Hi everyone. Beginner here. I have an MPPT 75/15 with a 400watt solar panel and two 12 volt AGM batteries wired to give me a 24 volt system. The system exists to power a standalone diesel heater (12 volt max 120w) through a 24v to 12v stepdown thing. The whole lot exists to provide heat during any power cut.
I am aware that during the summer when the batteries are charged, the MPPT is only drawing 10 to 20 watts from the panel so am thinking that I might be able to put a load on the system to use additional power. I connected a car headlight bulb to the MPPT through another 24 to 12v stepdown and could see on my phone that the MPPT was producing more watts to power that as well as the battery charging.
What would I need in the system to make a 24volt immersion heater work when there was more solar than was needed to charge the batteries? Would also need to cut off when the solar has no spare capacity.
Is this feasible or am I just thick?
You could try a battery protect to connect above a certain voltage and then disconnect when it is lower. It will need tuning because AGM wants to be 100% all the time so taking a small amount of charge out will be hard to find but not impossible. You could also look at the built-in load algorithms to control a relay or just use it directly if within the current rating. The other thing you need to think about is absorption and equalisation charge cycles and when you need to do them to maintain the battery’s health.