Running a 230V heating element using 120V

Question

Would a heating element that is rated at 3000W at 230V actually heat properly if the element was powered by 120V only? My hope is that it will just take longer to hear up, but worry is it can't get hot enough.

Get hold of a step up transformer of the correct power rating. — Andy aka, Feb 05 '14 at 18:08

score 3 · Accepted Answer · answered Feb 05 '14 at 17:50

3

I would guess not. The power output will only be 25% of the design power when operated from 120VAC (power is proportional to the voltage squared, so cutting the RMS voltage in half, cuts the power to \$1\over4\$.

The actual answer will depend on the heat loss (at operating temperature) from the boiler assembly, which is difficult to guesstimate.

The heater would not be damaged by low voltage, but if there's an electric pump in there, it could be (if it stalls it could draw excessive current and overheat, even at reduced voltage).

answered Feb 05 '14 at 17:50

Spehro Pefhany

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To Casey: if you have a way to see how often the heater is on in the 230V stable situation: if it is significantly than 25% it will probably be OK on 120V, if more 25% it will never reach the requires (boiling?) temperature. – Wouter van Ooijen Feb 05 '14 at 18:04
@WoutervanOoijen This is a good suggestion. – Spehro Pefhany Feb 05 '14 at 18:06
It turns out you are right, it will not heat enough. – Casey Gregoire Feb 15 '14 at 17:23

score 3 · Answer 2 · answered Feb 05 '14 at 19:05

You could make an argument to say it will get to the same temperature but take longer. It goes like this: -

The heating "coil" inside its hermetically sealed case will probably rise internally up towards 200+degC when powered. This might be the temperature on the surface of the actual Nichrome wire carrying the current. On the surface of the element's case the temperature will be definitely above 100 degC in order to raise the water towards the correct temperature (is it 93degC for good coffee?). If the heat losses are small (because of decent insulation) I'd expect that the average power needed to keep the well-insulated volume of water at 90 to 100degC will be no more than 10% of 3 kW or 300 W.

0.3 kW is easily got with a 3 kW element running at half voltage so the question remains how long will it take to get to "final temperature" and I'm not able to answer this but one interesting observation is that nichrome wire, for a 3 kW heater on ~230V has a cold resistance of about 15.7 ohms check this wiki page out. So, initially you'll be providing about 3,300 watts. But at half voltage that's only 825 watts.

It all boils down (forgive the pun) to understanding where the heat losses might be and if low enough then 800 watts will raise the water to the right temperature eventually.

Running a 230V heating element using 120V

2 Answers2