Circuit Design Q. - battery charger

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Lots of questions there but just to start with one of them:

The led you quote are typically 18000mCd @ 20mA. With their angle (2*theta1/2) of 15 deg this would calc to a bit under

Regards

RHRRC wrote in news: snipped-for-privacy@27g2000hsf.googlegroups.com:

Thanks for the info :) I've been having a bit of trouble with LEDs because for some, the specifications list lux, others list watts, others list mcd, or "lambert", or so on - I'm still very new at all of this, so I've been having trouble translating "watts" into "mcd (and lumens since

So I'll go ahead and look into more and different LEDs, and look for some additional generalized "LED tech" info as well - I didn't realize that the angle was so closely related to the actual light output; I'd assumed that it was teh same amount of lighting, just "squished" into a narrower beam, so I'm glad to know that's incorrect *before* putting it all together ;)

I'll visit the websites for the companies you mentioned, and look around for others producing sinmilar LEDs.

Thanks again :)

- Kris

innews: snipped-for-privacy@27g2000hsf.googlegroups.com:

Since your involved in product developement, it might be a good idea to test them personally. The LEDs are vital to the product and the choice is a "subjective" thing as well as an efficiency decision. You could likely get free samples, but the cost is minimal in the greater scheme of things ;-). Of course from the current and voltage you can find the power (watts). Regards Ken

"Ken S. Tucker" wrote in news: snipped-for-privacy@f36g2000hsa.googlegroups.com:

Hey, Ken,

That's a good point. I've been thinking "old" in that I keep forgetting that there isn't only one type of white any more - there is everything from Warm WHite up through the "white" ones that look more like blue than white, depending upon the Degress K of the light.

After I read the LED post, I also "just realized" that duuuuuuh!! an LED's wattage is Volts multiplied by Amps! Oh well, things like that are what helps keep me at least a *little* humble ;)

Heh, found one site that recommended cleaning the LEDs in ethanol - hmmmm, sounds like a way to combine two hobbies

ANyway, I continue to research it all. I found areference that I think is great, by searching on LED terms plus "binning", which the first reply had mentioned:

Teh problem with the "Star" type units is that they all seem to require

Anyhoo, good suggestion re: trying afew different LEDs :)

Thanks!

- Kris

innews: snipped-for-privacy@f36g2000hsa.googlegroups.com:

I think you should proceed on an evolutionary approach for this product. No criticism is intended but you need a learning curve. Begin with very simple circuits, a battery or voltage source and LEDs, get it working then improve it. You may be able to get a good product WITHOUT DC-DC converters which are a PITA and expensive, compared to a resistor. For example you can run an LED directly from a battery with a very small resistor for safety. You can set-up LED's in series or parallel configurations, or a combination to get a close match to the battery voltage and then a small resistor would do.

Suppose you improve the circuit by 20% adding more sophisticated electronics but at 3x the cost, is it worth it? Maybe make the solar cells 20% larger is cheaper. KISS Ken

"Ken S. Tucker" wrote in news: snipped-for-privacy@25g2000hsx.googlegroups.com:

{snip} Done ;) (It *was* getting way too long.)

Prob a good idea, I chronically try to run full tilt, before learning to walk so to speak...

Yup, expense is a bit of a problem - So far, the parts add up to just over $US42 (single-item cost - no volume discount) and I still have 17 resistors to go...

It's definitely verging on being a Rube Goldberg situation.

I probably need to rethink it from the beginning (personal shortcoming - if I can't think it through visually, i.e. can't picture/chart it, I can't do it - I'm unfortunately like that with pretty much everything - which is why I stank at non-Geometry math, couldn't/can't visualize it).

The two main parameters I am starting from are the very things that make the project unusual: (1) First and Foremost: high brightness (A) Light needs to get through stained glass and/or sometimes-heavily textured clear art/archetectural glass (B) Potential customers and sellers not at all enthused about "normal" brightness available in Solar Lights, but highly enthused over good brightness (2) Fast-charging of batteries (which in turn requires overcharge protection). (A) Increases liklilood of batteries acquiring sufficient charge in less-than-perfect insolation (B) Ensures sufficient battery power to give good brightness for a longer period of time (C) Allows brighter (higher power) LEDs to be used

It's a simple matter to do a basic thing like this: GRNDGRND , the fact is that it's just not really worth the bother, first because such things are already out there, and cheaper than I can make them, and second, it's not what my target market wants.

