I need to have a controller for charging a 12V 7AH battery and provide uninterrupted supply.

The source for charging would be 12VDC from a PSU or if there is a failure in that from a solar panel. I am confused , I found a few such solutions for lipo batteries but cannot find for lead acid batteries. I want to have auto charging and cutoff on full charge.

There are some ICs that provide solution for solar but they have no support for the other source.


A integrated solution for this task is found at Linear Technologies. They have a good white paper to introduce the concept of maximum power point tracking: Techniques to Maximize Solar Panel Power Output. A suitable solution for your application could be the LT3652 - Power Tracking 2A Battery Charger for Solar Power.

The second source you just put in parallel to the solar panel and in each circuit (dc source as well as solar panel) you put a diode. Make sure to use low forward voltage drop diodes (such as a Schottky diode) that are suitable to carry the current in your application.

  • \$\begingroup\$ I plan to use LT3652 as per your suggestions. There is a question though. Can I control charging ON/OFF using a GPIO? The circuit shown here linear.com/solutions/1463 connects load and battery at same place. So if I would stop charging will it also stop the output of the main supply to load? \$\endgroup\$ – dmSherazi Jan 6 '16 at 9:50
  • \$\begingroup\$ @dmSherazi: Yes, if you use the /SHDN pin to activate / deactivate the charger, the output would be disconnected and the battery alone would power the load. But as I understand the ic should keep your battery absolutely well charged and go into trickle charge when the battery is full. So there is no need to activate/deactivate the charging process. This way you could use this setup as an UPS. \$\endgroup\$ – Stefan Jan 6 '16 at 10:40
  • \$\begingroup\$ @dmSherazi: To power the load even when the charger is off, you could bypass the input dc power supply (that you planned in parallel to your PV panel) directly to the load and decouple it from the ics output (and the battery) by another diode. \$\endgroup\$ – Stefan Jan 6 '16 at 10:43

In the simplest case, you can float-charge a lead-acid battery using a 7812 with a green (1.8V forward voltage) LED in series with the GND pin of the regulator, which will give you a 1A-current-limited 13.8V output. That can remain connected to a lead-acid battery indefinitely without harm and the battery will remain full.

Regardless of which charge-controller circuit you use, you can supply that charging circuit from multiple power sources just by putting a diode in series with each power source. The diodes prevent the sources from trying to drive each other, and the source with the highest voltage will supply power to the load (charger).

I would suggest that you run it by default from the solar panel and have it fall back to mains charging when there is no sun. If you're feeling fancy, google up MPPT (maximum power point tracking) converters, which will get the most out of your panel. There are a few DIY designs.

  • \$\begingroup\$ can you suggest any charge-controller circuit? \$\endgroup\$ – dmSherazi Jan 5 '16 at 6:19
  • \$\begingroup\$ I haven't used anything smarter than a 7812, sorry. There are plenty of dedicated chips if you google for them, especially from TI and Linear, but I have no personal experience with any of them. \$\endgroup\$ – William Brodie-Tyrrell Jan 5 '16 at 8:47

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