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Topic: Peltier PWM controller (setpoint temperature) (Read 8 times) previous topic - next topic

Grumpy_Mike

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because of this the PSU needs to be able to withstand the 20A that is being drawn by the TEC 50% of the time even though that switching frequency in the TEC is over 2000 times a second?

Yes the peak current is the same PWM or not. The output capacitor on the PSU will be able to spread this a little but if full power gives a glitch (dip then rise in voltage) the a PWM will give the same glitch.

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Say that the TEC I am going to use draws 20A at 12V.
If I run a 50% duty cycle on the PWM then the the TEC will be as if it is working at 6V 10A.

No 50% would be running at 10A still at 12V. If you half both voltage and current you have a quarter of the power.

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will this method require cooling of the FET I might use

It depends entirely on what sort of FET you use.
This brakes down into it's package dissipation, the current you are drawing and the on resistance of the FET.


Grumpy_Mike

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"N-channel MOSFET 96A 100V TO220 IRFB4410"

This is not a logic level FET and so can't be driven directly from the arduino. You either need a logic level FET or you need to boost the arduino's 5V output signal to at least 10V with a transistor or another FET.

Pebbles


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"N-channel MOSFET 96A 100V TO220 IRFB4410"

This is not a logic level FET and so can't be driven directly from the arduino. You either need a logic level FET or you need to boost the arduino's 5V output signal to at least 10V with a transistor or another FET.



OK i looked up what you meant with logic level FETs.
Standard MOSFETs require a 10V gate voltage to be turned on 100%
Logic level MOSFETs require 5V gate voltage to be turned on 100% <----- this one i need to run PWM directly from the Arduino as the Arduino's operating and thus PWM voltage is 5V right?

daveg360

I think that based upon your level of knowledge you may better using a motor controller.  Something like:
http://www.robotshop.com/eu/cytron-10-30v-30a-single-brushed-dc-motor-controller.html?utm_source=google&utm_medium=base&utm_campaign=GoogleUK

This would make it straightforward to do.  I know it's a lot more than just buying a suitable mosfet but bear in mind that a simple mosfet circuit doing PWM will create a lot of interference and probably need cooling, especially if you are controlling it from an Arduino pin.
If your system involves lethal voltages/life critical/flamable elements - you probably shouldn't need to ask.
The Arduino != PC.

MarkT

I've looked around a bit and it seems you can't just drive a peltier with a PWM signal - it requires smooth DC drive so you need to low-pass-filter the PWM with LC filter.  To keep the filter components manageable that means a high switching frequency.

Peltiers physically wear out (thermal cycling)  if switched on and off at low frequencies and if switched at high frequencies you lose lots of power as they absorb the AC component as heat.  Well that's what some site say but I think the real problem is that they are very good heat conductors when not carrying current.
[ I won't respond to messages, use the forum please ]

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