So, if I can't achieve (1), I might as well just make candle-holders, because in terms of solar lighting, people want something they can *see* by. And (1) requires (2), to ensure that the batteries are "topped off" enough to run the needed number and/or brightness of LEDs. ((Anotehr complaint of people Ipolled, as well as myself, is that it takes so dang long to charge teh typical availabel lights, that you get little lighting, to no lighting whatsoever, unless the weather is Optimal - although solar cells won't charge in shade, they ought to be able to charge if the weather is, for example, hazy, or if the days are less than 10 hours long.))

A corollary is: (3) Minimize cost of solar cells.

Although it's not rocket science to make a matrix of SCs that will yield the 5V needed to run the battery charging IC, it's less expensive to use the boost circuit. OTOH, I *should* be able to find a simpler way to boost the Voltage - I found a source for encapsulated Soalr Cells rated at 0.5V and 800mA for $US6.34 each, so I figure I can connect two to get 1V and

Well, I need to look at it from the beginning and see whether I can't cut down on the "contraptionistic" aspect =:-o

- Kris

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I don't know where to start.

If you have at least 6 hours of daylight, why would you do any sort of fast charge scheme?

Boost converter, then a charger chip? Why not stack enough solar cells so you have sufficient voltage to charge the batteries? Then design a step down converter with current regulated output to charge the cells. I'd pick C/8. Sometimes you will be undercharged, and sometimes you will be overcharged, but it's a reasonable compromise. You may be able to find a charger chip that does this current regulated step down at C/8. The problem with doing a fast charge is you miss out on much of the solar energy.

Make sure your LED driver has undervoltage lockout so you don't kill the battery pack.

You shouldn't need a photodiode since you already have a solar cell to determine when it is night.

snipped-for-privacy@sushi.com wrote in news: snipped-for-privacy@z72g2000hsb.googlegroups.com:

To allow for half-decent charging when thr eis not 6 hrs of full bright sunlight in perfectly clear weather.

First, because it seemed to me that it was more expensive that way (tho' I have to finish my parts spreadsheet and tally up all the prices, before I can say for sure); second, because I was worried I'd fry the batteries...

I was told that NiMH bateiries don';t take well to either undercharging or overcharging, so, beleiving them to be persbickety, i figured that the charging control IC might be what they needed...isn't "c/8" the same thing as "trickle charging"...? I read that NiMH also don't deal well with trickle charging, and prefer fast-charging.

Sorry but I'm not sure what you mean by "miss out on much of the solar energy"... I just want to try to make the batteries "happy" so to speak, so that they will be able to drive whatever LEDs I need to get to achieve the brightness I hope to get...

I'll have to look up "undervoltage lockout" - that's a new term for me, I don't know what it means...I thought, tho', that the LED driver is supposed to smooth everything out in terms of the relationship between the LEDs and the batteries...?

Oh! OK, I thought that I needed it to be sure that the LEDs didn't run during the daytime - I wasn't clear on that...

Thanks!

- Kris

RHRRC wrote in news: snipped-for-privacy@27g2000hsf.googlegroups.com:

Hi and thanks!; - I'm trying to find the Math, but I'm confused - when the specs say that an LED delivers X Lumens, tha's not really true...?

I found one resource that said One Candela = 12.57 Lumens", but then I found another source taht said, "A 25,000mcd LED produces 25 lumens" *but* that it translates into *actually* being only 2.39 lumens"...

...and what does it mean when an incandescent light bulb package says, for example, "800 lumens"? I know how to translate that into a compact fluorescent light bulb, but with LEDs, it seems that sometimes Lumens means one thing, but other times it means something completely different.

So, from that, all I can figure is that using, for example, six 11,000mcd LEDs with the same 20 deg viewing angle as the above reference 25,000mcd LED), that should translate into only about 6.3 lumens, despite the one source that siad 1000mcd translates into 12.57lumens...??

The more I read, the more confused I get. It'd be nice if there was some online calcualtor that let you put in mcd value and viewing angle, and output the near equivalnet in terms of an incandescent light bulb - especially given that "lumens" actually has different meanings...

