Transformer to change 580watts to about 320watts?

Question

I have a 240v heating element that is 580watts but i need it to be about 320watts (for lower boiling temp), ive read that a transformer can do the job, but what would be your advice? I cannot change the element only the input.

Thanks

Answer 1

If the resistance of the heating element is fixed at ( R = 240 volts squared / 580 Watts) 99.3 ohms then you can reduce the wattage to 320 watts by lowering the voltage across the heating element to ( Volts) = [the square root of (320watts x 99.3 ohms)] =178.3 volts.  This could be accomplished by the use of a transformer with a primary winding that matches whatever commercial voltage that is available and a secondary winding output of 178.3 volts.

The above is what could be done but my advice would be to purchase a 320 watt heating element if that is what you need and forget about the transformer.

Answer 2

A heating element is a function of voltage(240) acting through a resistance  to obtain a devised wattage(580)..The resistance is a function of the ohms per dimensional length of element..to reduce the resistance and lower the amperage and effectively reduce the wattage you must shorten the element. use a tap  that uses the same ratio as your depletion concept..in this case 580-320= 260  now divide 260 by 580 to get the percent that you need to reduce the length and that is 44%..measure the physical length of the element and tap in leaving 56% one the long end..If your element is sealed you are stuck with the rating..Ohms law will show this P=I x e The 580 is p the I is the amps and E is the volts..If you change the voltage by decreasing it the only thing you change is the amperage drawn,,,The only way you can change the electrical length of a resistance heater is to tap at another point or change the heater...when considering placing a resistance load inline with the heater voltage supply the effect is reducing the voltage by increasing the resistance ..Lets say you reduce the voltage to the 44% amount 240 x .44=105.6vac is your taget..of reduction leaving 134.4vac...with this number you can make an assumtion ...that is that if you take the same heater (pure resistance) and place 120vac across it the approximate wattge output would be near your target..So a x-former with a 2:1 ratio would probably work or just find an available 120vac source.. The other application would be to find a variable resistor (measure you heat strip calculated to be 100 ohms) and buy an adjustable linear taper resistance to accomplish this ..such as an ohmite ....This last example would probably be the easiest to accomplish..if your in a lab use a variable output transformer and experiment...there you go lots of choices from the E...

Answer 3

First question is how does it do on 120V? Might be close enough for your purposes. My guess is that you'll end up with only about 200W.  You can get adjustable step up variable transformers that would do the job, but I think a new one runs about $200. It's a big old chunky thing. A 1:1.5 step up may do it, I'd go to 1:2 if available to be sure.

You could use a variable resistor, but it's gonna have to be like 150Watts or so... maybe a 240V light bulb or appliance in series! Kind of a kludge.

Better than a xformer, you should be able to use a 240V dimmer like a lamp  dimmer if you can find ond for 240V. Serveral countries in Europe use mostly 240V 50Hz, but this should not be sensitive to frequency, so you may be able to get off the internet from the UK. Resistive loads are benign, if it is rated for the 700W, you're good to go.  Alternately, a stove controller should be 240V. Mine is built into a computer gizmo, but you should be able to get lower end or older style parts on eBay for way cheap. The k**b to adjust is very easy. I believe it uses an scr or two to fire part of the waveform, reducing the power very easily. Looks like its a simple analog circuit, should behave nicely.

The great thing about a controller is that if your original power estimate is off a little, EZ to adjust.

Whichever you make, put it in an enclosure for safety.

Answer 4

Voltage regulators don't work on AC

Wings is correct, you may be able to find a controller.

E is totally wrong, tapping the resistance lowers the resistance and increases the wattage.

Mr is correct, a transformer will work as he describes it, but this is expensive.

Your best bet it to get a heater element of the proper size.

PS, the boiling temperature of water is fixed, you can't lower it with less heat.