DC water heating FAIL

I’ve been planning on heating water as an opportunity load.  The intent is not so much to heat water (though that is a nice side effect).  I really mean to bring down controller temps associated with overpaneling.

I was thinking something like a couple hundred watts.

So anyhow I was at the local Habitat for Humanity resale shop and picked up a water heater element for pocket change.  Figured for that cheap I might as swell snag it and figure out later if it would work or not.  It’s just a big resistive element so it doesn’t care about AC v. DC.


I hadn’t done (or even thought about) the math.   Today I did.  It is stamped 4500W and 277V.

** W = V × A** 4500W = 277V *  A A=4500W / 277V A= 16.24A 16.24A

V = I R 277V = 16.24A * R R = 277V / 16.24A R = 17.06 Ohms

So what does it look like at, say, 13.8v? W = (V × V) ÷ R W = 190.44 / 17.06 Ohms W = 11.16 11.16W


11W isn’t going to do much of anything. There are 12vdc heating elements for about $25 but I’m short on cash right now so I’ll put that off.