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Old 21-03-2015, 10:01   #16
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Re: Running 220v water heater on 110v supply

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Originally Posted by mike d. View Post
Am I missing something here? If you change from 220 to 110 you increase amperage by 2. Also your wiring to the water heater, if made for 220 apps. will heat up exponentially, and cook, ...
The myth was debunked and question answered expertly a few posts above ...

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Originally Posted by MarkSF View Post
Any understanding whatsoever of the physics involved.

P is not fixed. The formula to be used is P=V^2/R. R is the resistance of the element. You get a quarter of the power, at half the current.
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Old 21-03-2015, 10:06   #17
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Re: Running 220v water heater on 110v supply

Determine what gauge your wiring is and how long. It may be fine
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Old 21-03-2015, 10:16   #18
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Re: Running 220v water heater on 110v supply

Seems the point is being missed. The wattage is semi material. The element's resistance is not going to change. Half the voltage the current doubles.
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Old 21-03-2015, 10:18   #19
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Re: Running 220v water heater on 110v supply

Ok thanks so, the correct answer is half the current, no problem with the wiring to the water heater? Just wanting to clarify as others have posted the wires will fry etc...
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Old 21-03-2015, 10:20   #20
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Re: Running 220v water heater on 110v supply

This is a classic misunderstanding of the physics in play
The heater is a resistive element
The resistance remains constant regardless of voltage
A 1200W heater rated at 240v has a resistance of
R = V^2 / P
R = 240x240 / 1200
R =48 ohms
Power = V^2 /R
At 120 V P= 120x120 / 48
P= 300 watts
Amps = V / R
A = 120 / 48
A = 2.5amps
You get 1/4 the power
Wiring is fine in all regards
It will take much longer to heat the water
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Old 21-03-2015, 10:32   #21
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Re: Running 220v water heater on 110v supply

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Ok thanks so, the correct answer is half the current, no problem with the wiring to the water heater? Just wanting to clarify as others have posted the wires will fry etc...
You are halving the voltage thus doubling the current. I don't wish to hear you have fried wires or a floating ash.
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Old 21-03-2015, 10:40   #22
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Re: Running 220v water heater on 110v supply

Cadence you are mistaken
The resistance does not change
I am an EE and have dealt with hundreds of heating applications
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Old 21-03-2015, 10:46   #23
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Re: Running 220v water heater on 110v supply

Put another way the 1200 watt rating is based on running it on 220 volts
The wattage decrease watts = P
P = V^2 / R
Wattage is reduced by a factor of 4
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Old 21-03-2015, 10:51   #24
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Re: Running 220v water heater on 110v supply

Think of Voltage as available water pressure
Think of heating element as some restriction in a pipe. At 200 psi coming into the pipe you get a certain amount of flow (flow is current is amps)
If you cut the pressure in half to 100 psi you are not going to get double the flow right? You are going to get less... Much less current
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Old 21-03-2015, 11:04   #25
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Re: Running 220v water heater on 110v supply

Taking it to extremes with the bogus understanding posted above, if you lower the voltage to zero, you would have INFINITE current !!

Sailski has the correct answer.

To put a fine point on it, the heating element resistance will drop slightly, but not enough to matter in this discussion.
In other words, as it heats, the resistance goes up but only a tiny amount.
With 110 volts, the resistance will be slightly less than with 220.
Maybe a few percent, that's all.
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Old 21-03-2015, 11:28   #26
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Re: Running 220v water heater on 110v supply

I'll ceed, you won't double the current, you'll halve it/approx.. Just cold showers or high electric cost. I hope the power comes with the slip.


Not often saying I'm wrong.
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Old 21-03-2015, 11:32   #27
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Running 220v water heater on 110v supply

Cadence. The power bill will not change much. The only effect will be how long it takes to heat the water. It will take a little over 4 times longer. So if it takes 30 minutes with 220v it will take 2-3 hours at 110V. But the power cost is about the same.
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Old 21-03-2015, 11:40   #28
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Re: Running 220v water heater on 110v supply

And start turning off the electric element whenever you can. Showers or not. I find mine heats up in 20-25 minutes. Don't leave it on after the water is hot and you'll never run it dry with the element on. While I'd never heard of anyone doing this before (and I've been working with mine for almost 17 years and read boating forums daily) I have always counseled folks to turn the power off to the heater as soon as they can. Just another good reason to do so.
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Old 21-03-2015, 11:41   #29
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Re: Running 220v water heater on 110v supply

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Cadence. The power bill will not change much. The only effect will be how long it takes to heat the water. It will take a little over 4 times longer. So if it takes 30 minutes with 220v it will take 2-3 hours at 110V. But the power cost is about the same.
I will have to go with that. I know nothing about thermodynamics? Sorry I turned the Ohms law around. Only excuse is it's been a long time.
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Old 21-03-2015, 11:44   #30
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Re: Running 220v water heater on 110v supply

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Originally Posted by mike d. View Post
Am I missing something here? If you change from 220 to 110 you increase amperage by 2. Also your wiring to the water heater, if made for 220 apps. will heat up exponentially, and cook, because you are now forcing more electrons through the same narrow wire. , also your cycles are higher, though this should only affect some electronics? Also when you run your water tanks down to the point of pushing air, you will be pushing air into the water heater, which is detrimental to the elements, if they are on. When air hit air bubbles hit the elements, it will cause hot spots. If you have only air hitting the elements the elements will over heat and burn out.!!!!!!!!
Yes, you are missing something. If voltage is halved amperage will only increase if you replace the heater element with a heater element that has one quarter of the resistance of the European one. OP has not replaced the heating element. Only then the current will double and the power will be the same.
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