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I have a 6V, .7amp solar panel that typically puts out 2-5V under normal conditions.

I would like to charge a 12V 5 amp hr lead acid battery over a few days to weeks.

The device that I want to power is a lock that needs 12v at about .8 amps for a fraction of a second. The lock is used only once or twice a week. There is also a 3-5V microcontroller that needs to run for maybe 5min. to prime the lock.

Space and weight aren't an issue so I thought lead acid would be simpler.

Now I'm wondering if it'd make more sense to have a 3.7V lipo battery, use a charging board designed for solar and then boost it to open the lock?

When I looked up the charging info for this battery it says to charge it at 14v. It also says that lower voltages may be needed to trickle charge it if it's totally dead (which I don't see happening if this is set up correctly)

What I can't tell is if I can trickle charge it when it's at about 11.85-11.95V. I suspect that if I try to boost my sad little 6V solar panel to 14V the amperage will be so low what will be the point?

Furthermore, when I tried an out-of-the-box adjustable boost board with the solar panel it only turned on at all in direct sunlight. I need to capitalize on the indirect light too.

Are there any application examples of smaller, lower voltage solar panels being used over a long period of time to slowly build up a larger battery? Or do the loss factors make this unlikely?

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  • \$\begingroup\$ "The lock is used only once or twice a week." what is the minimum time that could occur between lock operations? \$\endgroup\$ – Bruce Abbott Jan 20 at 4:54
  • \$\begingroup\$ min would be about 3 min. \$\endgroup\$ – futurebird Jan 20 at 12:39
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how about a standard boost converter, that uses the battery to absorb the energy of the inductor?

and a low-power comparator to shut off the boost converter once charged to 14 volts

you might call this a flyback converter, with some shutdown.

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