Low voltage DC on-demand water heater. Considerations ?

Discussion in 'General Electronics Chat' started by Externet, Jul 5, 2015.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    Planning to build a showerhead or in-pipeline water heater, for on-demand use, on 12, 24, 36 or perhaps 48V DC from a battery bank fed by solar panels on roof of a hunting cabin.
    Considerations ?
    I believe 3KWatts should suffice. Do you agree ? How would you implement such heating element ?
    What about grounding, would it be necessary for a floating low voltage DC supply; and other considerations I may be missing ?

    Does such animal exist in the market ?
  2. MaxHeadRoom


    Jul 18, 2013
    Especially anything mounted on the roof, I would take a Earth Ground conductor bonded to the DC-ve say, and put a ground stake in.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I think you will need on the order of a 10kW to make a demand heater. I dealt with this in a when putting a demand heater in my hangar shower. I ended up using gas because of the huge electrical demand.

    Read this:
    Your Home’s Electric Service
    May Need to be Upgraded
    Tankless electric water heaters usually require
    an upgrade in electrical service, something
    the home improvement stores often do not
    A tank water heater with 4,500-watt elements
    operates on #10 wire and a 30-amp circuit
    breaker. One whole-house tankless water
    heater has four 7,000-watt elements, for a total
    electrical load of 28,000 watts. This load requires
    wire and a circuit breaker that will handle
    at least 120 amps, at a cost many times that of
    electrical service to a conventional tank water

    It came from this pdf

    Redo the power requirements using these formulas
    Last edited: Jul 5, 2015
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    My on-demand shower is rated 8kW. It needs all of that during winter months, when the incoming mains water is only a few degrees above freezing.
  5. Johann

    AAC Fanatic!

    Nov 27, 2006
  6. crutschow


    Mar 14, 2008
    How about a solar water heater?
    If the sun panel is mounted below the hot water tank (as shown below), the system can be completely passive.
    The water circulates by convection from the hot panel to the tank when the sun is shining and stops flowing when the sun disappears.

    These can be purchased or build, depending upon your needs and ability.

    Last edited: Jul 6, 2015
    #12 and Johann like this.
  7. Johann

    AAC Fanatic!

    Nov 27, 2006
    Yes, even a better option! Then you can use the PV for electrical appliances elsewhere!
  8. ian field

    AAC Fanatic!

    Oct 27, 2012
    I'd go one further than that and suggest proper job lightning conductors.

    Otherwise it might not be advisable to take a shower during a thunderstorm.
  9. #12


    Nov 30, 2010
    Crutschow has the right machine for the job. The direct heater is the most efficient because it has zero energy conversions and zero moving parts. If you demand the highest comfort levels and most dependable results, you can use the roof mounted water heater as a pre-heater for your regular water heater. The effects will come directly off your energy bill and the results will be indistinguishable from what you're accustomed to.

    There are several forms of this. One of my favorites is a coil of black plastic pipe (forgot which three or four letters describe the plastic) embedded in a form filled with asphalt driveway patching compound. Huge mass, no water tank to leak, and dead cheap compared to a commercial collector. Buy a cheap, paperback book on the subject. Lots of good ideas have been gathered, tried, and evaluated.
    Johann likes this.