Peltier cooling AND heating fermenter question

Hi everyone,

Me not being and electronics wizard of any sort, I have a query I would like to put forth here.

I am planning a temperature controlled 14 gallon SS conical. Here is what I have in mind:

12V dc switching power supply. 4 x 160W Peltier devices. 2 12V dc STC-1000 temperature controllers, (one for heat and one for cooling), unless I can find a 12v DC STC-1000 with auto switching capability.

My plan is to run all 4 Peltier devices at once for heat and all 4 at once for cooling. MY question is this, How can I reverse the polarity on the Peltier devices to provide heat when the temp controller calls for heat or cooling?

 

I don't have any handy software, so here's a hand drawing.

Assuming the STC is dual control, it drives high current relays using 12v.
When it calls for heat the top relay energizes and applies +12 & gnd to the wires that feed the Peltier devices as shown. When in calls for cool, the polarity is reversed.

The problem is 160 amps of 12v to supply this beast - 160 watts at 12v is 40 amps times 4 units is 160 amps. That's one big power supply, and monster relays.

 

Whoa!

Ohms Law - V=IR...

P = VI = 160w = 12 x I

I = 13.33 amps...

 

Oopsie, no clue what I was thinking. Still, it's 40 amps total.

 

Here's a 50a supply - http://www.ebay.com/itm/like/370977909796?lpid=82

 

Don't limit yourself by 12v controller. 120v STC will controll 12V circuitry with no problem. But as it was mentioned - you willneed additional 60A rated relay(s).

Or you can use DC-DC SSRs.

 

Hi -

I saw this old post. I'm also very inexperienced with wiring these types of circuts. I'd like to switch polarity on a peltier device too and I already have an STC-1000 with hot and cold relays in the same device. I'm wondering if this DPDT relay will work - it's a 12V, 10A model and I'm only doing one peltier device right now: http://www.ebay.com/itm/DC12V-Coil-...811252?hash=item3f3860daf4:g:yt4AAOSwT6pVieXm

I'm not very familiar with these relays and how the wiring takes place. It looks like you wire the base and the relay plugs into it. I've enclosed to diagrams. One is the DPDT Relay diagram below with a motor placed where the peltier device would be placed. The other diagram (DPDT-relay-diagram) shows the pins on the relay, I'm not sure how to wire the terminals. It looks like I apply 12 volt across the coil (both coils terminals are taken) and 12 volt to the input to the relay (the "com" terminals and then I would apply use the NC terminals for one direction and NO terminals for the other direction?

Thanks, Brian

 

I was also toying with the peltier idea once, I believe the diagram above is correct, the DPDT relay will allow for the peltier to heat or cool as needed. Don't forget to add a BIG heat sink!