Vacancy. Electrical genius required

[Malabarista]

Hi
How’s things?
I was talking to Ros on one of our epic drives down from Orkney and she suggested i talk to you lot. I am however going to write it down as i will only get confused and cry. ?
Right here goes…
This is all going into a 12volt system
I have solar (about 850watts) controlled by 3 Victron MPPT 30amp controllers.
I have a variable amps windvane.
I have a variable amps water generator ( which is using the same controller as the wind, so either/or).

I also have a 120 amp alternator, a 240v 30 amp battery charger but these are of lesser interest to my project.

What i would like to do is have a ‘magic box’ that could read the acceptance charge of my 900 ah battery bank ( which can be split into 2x 450ah banks if required) via a shunt and then when they were 90-100% charged divert the excess charging capacity to a 12v water heating element which is already fitted to my water tank. When the water was around 60 degrees it would then utilise a heat sink so it wouldn’t overcharge the batteries or boil the water. I would imagine that if a really clever person were to design such a ‘box’ it would be very popular with yachtsman the world over as I don’t think there is anything currently that can do this. I of course only want the prototype ? and you can have full rights to the further sales.
What do you think?

Dave

 

[roaringgirl]

Hi Dave, I have an alternator, wind-gen, 800W of solar and a towed genny, all with their own MPPT/charge controller.

Each MPPT monitors the voltage of the batteries and uses it to decide whether to push charge in, or not. Each MPPT can be set up with whatever voltage thresholds you want. The problem is that lead-acid batteries want to be charged and rested in cycles, and the MPPTs would have to be synchronised to do this.

You could just switch on the water heater when the batteries are full, it'll pull the voltage down and the charge sources will push electrons into the system to power it.

The only solution I've found to the difficult requirements of lead-acid is to replace them with LiFePO4 - so much easier to look after!

 

[RupertW]

I haven’t anything near as complicated a set of charging sources, just solar, but do have the water heating once batteries near full. I do it the simple way by a programmable relay that switches the heating on via an inverter when the battery reaches absorption voltage, and off again once the voltage has been pulled down a volt. Once the normal thermostat temp is reached the voltage quickly drops to float.

With only solar there is no need for a heat sink.