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Wayne Chirnside
Guest

Thu Dec 29, 2016 8:38 pm   



On Thu, 29 Dec 2016 22:53:50 +1100, Chris Jones wrote:

Quote:
On 27/12/2016 01:04, Wayne Chirnside wrote:
On Mon, 26 Dec 2016 16:51:36 +1300, ~misfit~ wrote:

Once upon a time on usenet Wayne Chirnside wrote:
On Sun, 25 Dec 2016 13:45:15 +1300, ~misfit~ wrote:

Once upon a time on usenet Chris Jones wrote:
On 18/12/2016 11:49, ~misfit~ wrote:
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.



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.

Thanks for the input. :)

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)

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 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.


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.

Computer Nerd Kev
Guest

Mon Jan 02, 2017 9:51 am   



~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Quote:

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.

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

Computer Nerd Kev
Guest

Mon Jan 02, 2017 10:14 am   



~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Quote:
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? Wink 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.

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.

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

~misfit~
Guest

Mon Jan 02, 2017 1:57 pm   



Once upon a time on usenet Chris Jones wrote:
Quote:
On 26/12/2016 10:18, ~misfit~ wrote:
Once upon a time on usenet Clocky wrote:
On 25/12/2016 9:26 AM, ~misfit~ wrote:
Once upon a time on usenet ~misfit~ wrote:
Once upon a time on usenet Wayne Chirnside wrote:
On Mon, 19 Dec 2016 14:21:21 +1300, ~misfit~ wrote:

Once upon a time on usenet Clocky wrote:
On 18/12/2016 8:49 AM, ~misfit~ wrote:
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.


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)

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,

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.

Thanks, I've ordered a couple. Probably be February before they
arrive though.

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.

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 ...

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 ...


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).

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.

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.


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. ;-)

Quote:
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.


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

~misfit~
Guest

Mon Jan 02, 2017 2:14 pm   



Once upon a time on usenet Wayne Chirnside wrote:
Quote:
On Mon, 26 Dec 2016 16:51:36 +1300, ~misfit~ wrote:

Once upon a time on usenet Wayne Chirnside wrote:
On Sun, 25 Dec 2016 13:45:15 +1300, ~misfit~ wrote:

Once upon a time on usenet Chris Jones wrote:
On 18/12/2016 11:49, ~misfit~ wrote:
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.



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.

Thanks for the input. :)

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)

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

~misfit~
Guest

Mon Jan 02, 2017 3:13 pm   



Once upon a time on usenet Computer Nerd Kev wrote:
Quote:
~misfit~ <shaun.at.pukekohe_at_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>).

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~
Guest

Mon Jan 02, 2017 6:05 pm   



Once upon a time on usenet Computer Nerd Kev wrote:
Quote:
~misfit~ <shaun.at.pukekohe_at_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? Wink 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>

Quote:
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).

Quote:
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
Guest

Mon Jan 02, 2017 11:01 pm   



~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Quote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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.

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

~misfit~
Guest

Tue Jan 03, 2017 8:30 am   



Once upon a time on usenet Computer Nerd Kev wrote:
Quote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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
Guest

Wed Jan 04, 2017 12:02 am   



~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Quote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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.

Quote:
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%."

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

Computer Nerd Kev
Guest

Wed Jan 04, 2017 12:47 am   



Computer Nerd Kev <not_at_telling.you.invalid> wrote:
Quote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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
Guest

Wed Jan 04, 2017 7:30 am   



On 03/01/2017 08:01, Computer Nerd Kev wrote:
Quote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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
Guest

Wed Jan 04, 2017 8:30 am   



On 2017-01-04, Chris Jones <lugnut808_at_spam.yahoo.com> wrote:

Quote:
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
Guest

Wed Jan 04, 2017 12:32 pm   



Chris Jones <lugnut808_at_spam.yahoo.com> wrote:
Quote:
On 03/01/2017 08:01, Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe_at_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).

Quote:
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
Guest

Wed Jan 04, 2017 8:00 pm   



On 04/01/2017 14:04, Jasen Betts wrote:
Quote:
On 2017-01-04, Chris Jones <lugnut808_at_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.

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