johnson controls thermostat ?

I'm building a incubator out of a display cooler and I'm considering using the johnsons thermostat connected to a fan.

has anyone used these before ?

here's my ?

if i go with the johnsons unit its a on/off unit so the fan will run when the heat element is on.

if i go with a helix or herpstat unit they are proportional units so i assume the fan would stay on all the time.

any input would be helpfull

thanks Jeff

Originally Posted by purehate

if i go with the johnsons unit its a on/off unit so the fan will run when the heat element is on.

The Johnson is an on/off deal. There is an anti-short cycle delay option and a "turn on or off in case of failure" option. I like both options.

Helix or Johnson, I'd put your fan on a separate plug. You want it running and moving air at all times - and not layering air (or partially letting the temps layer) when the heater isn't running full. That's be mu suggestion!
KJ

As far as incubators go I like the higher accuracey of the pulse proportional thermostats, the on/off ones will work fine though. Wiring the fan separately sounds great, maybe put it on a rheostat (dimmer) though so you can adjust the speed. Yes it needs to move air but not at hurricane forces lol.

thank you both for your replies.

I'm looking into the helix or herstat units now.

any comments on these would be helpful

thanks Jeff

You definitely want your fan(s) wired separately from your thermostat. The air should be circulating constantly not just when the heat is on. If you don’t there is going to be a large difference between top and bottom temps. I normally use 12 volt computer case fans for my incubators and have never had to adjust fan speeds. If you are using a 120AC fan you may but I haven’t played with them much.

I would also recommend going with a fully proportional thermostat not a pulse proportional. It is late but from my understanding the difference is the fully proportional will regulate the voltage output being supplied to your heat source where a pulse proportional varies voltage pulses per cycle to the heat source. The farther away from your target temp the more pulses per cycle the closer you get the less pulses cycle. So basically you are turning on and off the heating device at varying speeds to get you desired temp. Changing the voltage output as in a fully proportional thermostat is a much more efficient and accurate way of getting the job done. Both the Herpstats and the Helix are fully proportional but I prefer the Herpstat as it has more bang for the buck.

Hope this helps,
George

Actually pulse proportional doesn't intelligently fire within the ac cycle. (Had to call you out on that one george. :^) Basically it does pulse the electricity at various times and the longer the on time of the pulse the more heat you will get. No tracking of the ac sine wave is needed for that. True proportional gives actual control over the power output and allows a dimming style control that is easier on heating devices. 12Vdc computer fans are great start for incubators and you can always wire in a resistor from radio shack if the fan puts out too much. I also sourced some neat 120vac 4 inch fans from walmart the other day at $6 (right in their normal household fan isle) that I think would work well. They have plenty of airflow and you could just wire them direct to the same ac plug that you plug your thermostat in to. This route avoids having to use a 120vac to 12vdc transformer and would be cheaper. Haven't tried them out yet in an enclosure myself but they are neat and relatively the same noise level as the dc fans. Either way good luck with your project!

Dion Brewington
Owner, Spyder Robotics

thanks everyone for the replies.

george thanks again for your help on the heating element.

jeff