So I'm left wondering how to evaluate the following:

Similar:

It'd be nice if there was some sort of definitive reference...

TIA,

- Kris

innews: snipped-for-privacy@25g2000hsx.googlegroups.com:

Awhile back I designed this product,

Perhaps by-pass the solar-cells and use an adapter. There is still the manufacturing process to consider, then warranty and servicing.

What does your "target market" want? Retail$ ?

"0.8 watts", set your power supply to that limit and connect up your LED's and see if that works.

Ken

"Ken S. Tucker" wrote in news: snipped-for-privacy@c65g2000hsa.googlegroups.com:

Hmm, Interesting idea. The sound files were, no pun intended, pretty wild - esp. the loony loons ;)

"Adapter" as in, plug into an electrical outlet? It's an option, but I relaly like the idea of solar, since it can be used anywhere, no tether (and no cord to trip over). Now, people have and do sell not only Tiffany-style lamps, but more modern designs as well, that are plug-in lamps - the main thing with the solar idea is that I haven't seen anything like what I have in mind. So that's what I want to try to do.

Warranty, bleh - I can't get into warranty/service - it'll have to be "as is", with a cautionary sticker stating so.

I'll tell you what, I have looked for bare lighting-units to buy, but to no avail. The only people who make lighting units also only sell them stuck into some sort of fixture. So, either I build it from scratch, or I spend $$ on premade units, break tham apart, hope that the parts survive the process, and then stuff those parts into my item. Which strikes me as jut being goofy - the "cheap" lights don't light worth beans, and the brighter lights aren't cheap(and don't come apart all that easily).

Glass Art with fairly bright solar-powered lights - brighter than current garden Lights, maybe around what one might expect from a 40watt incandescent.

That's the tricky part. I'd have to estimate at least from $125 to over $200, and possibly more, for the glass work alone, based upon the glass work I've seen, and the work I am currently in the process of doing.

If I use a battery charge control IC, 1V would be sufficient, but if I'm going to charge batteries in series directly, AFAIK I need to have the voltage higher than the total battery voltage - at least, that's what the Maxim people told me...

At the same time, looking at all this, I'm wondering whether/why I even need an LED driver, if I stick with LEDs that use 3.2V-3.4V, especially since the drivers have a CTRL pin that seems to need to be connected to a "PWM dimmer", which I looked up and, although there is alot about waveforms, I've seen nothign to date about building the actual PWM widget, which is annoying.

THe thnig is that I *know* this is doable. If nothing else, there are solar party/holidya lights, such as these:

Well, it's late right now, I'll sleep on it and see whether I can come up with better ideas tomorrow ;)

- Kris

"Ken S. Tucker" wrote in news: snipped-for-privacy@x35g2000hsb.googlegroups.com:

That seems to be a pretty low hourly rate - is that standard, or mainly what is suitable for your own needs? I keep rememberingpeople who cahrged $75/hr or more just to fill in simplistic templates for "one web page with

that word "legalities" gives me the shivers. All I can figure is that I have to have a sticker on the item stating that "WARNING: GLASS! BREAKABLE! - no warranty is stated or implied; user assumes all responsibility for damages - art item, not suitable for sports, camping, or other vigorous activities; take into shelter in bad weather", or something to that effect. Anything else (materials, gas for deliveries to sales venue(s), boxes, etc) that is an expense, and different from hourly rate.

Lightening? It's just a solar yard light with three (MAYBE four but not likely) 1.2V NiMH batteries. The tallest thing I'm envisioning will only be about the height of a side table, *maybe* 24". I can't see anything taller than 36" (ro jsut under a meter ;) ) ebcause at that point, the weight of the glass would probably exceed the holding capacity of the soldered copper foil + zinc framing. As above, "take into shelter during bad weather" - if someone is dopey enough to leave an expensive glass item out in a driving thunderstorm, that will be their own responsibility. If they're nuts enough to stand out in a storm holding the thing, again, their own responsibility. IF they buy it, take it home, and drop it on concerte, again, their own responsibility - same as when someone buys a glass jar of pickels or jam - if one drops it and steps on the broken glass, it's one's own responsibility.

