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Message: <blockquote data-quote="Simon Liebentritt" data-source="post: 739827">I'm trying to build a 12V DC hot water tank for my camper.The aim is to use excess energy supplied by my 350W PV panels to heat water using a 600W heating element that is split into two connectable 300W heating coils.My idea was to run one 300W coil automatically when the battery (200ah LiFePO4 12V) is almost full, thus the voltage is above xV and the water temperature is below y°C.Additionally, I want to be able turn on both coils manually when needed and also be able to shut off the entire system when required.The plan I designed has an<ul> <li data-xf-list-type="ul">on/off switch</li> <li data-xf-list-type="ul">followed by a temperature-controlled relay</li> <li data-xf-list-type="ul">followed by a switch between a voltage-controlled relay going to one coil or just an on position for both coils.</li> </ul>The signal would control a relay closing the circuit for the 25amps (1 coil) or 50amps (2 coils) directly from the battery / PV to the heating element.Between the 50 amp connection to two coils and the 25 amp connection to just one coil would need to be diode so the power from the voltage-controlled relay doesn't go to both coils.The reason I want to separate 1 or 2 coils is that the one coil can run (almost) fully without draining the battery each time and therefore shutting on and off often.600W is for when I "quickly" need hot water regardless of battery level.This system should work but is quite complicated, space demanding and a bit pricey.Instead of decoupling the coils, is it possible to leave them connected and control the wattage going to the coils? Can a 300W 12V coil run on fewer amps (just not as hot) or on a different voltage?Do you have any ideas on how to make it simpler / better / different?Thanks in advance,Simon</blockquote>

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