/uk/products/food-and-beverage/portable-coolboxes/camping-coolers and many other vendors. Danfoss is making compressors for 12V DC operation.
 

Attachments


Toggle Sidebar

Part and Inventory Search


Welcome to EDABoard.com

Sponsor

Sponsor

Design Fast


×
Top