I had a thermo cooler/heater for soft drink cans/thermo mug, cold drinks in summer, hot drinks for winter device..
When I ripped it apart years ago, I recall pulling 1 transistor/fet I think it was ab irf something, on top of the unit you had 2 buttons (to switch hot and cold)..
Is it even possible to switch polarity with just 1 power fet? (About 4 years back, so no I don't have it lol)
Screw it, I'll go for my own design.....
Are you sure it wasn't a thermal cutoff switch? Every thermoelectric cooler I've pulled apart (about 10 or 12) just use a DPDT switch to change polarity, and have a thermal cutoff switch to protect against overheating.
This one looks just like a TO-220 package:
The ones I've removed look more like this:
Another style:
Yes... that!..
I figured that was a thermal protection (cut off if it got too hot) could that not be used to reverse a motor too? (The dpdt switch)
Re: reversing a motor with a DPDT switch. Of course, it depends. A brushless DC motor, only if you use it to reverse the connection between two of three of the connections to the windings (leaving them in the delta configuration). But not by reversing the + and -, as you know. An AC motor, maybe. It depends on the motor, but not by reversing the incoming AC.
A regular old brushed sparky DC motor, yes. Although not all DC motors run as well backwards as forwards.
polymorph:
Although not all DC motors run as well backwards as forwards.
How do you tell which way is forwards and which backwards?
No, no, don't tell me! I guess that forwards is the direction it runs best in. 
Heh. Some cheap DC motors use a strip of springy metal rather than a spring to press the brushes against the commutator. So if run backwards, the angle of the brushes may change, causing them to not quite make as good a contact.
polymorph:
Heh. Some cheap DC motors use a strip of springy metal rather than a spring to press the brushes against the commutator. So if run backwards, the angle of the brushes may change, causing them to not quite make as good a contact.
Or vice versa.
It's not your mechanics/electronics that I'm questioning but your nomenclature. A free running brushed DC motor has no forward or backward until you arbitrarily designate one direction as forward. Someone else may designate the other direction as forward and you would both be correct from your respective standpoints. Similarly, clockwise and anticlockwise [counterclockwise] are meaningless without a definition of which end is being looked at, especially with double ended motors.
All you can say is it's 'turning in one direction' or it's 'turning in the other direction.'
Even when you apply a load, it's the load that is being turned forwards/backwards, not the motor.
See these spring arms? They are made to work with the motor running so they drag away from the attachment point.
"Backwards" would be running in the other direction.
For a better motor with carbon brushes in holders with springs behind them, they can wear into a set. Or, as in the image below, they are made so they are angled and are meant to run in one direction.
I'm not saying that you can't run these in the other direction. I'm saying they may not work as well.
polymorph:
See these spring arms? They are made to work with the motor running so they drag away from the attachment point."Backwards" would be running in the other direction.
You're still calling the direction they (were designed to) run best in Forwards.
For a better motor with carbon brushes in holders with springs behind them, they can wear into a set. Or, as in the image below, they are made so they are angled and are meant to run in one direction.
I'm not saying that you can't run these in the other direction. I'm saying they may not work as well.
Agreed, when you use the terms 'one direction' and 'other direction'.
So what's the problem?