Identifying scavenged capacitor/battery? [SOLVED]

(Please go easy on me, I'm a hobbyist newbie.)

I'm taking apart a dollar store solar garden light for the sake of leaning. I've identified the parts in the very simple device--solar cell, on/off switch, white LED, resistor (so the LED doesn't get too much current), diode (so the power supply doesn't "backwash" into the solar cell, I imagine), and a capacitor to store the energy from the solar cell. I was surprised to see a capacitor rather than a rechargeable AA battery, but whatever.

But while there are markings on the resistor and there are markings on the diode, so I can look those up and know their stats, there are no markings on the capacitor, which surprised me. It is a cylinder about 1/4" in diameter and about 3/4" long. There is a positive lead to one end and a ground lead to the other. Near the positive end there's a dimple running around the circumference, but it's otherwise of uniform size up and down the cylinder. There is a yellow plastic covering over the cylinder, with no markings on it. The open ends of that cover show me a flat metal terminal at the ground end, and a smaller flat metal terminal in the middle half or so of the positive end, with a sort of "terra cotta" colour around that. That colour makes me wonder a little if it's not a ceramic capacitor, but aren't those always "flattish"--discs or squares or something--and cylinders like these are usually electrolytic, including that "dimple", the ring dent near one end, right?

As I type this, another thought occurs to me--is this perhaps just a less-standard-shape battery?

(If my descriptions are awful, I can add a photo later, it's just awkward from where I'm typing this right now.)

I put 3V through a 100 Ohm resistor and then across the LED to see if it would light, and it did, and then faded. I assumed it was charging the capacitor a bit, so did the same thing directly to the capacitor's terminals, and had the same result--the LED lit, and then when I removed the leads, it stayed on for a bit and faded out. It began to fade after about two or three times as long as I "charged" it (which was only about three seconds), and then faded down to a very dim glow which lasted for perhaps half an hour afterward (I'm still learning about my multimeter, but I know this component is putting out about 0.78VDC at this point).

Any thoughts on how I can identify this component? Is there a test I can do with my multimeter which will tell me more? First off, things I can try without removing it from the circuit it's in are best, as I hope to learn about it before I completely take it apart.

Sound very much like a battery to me.

We await the perfectly focussed photo.

Sounds like a battery to me. Just a small, cheap, crappy one :stuck_out_tongue:

No, not perfectly focused. :wink: But nonetheless, here it is. I did a search for non-standard batteries, and there are some camera batteries that look very much like this (they come labeled, though!), even with the same dimple.

Clearly a small battery. Likely NIMH variety. I highly doubt it would be a LiFePo4.

All solar garden lights I've opened contained a NiCad battery (can handle overcharging a bit better).
And a "joule thief" kind of LED driver.
Leo..

zenheathen:
No, not perfectly focused. :wink: But nonetheless, here it is. I did a search for non-standard batteries, and there are some camera batteries that look very much like this (they come labeled, though!), even with the same dimple.

These batteries are bought in bulk and since they are not for consumer
use, there is no reason to waste time marking them.
My guess is a NiCad.
What voltage does it go to, fully charged and right after it is
removed from the sun?
If it is under 1.4V it is most likely a NiCad. After about
10 minutes it would be at about 1.25V.
Dwight

I've opened two different ones now, and haven't seen a joule thief-type circuit. But these have been very cheap ones, mind you. The other one I took apart had more parts (at least three resistors, one electrolytic capacitor, more), but it also had a very obvious standard (though cheap) rechargeable AA. The clear difference between that AA and this yellow cylinder (along with that circumferential dimple) is what had me at first thinking it must be a capacitor.

I'll try leaving the solar cell in direct sunlight all day tomorrow, then read the voltage from the battery.

I have one that has a solar cell, resistor, LED, battery and IC ( under black epoxy )
When in the sun, LED is off. When in the dark, the LED is on.
I suspect this is the action of the IC.
Dwight

Common, garden variety, OEM nickel-cadmium battery with solder tabs. Almost always yellow or blue heatshrink. Very low capacity - 150 mAh at best? Pretty crappy light.

Thanks for your help, everyone.

zenheathen:
I've opened two different ones now, and haven't seen a joule thief-type circuit. But these have been very cheap ones, mind you. The other one I took apart had more parts (at least three resistors, one electrolytic capacitor, more), but it also had a very obvious standard (though cheap) rechargeable AA.

If you have a solar lamp with a single NiCD/ NiMH-cell and need to light up a white LED, you need a boost-circuit. The larger, often green "resistor" in the circuit is an inductor.

// Per.

Zapro:
If you have a solar lamp with a single NiCD/ NiMH-cell and need to light up a white LED, you need a boost-circuit. The larger, often green "resistor" in the circuit is an inductor.

// Per.

Ah yes, I hadn't thought of that. It must be a boot circuit.
Dwight

Here's the top of the little circuit board, while I go Google "boot circuit".

zenheathen:
Here's the top of the little circuit board, while I go Google "boot circuit".

It's "boost", not "boot".

You haven't shown us the other side of the PCB, but I suspect a "COB" or similar.

That blue thing looks very much like an inductor.

It occurred to me (just) after my last post, that there may be a colour code that yellow shrink indicates (deprecated) Nickel-Cadmium, while blue-green suggests Nickel-metal-Hydride.

It also occurs to me that there are a few of those teeny-tiny $1 garden lights somewhere around here in a storage bin.

Hi,
If you look in your old 386 and 486 CPU boards you will see these batteries leaking over the PCB, they were back up batteries for RTC and BIOS chips, still used in old PLCs as backup.

Tom.... :slight_smile:

So much for old PLCs!

@Paul__B:

It looks so much like a resistor to me. The only thing about it that looks wrong, I think, is that for a blue resistor, it should have a 5-band code, and this appears to have only four bands.

I'm still early in the learning process, and I've only just begun to look at inductors, but I would have expected something larger, perhaps even with visible coils.

Yes, there is a black glob on the back, approximately opposite where the "T H" logo is in the image of the top. I had assumed it was only to strengthen the solder points of some of the leads, but had wondered why not all of the leads were thus protected. There are so few attachment points and it's such a simple circuit layout visible on the back, it seems surprising there could be a chip under that glob.

@TomGeorge:

Yes, I think that's exactly what it is.

Here's the back, flipped over horizontally from the other pic (i.e. the black blob is under the "T H" logo on the front). The red and black wires connect to the battery, the white and yellow wires connect to the solar cell. The S+, S-, B+ and B- markings on the front of the PCB are now clearly pos and neg each of "solar" and "battery".

zenheathen:
@Paul__B:

It looks so much like a resistor to me. The only thing about it that looks wrong, I think, is that for a blue resistor, it should have a 5-band code, and this appears to have only four bands.

I'm still early in the learning process, and I've only just begun to look at inductors, but I would have expected something larger, perhaps even with visible coils.

Look at this:

// Per.