Peltier control?

[droptail]

My thought was to operate them at a max of 50%, about 7V/4.5A each, (9A total).
I prefer to connect them together in parallel, and drive or control as one device.

I was also considering a simple voltage divider to go from the 14V to the 50% state I prev mentioned to keep it real simple, but don't think the power resisters wouway to go would be practical/doable.

I won't know if this is an option until I receive my test modules soon and play with them. I would then have some "control" of them them based on on/off.

Thanks for the replys

[Charles Linquis]

Your choice. I can give you a "plug and play" circuit that will give you total proportional control, if you choose to go that route.

[BrianT]

I use an H bridge with 2 Pchannel and 2 Nchannel FETs on a 13.5 volt rail. The TEC pulls about 8 amps when flat out. The power supply can deliver 15 amps and the FETs can switch 75 amps. The H bridge is controlled via a dedicated 16F88 which reads a Microchip MCP9800 to give me 1/16 degree resolution and drives the H bridge. Because the FETs have just simple resistive gate drive via 2N7002 as level shifters there MUST be delays inserted between turning the FETs On or Off otherwise there is a short but deadly overlap where both FETs on the same side of the H bridge are conducting simultaneously. This leads to the FETs getting very hot or worse, it burns the traces off the PCB. My application is fully proportional and must both heat and cool. The drink cooler examples I have seen are simple cool-only with a thermostat to drop the drive once below the setpoint. Drive is flat out or off.

You MUST ensure the entire surfaces of each side of the TEC are thermally bonded to the cool chamber or the heatsink otherwise any small unbonded area will get very hot and burnout the TEC in no time.
TECs are poor coolers but good heaters. My device works between 1 Celsius and 45 Celsius -roughly Ambient +/- 25 Celsius. In cooling mode I must blow lots and lots of air over the heatsink to get down to the lower temperatures and supply high currents. When heating the chamber the average drive currents are about 1/4 of the cooling currents.
TEC life is severely degraded by thermal stress. If your controller drives full heat then full cool so that the average gives you the setpoint you are after the life will be short. The thermal stresses will break the bonds between the magic metal elements. I run a fixed frequency 50 Hz software PWM and vary the duty cycle from 0 up to about 19500 microseconds. I am only running a Proportional controller, not a full PID. Seems to regulate to about 0.1 Celsius but is slow getting to the setpoint which does not matter in my application which is left on for days on end.

HTH
BrianT

[Salman1]

hi..

i have already made hardware and there is no H-bridge used. the peltier module is connected with two PWMs i have to use 2 stage PID which has 2 outputs. the question is how it would like i have tried to make condition that if the current temperature is more or less than setpoint then switch PWM but it doesnt look like stable it switch and some how ocsillate. i have read about dead zone can any body give me more ideas how i can make it better or use and other condition?