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Re: Peltier question.
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Actually the LED driver (which will probably be switch-mode) is
likely to have a noisy output because it's only meant for driving
LEDs, which don't care about such issues. It might be tricky to
work out how well your additional filter caps are helping this
without an oscilloscope. I guess it will be a case of just
hoping it works well enough to do the job.

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Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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Yeah, so maybe not my brightest idea.

It might be better to see if I have a ~12v transformer of sufficient size in  
my junk collection and rectifying and 'filtering' the output (making an  
unregulated supply). But maybe there will be too much 50Hz ripple on that?  
I don't know enough (or likely have enough bits on hand) to make a regulated  
supply.

It's starting to look like running the little fridge at ~10 C is the best  
option.

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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It might work, but without a 'scope you'll just need to try it
to find out.

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The regulator in a linear (transformer) supply is there in one
function to avoid the ripple that would be on the output without
it. So an unregulated supply would have too much ripple. A 12VAC
transformer with output through a rectifier (dropping 1.4V) is
actually going to have an output voltage of around 15V, by the
way. Vout-dc = (12Vac * sqrt2) - 1.4Vrectifier

If the current boosting transistors on the standard voltage
regulator is too hard for you to do, you could go old-fashioned
and use Zener diodes in parallel with the peltier. From a 12VAC
transformer they would use about 21W power. Five 5W 3V3 Zeners
might do the job. A current limiting resistor would also be
required from the output of the rectifier/caps.

Sorry I'm out of time to draw you pretty diagrams etc. Maybe
tomorrow.

From an old (1976) electronics catalogue I happened to look
at yesterday, in a description of power supplies for Peltier
coolers:

"The only limitation on the supply is that ripple be
maintained at a point lower than 10-15%."

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Re: Peltier question.
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Make that five 5V 12V Zeners.

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Re: Peltier question.
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Actually two 5W 12V Zeners would be OK if you accept that if you
disconnect the Peltier while the power supply's on, they will
melt.
 ______      __________                   ___________ Resistor
|      |----| Bridge   |+____ ___________| 25W 0.47R |____ ____
|12VAC |    |Rectifier |     | Filter    |___________| ___|___ |
|______|----|__________|_  ----- Cap/s            12V |  / \   |
                         | ^^^^^                Zeners  /___\  |  
                         |___|______________________ _____|    |
                                                  - |__________| +
                                                   |            |
                                                   |  Peltier   |
                                                   |____________|

Assumes Peltier consumes 6A @ 12V (plus or minus about 0.5A).

The 25W resistor may be made up from 10W resistors in parallel.
eg. 3x 1.5R 10W

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Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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Thanks Kev I've saved all of this for future reference.

Much appreciated.
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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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By the way, the thermostat temperature switch would go between the
filter cap/s and the 0.47R resistor on the positive line.

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Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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Noted, cheers.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: Peltier question.
On 03/01/2017 08:01, Computer Nerd Kev wrote:
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Really you guys, Peltiers are not that bothered by a little bit of  
ripple or noise. If you had 5% ripple, maybe you could expect up to 5%  
worse performance (but probably better than that). Any SMPS that could  
run a computer etc. will be more than good enough for a peltier.

The idea about not applying a lot of ripple to the Peltiers comes from  
warning against the practice of some people to use a standard PID  
temperature controller that applies pulse width modulation to adjust the  
amount of cooling. That is, a square wave of e.g. 0V low, 12V high,  
applied to a Peltier. That is HUGE ripple, 12V peak-peak in this case,  
and it still works almost tolerably well (though it is not recommended  
and probably causes excessive stress due to thermal expansion and  
contraction in the peltier). I would not use on/off PWM to control the  
peltier, but any SMPS that has a filtered DC output with a few tens or  
hundreds of millivolts of ripple would be perfectly fine to run the  
peltier continuously. The difficult part would be how to reduce the  
cooling when full power is not required, as most SMPS do not have a wide  
adjustment range. Some LED drivers are adjustable, but some of those use  
on/off PWM, you need to look for ones with adjustable DC output voltage  
or current. The safe ones won't be cheap and vice versa.

I still like my idea of putting a tiny heating element inside a  
wide-mouth thermos flask, and putting that in any existing ordinary  
fridge. You could use a standard off the shelf PID temperature  
controller and thermocouple to regulate the temperature inside the  
thermos to any temperature above that of the fridge in which the thermos  
is located. The heater element won't be bothered by PWM, ripple etc. and  
will be cheap. Also it avoids the need for a huge heatsink that would be  
needed on the hot side of any peltier cooler.



Re: Peltier question.

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most adjustable buck converters will adjust down to 0V if you inject a  
little current into the voltage feedback divider. on a non-isolating  
buck converter this can be got from the input side.


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Re: Peltier question.
On 04/01/2017 14:04, Jasen Betts wrote:
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Yes that would work nicely.


Re: Peltier question.
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The LED driver may well have a far more noisy output than a PC power
supply with outputs designed to be suitable for powering logic
circuitry (and therefore would be OK for this application).

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He wants to use a thermostat type controller to maintain the desired
temperature. Not the ideal method of control but perhaps not as bad
for the Peltier as PWM.

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Re: Peltier question.
On 04/01/2017 21:32, Computer Nerd Kev wrote:
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I thought that a thermostat controller does basically do very slow PWM,  
if it turns the current on and off with no ability to produce  
intermediate current levels. I think this would not be as good as an  
adjustable buck converter, and choosing this type of thermostat would  
certainly make more difference to the peak-peak current variation than  
whether you use a SMPS or 50Hz transformer with linear regulator before  
you switch it hard on and off with the thermostat PWM.

