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wayne1yahoo · Feb 7, 2013, 09:00 AM

If I change the voltage on my 3800 watt water heater element from 220 volts to 120 volts wiill it now heat at 1/2 the watts or 1900 watts? I have solar panels and want to slow heat the water during the day and with the proper electrical equipment be able to turn the 220 volts back on should I ever need a quick hot water need.

tkrussell · Feb 7, 2013, 09:54 AM

Will not hurt to give it a try.

hfcarson · Feb 7, 2013, 10:23 AM

So if you manage to do this... what is the ROI ?

wayne1yahoo · Feb 8, 2013, 11:02 AM

Originally Posted by tkrussell

Will not hurt to give it a try.

Thanks but you did not answer my queston on the watts issue?

wayne1yahoo · Feb 8, 2013, 11:04 AM

Originally Posted by hfcarson

so if you manage to do this....what is the ROI ?

I would be able to heat the water slow over a @ 7 hour period when my solar panels are at max output thus saving me about 80% on the cost of heating water

stanfortyman · Feb 8, 2013, 11:05 AM

If you feed a 240V element with 120V it will put out and draw 1/4 the wattage.

wayne1yahoo · Feb 8, 2013, 11:09 AM

Originally Posted by stanfortyman

If you feed a 240V element with 120V it will put out and draw 1/4 the wattage.

Thanks and are you sure this correct? Do you have a basis for this? I just want to be sure before I go to the added cost of buying the new elements

stanfortyman · Feb 8, 2013, 11:16 AM

The math:
240V÷4500W=18.75A
240V÷18.75=12.8Ω
120V÷12.8Ω=9.3A
120x9.38=1125W

stanfortyman · Feb 8, 2013, 11:19 AM

Thanks and are you sure this correct? Do you have a basis for this? I just want to be sure before I go to the added cost of buying the new elements

Sorry , I used 4500 watt elements.

That said, you asked about running 240V elements @ 120V. I assumed you were going to use the existing elements.

If you change the elements to 120V elements they will run at the stated wattage.

stanfortyman · Feb 8, 2013, 11:24 AM

An easier way is the voltage squared divided by the wattage to get the resistance.
Then voltage squared divided by the resistance to get the new wattage.

wayne1yahoo · Feb 8, 2013, 11:52 AM

Originally Posted by stanfortyman

An easier way is the voltage squared divided by the wattage to get the resistance.
Then voltage squared divided by the resistance to get the new wattage.

May not use 3800watt elements, just used for the question.
The 4500 watt elements looks like will be about right. I will go to a chart for raising 1 pound of water 1 degree F. To calculate the time I will use average water temp in the 50 gallon tank at 10AM to raise the water temp to 120 or 130 degree F at about 5PM in the afternoon. These calculation will tell me what- watt element I will need to use for the 7 hours I will run the hot water heater elements in the tank. They make a timer and volt controler unit to allow me to run on 120volts unless I need some fast hot water by switching to 220volts. My current solar panels are putting out average 1.25Kwatts on a sunny winter day here in mid South Carolina. The elements will not operate at the same time. I may have to adjust the times after testing.

You have been so helpful, thanks so much