Power Chill 12v Circuit
Date: 08.11.10 - 8:03am
The last power chill post was an example of creating a thermostat controlled switching unit for a 120v AC socket. Fine if you are in a house, but since the unit runs primarily on 12v DC, its kind of a shame that you cant take the unit with you in the car and utilize the thermostat control. Plus soldering up the relay board is more than most people want to get into.
So i figured i would mess around and see if I could wire up a 12v thermostat control that didnt require any real soldering or circuit board work. I was mostly able to accomplish that.
Again i am not an electronics guy..use these designs at your own risk
To eliminate the relay board, we have to change the behavior of the thermostat so that it turns on when it is to hot, instead of when too cold. This was accomplished by cutting the trace on the circuit board that goes to the pin the relay switches on, and then running a wire from the relays other switching contact to that pin. (For me the pin was connected to the Normally Open side of the relay. I reconnected it to the Normally Closed side instead)
Now the thermostat circuit and the cnc4pc DC relay board inputs need to be on a low power DC circuit. For this, I tore apart an old cell phone car charger and used that as my power conversion board. All i had to do is wire the 12v power in to my main 12v DC power supply (already needed for the cooler), and then wire it through the thermostat to the inputs of the cnc4pc relay board.
The cnc4pc relay board is designed to use low power 5v inputs to switch on a heavier 12v DC load. The 12v switch works by allowing the ground to flow through it. One 12v input is connected directly to ground, and the 12v output is what switches a heavy duty car DC relay on and off by allowing its coil to find ground.
I was not able to control the cooler just with the cnc4pc relay board. The transistor on the board immediatly got super hot and the cooler would only run at 1/3 speed and was only able to draw 2.5 amps (instead of almost 5 it requires). This is why i had to use an automotive relay.
The auto relay always has its positive side of the coil live, as well as the common relay contact. The normally open contact is what sends the positive power to the female cigarette lighter plug. The negative side of this plug is directly connected to ground.
Couple post design notes:
Schematic and pict of finished circuit below.
If you want to remove the cooling element for use in another project heres how. Its actually pretty easy once you see how its put together. Although it will take some persistent prying.
Comments: (2)On 07.10.12 - 3:50pm Clayton wrote:
On 07.10.12 - 5:07pm dave wrote: