Still working on "understanding solar light", hopefully to build one. I know that it's bad to overcharge batteries, and that retail battery chargers have "overcharge protection" - I've been trying to find some sort of illustration/schematic/circuit for how this is done. I only want to recharge two to three AA NiMH or NiCad batteries for a solar-piwered light. I'm evidently not wording my searches correctly... Can anyone direct me to a site/reference that shows how to do it, or explains how it's done, or at least lists the required components?
I spent some time researching this a few years ago. There are various ways to terminate the charging cycle. A temperature spike is one. Another is noticing when the voltage stops increasing for a high current constant current charge. Time is also used.
However, for your application, you won't be able to do this. NiMH batteries have protection from overcharges of .1C. This means that if the battery is a
1700mAH battery, you can charge it using a constant current of at up to
170mA without harm for pretty much as long as you want. The batteries will not outgas, because there is some chemistry in them that prevents it and recombines the gasses.
So, just limit the current through them somehow. If your solar panel generates v volts with peak sunlight, then you need a resistor such that
v = vbatt + I * R
where I is the amp hour number divided by 10, and R is the value of resistor. As an example, suppose your solar panel generates 6 volts at max sun, and your batteries are 1700mAH batteries that will sit at 1.4V when being charged with 170mA. Then, for one cell, use
(6 - 1.4)/.170 = 27 ohms
The resistor must be able to dissipate the max power, which is
I*I*R = .17*.17*27 = 780mW
so it should be a 1W resistor.
On the other hand, buying a bunch of solar powered garden lights on the surplus market is going to be cheaper:
"Bob Monsen" wrote in news:XJ%2k.5153$ snipped-for-privacy@flpi144.ffdc.sbc.com:
Oh! OK, that's cool - I wasnt' clear on that. SO, for 1500mA, charge up to (but not more than) 150mA. THanks!, that helps me understand why one migh tuse one solar cell over another.
I'd though I'd have to figure out some way to sense when the battery was "full" so to speak, and I just don't know enough to do that, at elast not yet ;)
Saw those, thanks - mainly, I don't like the idea of wasting all the housings, esp. if my stained-glass-light bit takes off and I need to make a number of them, but also, I tired taking one cheapie apart and it pretty much diintegrated - not so good for putting into a hand-crafted item; plus, if I make larger lights, I'd like to use up to three or maybe even 4 LEDs, depending upon the eventual sizes I can build (I'm, primarily acrafts person, not an electronics person). To sell items, I want to be able to nto only keep teh price down as much as possible without comprimising quality, but also, as above, adjust the lighting, if need be, to the size of the individual items.
I'm still looking for places that might sell the "guts", actually, simply because it'd just be so much easier (prob. also cheaper), and wrote to Intermatics (which makes Malibu lights) and whatnot, but no replies yet, so I'm pretty sure I'll have to manage this on my own.
But anyhoo, thanks for the info re: overcharging, that helps a lot! :)
The problem with NiCd and NiMH batteries, is that it is difficult to "float" charge them properly. The proper way to charge, is to apply a current and then terminate the charging when the batteries are fully charged. There are different ways to detect full charge, depending mostly on how fast you are charging. Maxim's MAX712 and MAX713 may be of interest.
Normally, float charging NiCd and NiMH is done by simply constantly charging them at a low current, known as "trickle charging". This is effectively an infinite overcharge, but the batteries are designed to withstand this abuse without taking much damage.
Lead-acid batteries are much easier to float charge: Just apply a current-limited constant voltage to the battery to keep it fully charged. LiPo batteries have a similar property, but they are quite a bit more expensive.
Robert Roland wrote in news: snipped-for-privacy@4ax.com:
Yes, thanks!, they are - esp. since the price is reasonable. I'm calling up the info via Goggle right now. I'd like to be able to put the lighting units into my items, and still keep the overall cost reasonable. I'm looking to see what sorts fo circuit designs they recommend.
I'd like to be able to charge the batteries quickly, so that they'd operate duing times of short (or cloudy?) days, but also prevent overcharging.
