Peltier control?

[Charles Linquis]

I have controlled them with filtered PWM output. What voltages/currents are you dealing with?

[droptail]

I have controlled them with filtered PWM output. What voltages/currents are you dealing with?

I'm looking at a pair in parallel of 40mm, 15Vmax, 9Amp variety.
I understand operating at 50% capacity improves efficiency.

[Charles Linquis]

Sure, they aren't very efficient in the first place and very few devices of any kind are most efficient at 100% capacity. And if you want long life and you are cooling something with them, make certain that you do a good job of heat removal from the 'hot' side.

A couple of other questons:

I assume you need proportional control (Y/N) ?
Does the Peltier GND terminal need to be isolated from the PIC (and rest of the circuit) GND
Do you really have 15V available, or is it 12?
Military, commercial or home use?

[ivanrosales]

James, IMHO your best bet is using PID, "Master" Henrik Olsson have a neat routine in this post: http://www.picbasic.co.uk/forum/show...ghlight=incpid
You should give it a try.

Regards.
Ivan.

[droptail]

Charles,
Do you mean variable control? That would be ideal, but I may only need to voltage divide from 13V to 7.5V for the 50% efficiency.
I'm not aware of any needed isolation requirements.
The modules are rated at 15Vmax, I am working with a 13V power supply.
Personal use.

Are we talking MOSFETs using PWM control?

Ivan,
I have downloaded the file and am looking at the link.

Thanks

[Charles Linquis]

Yes, I'm talking about PWM control using FETs. Many devices (such as brushless fans), AND Peltiers don't like to see a "chopped" waveform, so you should filter the PWM signal to pure DC. Also the PWM frequency should be above 20KHz, so that it doesn't generate any noise in the audible range. Basically, the simple circuit where you connect a FET Drain to the load's (-) terminal, the FET Source to GND, the FET gate to a PIC pin and the load's (+) terminal to 12V just won't do.

At current levels like this, you will need a FET driver, a big FET, an inductor, a Schottky diode and some capacitors that can handle high ripple currents.

I asked about the use because I just got an RFQ from a military customer that is using Peltiers. I didn't want to compete against myself.

[ivanrosales]

James, we are talking about two different issues, control and drive... as per control (this was your original question) I still recommend you implementing some sort of PID. For drive, you have to deal with two 9 Amp loads which is a lot so Mr. Charles approach is the right way to go. Some time ago I repaired a small peltier commercial fridge (used for an energy drink promotion) and it had a good EMI filter, a small control board and two solid state relays, very simple indeed...

[ivanrosales]

One more thing, needless to say that the aforementioned fridge had a huge aluminium dissipation at the back (shared for the relays and the peltier plate)...