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PWM for TECs

 Post subject: PWM for TECs
PostPosted: Thu Mar 05, 2015 4:33 am 
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I'm trying to use a PIC to control a peltier to keep a liquid cooled to a specific temperature under slightly varying heat load. The PIC will be programmed to provide PWM to a MOSFET however is not capable of generating the 200khz frequency needed for the TEC. Probably will be more like 1k to 5k. I assume I can use a capacitor and or inductor to smooth it out enough to compensate but I have no idea what values to use or the actual circuit layout. I assume the waveform doesn't need to be flat just as long as I have some reasonable facsimile of DC. It will be driving from near 0 to almost 8 amps. Are there any links to forum threads or tutorials that can help me?


Great forum. Lots of info. You mention using the mcubed tbalancer to control the TECs. Is this something that can be programed for specific applications?


Thanks for any help.


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 Post subject: Re: PWM for TECs
PostPosted: Sun Mar 08, 2015 3:46 pm 
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I would say if you could get 3khz or around there you should be fine, obviously higher say 15-25khz is probably better. The thermal shock that is bad for TECs is slow thermal cycling like you find in a thermostat or say what you would find in many motor controllers (like 60-100hz). As for the Tbalancer as far as I'm aware it's just a USB PWM fan controller. Whatever software it ships with probably allows some level of control, although I wouldn't compare it to what you could do with an MCU. For instance with your MCU you could set up an NTC or PTC to measure the temperature of whatever you want, on the tbalancer it will probably on react to system temperatures, CPU, GPU whatever. So an MCU is probably a more powerful but more complicated solution.


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 Post subject: Re: PWM for TECs
PostPosted: Wed Mar 11, 2015 9:45 am 
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So you think 3khz would be ok? Is that without a capacitor? If I put it on an oscilloscope with a capacitor how much variation in voltage would be negligible as far as affecting the TEC performance? There are dedicated drivers you can get that will run at 200khz but it makes my circuit more complicated. Adding a capacitor is much easier if I get the same results.


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 Post subject: Re: PWM for TECs
PostPosted: Sun Mar 15, 2015 6:56 pm 
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You should be fine without a smoothing capacitor at 3khz or greater. The smoothing capacitor actually can be messy with PWM sometimes because the capacitor will want to charge to the peak value. The big problem with lower frequencies is actually thermal shock, 3khz should be enough to avoid any of those problems.


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 Post subject: Re: PWM for TECs
PostPosted: Mon Mar 16, 2015 2:41 am 
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I assume when you say low frequency your talking about a few hundred cycles. I see what your talking about when a capacitor want to charge fully with a a pwm. So a small choke would probably Need to be part of that. I'll go with your suggestions and shoot for 3khz and no capacitor. Thanks for the help.


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 Post subject: Re: PWM for TECs
PostPosted: Tue Apr 28, 2015 7:57 pm 
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3 k will be fine the TEC manufactures recomend 1k plus


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