EEs: Solar charge individual AA, use in series at night

[Pandamonium]

This is probably less technical than the stuff I normally see here, but I'm stuck and google isn't helping any, so here goes:

Big picture: I want to make solar powered backlit house numbers. I have a string of LEDs powered by 3xAA in series (4.5v nominal, looks like a 4.5ohm resistor in-line)

I bought some $3 solar-powered landscape lights to salvage the panels from them. The circuitry included is sufficient to recharge a 1.2V AA battery. (source: home depot)

I have a LED string light that is powered by 3xAA in series. (source: amazon)

I want each solar panel to charge each battery individually, but when the charging stops (ie: sunset), the batteries are used to power the string lights. How do I do this?

Alternative 1: I actually have 4 solar panels (the 4th one might be somewhat damaged in my extraction process....). If I can use 4 of them to charge the batteries, I'm all for that option.

Alternative 2: Can I make this system compatible with possibly wiring to 12v landscape lighting in the future?

 

[sm625]

What I would do is buy a TAOS Part# TSL13T, which is a light to voltage converter. It will give you more volts for more light. I would just cover it with tape until the voltage is near the trip point for a few SSRs. Then have the SSRs reroute the circuit how you want it. So for example when the LTV detects enough light, it will activate the SSRs to route the panels to the batteries. This solution would cost a few bucks though. The better solution would be to use a single panel that has the voltage output you require rather than trying to cobble together those cheap Dollar General junk solar lights.

 

[SecurityTheatre]

This is probably less technical than the stuff I normally see here, but I'm stuck and google isn't helping any, so here goes:

Big picture: I want to make solar powered backlit house numbers. I have a string of LEDs powered by 3xAA in series (4.5v nominal, looks like a 4.5ohm resistor in-line)

I bought some $3 solar-powered landscape lights to salvage the panels from them. The circuitry included is sufficient to recharge a 1.2V AA battery. (source: home depot)

I have a LED string light that is powered by 3xAA in series. (source: amazon)

I want each solar panel to charge each battery individually, but when the charging stops (ie: sunset), the batteries are used to power the string lights. How do I do this?

Alternative 1: I actually have 4 solar panels (the 4th one might be somewhat damaged in my extraction process....). If I can use 4 of them to charge the batteries, I'm all for that option.

Alternative 2: Can I make this system compatible with possibly wiring to 12v landscape lighting in the future?

Theoretically, you could actually do it, since the relative voltage output from each panel can sum over each battery, but on the same hand, if there is any grounding in the system, it won't work and may damage the batteries.

It will only work if the lights themselves aren't putting any load (are disconnected) during charging time.

There are a lot of variables. But with $3 parts, you can always just try it. Worst case, the batteries are destroyed. If you're using NiMH, it's unlikely to cause a fire. Standard disclaimer: as with all homemade charging systems, be aware of the safety here and make sure it won't take out your house if it does burn.

 

[Pandamonium]

This is getting complicated.

I could probably source a ~4.5 V panel, but then I'm in almost the same situation. I have no idea how to have it charge 3 AA's independently when they are wired in series for the LED lights. Also, I looked at the light to voltage converter: I might be in way over my head for something like that. (maybe this whole project was a little too ambitious- who knew $3 solar lights were so complicated?)

I did some googling of some parts I was able to identify. This guy has the exact same solar garden lights hacked up. He's got them wired to some kind of cell phone li-ion battery to charge it, and it looks like he turns the device on with a switch manually.

So it's sort of similar to what I'd like to do, but not quite. I want this to automatically turn on when the panels cease to charge. Anyway does the info/pics from that page help any?

 

[sm625]

There are so many cell phones around that it would be perfectly valid to use the guts of a cellphone for something like this. All you need to do is wire the solar panels in series so that they produce well over 5V@~300mA during daylight conditions. Then run that voltage into something like a LM117 regulator to produce a clean 5V suitable for usb. Then route that 5V into the phone via usb. It's charging circuit will charge the battery. Meanwhile you have two wires coming directly from the 3.7V battery inside the phone to power your LED house numbers.

But you want something that turns OFF your LED house numbers while charging. So you'd still need a SSR to connect the 3.7V battery to your LED house numbers. The SSR would need to be activated when there is a very low amount of current going from the solar panels into the regulator. That is the toughest part. Why not just let your LEDs run until the battery in the cellphone dies? It would greatly simplify your circuit. In that case all you'd need is a 5V regulator, a few more of those tiny panels, a usb cable, and an old cellphone.

You could place a relay on the output of the solar panels. You wire the normally-closed contacts of the relay to connect the cellphone battery to your LEDs. Then when the output of the solar panels goes high enough, it will trip the relay and the NC contacts will open and that will turn off your LEDs. The trouble with this is that relays are kind of power hungry and I would worry that the process of tripping the relay would cause an oscillation. So you'd need a capacitor and of course a reverse protection diode across the relay...

 

[Micrornd]

How 'bout something simpler and pre-built ?
Why make things complicated?

I bought a reflective house number panel, stuck my house numbers on it, bought a cheap 3 spotlight solar setup and pointed them at the panel.

All bought at Lowes, install time 15min and here in FL, the solar spots light the reflective panel all night long.