As in the ASCII chart:

| Now, people have and do sell not only

I *wish* I could just buy the units pre-made, but again, I haven't seen any "solar light guts" at all, and received no replies to my inquiries - they're always in some sort of housing that has to be bought retail. I could prob. manage to disassemble Solar Flood/Spot Lights, which might yield enough light with less "sturm und drang", but that would void any existing warranty anyway.

I'm assuming Yours Truely =:-O - again, problem is, no grants or other dole money, no loans, just cash-on-hand, so I simply cannot afford to pay someplace several thousands of $$ to make something that might not sell. OTOH, $100 worth of parts (not counting labor at this point, only counts if the thing works) for a few prototypes is manageable. So, to paraphrase the old saying, "Necessity is the mother of learning new stuff" ;)

This isn't small business, barely even micro-business - more like NANO- business.

Heh, I switched yrs ago to mechanical ones ;) , spent too much time sharpening!

Anyhoo, I'm taking a re-look at these parts, and some different ICs. I probably also need some additional references - I'd gotten "Electronics For Dummies", but it's really short on actual explanations beyond the simplest stuff tht I was able to find right online. What i'd like is a reference that would clarify why and how something of this complexity actually works:

I'd really like to be ableot look at somehting like that, and figure out on my own just how much I need and how much I can leave off for what I want to do. Hard part is finding the right textbook(s). Most references I've personally seen have either stopped at the most simple/basic stuff, or jumped right to something like "how to build a Tokamak reactor"...

Well, on to some more researching online - meanwhile, I might end up buying a solar flood light as a disassembly project, just for the heck of it; it wouldn't hurt to see how something brighter than the typical "garden light" is put together.

- Kris

I once got paid $60.00 to tell a client that they had to go to the Compaq store and buy a replacement battery. I felt like a thief.

Thanks, Rich

Rich Grise wrote in news: snipped-for-privacy@example.net:

That's kind of funny!

OTOH, I guess everyone knows different things, so if the person knew nothing at all about the equipment (sounds like a computer), better to pay the $60 than risk ruining the item. Look at it this way: you might have saved the client $2000! ;)

- Kris

hsb.googlegroups.com:

k,

Nicads and NiMH are more rugged than the manufacturers let on. Certainly Sanyo cells, which would be my choice. What I would do is insure the light stays on until the batteries reach the discharge voltage. Think of it like a discharge before chrage design. Then it will be very unlikely you will give the battery much of an overcharge.

If you try to quick charge your batteries, you need more solar cells. This will make the design more expensive for a questionable improvement. Think about it this way. You have 8 hours of sunlight, but you want the job done in two hours, so you need 4 times the solar cells for this quick charge design. The remaining 6 hours of sunlight go to waste

Now that I think about this, it might make sense to pick the capacity of the batteries such that you will never reach full charge. [Think about this a bit. Capacity is what you put into the battery, less charge efficiency losses. Nobody says you have to reach full capacity of the cells, but rather you need capacity just for your application.) The incremental increase in battery cost would probably be made up with the simpler charger design, i.e. just a current source and perhaps an overvoltage protection. [Weak cells get resistive and will achieve a high voltage under charge.]

You need undervoltage protection of the batteries not to discharge them too deeply. This should be in the LED driver datasheet. If the intent of the LED driver was to use primary cells, it may not have undervoltage lockout.

I'm not sure if I made this clear, but the solar cell can both provide power and act as a sunlight detector, eliminating the need for another photodiode.

I got a dirt cheap solar charged garden spotlight at Harbor Freight just for yucks. It is so simply built that everything is through hole.

Probably so - they were in a total panic; when I fired it up it was just obvious they needed a CMOS battery. And it was a Compaq, so it's a proprietary battery. Heck, the battery itself might have been more than $60.00!

Cheers! Rich

snipped-for-privacy@sushi.com wrote in news: snipped-for-privacy@79g2000hsk.googlegroups.com:

I made a note of that, it's good to know.

OK, you mean have an indicator light. THis will be an automaticv outdoors light, so nobody is goingto be checking it. I'm looking at an example Switch-Mode circuit that will stop charging when the batteries are charged. THe Maxim peopl etold me that the indicator LED and it's associated resistor can simply be left out wiht no effect on the rest of the circuit.

