75/15 smartsolar with 100Ah SLA battery, 240W panels.
I use my solar off-grid set up for a few weeks in July. There will be more than enough power for my van and devices. Thinking of setting up a ‘power dump’ water heater like I have in my home solar set up. Obviously it won’t be very powerful but would certainly reduce the need for gas water heating. The plan is to connect a 12v 100W thermostatically controlled immersion heater to the load output on the controller.
My question: how best to set up the load output settings to protect the battery? What would be a safe low-voltage limit to ensure I don’t kill it? I’d most likely only run the immersion heater during the day, say 11-4pm. With the battery in a charging and discharging state simultaneously, I can’t figure out what the safe limit would be. Has anyone else looked at this option? There was a great youtube video of a similar set up (500W solar and bigger controller than mine) but the guy had Li-ion batteries.
The output limit for your Load terminal is 15A or 180W max so your heater should be OK. However, when the water is cold and at start up the heater may draw more current, how much I can not say. Also if you have charging at 14.5V then that is higher voltage hence higher power.
You do nor want your battery to be discharged below 12.3V without a load, but with the load the voltage will be lower, there is some trial and error involved. Try something like 11.5V first.
Remember, lead avid do not like being left discharged, always make sure the battery is fully recharged the next day.
Thanks for the tip about the start up surge. I was thinking I might set the max. load output current to 10A anyway. This should help with bigger draws.
I suspected the low voltage limit might be a trial and error situation. Thanks for the guidance, I’ll try 11.5V first. I will be switching off the load output around 4pm each day to make sure the battery has a chance to get back to a good charge state. It’s all weather dependent, but it would be very satisfying to use surplus solar power in this way.