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Old 25-03-2015, 09:22   #76
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Re: Running 220v water heater on 110v supply

Quote:
Originally Posted by rwidman View Post
... Heating elements typically increase in resistance as they heat...
Actually, a nichrome 80/20 water heating element has a reasonably constant resistance (temperature-coefficient of resistance) between 0 & 100 deg C.
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Old 25-03-2015, 11:45   #77
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Re: Running 220v water heater on 110v supply

Same resistance, half the voltage, current is half!!!!!
With a motor, drop voltage, increases current. With a heating element, drop in voltage drops current!

Terry, long time electrical technician!
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Old 25-03-2015, 11:54   #78
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Re: Running 220v water heater on 110v supply

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Originally Posted by TTTech View Post
Same resistance, half the voltage, current is half ...
Which explains 1/4 wattage output on a resistance heater.

Same power, half voltage, current is double:
However, when a load is on a motor, the motor must draw a fixed amount of power. The required power is about equal to volts times amps. Should the voltage fall below the nameplate rating, the amperage will increase accordingly.
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Old 25-03-2015, 12:31   #79
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Re: Running 220v water heater on 110v supply

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Originally Posted by GordMay View Post
Actually, a nichrome 80/20 water heating element has a reasonably constant resistance (temperature-coefficient of resistance) between 0 & 100 deg C.
This 80/20 Nichrome wire is specified at +.000085 Ohms/Ohms/C.

For the OP of a 220VAC 1,200W heater, means this is a 40 ohm resistance heater.

Assuming the water is heated from 72F (22C) to 125F (52C) (per the UL-specified setpoint), that is a 30C temperature rise.

Per the +.000085 Ohms/Ohms/C formula, the resistance will change from 40 ohms to 40.102 ohms.

The power will change from 1,210W to 1,207W, a 0.3% change, a negligible amount.
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Old 25-03-2015, 12:35   #80
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Re: Running 220v water heater on 110v supply

sweet Jesus , die thread die
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Old 25-03-2015, 14:57   #81
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Re: Running 220v water heater on 110v supply

Aww come on now Dave, it's only just starting to get interesting.; there will pages more for sure
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Old 25-03-2015, 16:06   #82
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Re: Running 220v water heater on 110v supply

Dave,

Don't worry. I read the other day Google is going to start blocking search results wherein there are factual errors in the links. Wonder how much of this forum will not be found then?
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Old 25-03-2015, 16:32   #83
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Re: Running 220v water heater on 110v supply

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Originally Posted by TTTech View Post
Same resistance, half the voltage, current is half!!!!!
With a motor, drop voltage, increases current. ...........
So when the voltage equals zero the current is infinite?
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Old 25-03-2015, 17:18   #84
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Re: Running 220v water heater on 110v supply

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So when the voltage equals zero the current is infinite?
Ron, I'm sure you are just stirring the pot!

Some of us would think "so when the voltage approaches zero, the current approaching infinity"

However feel free to continue geting the stuff in the pot nicely stirred
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Old 25-03-2015, 17:23   #85
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Re: Running 220v water heater on 110v supply

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Originally Posted by GordMay View Post
.....
However, when a load is on a motor, the motor must draw a fixed amount of power. The required power is about equal to volts times amps. Should the voltage fall below the nameplate rating, the amperage will increase accordingly.
GordMay, is this universally true? With in reasonable limits that is.

I have always understood this was function of how the motor is wound (stators and rotors) and also partly a function of RPM and of course load. Nevertheless, I could be wrong
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Old 25-03-2015, 17:26   #86
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Re: Running 220v water heater on 110v supply

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sweet Jesus , die thread die
LOLZZ
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Old 25-03-2015, 17:28   #87
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Re: Running 220v water heater on 110v supply

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So when the voltage equals zero the current is infinite?
Cool! The answer to global warming! A zero voltage power transmission system. Although you'd have to dump the difference between the power you need, and infinity, which could be a problem. A really big heatsink could be the answer.
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Old 25-03-2015, 17:57   #88
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Re: Running 220v water heater on 110v supply

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I read the other day Google is going to start blocking search results wherein there are factual errors in the links.
If true, there go the RWNJ sites!

I have sympathy for Dave - having contributed so much about the safe installation of mains AC on a boat it must be hard to take a thread which starts with (roughly) feeding 120VAC into a boat's 220VAC system then asking after the fact if anything could have been broken.

Making hot water with an electric water heater is simply not a critical enough need to be taking such risks IMHO.

Greg
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Old 25-03-2015, 18:13   #89
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Re: Running 220v water heater on 110v supply

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GordMay, is this universally true? With in reasonable limits that is.

I have always understood this was function of how the motor is wound (stators and rotors) and also partly a function of RPM and of course load. Nevertheless, I could be wrong
For AC motors it is mostly true. Many AC motors try to turn at a speed that is a function of the AC line frequency. The power delivered by the motor is usually a function of speed (more speed requires more power). As the line voltage goes down the motor draws more current in an attempt to keep its speed/power the same. The higher current can cause the windings to overheat.

Running them at too low a frequency causes a different problem but the result is the same. The current gets too high and the windings overheat.
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Old 25-03-2015, 18:42   #90
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Re: Running 220v water heater on 110v supply

You can buy a 220-110 transformer for about $80 on E-bay.
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