It might also be possible to find a LED lighting SMPS that is of the  
type where the current is always continuous DC with an adjustable value,  
(not the type that does PWM for dimming that puts out a square wave  
because the PWM is too low frequency to be filtered out by the output  
inductor and capacitors).
Something like this but less powerful and less expensive might be nice:
http://au.rs-online.com/web/p/desktop-power-supply/7066684/


Re: Peltier question.
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The difference is that PWM control introduces a constant switching
at a particular frequency, whereas thermostat control switches at
a frequency that's orders of magnitude lower. Instead of the length
of the "on" pulses being longer for more effect, as with PWM,
thermostats vary the length of time between the pulses themselves.

With things like your fridge, these "on" pulses from the thermostat
can be minutes apart. I note now that there may be an issue with
using a Peltier to cool this way though: Once the power is turned
off by the thermostat, the Peltier will begin to conduct the heat
from its heatsink back to the surface to be cooled. This will
probably result in much shorter "off" times to "on" times.

An automatically adjusting supply using either a suitably filtered
switch mode buck converter, or a linear regulator, would indeed be
much better suited. However the OP has indicated that the
construction of the circuitry required would be beyond his
abilities.

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The OP's LED power supply does apparantly have some variable current
control. The problem with LED drivers is that they do not need to
design them for normally acceptable levels of noise on their output,
because LEDs don't care about it (hence why some controllers can use
PWM). Another type of switch mode or linear supply would be
preferable, though with the LED driver the only thing available, it
would be worth giving it a try.

Manually adjusting the current to the Peltier may allow the box to
be kept in the correct temperature range without even using the
thermostat, as the cooling may be set to balance exactly the heat
ingress from outside.

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Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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Thanks to you guys for running through all of this, It's not for nothing,  
I'm learning heaps.

My original intent was to use a >12v laptop brick for the DC power then put  
it reduce both current and voltage to the peltier something like this;
https://www.aliexpress.com/item/DC-DC-Buck-5A-CV-and-CC-module-LED-driver-solar-battery-charger-with-PWM/1000001788861.html
or this
https://www.aliexpress.com/item/New-LM2596-LED-Driver-DC-DC-Step-down-Adjustable-CC-CV-Power-Supply-Module/2036634791.html
(I have a couple of these with full sized heatsinks fixed to the back of the  
PCB with 0.5mm thick 'thermal transfer material' [which is surprisingly  
thermally conductive - I've used it in several applications]).

Then I was planning to swith the output to the peltier 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 was planning on setting an upper temp of perhaps 10 deg and lower of 8. I  
was thinking that I'd set the voltage and current so that, for an average  
ambient the cycles would be roughly equal on and off.

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The problem with that is my home isn't climate controlled. In the hottest  
part of summer the ambient can cycle between 28 / 18 day / night and in  
winter more like 18 / 8. With the climate the way it is the upper and lower  
temperatures can vary by more than 5 degrees from one day to the next.

Do you think that it's worth trying this as planned (I'm still waiting on  
the higher power peltier) or should I just drag the small fridge in from the  
shed that I'm storing for a friend and set that to it's highest temp and see  
how that goes? (Bearing in mind I don't have much space and moving fairly  
heavy shite around isn't easy for me. <g> )

Thanks again guys.
--  
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:
[snipped]
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(Please excuse typos and nonesense words, I changed the format of how I was  
saying this and made errors.)

I hoped that, because both of the 'LED drivers' are also able to be used as  
Li-Ion chargers that there'd be acceptably low ripple (or the cells being  
charged would suffer surely?). I know that sometimes I expect too much from  
these cheap Chinese modules.

Also I can't justify the cost of even a cheap scope (which then I'd only end  
up second-guessing - is it the scope throwing errors?). As it is last year I  
bit the bullet and bought a Fluke 17B+ as I find that measuring tools need  
to be trusted - or what's the point of 'measuring'?.

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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Ah right, I was on the wrong track. Try to find a 12VDC power
supply and use that without the LED driver, with just the
thermostat device for temperature control.

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I think it would be easier just to leave it out of the equation -
I'm not sure how it would help unless it were rewired to control the
temperature itself. I don't think I'd charge Li-Ions with it myself.

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Re: Peltier question.
Once upon a time on usenet Computer Nerd Kev wrote:
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I can do that, I have one 12v / 4A brick (But half a dozen 16 to 21v laptop  
PSUs.)

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Ok thanks again 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.
Once upon a time on usenet Chris Jones wrote:
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Thanks for the input Chris.

I'm intending to presevere with the peltier idea because I've already got  
the polybox, large internal passive heatsink (cold side) and really good all  
copper ex-CPU heatpipe based cooler for the hot side. I don't have a wide  
mouthed thermos and getting wires inside the fridge is likely going to  
compromise the seal.
--  
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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So far my only personal implementation of peltiers has been to cool
the tip of a curious finger, however I noticed in this teardown video
(at around 5min) a comment relating to "stacking" Peltiers:

https://www.youtube.com/watch?v=2WnGhbub6LM


Basically because the lower peltier has to cope with the heat of
that above, it has to be bigger or have more elements than the
one at the top. Or you could transfer the heat from the top
one to two others below, in parallel as it were. There are
probably better references for this elsewhere online.

In your case, I'd be inclined to just use all three (or
as many as you can power) on their own, one layer deep.

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