Sunday, November 28 2010 @ 11:50 AM EST
Contributed by: Admin
Though Tony runs his system on 220V, we've opted to start with 110V. It's our hope reducing the amount of water to heat will enable us to raise the temperature of the water in the mini-exchanger at an acceptable rate. Given our limited math abilities, we estimate the 1125 watts through our heating element will raise the temperature by 2.6 degrees F per minute. Should we decide 110V is not enough power, the SSR used to switch the element is rated for 240V at 40A -- more than enough for us to convert to 220V.
In June of 2003, we replaced the 220V element with a 2000W 110V element. While the 220V element gave us an acceptable temperature rise, we thought the extra wattage offered by using a 110V element at 110V would allow us to boost temperatures more quickly. The result is a more robust, 3°F a minute rise in the water temperature without recirculation. While doing a recirculation, we get closer to 2°F a minute.
The mini-exchanger is constructed from a hacked Cornilliues keg. You'll probably recognize this as a soda keg from a restaurant or convenience store. The top was removed with a Dremel tool fitted with a heavy-duty cut-off wheel. Water was put into the keg in an attempt to keep the side walls cool and flying sparks from damaging the keg's interior. Sharp edges were ground with a grinding attachment on the Dremel. Once the top was removed, it was scientifically attached (what's a project without the use of duct tape?) to the bottom.
A 4500 watt 240 volt heating element (run at 1125 watts, 110V) was attached to the bottom of the keg. Here we had to rig a hack-job as the desire to cut the keg overran the ability to think and plan ahead. Once the hole for the element and connection bolts were drilled, the element was placed into the keg through the now way-too-large hole in the bottom. Seating the element was easy; getting the seal watertight was not. Every time we attempted to screw the element down onto the rubber gasket, the gasket would be pushed into the tank through the hole.
To make the element seat watertight, a 3/4 inch stainless steel washer was cut in half with the Dremel tool. The heating element was suspended into the keg and the two halfs of the washer were pushed together around the element and siliconed to the bottom of the keg. Once the silicone had dried, the element was wrenched down and an effective watertight seal was enjoyed by all. And there was much rejoicing.
The 1/2" copper tubing was coiled around a piece of 6" ducting. Once the desired height of coil was achieved, the tubing was bent to the compression fittings with a tubing bender. The tubing bender turned out to be too difficult a technology for us to master so we put a couple of 90° elbows in and ran extra tubing to our bulkhead fittings.
Bulk head fittings for the mini-exchanger were created with items available at the local hardware store. A 1/2" close nipple was placed through a hole in the keg wall. On each side of the keg, an O-ring, stainless steel washer and NTP nut was screwed onto the nipple. Compression fittings bind the coil to the nipples. Simple, watertight and easy.
Because we are using only one-quarter of the wattage for which our heating element is rated, the thermal properties of the mini-exchanger become important. We did not want to lose our heat through the walls of the keg and decided some insulation was in order. A regular water heating blanket was cut, stapled, bound with more duct tape and wrapped around the keg. The same 6" ducting used to coil the copper tubing was cut apart, pop-welded and refastened around the insulation and keg. Of course, some nifty holes had to be drilled to allow the coil's outlets to be accessed -- tin snips and the trusty Dremel tool was used for this (about time to replace the brushes on the Dremel, I'm sure!)
Circulating the warm water over the coils helps distribute the heat and give the thermocouple a more accurate reading. A cheap motor was joined to a paint stirrer. A plastic stirrer was melted off it's iron post by heating the iron with a brasing torch. The soda's keg stainless steel pickup tube was cut down, heated, and pushed into the plastic stirrer. Some grinding of the motor's post was required to fit the tubing around the post. A small slit in the stainless pickup tube ensures the visible hose clamp can effectively clamp the pickup tube to the motor. The motor runs during circulation; however, we do have the ability to stop the motor from a switch on the control panel. Thanks, Steen!