Now-- I dont know what a relay is-- first time ever pursuing a project like this, so lease forgive the amateurish questions. Can you briefly explain what that is-- and what its function is and where one could pick one u or buy it from-- if NEEDED.
A "relay" is a device triggered by an electrical current to switch on or off another electrical circuit. The Ranco device has such a relay built into it; this relay turns the device connected to it, such as a heating element, on or off. I have configured my Ranco to use an external relay because the internal one can not power a device that requires over 16 amps (for a 120 vac device) or 8 amps (for a 240 vac device). Where as the internal relay is sufficient to power a 1500 watt vac heating element (1500 watts / 120 volts = 12.5 amperes) it can not power a 4500 watt 240 vac heating element (2500 watts / 240 volts = 18.75 amperes). I have a non-cheese making use for the Ranco that draws more amps than the internal relay can support. A 2000 watt 120 vac would require an external relay (2000 watts / 120 vac = 16.66 amperes).
And secondly-- I've myself been trying to figure out which heating elements to buy.
I find the 1500 watt element sufficient for my cheese bath. The trick is to figure out how hot to heat the water initially (and then turn off the element) in order to heat up the milk to the target temperature and get the water bath temperature to drop to that temperature as well. My first go around my water bath was too hot and thus the milk temperature continued to rise after hitting the target temperature. I'm still working on refining my procedure.
One important construction note is that the material that the water bath tub is made of must be able to be exposed to high heat without melting. The tub I bought at "Cash and Carry" is made of polypropylene, as I recall.
My common goals for my bath are to hopefully:
A.) Heat u quickly whenever need be at preferably a rate of either 2 degrees or maybe even 3 degrees er minute
B.) Slow down the heat to be able to heat the bath u to 1 degree er minute whenever the initial cooking/acidification process begins.
C.) And most importantly-- be able to maintain a stable target temperature over an approximate number of hours.
Now I figure C would be tackle with the use of a Ranco controller. And that simple math of the size of my vat plus water bath could approximate the amount of heat I would need in order to tackle the requirements of both A and B.
"A" and "B" really are contingent upon the amount of milk being heated and, of course, the surface area of the "double boiler" vessel exposed to the water bath, as well as how quickly the water bath can be heated. The more watts the element is the faster the water can be heated. I may put a second 1500 watt element in my vessel; I need to play with it more. Controlled stepping is the most difficult thing to do and I don't have it perfected yet. It really is a matter of technique; how hot to heat the water in order to step up a temperature without over shooting for a given time frame.
"C" is the fairly easy to do with the controller and the 1500 watt element works perfectly for my system.
Its just that I have a hard time trying to differentiate between how much heat a 1500 watt element would put out versus, say, a 2000 watt. And I'm not even CLOSE to understanding what the "120 vac" or "240 vac" label means.
So what element to use? I'm no physicist but I'll pretend. A BTU (British Thermal Unit) is the energy needed to raise one pound of water one degree Fahrenheit. 1 kw/hr = 3413 BTUs. Water weighs 8.34 pounds per gallon.
Say there are 5 gallons of water in your water bath then to raise 5 gallons of water 3 degrees requires 5(gallons)*8.34(lbs/gallon)*3(degrees) = 125.1 BTUs. So 125.1 BTUs/(3413*1.5 kWatt hours) = 0.0244 hours or 1 minute 28 seconds.
But we are not just raising the temperature of the water, we are also raising the temperature of the milk; and milk, not being water, requires more energy to raise its temperature. But let's just assume the milk is water. And let's ignore the fact that we are also raising the temperature of the vessels and also losing heat to the environment. So if we have 4 gallons of milk then it should take less than 3 minutes to raise the temperature of the water and milk 3 degrees with a 1500 watt heating element.
As I mentioned, I'm no physicist and these calculations might be not entirely correct.
As mentioned above by others, "vac" stands for "voltage alternating current." 120 volts is standard for homes in the US. Most electric ovens, clothes dryers, and hot water heaters, however, use 240 volts. A standard 4500 watt water heater element uses 240 volts.
