Peltier question.

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

Thanks Kev. I'm subscibed to Mikes channel but haven't investigated it to
any extent yet.

Now that you mention it I recall seeing stacks of maybe five peltiers of
increasing size on an overclocking site years ago. For the sake of this
experiment I'm just going to use one of the high rated devices (when it
arrives - and then I get my arse into gear <g&gt.

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)

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Wayne Chirnside wrote:

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. ;-)

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.

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.)

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.

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.

> The Aliexpress item is a switch mode regulator, not what you want.

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>

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.

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).

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.

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
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

Yeah, so maybe not my brightest idea.

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

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.

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%."

--
__ __
#_ < |\| |< _#

 

[Computer Nerd Kev]

Computer Nerd Kev <not@telling.you.invalid> wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

Yeah, so maybe not my brightest idea.

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

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.

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

Make that five 5V 12V Zeners.

--
__ __
#_ < |\| |< _#

 

[Chris Jones]

On 03/01/2017 08:01, Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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.

 

[Jasen Betts]

On 2017-01-04, Chris Jones <lugnut808@spam.yahoo.com> wrote:

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.

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.


--
This email has not been checked by half-arsed antivirus software

 

[Computer Nerd Kev]

Chris Jones <lugnut808@spam.yahoo.com> wrote:

On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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 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).

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.

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.

--
__ __
#_ < |\| |< _#

 

[Chris Jones]

On 04/01/2017 14:04, Jasen Betts wrote:

On 2017-01-04, Chris Jones <lugnut808@spam.yahoo.com> wrote:

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.

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.

Yes that would work nicely.

 

[Chris Jones]

On 04/01/2017 21:32, Computer Nerd Kev wrote:

Chris Jones <lugnut808@spam.yahoo.com> wrote:
On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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 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).

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.

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.

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/

 

[Computer Nerd Kev]

Chris Jones <lugnut808@spam.yahoo.com> wrote:

On 04/01/2017 21:32, Computer Nerd Kev wrote:
Chris Jones <lugnut808@spam.yahoo.com> wrote:
On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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 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).

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.

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.

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.

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.

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/

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.

--
__ __
#_ < |\| |< _#

 

[Computer Nerd Kev]

Computer Nerd Kev <not@telling.you.invalid> wrote:

Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:

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

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.

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

Make that five 5V 12V Zeners.

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

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Computer Nerd Kev <not@telling.you.invalid> wrote:
Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:

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

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.

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

Make that five 5V 12V Zeners.

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

Thanks Kev I've saved all of this for future reference.

Much appreciated.
--
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)

 

[~misfit~]

Once upon a time on usenet Chris Jones wrote:

On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.


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.

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
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet ~misfit~ wrote:
[snipped]

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]).

(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
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Chris Jones <lugnut808@spam.yahoo.com> wrote:
On 04/01/2017 21:32, Computer Nerd Kev wrote:
Chris Jones <lugnut808@spam.yahoo.com> wrote:
On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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.

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.

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.

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 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).

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.

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.

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.

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.

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/

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.

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.

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.

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
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Computer Nerd Kev wrote:
Computer Nerd Kev <not@telling.you.invalid> wrote:
Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:

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

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.

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

Make that five 5V 12V Zeners.

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

Thanks Kev I've saved all of this for future reference.

Much appreciated.

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

--
__ __
#_ < |\| |< _#

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet ~misfit~ wrote:
[snipped]
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

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.

(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]).

(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.

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.

--
__ __
#_ < |\| |< _#

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

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> )

They've both got scope for failure or success, so I'd go with
whatever was easier. Silicon Chip published a fridge temperature
controller project that Jaycar made a kit of:
http://archive.siliconchip.com.au/cms/A_104576/article.html
http://www.siliconchip.com.au/Issue/2005/June/The+Coolmaster+Fridge-Freezer+Temperature+Controller

--
__ __
#_ < |\| |< _#