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# Water heater with nichrome

hi ... i want to make electric water heater with solar panel how much nichrome wire in lenght should i use and how much gauge of nichrome wire should i use. is that possible ... i heard about 32 gauge nichrome wire which can work on dc.... is that possible....

## Discussions

4 weeks ago

This can work on a small scale, like in the range of a few watts or 10s of watts. This is the scale of, like, a demonstration, or science fair project.

However, if you need significant amounts of hot water, like the same scale as a household water heater. In terms of power, or energy used per day, this is several kilowatt*hours (kW*h) per day or 10s of kW*h per day. Then you would be better off using solar thermal collectors, plus hot water storage tank to go with it.

https://en.wikipedia.org/wiki/Solar_water_heating

https://en.wikipedia.org/wiki/Solar_thermal_collec...

The reason why, is because converting sunlight to heat, is more efficient than the indirect process of converting sunlight to electricity (using photovoltaic (PV) panels) then converting the electricity to heat (using a resistive heating element). Also it is more efficent by a significant amount, like, roughly a factor of 5. Or at least that is what you would get for a PV setup capable of converting sunlight to heat at 20% efficiency, which is typical.

Reagarding nichrome wire, and the construction of a heating element from the same,

https://en.wikipedia.org/wiki/Heating_element

https://en.wikipedia.org/wiki/Joule_heating

https://en.wikipedia.org/wiki/Electric_heating

the trick is to pick a resistance R, that is well matched, electrically, to whatever source of electricity is going to be powering it.

What I mean by, "well matched," is to choose a resistance R that will dissipate the same amount of power that you want to pull from your source, in terms of voltage V and current I.

For example, supposing your photovoltaic panel can comfortably supply 1.0 A (ampere), at 12 V (volt) DC, that is 12 W (watt) = (12 V)*(1.0 A) of power.

What size resistor will dissipate 12 W of power, when 12 V is placed across it? (Or when 1.0 A of current is pushed through it?)

To answer that question, solve P = V^2/R (or P=I^2*R), for R.

Get R= V^2/P (Or R = P/I^2)

So R = 12*12/12 = 12 ohm. R= 12/1^2 = 12 ohm.

For making a resistor out of nichrome wire, or any other kind of resistance wire, it is mostly a matter of cutting the wire to the right length. The resistance of a wire is proportional to its length, and there are tables that can tell you how much resistance a particular wire material and thickness (aka gauge) has per unit length.

For example the table found on this page,

https://www.easycalculation.com/engineering/electr...

says 32 AWG nichrome wire has about 10 ohms resistance, per foot.

Confusingly, that table lists 2 alloys, NiCr-A and NiCr-C. Also it does not mention what temperature for which the numbers in their table are valid. Guessing those numbers are for room temperature, circa 25 C.

Actually the change in resistance between room temperature (25 C) and orange hot (1000 C) is only about 10%. So it is not a difference you would notice in an application that boils water (at 100 C).

Also that length unit, feet. 1 feet = 1 foot = 0.3048 meter

I am still looking for a better reference for resistance per unit length for nichrome wire. Normally I would point you to Wikipedia. Their article for "Nichrome" has a whole bunch of tables in it, but none of those tables are the simple one I want; i.e. just a table of resistance per unit length, at room temperature, for a wide range of AWG wire sizes.

Actually, I like the table in Wikipedia's article for "American wire gauge",

https://en.wikipedia.org/wiki/American_wire_gauge#...

The resistance per unit length given in that table, is for copper wire, of course the electrical grade kind.

Although I suppose you could convert that table to a table for nichrome wire, just by multiplying by the ratio of bulk resistivity of nichrome to that of copper, which is about (106.7/1.724) ~= 62.

That is to say, multiply all the numbers in a table for the (resistance/length) of copper wire, by 62, and that will give you a table of numbers for (resistance/length) of nichrome wire.