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I have a hybrid power system: 3kW solar; 2kW wind turbine; 1kW water wheel, that feed a 48v (flooded lead acid) battery bank.

Presently, after absorption charging is complete and the system goes into 'float' state (of 54 volts), I turn on my 3.5kW water heater. The water heater is configured to draw power when the battery is above 53 volts, until the battery drops to 51 volts.

As I usually do not have a lot of wind, or rain, solar is my primary generation source.

What happens is the hot water (immersion) heater runs for about 10 seconds, while the voltage drops to 51 V, then it stops while the voltage creeps back up to 54 V, and repeats.

I understand that with the 48 volt system, the '100%' voltage is: 50.4 volts (2.1 volts per cell), so in theory if my system voltage is above that, I should not be eating into my battery's precious cycles.

Or, should I de-rate my hot water heater (e.g. connect the middle and bottom element in series, to reduce the draw to 1.75 kW)?

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