I finally got around to doing something about my home made nitrous bottle heater problems last week. I've had issues for years trying to keep a constant temperature for the Nitrous Bottles in my Bottle Heater. The old controller I was using was a mechanical thermostat setup from Johnson Controls, it worked, but it didn't hold a very tight temperature and I was always wondering exactly where I had the temperature set. The dial wasn't really a high accuracy deal. So I pulled the old controller off and switched to a Johnson Controls A419ABG-3C Digital Thermostat and it was a HUGE improvement. The A419 allows you to hold the temp at +/- 1 degree F, far better than the old mechanical control.
Note:The Model A419 has been superseded by a new model #421, the new part number to use is the Johnson Controls A421ABG-02C A421 Series Electronic Temperature Control with Pre Wired Power CordDo read the instructions before you put one of these into service, you may need to move both of the jumpers on the inside to the on position to set it for Heat Mode and adjust the settings in the program. One thing I found out is the sensors for units like this need to be kept dry, which requires a bulb well which transfers the temp from the hot water bath to the sensor to keep the sensor dry. This particular model is nice because it comes with the electrical cords all setup.I used a Johnson Controls Bulb Well Assembly WEL11A-601-R which I picked up on ebay cheap - note, make sure you get one with the spring which helps hold the sensor seated inside the well. I also used thermal paste to help it transfer the temperature to the sensor better. It's the same kind of paste you find on heat sinks for computer chips. That all seemed to work pretty darn good, the A419 holds the bottle temperature very steady, combined with the large volume of water and the insulated Igloo cooler tank it doesn't vary much at all once it gets up to temp. To generate the heat, I'm using a 1500 watt heater element, it's a PN# TG-1153L 1500 watt element. I'd like to find a lower wattage one to lower the generator load, but 1000 watt elements are not easy to locate I've found. I also use a little pond pump inside the heater to stir the water up some to keep the temperature even, it does seem to help a little bit. You can find these at most Lawn Centers for about $25 or so. With the upgraded controls the nitrous bottle heater is very accurate , on par with anything you can buy for a lot more money, and compared to the non-insulated tanks most store bought setups use, the Igloo cooler insulates the bath so the unit doesn't have to cycle so often to maintain it's temperature. Update - Do remember to put water in the bottle heater BEFORE turning the power on. Here's the results if you forget sometime... Also check out the new Trailer Mounted Nitrous Bottle Heater I built, complete with secondary safety switch.