NWS Heating Element

HumMichaelHumMichael Registered Users Posts: 26 ✭✭
I have some extra panels and was looking at our host's dc heating element which are significantly expensive than other ones I can find.
I don't mind paying extra if I know why it costs more.
It will be just for pre-heating purpose before going into main water heater.
Anyone wants to share this brand experience?
I would like to stay 24 or 48v setup.
Thanks

Sincerely
Michael

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    You can get a high wattage element from a hardware store and use it at lower voltages/currents:

    http://www.homedepot.com/p/4500-Watt-240-Volt-Low-Watt-Density-Watt-Fold-Back-Screw-In-Stainless-Steel-Alloy-Water-Heater-Element-15011/204834493
    • P=I^R=V^2/R=V*I
    • R = V^2/P = 240v^2 / 4,500 watts = 12.8 Ohms
    • P = V^2/R = 24^2 / 12.8 Ohms = 45 Watts
    • P = V^2/R = 48^2 / 12.8 Ohms = 180 Watts
    If you can find higher rated power elements, you can figure out the actual heating at lower voltage.

    http://www.homedepot.com/s/water%20heater%20elements?NCNI-5

    Also, lower rated voltage / wattage (AC input) does not mean lower power at lower DC voltages:

    http://www.homedepot.com/p/1500-Watt-120-Volt-High-Watt-Density-Screw-In-Water-Heater-Element-15024/204834407
    • P at voltage = element rating at AC power * DC volts ^ 2 / AC volts ^2 = 1,500 Watts * 48v^2 / 120v^2 = 240 Watts
    One thing to watch for--The AC thermostats are not rated for full power at DC volts... It is very possible for a non-DC rated thermostat to burn out the contacts or even spot weld them together (short).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HumMichaelHumMichael Registered Users Posts: 26 ✭✭
    Thanks Bill. I've done search function and have read other folks trying to do the same.
    I was just curious if our host's listing was much different than Hurricane solar guy's items.
    I am assuming that SSR is necessary when using "waste-not" auxillary function on my Midnite Classic.

    Thanks
    Sincerely

    Michael
  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    I don't work for NAWS, and I rarely talk with them (just details about the forum).

    I would guess that elements are Similar between vendors (and there are good and bad).

    Low volume stuff (solar only stuff) is going to be more expensive.

    If you have questions, please give our host a call. They have more information than I.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited March 2017 #5
    Maybe wire the thermostat (or any thermal switch) and the aux output in series and then to the input of a DC SSR.

    I am available for custom hardware/firmware development

  • HumMichaelHumMichael Registered Users Posts: 26 ✭✭
    Bill, I certainly didn't think you had any affiliation with NWS.
    You have been a great moderator for a short time I have been on. Thank you.
    Sincerely
    Michael

  • BB.BB. Super Moderators, Administrators Posts: 32,314 admin
    Michael,

    No problem... Sometimes new folks may not understand why I do not speak for NAWS. I don't work for them--I am just a volunteer here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    I think Bill does a great job.

    I am available for custom hardware/firmware development

Sign In or Register to comment.