How to connect a bare solar panel to a rechargable battery

It will need a controller and the batteries will need to be less volts than the cells unless a boost circuit is employed.

Likely the fault is with the squishy lithium batteries.

If you want to use just the panel, some allow dark current leakage, some don't. Hook it to a battery, put it in darkness and measure. If it leaks add a diode.

Charge control depends on battery chemistry & size. NiCd & NiMH can be charged by just limiting current delivery to C/16, so measure your panel output current in full sun as well as offload voltage. Lithium is much more fussy, hence some of the circuitry.

NT

Those are LiPo (lithium polymer) batteries, normally used in cell phones and quadcopters. Photos:

That's the charge controller.

You'll also need specialized tools to build and repair those, such as a hot air desoldering station, reflow oven, solder paste, and various chip manipulation tools.

You might also want to measure the short circuit current. Just put an ammeter across the solar cell leads and see what you get.

No.

Yes, a solar charge controller. What type and size depend on the ratings of the solar panel and LiPo battery, neither of which are currently well defined.

They also do a great job of killing batteries. LiPo lasts longer than most, but few batteries will last very long after being cycled between full charge and total discharge every day.

True. Schottky diode for minimum voltage drop. It's often inside the charge controller chip.

In the end, if you use it as a solar powered garden light, you'll likely kill the battery. You need to match the battery, charge controller, and solar cell to each other. So far, you're not doing that.

Better numbers.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

The first step to solving a problem is to blame someone or something. However, in this case, you're probably right.

Unless the solar cells (or panel) have built in diodes, most everything I've seen exhibits dark current (leakage).

I beg to differ. You might be able to trickle charge NiCd, but NiMH is considerably more picky: "It is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold."

In other words, C/16 or 0.06C charge rate for NiMH screws up the NVD (negative voltage detection) mechanism used to detect EoC (end-o-charge), which can easily overcharge a NiMH cell or battery.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

If the OP had the skill to fault find I'd think they''d already have tried to

My cordless phones use NiMH with no charge control. They get charged or discharged all the time. Last set of cheap cells lasted at least 1500 cycles. So you can do it.

NT

Maker and model please. I want to see if I can find a schematic.

I hate to admit it but you are probably correct.

My AT&T EL52210 Dect 6.0 handset uses two AAA 2.4v 400ma-hr NiMH cells. The battery label demands that I charge the battery for 16 hrs prior to use. Doing the math and assuming constant current charging, that's a C/16 charge rate.

I disassembled the charger base and took some photos: Not much inside. 6VAC 300ma wall wart, diode bridge, filter cap, and some unidentified diodes and transistor. I'll trace out the circuit and identify the parts if I have time. Without an IC to do the NVD detection, this charger is rather crude and probably does not follow the recommendations from the Battery University site.

Incidentally, the phone is 5 to 8 years old and shows no sign of battery problems. The handsets spend most of their life in the charger base and the batteries have never been discharged to the point where the handset complains. Open circuit battery voltage is now

2.68V which is very much full charge for NiMH.

Very strange.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Yep, that's what they look like. I have never seen these before now...

Yep, I'm sure they sell all this stuff, but I'm not investing the money in it. I'd probably spend several hundred dollars to get all this stuff, then spend a thousand dollars to my eye doctor for eye strain, trying to see these parts. Then I'd remove parts, which are not labeled, and after wasting hours trying to understand it, I'd still end up tossing it in the trash. I think I spent around $25 for this charger, and dont think I got my money's worth out of it, but I am fully aware it is not meant to be repaired. Like most stuff these days, it's disposible.

I'm not even considering repairing it, I just want to salvage the solar cell and make use of it.

I should also mention that last winter Walmart had some portable cellphone chargers that are meant to be used when the phone's battery dies. You charge these power packs by connecting them to any phone charger or USB port. These battery packs sold for $6. I bought two of them. If I plan ot use my phone in a place that has no means to recharge the phone's internal battery, I just carry these power packs in my pocket.

I thought the solar charger was better, but since it did not last even a year. I spent close to $20 to save about 50 cents worth of electricity to recharge a battery pack.

So, does this have to be designed by hand with individual components, or is there a chip available that does it all? -OR- can a ready made board be purchased that is intended to control solar chargers?

I have to disagree about these solar lights killing batteries. I have several of these lights mounted on my house, and several more on my workshop shed. I paid from $5 to $10 for them. I attach them with 1/2" conduit straps to the wall. Some of them have lasted 5 years, others have died after 2 years. But considering they are charged and drained

365 times each year, and operate off of one NiCd battery, I really cant complain, about their life expectancy. Every so often a local store sells replacement batteries in a 4 pack, ON SALE for about $6. So, for $1.50 per light, I just replace the dead batteries, and get another two or more years from the lights.

Now, if you buy those solar lights that cost $1, they DO NOT last long. And I also found that if you stick them in the ground along a sidewalk, they get broken faster than the batteries die, and if you dont step on them or chop them up with the lawn mower, they wont survive the snow in winter. Wall mounted is so much better, and in my case they perform an inportant task, they light up the stairs by my door, without needing to operate an AC porch light, which will cost a lot more on the electric bill.

So, would one of these diodes be all that I really need to use this solar panel?

I guess you mean I need to determine the output of the solar panel. I'll have to see what I can measure.

A couple of years ago I decided I needed to get set up for the small stuff. As this is just a hobby I bought some inexpensive gear. The 10 x stereo microscope was the most at $ 200. The a hot air rework station with a small soldering iron was another $ 60. Then about $ 800 for solder wick, solder paste, tweezers and a few other things. The most expensive was the pound of.015 inch solder that will last me a lifetime.

I agree, many things are not made to be repaired. The parts cost more than a new item. Like one older battery drill. The batteries would not hold a charge. For slightly more than one battery, I bought another drill of better quality that had 2 batteries.

BT graphite 1100 series. I saved you the time & googled, no trace of a circ uit anywhere. So I could be wrong, but I'd be surprised if there were any c harge control electronics in such equipment. Such non-ideal battery chargin g schemes are widespread, more or less universal really, in many types of e quipment.

NT

any diode, doesn't need to be schottky. But you've still got to get the numbers right. Start with measuring the panel's offload voltage & short circuit current in full sun.

NT

This is a hobby for me too, but I dont even want to work on the extremely small stuff. I'd leave the hobby real fast. I find stuff that small very nerve wracking to work on, and since my eyesight is not real good, I cant see the stuff too well. Not to mention that for most of that stuff, you cant even get parts since they dont ID the parts anymore, and even if they did, as you said the parts cost more than the item.

I enjoy working on tube stuff. I will tackle some early transistor stuff if it's worth fixing, but I usually only work on stuff that I enjoy doing.

I only tore this solar charger apart to save the solar cell panel. I know the unit was trash before I even opened it. None of the chips on it even have any numbers. Before I even spend an hour on that thing, I'd sooner buy another solar phone charger for around $25. (not that same brand though). But I dont really need one anyhow. Those $6 battery packs work just fine and I can charge them on my computer, with my AC phone charger, or in my car with my car phone charger. I dont even use my phone real much, but it always seems to need charging when I do need it. Those power packs work just fine.

Surface mount parts are trivial to get for nothing.

NT

I did see a typo in my price list. Put in 800 instead of just 80 like I should have. It will take about $ 350 to get set up for the SMD repairs.

Sometimes it is fun or interisting to take broken items apart to see what is in them and maybe salvage some parts.

Many of the SMD parts are really very inexpensive. The older tube parts are getting very expensive, and some that were common years ago are getting hard to find.