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  1. #31
    Talbot's Avatar
    Talbot is offline Registered User
    Location : Stavanger, Norway
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    Not a single post in favour of the concept. However, if you size your PV large enough for all normal needs when sailing, (fridge, freezer, lights, radios, autopilot etc) and are then sat at anchor, there may well be a large surplus that needs to be used. For example, I am considering 500w of panels. Using an additional inverter specifically to heat the water in the calorifier may well be a useful means of absorbing additional power.
    "Be wary of strong drink. It can make you shoot at tax collectors - and miss."
    Robert A Heinlein

  2. #32
    Join Date
    Jan 2003
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    Quote Originally Posted by Talbot View Post
    Not a single post in favour of the concept. However, if you size your PV large enough for all normal needs when sailing, (fridge, freezer, lights, radios, autopilot etc) and are then sat at anchor, there may well be a large surplus that needs to be used. For example, I am considering 500w of panels. Using an additional inverter specifically to heat the water in the calorifier may well be a useful means of absorbing additional power.


    Actually, this the conclusion I came to as well. I often boost the hot water (via inverter) when the atteries are full to save the engine being run- only enough for 15/20 mins, but it does make a diffetence.
    I used to be indecisive, but now I'm not so sure...

  3. #33
    Join Date
    Oct 2003
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    554

    Default 12 volts immersion heater = many many amps

    200 watt immersion heater consumes XXXX amps at 12 volts
    .
    .
    .

    using ohms law in this excellent online calculator


    the current is approx 16 amps at 12.4 volts !
    .
    .

    see this calculator


    http://www.the12volt.com/ohm/ohmslaw...rs.asp#current
    .

    and these people sell one to fit most tanks


    http://www.reuk.co.uk/200W-12V-Immersion-Heater.htm
    + 200 watt immersion hea
    Last edited by ianabc; 23-02-12 at 20:39. Reason: lot original and rewrote
    37 foot steel sailboat in Comox, B.C. Canada.

  4. #34
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    Nov 2009
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    Quote Originally Posted by Andrew_Fanner View Post
    Water has a specific heat of 4.2kJ/kg/K. To get 100cc of water to boil for 20deg is
    4200 x 80 x 0.1 = 33.6kJ. In 1 second this would require 33.6kW (!), in 10 seconds 3.36kW (big domestic kettle) and in ten minutes 33600/600 = 56W. At 12V this would be 4.67A.
    A normal mug is 250 ml so taking Andrews maths as correct, which I'm sure it is, the 5 amp output of your solar panels would take 25 mins to boil the water for a cup of tea.

    A typical calorifier is 25 litres and the normal temp you would run one up to is 60 C which would require 5 1/2 hours at your 5 amps or so. So yes it is feasible - in theory

  5. #35
    Join Date
    Oct 2003
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    554

    Default solar herating / ohms

    5 amp actual solar panel output at solar panel voltage of 18 volts according to Ohms is


    5 amps at 18 volts = 90 watts (for heating)

    10 amps at 18 volts = 180 watts



    It might take a while!

    Also consider running an inverter to power a 1000 watt heater in a tank requires from a 12.4 volt battery bank a battery killing
    80.6 AMPS



    2 car headlamps ( 100 watts ) for example require at 12.4 volts 8.06 AMPS

    and we know how long the battery will last with the engine off and the headlamps on!


    So it might be back to a 200 watt heater running at 12.4 volts using around 16 amps and using the heater only when enough amps are

    available.

    But

    500 Watts from huge solar panels at 18 volts would give 27.7 amps so this would heat a custom immersion heater !!!


    Now reverting to the 200 watt 12 volt immersion heater....


    With the 200 Watt 12 volt heater running at 12.4 volts using 16 amps now
    now converting to Joules

    shows that with a 20 L tank
    raising the temperature from 10 C to 25 C

    requires 1 200 000 joules

    so dividing by 200 watts means that it takes 6000 seconds

    which is 100 minutes to heat the tank
    Last edited by ianabc; 24-02-12 at 01:44. Reason: added joules calculation for energy and time
    37 foot steel sailboat in Comox, B.C. Canada.

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