Peltier question.

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Quick question about peltiers.

I have a small polystyrene box (250mm x 200 x 250 tall) that I want to keep  
at aroud 8 deg C to keep earthworms alive in 'tupperware' and a bit of  
water, for up to three weeks for my axolotl. I know the worms will survive  
at that temp for that time and even empty out their guts which is an  
advantage.

I'm going to mount a 150 x 80 x 25mm fins aluminium heatsink in the lid, cut  
out a square of the lid big enough to fit a 40 x 40 peltier
https://www.aliexpress.com/item/Free-Shipping-1PCS-TEC1-12706-12V-6A-TEC-Thermoelectric-Cooler-Peltier-TEC1-12706-If-you-want/32517842372.html?
and the base of a CPU heatpipe heatsink (an all copper Thermaltake Mini  
Typhoon) with 90mm fan sucking up rather than blowing down. I have a few 40  
x 40 x 5mm nickel plated copper spacers (scavenged from the bottom of AMD  
Athlon aluminium CPU heatsinks) which I can use to shim up to the thickness  
of the 20mm thick poly.

I have a 12v 5A power supply that came with an early LCD computer monitor  
and will control temperatues with one of these;
https://www.aliexpress.com/item/1PCS-W1209-DC-12V-heat-cool-temp-thermostat-temperature-control-switch-temperature-controller-thermometer-thermo-controller/32519582116.html?

I ordered three of the peltiers. My question is should I just use one  
peltier or would it be more efficient to stack two or more? I intend to use  
an adjustable LED driver to control the current to the pelteir/s. (I have  
more than one LED driver available.) I'd rather get input  before I assemble  
it than have to modify it afterwards. My concerns are ability to maintain  
the required temperature in ~25 degree ambient and power consumption.

As the box will only be opened once a day I doubt I'll need to drive the  
peltier/s to the advertised amount. I have alternate, more powerful PSUs  
available of needed and thermal interface goop. Input appreciated, I've  
never used peltiers before.

Happy holidays etc etc.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On 18/12/2016 8:49 AM, ~misfit~ wrote:
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With my limited experimentation using the same device and similar manner  
to keep a polystyrene box cold I found that a single 12706 wasn't very  
efficient at cooling and using more of them would have raised current  
consumption to the point where it wasn't viable.

I also used a CPU cooler and fan drawing through the fins rather than  
blowing and I found that to be more efficient. I also attached a smaller  
heatsink and fan on the cold side with the fan running at low speed  
(small 12V fan running at 5V) just to move the air around as I found  
that the peltier would get ice cold and freeze which reduced overall  
thermal transfer efficiency.

It may be better to use a larger cold plate on the inside of the box but  
my experimentation didn't get that far.

You can probably get it to cool down to 8C (from memory I achieved 11C)  
over a longer period of time, but I abandoned the project. Polystyrene  
boxes are usually available for free from some chemists so you may need  
to get a few and experiment.

You could even extend the project with an arduino to monitor the  
temperature and regulate the Peltier/fans automatically (MOSFET PWM  
controlled by the arduino to drive the Peltier/fans for example)





Re: Peltier question.
Once upon a time on usenet Clocky wrote:
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Thanks for the info Clocky, that helps quite a lot, I had zero info before.  
;-)

I thought of a small interior fan but thought that, with the lavck of  
efficiency of peltiers in general having a fan producing even a small amount  
of heat inside the box wouldn't be a good idea. My 'cold plate' is quite  
large as I said above, 15cm x 8cm with 2.5cm fins 1cm apart, a bit big to  
'fan'. I was planning to mount it on the side so that the air would cool and  
flow down through the fins (a reverse thermal siphon thingy) but it's going  
to be so much easier to mount everything in the lid.

I hadn't thought about chemists for the box. I've got them from the fish  
counter at the supermarket before but they're all too large for this  
project. Thanks, I'll ask my chemist when I go next (I have to go every 10  
days for my morphine ...) but hopefully I'll do it once and do it right.

Even if I don't get it down to my desired 8C anything below ambient will be  
an improvement over my current method of storing live 'nightcrawlers'.  
(Polybox with no cooling, swapping the water for chilled water when I open  
it.) I tried the fridge for a while but it's too cold. I'll try it with a  
single 12706.

Thanks again,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On Mon, 19 Dec 2016 14:21:21 +1300, ~misfit~ wrote:

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TEC-Thermoelectric-Cooler-Peltier-TEC1-12706-If-you-want/32517842372.html?
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thermostat-temperature-control-switch-temperature-controller-thermometer-
thermo-controller/32519582116.html?
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I think you'd like the performance of the 12715 for what it is worth.
Very much better to the 12706/s I have on hand.
A simple a test as between two fingers and hooked up to a 4.2 volt 18650  
tells the tale the better of the two types.

