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21-03-2015, 09:01
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#16
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Registered User
Join Date: Dec 2012
Posts: 449
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Re: Running 220v water heater on 110v supply
Quote:
Originally Posted by mike d.
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, ...
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The myth was debunked and question answered expertly a few posts above ...
Quote:
Originally Posted by MarkSF
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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21-03-2015, 09:06
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#17
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Registered User
Join Date: Aug 2006
Location: Skagit City, WA
Posts: 25,477
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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
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard
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21-03-2015, 09:16
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#18
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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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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21-03-2015, 09:18
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#19
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Eternal Member
Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
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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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21-03-2015, 09:20
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#20
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Registered User
Join Date: Feb 2012
Location: Manchester, MA
Boat: Beneteau 473
Posts: 8
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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
Best of luck
Captain Tony C.
S/V Limonata
B473
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21-03-2015, 09:32
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#21
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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Re: Running 220v water heater on 110v supply
Quote:
Originally Posted by monte
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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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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21-03-2015, 09:40
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#22
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Registered User
Join Date: Feb 2012
Location: Manchester, MA
Boat: Beneteau 473
Posts: 8
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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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21-03-2015, 09:46
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#23
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Registered User
Join Date: Feb 2012
Location: Manchester, MA
Boat: Beneteau 473
Posts: 8
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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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21-03-2015, 09:51
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#24
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Registered User
Join Date: Feb 2012
Location: Manchester, MA
Boat: Beneteau 473
Posts: 8
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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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21-03-2015, 10:04
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#25
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Registered User
Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 7,145
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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.
__________________
The question is not, "Who will let me?"
The question is,"Who is going to stop me?"
Ayn Rand
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21-03-2015, 10:28
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#26
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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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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21-03-2015, 10:32
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#27
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Registered User
Join Date: Oct 2011
Boat: Valiant 42
Posts: 6,008
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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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21-03-2015, 10:40
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#28
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Registered User
Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,704
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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.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
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21-03-2015, 10:41
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#29
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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Re: Running 220v water heater on 110v supply
Quote:
Originally Posted by transmitterdan
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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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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21-03-2015, 10:44
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#30
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Registered User
Join Date: Jun 2009
Location: BVI
Boat: Leopard 40 (new model)
Posts: 1,385
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Re: Running 220v water heater on 110v supply
Quote:
Originally Posted by mike d.
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.!!!!!!!!
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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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