Peltier question.

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~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

Thanks.

The peltiers arrived today and I've already sorted out the heatsinks to use
and polybox etc. so will probably try this method first.

After all this it could be acedemic anyway. The other night it was perfect
'night crawler' catching conditions but my back gave out after I'd snagged a
couple. I used to be able to get ~20 relatively unhurt worms in about 10
minutes on a good night but exacerbated my injury a few months back by
pushing through the pain to complete a job.

(Having healthy topsoil is one of the advantages of not being able to empty
a mower catcher without crying like a baby, and so using a good quality
mulcher / mower instead.)
--
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 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.

Noted, 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 ~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 can do that, I have one 12v / 4A brick (But half a dozen 16 to 21v laptop
PSUs.)

(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.

Ok thanks again for the input.
--
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)