Re: Peltier question.
Once upon a time on usenet Wayne Chirnside wrote:
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Thanks, I've ordered a couple. Probably be February before they arrive  
though.

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I never test with an 18650 as the cells I have around can dump a shitload of  
amps into something fast. I tested my 12706 'collection' (I've bought a few  
but never used one yet) with an Eneloop AA cell and that's plenty of juice  
to find which is working and to find the hot and cold sides (I know it  
changes with polarity).

Maybe the 12715 simply has less internal resistance and so seems far better  
with your 18650 test? As the sites I use to buy are hard to decipher I  
haven't found anything about comparisons between the two types ...
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
Once upon a time on usenet ~misfit~ wrote:
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Ok so youtube tells me that; TEC1-12706 means:

TEC = Thermoelectric Cooler
1 = One layer
127 = 127 thermocouples
06 = 6 amps

So according to that the 12715 is the 15 amp version.

I would have thought the '12' part signified voltage. Perhaps more research  
required ...
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On 25/12/2016 9:26 AM, ~misfit~ wrote:
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I ran the 12706 at 14.5V. (The power supply limiting current to 5A max)

The cold side generally has the writing on it when the polarity is  
matched to the wiring (red-positive).





Re: Peltier question.
Once upon a time on usenet Clocky wrote:
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Cheers for that mate, all info gratefully received. I may wait for the  
12715s to arrive as (I assume) I can always use less current than they're  
capable of handling but crank then up if I need to.

If it starts using too much power there's a small fridge in the shed that  
I'm storing for a friend. I guess I can always reversably mod that to be run  
from a digital controller and at a higher temp than designed for. The  
problem is finding somewhere to put it where I can access it regularly  
though.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On 26/12/2016 10:18, ~misfit~ wrote:
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Also beware that some fridge motors can't re-start when there is still  
pressure at the outlet of the compressor, so the motor stalls and  
overheats if it is switched off for a short period and then back on.  
i.e. if you switch off the motor, you have to leave it off for a  
guaranteed minimum time before turning it on again.

To deal with short power outages, it would be good to keep the motor off  
for a while after power is applied to the controller also.


Re: Peltier question.
Once upon a time on usenet Chris Jones wrote:
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Thanks. The controllers I use have adjustable hysteresis and if I go this  
route I'd set it quite high. As an ex automotive engineer and general  
dabbler I'm aware that too many short duration stop / start cycles are bad  
for almost everything. ;-)

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To achieve this I could add an extra layer of control with a delay timer but  
considering I've only been getting a couple outages a year (if that) I doubt  
that it's needed.

Thanks for the replies.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On 18/12/2016 11:49, ~misfit~ wrote:
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Peltiers are a bit of a pain as they don't like water but water  
condenses onto cold things. The "sealed" ones aren't really.

You might do better to put an insulated box (I suggest a $7 wide-mouth  
ALDI thermos flask) in the fridge (which is at maybe +4 deg C) and then  
heat the inside of the insulated box by 4 degrees with a resistor or  
length of resistance wire wound onto a convenient heat spreader. If the  
box is well insulated, a heated box in an existing fridge might even be  
more energy-efficient, as peltiers are not very efficient compared to a  
normal fridge and they are thermally conductive so they thermally  
short-circuit your insulated box to some extent. You could use a  
standard off-the-shelf PID temperature controller and thermocouple to  
control the heater. Please tune it without worms. (Reminds me of  
scratch-monkeys.)

I wish someone made a vacuum flask with a peltier built into the vacuum  
space beteween the walls. That would keep the water out of the peltier.  
I appreciate there would be two difficulties with this: one they bake  
the vacuum flasks very hot during evacuation and the peltier would not  
withstand that, and two, thermal expansion would probably stress the  
peltier if attached firmly to both inner and outer walls. I think the  
second problem could be solved by using a copper water block soldered to  
the hot side of the peltier with thin copper water pipes connecting the  
water block to the outside world, and the first problem might be solved  
by baking the stainless parts in a vacuum before installing the peltier,  
not after.




