Quote:
Originally Posted by peter_4059
The other thing I did was use both halves of the relay for switching the peltier (I think you'll find it has a pair of parallel contacts) to minimise the load on each set of contacts. From memory my peltier draws 3-5A and this was near the limit of each switch in the relay. It looks from your photo that you are only using one set however it is very easy to parallel up the connections on the blue terminal block.
Peter
|
Thanks for the tip Peter,
my 40x40mm pelt draws 2.8A @ 12 volt so I wasn't worried about that.
And as I want to drive it all with a milder control (see below) the
measured amps were about 1.5. Appreciate the advice. No sense in
making the relay contacts work hard!
Quote:
Originally Posted by Scorpius51
Hi guys
Thought you might like to look at this TEC controller chip. I have been involved with a Peltier controller for a photodetector (discussed in another thread) and have used a circuit based around this controller. It has given us control from +25C to -45C with ~+/- 0.1C variation.
Take a look at
http://www.analog.com/static/importe...ts/ADN8830.pdf
and
http://www.analog.com/static/importe...027AN705_0.pdf .
We made up a sealed enclosure to house the TEC/detector module and used a desiccant sachet. It was able to give us -45C with no significant frost.
Cheers
John |
Great advice John thanks. that is the sort of idea I wanted in the first
place rather than bodging up a heap of semi-applicable kits to do
a 3/4 functional job. (hehe see below...again!)
A very wise man once told me to get things working for you rather
than waste time the other way round (Rally
)
Anyway.... going against that advice somewhat
:
today after work I tried feeding the pelt/fan assembly
with some Pulse Width Modulated 12V.
I used the Jaycar KC5225 kit: A TA494 PWM IC driving a Mosfet.
Capable of 10A with one Mosfet fitted..and 20A with a second in parallel.
Results were that straight away the fan struggled sometimes to rotate
at lower duty cycles. Temp was very controllable though. I could
keep a setpoint almost stable at 5 deg C .
Because of the fan problem I decided to feed the fan with the full
12V and only the peltier got the PWM.
A slight improvement in setting a reliable setpoint. 5 deg C only drifted
from between 4.7-5.5 C.
The thing that made it drift was the dropping AMBIENT temp of course.
With just a slight tweak of the 5k Pot on the PWM board I could get it
back on 5 C straight away.
Ambient needs to be kept an eye on as well.
My Fluke DMM only has one K type thermocouple input.
Jaycar sell a great little 2 input meter with fairly fast update and max
and hold functions. In the last shot you can see the screen of this
meter holding 5 C. A quick press of the T2 button and I can read ambient
with the other K thermocouple (meter comes with 2 of them)
It also has a T1-T2 function where you can see the delta the peltier
is working with.
Steve