Peltier devices

[Wayne Chirnside]

On Fri, 25 Dec 2015 21:18:30 +1100, Chris Jones wrote:

On 25/12/2015 12:11, Wayne Chirnside wrote:
[...]
On - off works just fine for this application.

I wouldn't dispute that it works well, but you might find that with
on-off control, the peltier devices don't last as long as with
continuous current that varies only slowly (especially for large peltier
devices and high currents). When the current is switched on and off,
there is slight expansion and contraction of the ceramic plates, which
could fatigue the semiconductor pillars within the peltier device
eventually. At least some peltier device manufacturers recommend against
on-off control. If you never experience failures than don't worry about
it.

Got 3 yrs on the one to my left where I keep chilled gatorade on - off
$2.30 peltier.

If you care about the input power requirement at less than full output
then there can also be a very slight efficiency advantage with variable
current rather than on-off, provided a very efficient switched-mode
controller is used (with filter inductors and capacitors so that pure DC
comes out). The efficiency advantage is because there are resistive
losses inside the peltier device, which are proportional to I squared
times R, and that works out to be more losses on average for e.g. 20
Amps at 50% duty cycle than it is for 10 Amps at 100% duty cycle. It
won't make any difference to the maximum cooling capability since even
with on-off control that will produce 100% duty cycle, which is the same
as you would get with variable current control.

I use an analog supply and a switching supply on two differing
applications.

The switcher is more efficient however any ripply no matter how small
will lead to dramatic inefficiency to the point as to make the whole deal
less than worthwhile.

I use a capacitance multiplier after the switcher and give away about 70
millivolts in order to achieve the greatest possible efficiency.

 

[~misfit~]

Once upon a time on usenet Wayne Chirnside wrote:

On Thu, 24 Dec 2015 18:39:35 +1300, ~misfit~ wrote:

Once upon a time on usenet Wayne Chirnside wrote:
On Wed, 23 Dec 2015 12:44:55 +1100, F Murtz wrote:

13:25 +1300, ~misfit~ wrote:

Once upon a time on usenet Wayne Chirnside wrote:
On Sat, 19 Dec 2015 12:4

Big Clive reviews cheap Chinese thermostat.

https://www.youtube.com/watch?v=yVD0zkZTe00

Took me all of two minutes to find after not finding it on my local
drive.

I saw that in the search results but ignored it as you specifically
said the thermostat came from Aliexpress.

The Chinese make these things in volume, he got his ebay.uk

I got mine, more cheaply, at aliexpress.

I referred to Big Clive because his was the explanation as to how to
program the device.

To date I've never had a problem with a vendor on that site though I
do have to wait a bit for the item to cross the Pacific in a
container.

I also downloaded the programming instructions using the Linux cclive
youtube downloader for future reference should I forget the first
button cycles through the various parameters to be set.

hystersis being of some importance with a peltier.

I also downloaded the youtube video using some firefox add-on, the name of
which I can't recall or find now that the latest version of FF doesn't give
me a proper list of installed add-ons. Haven't watched it yet though.

The Aliexpress page that I ordered my thermostats from had some basic
instructions that I cut'n'pasted into a text document (at end of messge).
That way I don't need to watch a video to work out how to programme it. It's
written in 'Chinglish' but is decipherable;
+++++++++++++++++++++++++++++
Connect the power supply and the load, you can supply to the controller,Is
displayed as a measured temperature,Press the SET button, the display
flashes the temperature,Press + - to set the desired temperature,After
setting press SET to confirm return,The controller automatically performs
the relay by setting off!

Lights, LED status descriptions:Indicator: Off The relay is switched off,
Always indicate the relay is closed.LED: Shows LL is the sensor open,
showing HH is out of range, the thermostat will be forced to close the
relay, the display --- as high temperature protection.

Parameter Function:Long press SET 5 seconds to enter the main menu settings,
press the + - toggle P0 ... P8 long press SET or 10 seconds of no key
activity confirmed their return to the controller

Code Code Description Setting range Factory
setting

P0 Cooling /Heating C/H
C

P1 Hysteresis setting 0.5-15
2

P2 Highest setting upper limit 110
110

P3 Lowest setting upper
-50

P4 Temperature correction -7+7
0

P5 Delay start time 0-10 Minutes
0

P6 High temperature alarm 0-110 OFF

Off state, long press + - boot to restore the factory settings
+++++++++++++++++++++++++++++
Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[BuckyBalls]

On 17/12/2015 1:45 AM, F Murtz wrote:

Anyone know about peltier devices? Can you drive them at half voltage?
I wish to make a container that is limited to between 18 and 20
centigrade and apparently they do not like to be cycled much for temp
control,I would rather have it on constantly but at less than full
capabilities.

I don't think they work very well at all at less than 100%.
Why don't you just buy one (they won't break the bank) and find out for
yourself?

 

[Computer Nerd Kev]

BuckyBalls <"The Pres"@yahoo.com> wrote:

On 17/12/2015 1:45 AM, F Murtz wrote:
Anyone know about peltier devices? Can you drive them at half voltage?
I wish to make a container that is limited to between 18 and 20
centigrade and apparently they do not like to be cycled much for temp
control,I would rather have it on constantly but at less than full
capabilities.

I don't think they work very well at all at less than 100%.

Well they naturally don't work as well, but for temperature regulation
that's the idea. They are often implemented to run at varying voltages
and achieve their task well.

Why don't you just buy one (they won't break the bank) and find out for
yourself?

Some issues can be unclear when simply testing as you suggest, such as
life expectancy. In any case, he decided what he was going to do some
time ago now.

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