Peltier (TEC) with Pololu VNH3SP30 motor driver

I am driving 2 peltier coolers using 1 pololu VNH3SP30 motor driver. In my system, it seems these coolers work best at about ~2.5amps each. Later on, I am going to introduce them to a larger system that is being run off of a 12V 30A power supply. While driving these coolers with PWM, the voltage and current being supplied jump around a lot.

The question: Since I am going to attach this to a 12V supply that is powering other subsystems, won't it mess with my supply voltage to those other systems? Should I use a voltage regulator or something and run the coolers off say 8V? (I say 8V because when I current limit my supply at ~4.9A, the voltage settles at ~8V).

I did some looking online, and it seems that people have been able to drive peltier coolers using motor drivers and PWM signals from an arduino of sorts. If you have done this, did you notice anything about the kind of power you were drawing? Ideally, I would be current controlling these with something like an LED driver, but nothing really supplies a high enough current for what I'm doing so I went with the motor drivers....

PS, these are the items I am using: -Arduino Mega 2560 -power supply A, for testing (amazon: http://www.amazon.com/KORAD-KA3005P-Programmable-Precision-Adjustable/dp/B0085QLNFM/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1401838076&sr=1-2-catcorr&keywords=korad) -power supply B, for my larger system http://www.amazon.com/Universal-Regulated-Switching-Computer-Project/dp/B00D7CWSCG/ref=sr_1_3?ie=UTF8&qid=1401838142&sr=8-3&keywords=12v+power+supply -2 TEC/peltier coolers (similar to http://www.amazon.com/YKS-TEC1-12706-Thermoelectric-Cooler-Peltier/dp/B007H2IXV2/ref=sr_1_1?ie=UTF8&qid=1401837553&sr=8-1&keywords=peltier+coolers+12+v) -1 pololu VNH3SP30 motor driver (driven by arduino PWM) http://www.pololu.com/product/705

Thanks in advance for comments/suggestions etc! :)

Peltier modules like the one shown on Amazon typically draw 5-7 amperes at 12 V. The ad you linked says 60 watts, which is most likely the maximum input power, so 5 amps at 12.0 V.

There is a range of opinions on whether it is wise to run Peltier modules with PWM. Some people have suggested that PWM can damage the modules, possibly due to rapid temperature cycling. Spend some time looking on line and draw your own conclusions.

Be careful to use a heat sink with thermal transfer compound and not to let it overheat. The standard ones can't tolerate temperatures much above 80 degrees Celsius (although there are some rated at over 250 C). They will be destroyed if you allow the hot side to go over the maximum. For some useful info see https://tetech.com/faqs/

Yeah, before ordering anything I was already reading around, & the conclusion I drew was that it should be fine to run the coolers with PWM (which is why I went ahead and ordered the drivers). However, it is best for my system if the coolers don't run at their full wattage & they run lower (because we can't get enough heat out of them if they run @ 5A/12V). That's where the motor drivers should come in- so I can manage the power going to the peltier coolers & not overheat my system.

But I'm finding that the drivers are changing my supply voltage- which I want to stay at 12V. I thought the motor driver would regulate the voltage/current output without messing with my supply. Now that I think more about how H-bridges work I can see how I went the wrong though. I guess maybe I'll try the voltage regulator thing.

I may be thinking about these TECs the wrong way. If a lot of other people are running them just ON/OFF maybe that's the better way to do it. But the cycling is supposedly bad for them. Hmmmm...

If the power supply voltage is dropping, then it is not capable of supplying the current that the load would draw. The motor driver won't "regulate", it will just reduce the average current by rapid switching.

I'm not sure what you mean by "But the cycling is supposedly bad for them" -- PWM is just very rapid on/off cycling.

Your PWM driver needs decoupling to avoid polluting its supply. That means large
electrolytic capacitor(s) with high ripple current rating.

The problem, as I understand it, with PWM’ing peltiers is that the devices conduct
heat very well with 0V across them, so that you waste a lot of power if cycling
as opposed to steady-state current. The solution is to add a suitable inductor
in series to even out the current. This implies a high PWM frequency to keep the
inductor reasonably small, and thus fast switching devices.

Your suggestion to use a regulator at 8V is a poor idea. At those sort of currents, you will be wasting a lot of energy and have a heating problem. If you really want to run the peltier device at a lower voltage, get a more effficient switching voltage converter device, preferably an adustable one.

But I'm finding that the drivers are changing my supply voltage- which I want to stay at 12V. I thought the motor driver would regulate the voltage/current output without messing with my supply.

If you try and draw 10 amps from a power supply rated to supply 5 amps, then of course you will have problems. But it may work perfectly well with the other power supply supposedly rated at 30 amps,

Hi, check out this link with reguard to peltier and PWM operation.
We have a cooling/heating calibration bath at work that uses PWM and a peltier device to control a small bath (150ml).
The PWM driver is discrete using MOSFETs and it has an inductor in the output to help limit peak current.

http://redlum.xohp.pagesperso-orange.fr/electronics/PWM-TEC.html

I have no circuit for it, or what value it is, but the above links do make sense as the peltier is a resistive device rather than inductive like an electric motor.

Hope this helps.

Tom… :slight_smile: