Journal Alioth's Journal: More circuit bugs 1
Another thing I didn't anticipate...when the sun comes out, the voltage of the solar panel when unloaded vastly exceeds 13.8 volts, and it seems that when the voltage being input to the comparator exceeds the supply voltage, undefined behaviour happens in my circuit - it seems like the electronic equivalent of a buffer overflow. The oddity was this. When the voltage exceed's the comparator's supply, the comparator's output switches on, switching on the LED array. This then presents a load across the solar panel (the battery wasn't - it's fully charged so was not putting any real load on the panel). The load then drags the panel's voltage down to about 12 volts or so. The comparator then reverts to working as I designed - it turns the LEDs off because the voltage now is higher than the reference voltage.
So the LEDs turn off - and the load goes away, and the voltage from the solar panel then goes back up again, exceeding the comparator's supply voltage, and then the LEDs turn back on, dragging the voltage back down until the comparator's output goes off...i.e. all my garden lights start flashing off and on at a frequency of (I estimate) 5 to 10 Hz!
There's so many pitfalls on even a simple circuit! But it is good fun to do this stuff.
The permanent fix will be to introduce Zener the Warrior Diode.
I don't have a zener diode at the moment, so a resistor network sufficed (I changed the values on the reference voltage input to bring that down, then a resistor network to half the voltage presented by the solar panel to the other input on the voltage comparator). However, along with some other bits and pieces, I ordered some zener diodes, amongst them one rated for 12 volts which I'll use to clamp the input to the voltage comparator to no more than 12v.
I also updated the photos of the solar project so far, to include the prototype circuit and the ammeters that I added to the control board.
Good work Sir! (Score:1)