Reversing load polarity via MOSFET

[Mosaic]

Hi,
I am working on a project to drive a load that requires reversing the voltage from time to time.

Basically a peltier heater/cooler gizmo.

Also I want to use 'burst fire' to limit the Peltier heater temp. On for 5s off for 5s for a 50% DC etc.

This means the PIC will have to use a temp sensor for feedback control to limit the DC% and so manage temps.
Also, with an LED it can indicate temperature setpoint accuracy.

Anyway, I'd like some advice on the solid state switching of polarity to the Pelt. Max pelt load is around 24 Amps/12V.


Thanks.

 

[be80be]

That's a big peltier heater where you find it at?

Most I've looked at are 100 watt

You would use a H-bridge

 

[Mosaic]

Hmm, given my load at 20+ amps.....4 mosfets might be a bit expensive, BJT's won't work off a PIC ..base current draw might be 2 much at that level of collector Current.

Perhaps a DPDT relay for polarity with a single MOSFET to control the burst fire duty cycle?

EDIT; Ok, I have 6 of these on hand:
https://www.electro-tech-online.com/custompdfs/2010/11/91328.pdf

Suitable do u think?

 

[be80be]

Should work ok

 

[Mosaic]

Hmm...high side issues with an N Fet....

Got no hi current P FETs now...

How about using a 30Amp SPDT relay to handle the hi side (I have those) and 2 N Fets for the low side.

I'd have to code a custom H bridge routine to handle the latency of the relay...by shutting off the N FETS, waiting 10 mSec for the relay to transition and then renableing the correct N Fet for the new polarity.

I'd still use the N Fets to do the slow PWM. to manage the temp.
Seeing that a 30A SPDT relay (driven by a 2n3904) is about $3.00 and a pair of logic level P Fet at 30A is over $8.00, that's a better deal. The relay son't be doing much switching, just when I need heater mode rather than chiller mode.

 

[be80be]

you can make a h-bridge with just 4 n channel fets **broken link removed**