Very cheap demijohn warmer

[Richie_asg1]

I came up with this yesterday as I had to move two DJ's out of the brew fridge.

It all runs off a standard 12v power supply. I used a 2A rated one but it draws just under 1A so should be fine with that type too.
It uses a pair of 12v handlebar heaters - available as two for £3.80 - Linky
And a thermostat module W1209 for £1.53 - Linky
Also a base that you can cut into a bit as the connections are a little bulky, and so is the wire cover. I used double wall cardboard.
Make sure to tape the temperature sensor onto one of the demijohns. Both should warm up and cool at the same time.
Cover the top in tape to keep it still and make it waterproof. I used wide clear tape.

Now this thermostat is a bit clever (and confusing), but it can function as a cooling type or heating type. You need to set it to H for heating, then adjust the temperature to the lowest value you want. I chose 16°C. It comes pre set with hysteresis of 2°C so will cut in at 16°C and turn off at 18°C. You can change this if you want as it is all programmable. Full instructions here - W1209 Thermostat module.

So for £5.33 you can keep your brew warm and not risk it boiling.
As it is all 12v it is nice and safe to play with. As you get two heat pads you can use them under 2 demijohn as I did, or strap them both to the sides of a larger FV.
Heat rating is 12 Watts for two pads, and 6 Watts for one so should be plenty without going OTT.

 

[lupinehorror]

this is most helpful. thanks for the detailed info. only have one heatpad at the moment so with the colder approaching i'll give this a go.

 

[Richie_asg1]

I forgot to add you also need a socket for the 12v charger. I had a load from CCTV equipment, but one of these will be ideal to connect things easily - They are a standard size of 5.5mm(outer) 2.1mm pin. You can get them as solder type connections, inline or screw terminals, but a type with moulded socket and short flying leads will probably be easier for this project.

Linky