Peltier Fridge

Discussion in 'General Electronics Chat' started by R!f@@, Feb 27, 2015.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    I am too freakin' tired of loosing my glues, silver circuit markers and solder pastes time after time.
    I throw away 90% of them each time I buy. Cause it;s just too hot here. :(

    So I got me a Peltier fridge. Small one with blown compressor o_O ( Peltier).
    Me got a spare one, 48W one. Clamp it up, replaced the fan and goes down to 15 °C. Not lower. Kept for around 10Hrs
    I like at least 10 °C.
    I did buy around 10 pcs of 84W peltier. They're on the way.
    Q....⇒ Is it possible to bring down the temp fast (lower than 10 °C using multiple Peltier's or not ???

    I think I need to make a controller to protect the Peltier in case of fan failure and temp set. Right ?

    What would be the best stuff to insulate the walls of the fridge that I am going to make.
    The one I got is a bit small. So I am going to make one with plastic and wood or something.
    Me got plenty of heat sinks around that can accommodate 4 peltier.

    Q ⇒ Is it advisable to use a fan to circulate the cold air in the fridge from the sink ?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    My wine fridge would easily do the job. It uses just one peltier drawing, I think, ~5A. It has two fans, a small one inside and a larger one on the hot side. You might look around for one of these. It's common for the power supply to fail (main had bad caps and a blown transistor) and they are often free to take away if you can find it.
     
  3. PeterCoxSmith

    Member

    Feb 23, 2015
    148
    38
    I sent a few years of my precious life working with Peliter coolers for biotech products. If you really want to build your own you have sort of hit on the main points already. You want the best insulation you can get on the cool box. The Peltiers take a lot of current to produce the heat pump effect and you have to remove the heat (current produces heat) otherwise your Peltier is just a heater and not a cooler at all. So good heat-sink, plenty of fans. If you want a temporary speed up you can add a copper pipe to your heat-sink and pass a bit of water through it.

    Putting a fan in the cool box dissipates a bit of heat. It may help but get an efficient one.
     
    R!f@@ and planeguy67 like this.
  4. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    RAIF it. Redundant Array of Inexpensive Fans. if one fan fails at least a few others keep going. and then maybe add a surface mnt temp switch so that if it gets to hot the power is cut. as for insulating, a box of 3" styrofoam for core. a cold fan for circ will help keep inside all mixed up at same temp thus avoiding local cold spots.
     
    Last edited: Feb 27, 2015
    R!f@@ likes this.
  5. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    Does your fridge not already have a controller? My wine cooler watches the temp on the cold side of the peltier, I think, and shuts off power if it gets hot for any reason (such as fan failure).
     
  6. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Peltier devices wont keep up mutch in Ambient temeratures above 35Deg C. It gets hot here in Australia & these things are next to usless. A compressor driven fridge is far better. I keep my glues & silver epoxy in a fridge for long life.
     
    PeterCoxSmith likes this.
  7. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    I got this one from a throw away. Peltier blown, fan failing and no PSU.
    Currently I had a 48W one so I replaced with it and it goes to 15°C. So I guess it's do able here debe.
    I am getting 84W ones soon.
    Real question is, is it possible to go down to 10°C. If no one had checked it I guess I have to do it to see it. Eh!.

    I will be making a controller to cut off the peltier after monitoring the cold and hot side temps for temperature control and fan failure protection and I got a 48V PSU which can handle more than 7 amps.
    I'm thinking of wiring 4 of them in series.
    Never tried in series with peltiers, is it a good idea to series them. ?
     
  8. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    Not this one.
    It's just a box with a Peltier, small heatsink and an unreliable fan. Nothing more. No wonder it failed
     
  9. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    This is just my personal experience with Peltier coolers. This unit was purchased in 1992 & draws about 4.5A on 12v DC. Here in Australia it was ok to use in the Winter months, & would go down to O Deg. But when ambient temps reached about 30Deg C, the internal temp rose 1 deg C for every deg C rise in ambient temp. So any thing above 30 Deg C ambient a thermostat is never going to cut out for fridge temp. So in an ambient of 40 deg C the internal temp is going to be around 10 Deg C. Definitly not fridge temp. This thing lives in the shed gathering dust as it was replaced with a Waeco 12V compressor fridge. The compressor fridge draws 5Amps on 12v & cycles on/off even in 50 deg C ambient mutch more efficient. PELTIER FRIDGE.JPG PELTIER FRIDGE.2.JPG
     
    Last edited: Feb 28, 2015
  10. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    debe we are in the same boat.
    U say yours can go down to 10°C. Since your one is of higher power I think my new Pelt's can bring down the temp..don't you think so ?
    I think I will try this. Will keep posting on the progress.

    by the way , how did you figure out the BTU?
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    A peltier with its heat exchanger can maintain a certain ∆T at a certain current draw and power input, even if the cold side is perfectly insulated. So I'm not certain that adding another one in parallel will increase the ∆T in your cooler. You will often see pelters used in series, in stages, when a larger ∆T is required.

    However, if the problem is heat leaking into the chamber, then adding more capacity in parallel will help mitigate that.
     
  12. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    Worth the try, right ?
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    That's your call, but I'd say so. A big advantage of adding parallel capacity will be the increased heat transfer surface. Keeping the hot side cooler will reduce the cold side temperature.
     
    R!f@@ likes this.
  14. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    The Btu was on the orig spec sheet that came with the fridge.
     
    R!f@@ likes this.
  15. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    Does adding more peltier means staking them on each other or side by side.
    I was thinking side by side u know. Stacking them looks kinda weird to me.
     
  16. camerart

    Active Member

    Feb 25, 2013
    517
    30
    Hi,

    In hot temperatures, if you put the first box inside a second insulated box also with a peltier and fan, would this work? Perhaps the inner fan needs to be ducted to the outside?

    Camerart.
     
  17. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    I think that would be waste of power and a peltier.
     
  18. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    That's the difference of series versus parallel that I was talking about. I wouldn't plan on putting them in series except as a last resort. For one thing, a peltier adds additional heat up to 10x the amount of heat that it is moving from its cold side to its hot side, so the second peltier now has 10 times as much heat to move as the first one removes from the chamber. For this reason, when they are stacked, the second peltier is often larger than the first. It has to move all the heat created by the first peltier, plus the small amount removed from the chamber.
     
  19. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    By series I was talking about connecting the PSU. Like 12V 4 pc peltier in series to a 48V PSU.
    So stalking same size peltiers is not an option.
    OK then I will try side by side with a bigger sink.
     
  20. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    As far as I know you can place peltiers in serial (electrically), and that would help with the big current need. In fact with even a 12V supply and two 12V pelters in serial, you'll get a lower max current but this will help the pelters operate more efficiently They are quite a lot more efficient at less-than-max current. Having two peltiers doubles the surface area for heat flow and this tends to be the limiting factor in my opinion. What this arrangement may NOT help is the ∆T issue, if that is the limiting problem. The maximum ∆T across a peltier partly depends on the current it is drawing.
     
    debe and R!f@@ like this.
Loading...