0
\$\begingroup\$

I want to control peltier element's temperature with a PWM driven bipolar DC motor controller to be able to switch between heating and cooling and also control the level of it. The peltier element is 12V/8.5A. I also have 12.5A DC power adapter.

I want to buy a motor controller (like this 13A controller) in order to simplify the project as much as possible. This particular controller can be driven by 20kHz PWM.

I was thinking about a following circuit:

in1 and in2 would be connected to outputs of a controller. out1 and out2 would be connected to peltier.

Using 1mH inductors and 470uF gives 232Hz rolloff frequency which is 86 times smaller than 20kHz.

I have a few questions:

1) Does this circuit make sense and is it enough for my situation? 2) I found 1mH 10A inductors, but I'm not sure if I should take into account anything else regarding L and C proportions and this particular circuit 3) Do I have to look for anything specific in capacitor or will any 470uF capacitor be fine? Is bipolar capacitor required?

\$\endgroup\$
1
\$\begingroup\$

To a first approximation you should be fine. As long as the inductors have decent frequency response, so you don't get much in the way of current spikes, the capacitor will be OK, and does not need to be a low-ESR type. But a better cap, one specified for use in switching applications, would be good insurance.

But hey, the worst that can happen is the cap blows up. Just put a paper cup over it. These things don't send shrapnel flying when they fail.

\$\endgroup\$
  • \$\begingroup\$ One thing that I just realised is that I probably need bipolar capacitor (like this one), is it correct? \$\endgroup\$ – Piotr Sarnacki Feb 18 '15 at 8:13
  • \$\begingroup\$ Yes. Sorry I missed that. \$\endgroup\$ – WhatRoughBeast Feb 18 '15 at 12:19
  • \$\begingroup\$ You will probably find a smaller capacitor (10uF or less) is fine, and easier to find in non-polar form. \$\endgroup\$ – Brian Drummond Feb 18 '15 at 12:34
  • \$\begingroup\$ @BrianDrummond what's the easiest way to find out if the smaller capacitor is OK? I suppose I'd need to check the output signal on the oscilloscope, which may be problematic, cause I don't have access to any oscilloscope. \$\endgroup\$ – Piotr Sarnacki Feb 18 '15 at 13:22
  • \$\begingroup\$ You can simulate the current filter to see the ripple voltage, and substitute capacitor values. Or scale your current analysis : 100x lower capacitance gives 10x frequency increase - still 8.6x less than switching frequency. Very roughly : call it 10x less or one decade. For a second order filter, that's 40dB attenuation of the switching frequency, or 120mV ripple from a 12V supply. (Even if you double that because of all my approximations : still fine) \$\endgroup\$ – Brian Drummond Feb 18 '15 at 13:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.