shower

[RupertW]

and the 240 can come from either shore power , invertor or genny ? do you just splice the wiring , or what ?

Wish I’d taken a photo of the circuit diagram I drew as that’s so much easier than words. I basically then used eBay to fill in the components.

Solar charges battery bank through MPPT controller.
Programmable low power VSR switches on high power simple VSR when battery bank is above 14.2v for 120 seconds and switches it back off again when voltage drops below 13.2v. (That was just the first setting I tried but seems to allow the batteries to eventually reach float)
Simple VSR switches on invertor which has 240-110v transformer plugged in
10 amp DPDT switch to choose between main and transformer supplying the immersion coil (and this stayed on solar for nearly 4 weeks before we had a cloudy day in a marina with lots of clothes washing to do)
Immersion coil thermostat switches off immersion coil supply when hot temperature reached and battery then stays above 14.2 volts for a sustained time and battery bank goes to Float, dropping to 13.2 volts so invertor not triggered again

No genny on board.

 

[cherod]

great,, what is a VSR,, ans DPDT ? ,, i know for sure that my batteries will not float

 

[cherod]

the 240 can come from either shore power or invertor ???

 

[RupertW]

great,, what is a VSR,, ans DPDT ? ,, i know for sure that my batteries will not float

Hmm...sounds like you are not quite a hobbyist on boat electrics yet - which is a great thing because you will probably concentrate on sailing instead.

Google is your friend here and it’s a good idea to get Nigel Calder’s book on boat electrics. I haven’t read it but it comes highly recommended.

So VSR is Voltage Sensing Relay - it switches things off and on depending on the voltage it senses so you use them to run things off your batteries only when they have plenty of juice in them
DPDT - a usually three way switch, in this example the three positions are Solar, Off, Mains
Float - To work on almost anything in 12v electrics then reading about the different charging states of batteries is really useful. Float is when the battery is considered to be fully charged so just a trickle goes in to keep it that way.

 

[cherod]

OIC , ,,, i am alright when it comes to mechanicals etc but electromagicality is not my thing !!! you make it sound easy

 

[atol]

basically a 1000w heater element with 240V draws 4.2Amps
the same 1000w heater element with 12.5V would require 80Amps

so you would need a minumum of 1000watts of solar panels for it to work effectively with out drawing from the batteries,which is effectively what happens with a VSR ,ie the surplus is transfered from the batteries to the heating element once the batteries are fully charged by the solar panels

 

[cherod]

basically a 1000w heater element with 240V draws 4.2Amps
the same 1000w heater element with 12.5V would require 80Amps

so you would need a minumum of 1000watts of solar panels for it to work effectively with out drawing from the batteries,which is effectively what happens with a VSR ,ie the surplus is transfered from the batteries to the heating element once the batteries are fully charged by the solar panels

And if it is left on just trickle feed from say 750 / 800 w then it would keep the water warmish and could be boosted from genny if / when required ?

 

[atol]

And if it is left on just trickle feed from say 750 / 800 w then it would keep the water warmish and could be boosted from genny if / when required ?

no it would just take longer to heat the water untill the thermostat turned off,as your heating element would only be putting out 750/800watts if connected directly to panel output by the VSR

the hot water in the tank effectively becomes your battery and stores the energy.
the thermostat is the switch that starts or stops that process when the water reaches the desired temperature(85centigrade) as long as there is sunlight and your batteries are fully charged