I'm looking at NiMh as what I think is the best balance of cost, availability (in case the eventual buyer needs to replace the batteries for some reason), and potential length of nighttime operation.
I've actually tried to find whether I could just buy the innards (no repolies from my various letters of inquiry), or even have someone design and build the 4 types of circuits (i.e. for one bright-as-possible LED, or 2 or 3 or 4 LEDs)(the cost of which would prob be prohibitive). So I'm left with trying, as a non-electronics person, with gettign as much info as I can, and trying to figure it all out for myself. I did try taking a garden light apart, but the cheap piece of junk fell apart, so that's not really a reliable source of low-cost Solar light innards for what I'm tryuing to do (i.e. design and hand-craft original stained-glass pieces that also function as "mood lighting"/garden lighting).
Well anyhoo, I'll look for mroe info ont he item you recommended. There
*has* been a lot of good info offered by diferent folks here, which is great and I appreciate all of it :) Just have to try to put it all together, figure it all out.
"Bob Monsen" wrote in news:Xh%3k.4834$ snipped-for-privacy@nlpi068.nbdc.sbc.com:
THe problem is that those are red.
Maybe I ought ohave better-clarifgied wat I'm doing, which will explain why I'm asking so many questions.
I'm making stained-glass items that will function as Solar Lights. ALthough I'm starting with clear textured glasses, which transmit more light than do the Tiffany-type colored glasses, I'll still need a good bit of light to make them look right. And the major complaint I've heard from potential customers and sellers is that most normal solar lights are already way too dim. SO, I'm figuring that I'll need to use more than one LED, and prob. the new extra/ultra/super/whatever bright ones. So, a couple of LED drivers were recommended, which I'm looking into, and there are some amplification methods as well, but I'll need to charge three to four NiMh batteries (I'm planning on 1500mA), and I want them to charge rather quickly, but that brings in the question of possibly overcharging them.
Also, I've seen solar cells of a suitably small size rated at, for some examples, "0.5V/400mA", "0.5V/800mA", "1V/200mA", "2V/200mA", and a few others, and I've not been able to find explanations re: which is best matched with what sort of battery and how many thereof - for example, soem applications call for 9V or 12V batteries, but I'm planning for
1.2V/1500mA NiMh (not because I "know" it's the best choice, just that I know they're available). So what I need is either (A) 4 available types of "innards": one super-bright LED for small glass items, 2 such LEDs, 3 such LEDs, and 4 such LEDs, or (B) a set of rules that will elt me look at the LED specs, and number thereof, and work backwards to calculate the necessary components,and values thereof, including battery number and solar cell rating, whcih in turn will let me look up what parts I need, and where to get them.
Cost is a factor, it's true, but the thing there is that my main goal is to keep the "innards" to around $20 - see, given the sort of thing I'm making, that's still a rather minor percentage of the eventual asking price, *however*, given that the price (for a handcrafted piece of glass art) will be what it it will be, the thing is that teh Light part dang well better work, and work *well*, or I won't *have* a market. So cost is a consideration, but "cheap" is out of the question. At teh same time, regarding having them pre-made, I would expect that it'd cost a whole heck of a lot more to have tehm made (because people do want and need to be compensated for their time) than it's cost if I could figure out the general rules, and make them myself.
So that's the situation...hopefully it's a clarification of what I'm doing, and why I've been asking what I have (and why the surplus red single-LED won't work for me, tho' I do appreciate the effort :) !)
Kris Krieger wrote in news:JPadnUjmOeQPzMzVnZ2dnUVZ snipped-for-privacy@earthlink.com:
Actually, I earlier today found and printed some info that does clarify solar cell volts and current and the relation of each to battery charging (basically, higher voltage charges more batteries at once, higher current charges faster, so now I can apply the rules that had been provided earlier on in this thread to figure out what I'd need for charging - but the question of "how to sense when the batteries are fully charged, and then cut off current to prevent overcharging" is somethign i still haven't resolved).
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