I have a portable solar panel that generates 21w of power, seen here: enter link description here . It has a USB connection wired into it that will accept a USB cord to charge small devices via USB. Separately, I have a Panasonic wall charger device (model BQ-CC75) seen here: enter link description here that will plug into a wall outlet to charge 1-4 rechargeable Ni-MH AA batteries. I would like to figure out if it is possible to find a way to connect the solar panel to the wall charger device in order to charge the AA batteries by solar. I know there are other devices out there that are designed to charge AAs from a solar panel, but I am wondering if the Panasonic can do it using an appropriate connection, and if yes, what that connection type might be.

So far, I have considered running this connection cable: enter link description here that would go from the solar USB connection to a cigarette-lighter plug, which is connected to a "wall outlet" style plug, such as this: enter link description here or this: enter link description here , and from there, plug in the Panasonic AA charger ... the hope is that this would charge 1-4 AA batteries successfully via solar.

  1. Would this approach work?
  2. If not, what would work?
  3. If it works, but there is an easier way, what would that look like?

Thanks so much in advance for your advice, and thanks again for forgiving me for not knowing enough to figure out the good and bad of this idea on my own, and for not knowing the proper terms to describe things.


closed as off-topic by Michael Karas, Chris Stratton, Nick Alexeev Jul 8 '18 at 20:58

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  • \$\begingroup\$ you need to change your title .... right now it says that you are trying to charge a wall charger ..... some people will see the title and not bother to read the rest of your question (i almost did that) \$\endgroup\$ – jsotola Jul 8 '18 at 20:28
  • \$\begingroup\$ VTC - Taking this to be more of a product recommendation question this is thus off topic here. You already probably know you should just purchase the solar AA cell charger instead of the awkward kludge if interconnected equipment that you proposed. \$\endgroup\$ – Michael Karas Jul 8 '18 at 20:42
  • \$\begingroup\$ This will not be practical. Questions about the usage of consumer electronics are generally off topic here, as this is a site only for electronic design problems. It is entirely possible to charge a AA cell in a charger powered from a 5v supply, but the item you link does not do that, and the necessary conversion circuitry would not be practical in terms of space, cost, or efficiency. \$\endgroup\$ – Chris Stratton Jul 8 '18 at 20:44
  • \$\begingroup\$ Thanks for the comments so far. I'm not looking for a product recommendation. I'm looking to know if this setup will work, and if not, what change(s) are best to make so it can work. TIA \$\endgroup\$ – deltabravo Jul 8 '18 at 20:44
  • \$\begingroup\$ also, you've been lied to. If the drawing on that solar cell's product page is somewhat accurate, then that solar cell has an accumulative active area of maybe 0.12 m². Now, best-case solar irradiance on the earth surface is about 1000 W / m², leaving you with 120 W on your solar cells. The customer photos clearly show amorphous cells, and these provide an efficiency of less than 10% – so, if you get 12 W out of this, be happy. \$\endgroup\$ – Marcus Müller Jul 8 '18 at 20:52

You're approaching this from the wrong end:

What you're trying to do is:

solar cell -> step down or down -> USB (5.0V) -> step up -> cigarette plug (12V) -> step up -> wall plug (120V or so) -> step down -> NiMH cell

That's ... very bad. As every step up and step down wastes energy, this will hardly work.

Instead, just use a charger that works directly off 5V (since I guess you can't access the solar cell's output directly).

Chips like Maxim's DS2710 have been around forever. There's plenty of even cheaper alternatives – but using the DS2710 would kind of feel like the "least effort, works instantly" alternative for designing this.

I'm also pretty sure you can buy charger devices that you can plug into USB directly. Every solution's bound to be cheaper than your convert-all-over-the-place approach.

  • \$\begingroup\$ In the checkout line of a clothing store I once found some AA-size-outline rechargeable cells each having a USB "A" connector that folded out of the side for charging. No idea how well they worked, gave them as a holiday gift... \$\endgroup\$ – Chris Stratton Jul 8 '18 at 20:45
  • \$\begingroup\$ Thanks for helping me by explaining why it's a bad idea. I really appreciate it. \$\endgroup\$ – deltabravo Jul 8 '18 at 20:49
  • \$\begingroup\$ @ChrisStratton not this one, I hope? ( start at 11:00) \$\endgroup\$ – Marcus Müller Jul 8 '18 at 20:53
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    \$\begingroup\$ @MarcusMüller Yeouwch! Fortunately no, these were low voltage DC, individual USB charge in and 1.5v AA sized form factor. Though I could imagine interesting things happening if you try to charge several of them from a common supply while they were in a series holder. Hopefully folding out the charge port opened the circuit to the end contact, but I never opened the retail package to try them. \$\endgroup\$ – Chris Stratton Jul 8 '18 at 20:58
  • \$\begingroup\$ I appreciate the responses, I have learned what I hoped to learn, and I am happy for you to close this topic if you believe it is off-topic. Thanks very much. \$\endgroup\$ – deltabravo Jul 8 '18 at 21:10

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