by ericmark » Sat Sep 03, 2016 10:36
Yes well done, a few questions as when I did it the control was exterior to the freezer and the freezer was upright and frost free. With that set up the problem is keeping the freezer running for a reasonable time, there was in my case two delays set, one in the external controller this was set to maximum, and two the freezer went through a self check which further delayed the start. This means the pressure has plenty of time to drop before the compressor tries to restart.
However that was not enough, there is a large mass with a fermentor and the freezer air reached 8°C when first switched on with the fermentor at 23.8°C and set temperature 19°C it ran for 40 minutes with the sensor strapped to fermentor and insulated from the ambient air in freezer with a sponge. In the 12 minutes before it could restart the fermentor temperature rose to 19.8°C so clearly I was not running motor too long. The aim is to run the motor for a reasonable time each time it switches on, but not long enough to cause the temperature of the fermentor to go below the 0.5°C set as the differential or it will cause the heating and cooling to cycle with the over shoot.
With the chest freezer unlike my upright there is no cooling fan, also the evaporator is not hidden behind a plastic panel meaning as soon as it switches off the cooling stops. So the sensor placing could well be different to that used with a upright freezer. However using the sensor pocket used by the original sensor with a fermentor which is rather a large mass, is possibly not the best location. The chest freezer is designed to maintain the temperature at -18°C where the upright is often designed to freeze fresh food with special locations where the fresh food can be placed so it will not heat up existing food, and the ability to cool the warm air every time the door is opened, so there are very different in design. With mine I found the existing control was too complex to consider bypassing, including solenoids to cool freezer before it starts cooling fridge. Hence selecting external control.
So now yours has been running a year, how have you found it? Have you done any further mods, where is the sensor?
Mine is set to 0.5°C differential so setting at 19°C the fermentor is held at 18.5 to 19.5°C since monitoring fermentor temperature with a Wherry I could select 1°C differential however unsure about using 2°C as you say was done with yours, as with a STC-1000 with heating as well that means 4°C total and unless on the fermentor the fermentor temperature would vary more.
However I found my set-up did not run as expected, I thought it would over shoot on cooling, that is what I expected, but when I came to use it I found it did not over shoot by even 0.1°C the same however was not true for heating, started with an 18W underfloor heating tile, it was too high in wattage and to large in mass, swapped to an 8W bulb.
I use both the freezer and fridge compartment, I have a STC-1000 running freezer with cooling and heating, and a second similar device in the fridge only heating, the fermentor spends 5 ~ 10 days in freezer, then a further 5 ~ 10 days in fridge, as once the first 5 ~ 10 days are up I find it does not need cooling.
So again what have you found now it has been running a year? Please give us all an update.
Despite that, the keezer has run happily all year 