Im trying to control a Peltier Cooler, but I need be able to switch the polarity from hot to cold, in order to maintain a certain temperature. The peltier is 12v, the heatsink fan will be 12v most likely. The fan will stay on constant so no worries there, but I really have no Idea where to begin to try and control the reverse polarity issue.. Im using a Duemilanove.. Any Ideas?
IIRC, Peltiers need a TON of current. So you may need something like a H-bridge motor controller to do what you need. You could also get away with a DPDT relay. But that would force you to always either be cooling or heating (no "OFF" state).
What is the current (amps) or the power (watts) rating of the Peltier module?
Ya, Ill need it to have an off state in order to maintain temp.. It shouldnt switch back and forth all that often, as it will be insulated to keep temp stable.. Here is the model specs on the peltier:
Model CP1-12726
50mm x 50mm x 3.64mm
Maximum power consumption 400 Watts
Operates from 0-15.4 volts DC and 0-26 amps
Operates from -60 deg C to +180 deg C
Each device is fully inspected and tested
Fitted with 6-inch insulated leads
Perimeter sealed for moisture protection
Operates from 0-15.4 volts DC and 0-26 amps
Ouch. That's a lot of current. Assuming the device draws current linearly with the applied voltage (behaves like a resistor), then at 12v, you're going to draw about 20 amps.
So you need a controller that can supply 20A or more @ 12VDC. The H-bridge motor controllers are nice because they can reverse polarity. But that's a big load and you're going to need a massive controller for it. The ones I'm familiar with are only good up to about 4A.
The first thing that came up on a Google search for "20a h-bridge" was this:
Poke around and see what you can find.
BTW: motor controllers usually can take a PWM input that will vary the speed of the motor. Check the specs of the Peltier module, but you may be able to use this feature vary the cooling/heating power of the module.
Another thing to watch with a Peltier device is that if you exceed a certain temperature difference between the hot and cold sides the effect breaks down and the unit goes into a heating mode irrespective of the direction of the current flow. So you might want to monitor the temperature.
I would go for a mechanical relay, get that working and only then think about solid state switching.