Re: Peltier question.
Once upon a time on usenet Chris Jones wrote:
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Thanks for the input. :)
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On Sun, 25 Dec 2016 13:45:15 +1300, ~misfit~ wrote:

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TEC-Thermoelectric-Cooler-Peltier-TEC1-12706-If-you-want/32517842372.html?
Quoted text here. Click to load it
thermostat-temperature-control-switch-temperature-controller-thermometer-
thermo-controller/32519582116.html?
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One additional thing, the power supply must not have any ripple as that  
acts as a reversing voltage and impairs efficiency.
Beefy linear supplies beat switchers in this case unless the switching  
supplies output is well filtered ( clamped below the ripple)

Re: Peltier question.
Once upon a time on usenet Wayne Chirnside wrote:
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Thanks Wayne. I don't have any beefy linear 12v supplies, only SMPS. Would  
it pay to put a big cap or two and maybe an inductor on the output? (I'm a  
relative newbie to electronics.) I have an Hitachi 50v / 10,000uF electro  
that I've been looking for a use for. ;-)
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On Mon, 26 Dec 2016 16:51:36 +1300, ~misfit~ wrote:

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TEC1-12706-12V-6A-
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want/32517842372.html?
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thermometer-
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Try a capacitance multiplier.
Regulate the output of the switcher throwing away the last 150 millivolts
or so to loss, barring that yes large capacitance will help however what  
that does to the switching power supply is another matter.

I use switchers myself with a linear regulator afterwards taking the heat  
loss at the power supply rather than the peltier.

Re: Peltier question.
On 27/12/2016 01:04, Wayne Chirnside wrote:
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I think a decent switcher would be good enough - as its ripple would be  
below a couple of percent. An unregulated linear supply would not be  
great, and PWMing the peltier to control the temperature would be awful  
(and against the advice in peltier app notes), though I have seen people  
do it (in spite of my advice) and it worked well enough and long enough  
for them.



Re: Peltier question.
On Thu, 29 Dec 2016 22:53:50 +1100, Chris Jones wrote:

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Can be good enough however for my design I can well afford 4 watts heat  
at the linear regulator to gain the desired sub freezing temperature at  
the box without multi-staging peltiers.

Temperature control here is a $2 aliexpress temperature control module  
with hysteresis and led display.  

Re: Peltier question.
Once upon a time on usenet Wayne Chirnside wrote:
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I mentioned that I'm not a skilled electronics engineer yes? ;-) I dare say  
that, with some research and parts purchases I could add a another layer of  
regulation but it's not something I could do easilly.

Unless adding one of these  
https://www.aliexpress.com/item/1pcs-LM2596-DC-DC-buck-adjustable-step-down-Power-Supply-Converter-module/32757565687.html
and more smoothing capacitance to a laptop power supply would do the job? (I  
bought half a dozen of them a while back as I have a few 16v - 21v laptop  
PSUs spare and often need a high amp 12v supply.)

Cheers,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
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To improve the regulation by using a linear regulator after the switch
mode one, you'd want to use one of your 16V laptop PSUs and either a
7812 12V 1A linear voltage regulator with additional power transistors
to handle the current (like this:
http://www.circuitstoday.com/12v-15a-voltage-regulator
but without the transformer, bridge rectifier, or 47000uF filter cap),
or a few high current linear regulators in parallel (eg. MC78T12 12V
3A), preferably use one more than the minimum required.

The Aliexpress item is a switch mode regulator, not what you want.
You might not need a second regulator unless your switch mode supply
is particularly noisy anyway, I'm not sure of the figures for how
ripple affects efficiency.

Strapping huge filter capacitors to the output of the switch mode
power supply might upset its operation depending on the design.
If the inrush current to the caps is high enough when the thing
is turned on, it might just go straight into an overload shutdown
mode.

--  
__          __
#_ < |\| |< _#

Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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Thanks for that. It's a bit beyond my abilities to make up something like  
that (also I've got shitloads of  higher-ptiority 'projects' waiting for my  
attention. LOL, the only part of that circuit that I have on hand is a part  
that I wouldn't need - the 15A bridge rectifier.

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I thought that it might be, going by a quoted switching frequency of 65kHz.  
I mentioned I'm not very knowledgable about this stuff yeah? <g>

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Nor am I. I don't have an o'scope - and wouldn't know how to use it if I did  
(but could probably pick it up, I'm quite good at the old RFM).

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Yep, I can see how that might occur. I was intending on supplying the  
peltier with a grunty heatsinked cc / cv  adjustable LED driver so that  
hopefully I could find a power setting for it that mesant it wouldn't  
switvch in and out too often - or not often enough. However those LED  
drivers are switch-mode doodads right? Maybe if I add a bigish capacitor  
after it might help.

Heh! The damn axolotl's more than 15 years old - I was told they only lived  
for 12 years maximum.

Cheers,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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