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I have some battery powered roller shades that I'd like to convert to using rechargeable batteries using a solar panel as the charger. My blinds are Norman Pro-Lift 25 CE blinds. They run off a long tube of 8 AA batteries in a series (so 12V when fully charged).

I found a 12V solar panel that seems made for this purpose on Amazon:

https://www.amazon.com/dp/B07J5B7RFS

I purchased one unit so I could test with it. From my the inside of a window it actually got up to 19V output. For amps it's supposed to get up to .08, but I'm seeing .01 so far but it's pretty cloudy today.

Questions:

  1. Would it be as simple as replacing the AA batteries in the tube with rechargeable AA batteries and then connecting the battery tube to both the solar charger and the roller blinds motor?

  2. What type of batteries are best?

  3. I am unable to get an answer on whether the solar charger shuts off when the batteries are fully charged. Assuming the charging does not shut off and is exposed to sunlight 6-8 hours a day, would it be reasonable to expect the batteries to last a year?

  4. I can't find any details on the above solar charger, so I don't know if it has an integrated diode to prevent the batteries from discharging into the solar charger at night, how quick will the batteries discharge? Perhaps this would actually be helpful to prevent batteries from getting overcharged? Or will the batteries be completely drained after a single night?

Any other tips on how to make this project would be appreciated. Thanks!

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  • \$\begingroup\$ How to convert battery powered roller blinds to be solar powered? ... they would still be battery powered ... you should be asking how to charge a battery by using a solar panel? \$\endgroup\$ – jsotola Jan 30 at 22:01
  • \$\begingroup\$ @jsotola, thanks for the suggestion. My question is more specific than how to charge batteries with solar... I'm asking about whether the components I have available will work together to create a workable solution. \$\endgroup\$ – spockdude Jan 30 at 23:06
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A solar panel by itself isn't a charge controller. It will keep putting out whatever voltage and current it can.

NiCd cells are pretty tolerant about being overcharged at low currents up to about 0.1C, where C is the capacity of the battery in amp-hours (or milliamp-hours). So you could trickle charge an 800mAH pack of cells at 80mA. However, NiCd cells are harder to find these days, because they contain toxic cadmium.

NiMH cells are much easier to find, but don't like being over-charged and need a proper charge controller. If you constantly trickle charge them all day, they will soon fail.

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Be aware you have to attach a load to a solar panel to get an idea of how much power it's actually generating and if the load is too big or too small you decrease your power output. A panel will only give its rated output in bright direct sunlight, and only certain panel types perform well in lower light levels.

Because the maximum power point varies with load and brightness of light, you use maximum power point tracking. This is a circuit that increases or reduces output to maximise power, and it can be combined with the battery charge circuit to provide pulses of charging voltage

If the battery charging circuit is separate, it has to work with variable/intermittent input and be built for the type of battery you want to charge. For some battery types you need a safe discharge or other protection circuits as well.

A block diagram of what you would want to do this safely would be

Solar panel -> MPPT charge/discharge circuit <-> Battery bank
                                |
                                V
                              Load

It would be wise to select your battery bank so you can disconnect it and charge it with a line voltage charger if you don't get enough sun for too long.

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