getting relative +12 and -12v from 24 and 12v power supplies.

ok so ive got a pelt unit, when you run it with 12v you get side one cold side 2 hot, if you reverse the wiring side 1 hot side 2 cold. i have a switch with 1 pole and three throws, so it has three pins if the switch is in position one it connects pin 1 and 2, if its in position two pin 2 is disconnected, in position 3 pin 2 and 3 are connected. if I connect the positive wire of the pelt unit to +12v and the negative wire of the pelt to pin 2 on the switch, will connecting ground to pin one of the switch and +24v to pin 3 give me + and - 12v through the pelt unit? also will it take the same watts to run it either way? i can make a diagram if it helps, my main concern is that running the pelt between the +12v and +24v with use more watts than between gnd and +12v, although in theory it shouldn't

Connecting load between +24V and +12V depends on ability of +12V branch to sink current. Now imagine simple PSU construction with transformer, diode rectifier and filtration capacitor. Diode rectifier on +12V branch will not allow to sink current, because it'll be polarized in reverse. This will result in charging filtration capacitor of +12V branch to 24V, that's possibly over its rated voltage and destroying it.

probably best to make an h bridge circuit. this will switch your peltier circuit for you.



Edited 1 time(s). Last edit at 01/06/2014 08:00PM by jamesdanielv.

If the Peltier isn't that big (<3A or so) you might want to use a motor driver IC like the L293 that has an H-bridge with logic level inputs.

Yup.

Read up on H-Bridge.

5 amp h bridge? how about just a dpdt relay, as long as there is no crossover it should be ok.



Edited 3 time(s). Last edit at 01/09/2014 11:29AM by aduy.