by Richard Lewis
Some of you have read my ebook Homemade Amp Meters. In it I talk about using cheap metal such as zinc plated or stainless steel "all thread" or "ready rod" as a shunt for measuring amps. You can run the current through this all thread and take a cheap multimeter and connect the two leads at a very precise distance apart, then the milivolt reading would equal the amps. I include free software with the ebook that computes that distance among other things.
But, what I don't say in the book is that you can use stainless steel all thread as a heater element. For instance, if you were to put in the calculator "shunt calculator" 1/4 inch stainless steel and you have the 1 milivolt (mv) setting, then it would show 1.027 inches as the result. What that also means is that every 1.027 inches of 1/4 inch stainless steel all thread would be 0.001 ohms in resistance at room temperature.
If you take the equation Power = Voltage ^2 / Resistance, and took a 36 inch piece of all thread, then...
12 volts ^2 / (36/1.027) * 0.001 = 4,108 watts. After the stainless steel gets very hot, it increases the resistance and then puts out about 3,000 watts or so. If you were to put cooling fins of some sort that were painted with flat black high temp paint, you could keep it at 3,500 to 4,000 watts or so. Same is true if it were in water.
I know it sounds crazy, but people are spending lots of money on heating elements or some other load for their windmill (when the batteries are charged but the windmill is still spinning). I've seen $25 to $80 per 12 volt heating element and they are only 600 watts. You would have to buy 7 of these and spend $175 to $560 plus shipping just to get 4,000 watts of heating. And those heating elements will burn up if they aren't exposed to water. With the stainless steel, you can use it in the air for an air heater system or you can use it in water. Coolest part is, you can go to the local building supply store to pick it up. I found it at Home Depot. But, make sure it is stainless, not galvanized.
I've also seen the use of light bulbs. But remember, a 100 watt light bulb is meant for 120 volts. If you put 12 volts through it, then you will only be at 1 watt (NO, that isn't a typo, it is really only 1 watt). So, that wouldn't work. You could take car headlamps. They are about 2 to 3 amps. So, that would be 24 to 36 watts each. You would need more than a hundred of them (to equal the stainless steel option) at $5 each. Hmmm, still not a good solution.
You could try a 120 volt heater. But, at 12 volts you would be at 1/10th the voltage and therefore 1/100th the power. So, a 1500 watt space heater would put out 15 watts of heat at 12 volts.
Anyway, I hope you can see the merit of using a simple all thread stainless steel rod as a heating element.