I have been running the work lights in the barn using the little third-world solar power system that I built a number of years ago. I think I described it in a previous post; I’ve got a little 11 watt panel and a big hundred-amp-hour AGM battery, and it works very well. My thinking there is that since I’m not at the site during the week, the thing has five whole days to recharge the battery with no load.
That is, as long as there is no load.
When I arrived to start working this morning, there was a distinct whining noise coming from the shed that the solar stuff is in. It appears that I left the inverter turned on when I left last weekend, and it has been drawing a slight trickle of current ever since then. Over an entire day that must exceed the amount of power generated by the little panel while the sun is up. The whining noise is the under voltage alarm on the inverter announcing to the world that the battery voltage is insufficient.
It’s probably still going right now, as I am writing this. I took the key for the condo that I’m moving out of off of my key ring this week. I don’t really need it every day anymore because I’m now staying in my house. The problem is that the same key opens the little solar shed, a fact which I didn’t even think about. So I couldn’t get in today to turn the inverter off. In all likelihood it is this very moment announcing its alarm condition for all the critters and the trees to hear. Perhaps it will give pause to the one of the local deer, which will stop to listen for a moment to the strange noise coming from the human building. I am confident that the grave urgency of INSUFFICIENT BATTERY VOLTS will be completely lost on the animal as it bounds blissfully off into the night in search of some tasty shrubs to munch on.
Time for a low voltage cutout..
I’m visualizing a beefy relay for the inverter, wired NO in a latch configuration, with a smaller relay in the coil circuit wired NC with it’s coil fed from the low voltage alarm on the inverter.. add a beefy cap, zener, and a resistor to provide a time delay before it dumps the load..
The inverter is supplied via the NO contacts of relay K1.
The K1 coil is supplied via a diode from the load side of K1, with the other side of the coil connected to ground via the NC contacts of K2.
A momentary switch supplies the K1 coil from the line side of K1 to engage K1.
Once K1 is engaged, it will remain closed until K2 is opened, or power is removed.
A large electrolytic cap is connected between the buzzer of the LV alarm and ground, with a bleeder resistor to ground. The positive side of the cap is connected to a reverse biased zener of the appropriate voltage, which connects to the K2 coil. The other side of the K2 coil is grounded.
When the LV alarm starts whining, it charges up the cap until it reaches the trigger voltage, and the zener fires, pulling in K2, which opens the coil circuit of K1. K1 will now stay open until manually reset.