I'd like to shoot for 4 hours, which I think would allow for charging on less-than-perfect days (light haze or shorter WInter days, for example). A big complain of people I polled (and myself as well) is taht the existing lights charge *so* slowly, that you get almost nothing at all if the day isn't perfectly clear with bright sun. Few places have continual perfect days. One simply cannot expect/count on a full 8 hours of perfect weather with bright sunlight - especially given that the people who woudl buy a solar Art Glass lamp are not likely to have bare treeless/shrubless yards with zero shade, so one has to plan for less than 8 hours of full sun. The fact that manufacturers don't, is what gets so many people disgruntled with the existing products.

So, if I'm going to make something, I'm not going to waste my time making what is already available (and for less $$ than what I can make it for). It's only worthwhile if I can think outsize teh proverbial box, and come up with somethign that isn't already available at every WalMart...

So, if it charges in 4 hours, and is dormant for the rest of the day, so what? Meanwhile, if sunlight is not perfectly bright, that 4 hour charge time will be expanded, since it'll take longer to collect the required photons so as to charge the battery. There is no "waste" - it's not like keeping a porch light on all day; the sunlight is there whether it's being collected or not. OTOH, if the outdoor area only *gets* 4 hours of direct sunlight (due to shadows from trees, other houses, or so on), it'd instead a waste of one;s money to pay for something that simply cannotr charge within that 4 hours - been there, done that, and my huge annoynace with current "standards" is what's motivating me to try this.

True - I'd started out thinking of 1500mA AA's, but now I'm giving serious thought to 2000mA. THe Example Booster Circuit (using the MAX866 and MAX1771) that I'm looking at requires only 0.8V up to 4.5V, but the AppNote doesn't mention

Yup, I looked it up, and the "UVLO" rating for the MAX1848 means indicates - it won't send anything to the LEDs once the voltage drops to about 2.10V-2.15V.

I'm thinking of it as an added thing to be sure the LEDs don';t lgiht up during the day - IOW, any time the batteries have been charged. While tracing through all of the App Notes (and their sample circuits I'm trying to adapt), I can't see any way for the solar cell to influence whether teh LEDs light up - the sample switch-mode circuit for the DS2715 battery charging IC simply switches from charging, to discharging, once the batteries are "full". So I figure that a photocell between the battery-circuit output, and the LED driver, should do the trick. I've seen them for under $2.

I looked at commercially available solar lights until my eyes got bleary, and not one of them provides the requisite amount of light. After all, this also has to shine through stained glass - not just one or two dabs of the stuff, and not that faux-stained-glas spaint stuff, but real stained glass. These will be primarily Glass Art pieces - the night- lighting is something I want to do to expand both the enjoyment time of the piece, and the use of the piece.

So, Yes, the "cheap" ones *are* simple - and cost less than it takes to build tham, which makes building a cheapo one IMO a waste. Basically, tho', I am thorougly and completely fed up with and sick to death of "cheap" =>:-p Cheap is common, cheap is *everywhere*. If people want "cheap" solar lights, they sure ain't gonna spend $200 or more on a stained-glass lamp/lantern/3D-piece. OTOH, if they *are* going to spend that much, they most certainly will *not* be satisfied with "cheap"-level lighting...

sk.googlegroups.com:

No, not an indicator light. Burn the existing LEDs during the day to bring the battery down to the discharge level. This would be needed if you picked my simple scheme where you don't use a smart battery charger but just dump current into the cells.

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This means you doubled your solar cell cost.

And just how are you going to expand the charging? You will somehow have to bypass any safety fimers in the chip.

of

To be clear here, I was picked the battery capacity to be at a level when you won't reach full capacity of the cells. This sounds odd, but it makes sense if you picked a simple current source charging scheme. Having more capacity than you require means you won't overcharge the cells.

There is UVLO for the sake of the chip, and UVLO for the sake of the battery. For instance, if you had 3 cells, then the batteries would be discharge to 0.7 v per cell, which would damage them.

UVLO for a chip is designed such that the chip will behave if the supply is too low. Generally it is a cascade of many circuits, i.e you first make sure you have enough voltage so that logic will function, then you insure there is enough voltage for the voltage reference to work, etc. It will only be a battery protector if you use two cells.

The off the shelf units manage to use the existing solar cell to detect if the sun is shinning.

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