12V Peltier "Dump-Load"...?

[SteveH]

 Things are progressing with the move to Crete, this is in another thread on here ( Update shortly). We have sold our house & I'm now working on our mobile site hut/home/caravan...

 The power side of things are a 300W Wagtail turnip & a 105W Peeve into a 440 Ah 12V bank...

 I've got a 10A solar controller (Nice & small & more importantly lite) & the waggie is self regulating... but I would rather dump from the battry bank & use the extra power plus it gives me an extra backup should either controllers fail closed circuit... so I have that arranged too....

 Now I was going to dump into a 12v element grafted into the on-board gas water heater... about £50 for 500W one...

 Just noticed 2 x100W peltiers for £8 on Ebay... Now here sprang an idea... I'm moving to a place that is hot so why not use these as a dump load... If I'm clever I can use both sides  & drop the cool air into the fridge & save some gas, or a low volume aircon & water cool the other side of the chips. this could be used to preheat water going into the gas heater...

 i know the efficacy is quite low on these... you get about 3 times the volume of heat raised than lowered but it might work OK...

 Any thoughts ladies & gents...? ...Other than " He's as daft as an ebony frying pan"!

[KenB]

Steve,

You could find a peltier based cool box, which have a 12V input and consumes about 48W.

Solar powered beer cooler? - Sounds great for Crete 


Ken

[SteveH]

 Thanks Ken... But Carol saw you'r post & the mention of cold beer has killed that idea...

 So I have started the project already... let the experiment begin...

 I'll start with a split blown hot & cold air system & if all goes well I can convert the hot side to water at a latter date.  I have some (x10) 50mm square X 200mm long extruded Aluminium steralizing containers. I also have, some old CPU heat sinks & small 12v computer vans...

 The construction will be two square ally tubes with heat sinks thermally pasted & fixed to one internal side. These will be clamped either side of 3 of these:

91.2W TEC Thermoelectric Heat Sink Cooler Peltier 12V


Specifications

- Product Number: DC-CL011
- Product Name: 91.2W TEC Thermoelectric Cooler Peltier 12V
- Type Number: TEC1-12706T125
- Couples: 127
- Umax (V:) 15.2
- I max(A): 6
- Dimensions(mm) 40 × 40 ×3.9 mm
- Item Net Weight 80g/2.9oz


http://www.hebeiltd.com.cn/peltier.datasheet/TEC1-12706.pdf

 (Have ordered 6 of... £22 delivered so still cheaper than the 12V imersion heater... )

 Two Fans, One fan blowing into the hot side & the other the cool side... I can also include thermostsic control of the fans, either with a small simple thermister in the air flow or a more conventional thermostat...

 I did notice that these chips can exceed 100°C (138°C) so I have high hopes for the water heating side when/if I get there....

 More to follow...

 

[SteveH]

 This project is moving a bit slowly... There are lots of more important jobs to do like trying to get the PV panel mounted & wired up on the caravan...

 But a little picture of the "Hot side" heat sink... I'm going to fabricate a Cool sink from lots of thin aluminium Li-tho plates I fished out of the skip behind the school of art... my thinking is, these will need the maximum surface area to cool the incoming air...?

 

 I have strapped a couple of PC processor heatsinks to one of the pelts & connected it across a 12v source... heats up one side & cools down the other side very quick...  I haven't checked the temperature difference or power consumed yet...

 nice to have a "Tinker"...

[nickzzzzzzzzz]

Amazing project. I've been thinking along these lines too and it is great to see it actually set up. How has it worked for you? I'd like to make one to use in a hut i live in and to have a dumpload that cools a box and heats the space sounds too good to be true! Please tell me it works!

[Ivan]

For good efficiency, these things need to be CLAMPED between the heatsinks. The manufacturer will specify the force required. You also need to use springs in the clamping bolt arrangement, so that as it expands/contracts, the clamping force remains more or less constant.

[knighty]

Ivan beat me too it, I was just about to say the same thing they need to be TIGHT!

when I used to use them in my pc... I'd have them between 2 lumps of copper (iirc 6mm thick was optimum).... I'd clamp the whole lot in a vice as tight as I could, and then put the bolts through as tight as I could after... never did any damage to any of them and I used a few :-)



as a side note... if you're not going to use the heat/cooling for anything.... why not stagger them ?

have one hot side up, then the next cold side up, then the next hot side up ?

that way they even out a bit and help keep each side hot/cool ?

iirc, for every watt of power used, 1 watt of heat is moved from the cold side to the hot side.... (but also produces 1watt of heat)

so 1 watt in =
cools cold side by 1 watt
heats hot side by 2 watts


most of them have a max temp difference between the plates of 60'C
and you need to make sure the hot sides don't overheat of they'll die :-(
(they will get pretty hot without damage first, 120'C+ is normal iirc.... but they;re probably all different :-) )

[Baz]

How many cool boxes using these things do you know more than a few years old. These things have a low life expectancy so make sure you have a conventional load for your turnip and failsafe switchover. Also put an over temp sensor on as when the water gets to boiling therfe may not be enough heat tranfer to keep them below meltdown. I think one of the failure modes is corrosion/crystalisation of the connection joints owing to the continuous heat rather than the peltier material decomposing.

[SteveH]

 Apologies for my tardy reply...

  I'm afraid this project has got no further in the 3 years from my last posting on August 04, 2008.

  The original plan was to install the cold-side into the small gas fridge in our living caravan to assist with cooling & save some gas... It turned out there was no way to thermostaticly control the gas flame, Just 3 fixed flame settings. Then arranging for cooling the hot-side would have demanded a degree of ducting... I just ran out of time before we left the UK to finish & install the dump load before traveling to Crete to build our new home. Other issues have fully occupied all of my time since then.

 For reference the system was 1 x 110W 12V PV, 1 x 300W (500W peak) Wind turbine, 400Ah 12v batteries.

 Thinking back I was pondering a couple of issues before the project got shelved (Still have the parts for a future project).

 Insulation:- HT/Armaflex tape seemed the ideal material to use as insulation between hot & cold sides, Suitable heat rating, easy to cut & install, also able to accomadate clamping movement & thermal expansion. (Available from Navitron in 3m role)

 Clamping fixture:- The clamping through fixing provide a short distance thermal bridge between hot & cold sides. Mica washers & or ceramic ferrule's would help to break the conduction path. There would still be conduction through the fixing itself, but very much reduced.

 Ohhh & lithograph sheets are not alley...

 

[knighty]

oops, didn't realise this thread was so old

[nickzzzzzzzzz]

Amazing knowledge about the peltier modules. Thanks for the advice. I anticipate using them just in the summer with an insulated box in an attempt to switch off the fridge. Will start looking for decent copper plates and heat sinks to ensure they stay at a reasonable temp. Cheers