brunnhilde's digital thermostat

I have been dissatisfied with the air conditioner's mechanical thermostat. Its temperature range does not allow one to keep a warmer cabin temperature so the air conditioner when used making the cabin temperature too low. Due to the small cabin space and you cannot escape from the high velocity of the frigid air streams. I tried tuning the thermostat to no avail. Time to do something about it. I didn't want to buy any digital thermostat made by any of the RV AC companies as they are all crap, designed by idiots, and for the kind of RVs that I have no interest in. I decided to look into the low cost Ink Bird temperature controller which you can get for around $16 USD. I ordered one with 110Vac powered to explore if it can be integrated well with the Coleman Mach 8 Polar Cub we have.

There are many things to think about, and high on the list is ease of operation when used in conjunction with the recently added variable blower speed control and the master power switch. Of course the ability to properly regulate the desire temperature is of utmost importance. Also it must not cause short cycling of the compressor which can cause the Honda generator to overload and enters overload lockout.

the temperature controller consumes about 55mA at 12Vdc worst case

The power consumption of the temperature controller is not a concern as compared to that of the air conditioner it is immaterial. What is important is it be powered by 110Vac as the Coleman is so when the master power switch is off, the controller is switch off. It should also retain the power off on/off state when power is applied. In my testing with 12Vdc it is.

I jerry rigged up the controller for functional tests

This controller allows me to set the target temperature to any reasonable ambient desired. The dead band for the temperature can be anything from 1 degree C or 3 degree F to a very large spread so that too should permit me to dial in how the compressor would cycle. The other excellent feature of the controller of the programmable compressor lockout from 0 to 10 minutes, albeit at one minute increments.

in this test cycle I set the target temperature at 76F; the value in the display shows the actual temperature the NTC thermistor sees while I placed it in the air stream of the cold air outlet

If you ever play with HVAC controls you would know that there are many variables that influence the cycling of the compressor. The ability to set the dead band spread is very important as well as the placement of the temperature sensor. Without getting into the details of my tests I would just say I am quite pleased with the Ink Bird controller as the viable candidate. Unfortunately it turned out the Amazon listing wrongly represented the 12V version as the 110-220Vac version. I blew up when I set out to verify it is really the AC version. I re-order one from another brand but is really the identical design as the Ink Bird because I saved a few dollars.

The next challenge is to find the most ideal location for it. The Kerstner control panel is already jam packed. While I can make a customer faceplate for it I don't want to enlarge the existing cabinet cutout if I can avoid it.

fitting the Ink Bird to the Kerstner control panel is out of the question; however I think I have a shot at fitting it with the other controls if I make a custom faceplate using the existing cabinet opening

I can also use this location that is the now defunct black water level indicator

The Ink Bird controller would fit in nicely in the location of the defunct black water level indicator. However it is too far away form the other AC controls and would lose functional association with them - a major usability issue for me.

By fabricating a custom faceplate in place of the Kerstner control panel I can pack the speed control dial closer to the master power switch to make space for the Ink Bird. From the photo above it looks viable without having to enlarge the cabinet opening.

I also thinking ahead in the future should I want to use another Ink Bird for controlling the DC refrigerator the black water level indicator location would be a nice home for it. Why? With the glaring LED display it is in a location that is not so glaring at night when all the lights are off. I can also hack the Ink Bird to add a display enable switch. Again, I want to have the cakes and eat them too with thoughtful designs.

I order two temperature controllers, one AC and one DC.

Somewhat related, I also planning to tame the excessive exterior noise of the Coleman Mach 8 Polar Cub. While there are aftermarket kits out there for it, I want to create my own. I already have some ideas as well as researched the costs of these components and their feasibilities.

While this post is not about converting the DC fridge form the Westfalia's central control console to the Ink Bird temperature controller I thought of how to tame the glaring right red LED display at night time. I can hack the Ink Bird and add a display enable switch with a SPST small rocker switch next to the controller. I can make it press to enable so the display only illuminates when I want to set or check the temperature. The benefit of converting to the Ink Bird is it allow for real time readout of the actual temperature, without using another thermometer which invariably requires bring in a sensor to the inside of the refrigerator.