Defrost element in fridge as heater: duty cycle

Hi all,
I’ve got my fridge up and running. It has a defrost element, 450W, originally on a timer to defrost the cooling coils in the fridge. I have removed the thermostat and defrost timer, and I am using the defrost element as a heater. It is scarily hot, though, so I’m using a 555 astable circuit to run it at a duty cycle of about 15%, which makes the average power about 67W. What I would like is to change the brewpi code to do this without the external 555. Can anyone help?
Cheers BobbyG

I will add PWM functionality to the official code base soon (I think this month).

now that you say that, my fridge had a defrost element on it as well. I ripped out the thermostat and defroster button that was inside the fridge. But now when its on, the sides start to get really warm. Is that from the defroster? If so how can I turn that off. I have a magic chief 4.3 cube feet black. I hope that it doesn’t burn my fridge up. Please help.

Hi Joe
I have a mini fridge (we call them bar fridges here in Australia!) which I have modified. It had a push button defrost, which just turned off the cooling for a while, to let the ice melt. There was no defrost element. If the fridge gets warm on the outside sides, it’s probably because the evaporator coils are inside the sheet metal casing. Can’t speak for your fridge model, but that is what I found with mine.


Thank you. I think that’s what is. When you look at the back were the compressor is, you can see two small lines running to each side. I am almost done with my wiring for my BrewPi Box. I will take picture this Friday when complete. I will be conducting a brew and fermenting with it for the first time. I just got my new 7gal SS brewtech fermenter in so I am SOOOOOOO excited to use it.