I recently bought two 15 watt amorphous solar panels to charge a 100ah deep cycle battery. The kit (Sunforce) was cheap, and I accept that quality is equivalent. I noticed that output voltage from one panel is down about 10-15% from the other, and they connect in series. The charge controller simply limits to about 14volts maximum, so excess power is lost. Panel output voltage may run 16-24v.
I was thinking that I could use the comparators in a 555 timer to drive a double pole relay to go from series to parallel connections when the output voltage of the low panel rises above, say, 15v. When the voltage drops, it would release the relay to series. That should provide some improvement in power utilization without having to go to a DC-DC controller.
Now, a couple questions. What happens when two panels at slightly different voltages are run in parallel? Literature says panels have a blocking diode to prevent reverse current. And if current is also low in one panel, that would seem to limit series output.
This is a non-critical installation, just want to maintain battery charge for incidental daily use (10-20 ah) or power outage. I haven't measured output yet to see if solar can handle it. The amorphous panel does indicate it is providing some charging current in light levels even before sunrise. Just experimenting.
Also trying to work out 555 circuit. Figure on using 5v zener for vcc, and voltage divider to pins 2,6 to change state. Thinking I may have to isolate sample voltage from the low panel so that strong panel doesn't prevent drop out when two are in parallel--if that is possible. Perhaps I need to run sample voltages to different pins. I would want to pull in the relay above an adjustable 14-15v, but also cut it out below around 14v, and I'm not sure how to set up close voltages to change state. Perhaps a zener reference would help, or raising 555 supply above ground? This circuit needs to work over a ride range of input voltage, since the panel is the supply.
I appreciate the opportunity to post these questions. Just signed up on list after google brought up some past posts--but not quite on topic. Thanks for any help.
David
I was thinking that I could use the comparators in a 555 timer to drive a double pole relay to go from series to parallel connections when the output voltage of the low panel rises above, say, 15v. When the voltage drops, it would release the relay to series. That should provide some improvement in power utilization without having to go to a DC-DC controller.
Now, a couple questions. What happens when two panels at slightly different voltages are run in parallel? Literature says panels have a blocking diode to prevent reverse current. And if current is also low in one panel, that would seem to limit series output.
This is a non-critical installation, just want to maintain battery charge for incidental daily use (10-20 ah) or power outage. I haven't measured output yet to see if solar can handle it. The amorphous panel does indicate it is providing some charging current in light levels even before sunrise. Just experimenting.
Also trying to work out 555 circuit. Figure on using 5v zener for vcc, and voltage divider to pins 2,6 to change state. Thinking I may have to isolate sample voltage from the low panel so that strong panel doesn't prevent drop out when two are in parallel--if that is possible. Perhaps I need to run sample voltages to different pins. I would want to pull in the relay above an adjustable 14-15v, but also cut it out below around 14v, and I'm not sure how to set up close voltages to change state. Perhaps a zener reference would help, or raising 555 supply above ground? This circuit needs to work over a ride range of input voltage, since the panel is the supply.
I appreciate the opportunity to post these questions. Just signed up on list after google brought up some past posts--but not quite on topic. Thanks for any help.
David