Need Help With Solar/Rechargeable Battery Powered LED Lights

[JohnH2889]

Although educated as a mechanical engineer, electronics have always stumped me. Here’s my problem...

Per request from my Mrs., I constructed a ‘little library’ for the front of my home and would like to put solar/rechargeable battery powered LED lights in it. I purchased an Alpine Corp SLA200SB garden light. It came with (2) white light LEDs (connected in parallel) powered by one 1.2 V, 600mAh, size AA battery, a small circuit board (containing a 40 Ohm resistor), an ‘ON/OFF’ switch, and a solar charger. I disassembled it, tagging each lead to show where it went. I bought new battery holder for (2) size AA batteries, and modified it so the batteries would be in parallel rather than in series. The new size AA batteries are from Radio Shack, re-chargeable Enercells, each 1.2 V, 2500 mAh. I then reassembled everything, adding add’l length leads as I thought appropriate for my project. All splices were soldered and insulated. I left the new assembly under a 60 watt bulb overnight to charge the batteries, making sure the switch was ‘OFF’. The batteries charged for approx. 10 hrs. In the morning, I checked to ensure the batteries were charged. My volt meter indicated 1.2 V’s. I covered the solar panel and turned the switch to ‘ON’, expecting the LEDs to light up. They didn’t. Using my volt meter, I checked to ensure the LEDs were getting power. The meter indicated 1.2 V’s. What did I do wrong? What should I do to get the LEDs to light?

[Mike90250]

White LEDs (UV with a dab of phosphor on the diode) require about 2.2V for forward voltage conduction. The resistor is to limit current, and prevent the diode from shorting out. There was likely a voltage booster IC buried in the circuit board - otherwise they leave out the board, and use the resistor leads as a jumper wire.
A 60W bulb does not produce sunlight. Going to much larger batteries, will require either more PV cells or longer "sun" time.

I'm an electronics guy, but I chainsawed a wall out of my house to make a room bigger, but the roof fell in, what went wrong ? I used a sharp chain.

[SunEagle]

In most of those garden lighting fixtures there is a photo eye that determines it is dark outside before it will turn on the LED's. See if you can find it and block it to test the lights.

I would also try to use only one of those batteries in the circuit for testing. Why complicate the circuit?

Mike is also correct that a 60 w incandescent may not provide the correct amount of voltage or light frequency for the little solar panel to properly charge. Try the test again in bright sunlight to see if the charging circuit is working.

As for Mike;

Did you at least use a hard hat when you did that sawing?

[Mike90250]

......
As for Mike;

Did you at least use a hard hat when you did that sawing?

naw, I've seen folk use a baseball cap on backaswards and I thought that was OK enough.

[PNjunction]

The new size AA batteries are from Radio Shack, re-chargeable Enercells, each 1.2 V, 2500 mAh.

These are standard high self-discharge nimh AA's. For your project, you'll want to boost quality by using "low self-discharge" or "pre-charged" AA's. This indicates that not only are they low in self-discharge, but also have lower internal resistance and maintain a higher voltage during discharge and of course won't be discharging much while not in use. Due to their lower internal resistance, they don't get as hot during charge, and seem to survive better in solar projects that are in direct sunlight (although shaded by casing) Sanyo Eneloop 2000mah is a common favorite, and based on your charger circuitry is about as far as I'd take it.

Note that "pre-charged" does NOT mean *fully* charged. They are not fully charged at the factory, and consumers should use a quality charger to get them ready for use.

I left the new assembly under a 60 watt bulb overnight to charge the batteries, making sure the switch was ‘OFF’.

This did not charge the batteries to any great extent. You HAVE to be in sunlight to get an effective charge. You can also be fooled by the 60 watt bulb merely having just enough energy to trick a charger's led to come on, yet the batteries starve.

Also, using a voltmeter does not indicate a AA's state of charge with any real accuracy. Typically if you take them right off a quality charger, you'll measure about 1.4v, BUT they will eventually drop to about 1.3v, and then can stay at 1.2v for most of the discharge cycle until the voltage falls off the cliff. In your case at 1.2v, the actual charge could be anywhere from 20 - 80 percent. You'll never know by voltmeter alone, and only a discharge capacity test can get you an answer. (A maha / powerex MHC9000 charger will do this test)

I hate to say it, but that existing charger was designed for a 600mah battery. You have multiplied the capacity by 4 times, so essentially you'd want 4 times the charging power if you wanted to get them fully charged. Scale it back to a 2000mah Eneloop, and you might have a chance.

In this case, you'll be short-cycling the AA's, and will probably never get a full charge, which is detrimental to their health - however with the low-self-discharge type, you'll be conserving what precious little charge they will receive during the day. What I'd recommend is to fully charge them with a quality AA charger, and then place them into your project. When they eventually walk-down their capacity to the point they will no longer power the lights in your project, just charge them up again in the charger and repeat. The solar charger you have now will just slow down this process.

In fact, I use Sanyo Eneloops in my disposable solar led lighting in my walkways, even though they are being short-cycled and not fully charged each day. When they eventually fail to light up, I give them a charge with a charger, and replace them in the lights and get a few more months out of them. Perhaps this will be good enough for your project.