Author Topic: Led master class Parts 1 thru 5  (Read 13654 times)

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commanda

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Led master class Parts 1 thru 5
« on: October 31, 2007, 06:04:08 AM »
If you haven't already done so, I suggest you read the previous installments here;
Part 1
http://fieldlines.com/board/index.php/topic,131213.0.html
Part 2
http://www.fieldlines.com/board/index.php/topic,131214.html
Part 3
http://www.fieldlines.com/board/index.php/topic,131215.html
Part 4
http://fieldlines.com/board/index.php/topic,131296.0.html

As mentioned at the end of part 4, this is how to extend the circuit to make a nite-light.

Whilst mains powered nite-lights are prolific in almost any $2 shop, I have yet to see one

specifically for running off 12 or 24 volts.<p>
My original intention with this was to use a phototransistor. And whilst circuit 5.0 does indeed work,

it is less than what I would describe as optimal. It suffers from a lack of sensitivity, and tends to come on too early.

Also, the phototransistors tend to be very directional.

At night, if you turn on the overhead room light, the nite-light won't switch off unless the phototransistor is

aimed directly at the light. But then it tends not to see the daylight coming in through the window.

It also has a fairly wide transition range, where it's not fully on.

So, having explained the short-comings of this circuit, I present it here anyway; with a photo of the bread-boarded prototype.





Note that is important to shield the phototransistor from the leds. It is usually necessary to point the phototransistor

90 degrees away from the leds, and then cover the underside of the phototransistor with opaque tape.<p>
Circuit 5.1 is a bit more complex, but gives very satisfactory performance. Q3 & Q4 form a differential pair. Basically, if

Q3 is on, Q4 will be off. And vice-versa. When there is no light, the LDR resistance will be high. So the voltage at the base of Q4

will be higher than the voltage at the base of Q3. So Q4 will turn on, and Q3 will turn off. Q3 off will allow gate voltage on the fet,

and the leds will turn on.<p>
When light is applied to the LDR, its resistance will be low, so the base voltage on Q4 will be lower than the base voltage on Q3.

Q3 now turns on, preventing gate voltage from being applied to the fet, so the Leds will not be on.<p>
P1 is optional, and can be used to fine tune the sensitivity of the circuit.

R5 & D1 is also optional. It provides positive feedback to enhance the switching from off to on, as well as hysteresis.<p>
My first unit built on the circuit of 5.1 has been running off a 24 volt plug-pak in my bathroom for some time now.<p>
The component values shown are for my 24 volt system. You may need to decrease the values of R1, RG1, RG2, and R3 for a 12 volt system. (based on feedback from richhagen with experience of the previously published circuit 4),

Again, the LDR should be pointed 90 degrees away from the leds, and the underside covered with opaque tape.<p>
I've also just cornered the Australian market for LDRs. I ordered 10 pieces, and received 10 packets of 100 each. (1000 pieces).





Amanda
« Last Edit: December 15, 2010, 09:56:58 PM by wooferhound »

sdscott

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Re: Led master class pt 5
« Reply #1 on: October 31, 2007, 08:47:01 AM »
Bravo!  I enjoy your Led-Master series of articals...
« Last Edit: October 31, 2007, 08:47:01 AM by sdscott »

Devo

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Re: Led master class pt 5
« Reply #2 on: October 31, 2007, 10:10:25 AM »
Yes excellent reading, probably someone will read & start marketing these nightlites for rv use etc- lol


Next year wal-mart will be mass producing them :-)


Thanks for sharing , I am either 12 or 48 volt so if anyone alters the values to make them work please post what you used so the electronically challenged like me can

try it.


Devo

« Last Edit: October 31, 2007, 10:10:25 AM by Devo »

richhagen

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Re: Led master class pt 5
« Reply #3 on: October 31, 2007, 12:09:39 PM »
Thanks for posting the circuits and the explanations of their function.  They are educational and appreciated.  I have already copied some of them.  Rich Hagen
« Last Edit: October 31, 2007, 12:09:39 PM by richhagen »
A Joule saved is a Joule made!

Brian H

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Re: Led master class pt 5
« Reply #4 on: November 02, 2007, 11:45:27 AM »
Excellent post, as always, thanks!


Regards,


BrianH

« Last Edit: November 02, 2007, 11:45:27 AM by Brian H »

commanda

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Re: Led master class pt 5
« Reply #5 on: December 09, 2007, 04:05:02 PM »

http://www.otherpower.com/images/scimages/2006/led_cct_51.pdf


Hopefully this will be a little easier to read.


Amanda

« Last Edit: December 09, 2007, 04:05:02 PM by commanda »

BigBreaker

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Re: Led master class Parts 1 thru 5
« Reply #6 on: January 27, 2011, 07:23:36 AM »
Commanda, is there any reason your circuit couldn't be the driver for an IR blaster?  The switching speed would need clean edges on the order of 40khz.  I'm a bit rusty on using transistors in the forward active region.

georgec

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Re: Led master class Parts 1 thru 5
« Reply #7 on: March 16, 2014, 12:02:32 AM »
well I'm kind of too late for the party I hope some of you are still around to answer some questions, I have been tinkering with LEDs lately, various batteries and renewables options, it all started with an interest in solar panels but it never made much sense the way it is commercially done.
bit off topic but a 18v panel charges a 12v dc battery, which than gets inverted to 110 AC grid or not through wiring to your average department store expensive bulb which has some sort of PS built in to step it down to 3.6v DC I assumed
well I now know LEDs are current devices, just reading the specs I was stuck on the voltage myself,

Initially my thought was to build a custom panel just for the lighting in the house, to charge a lithium parallel pack, or a 20AH pouch, lifepo4 ranges, 3.2v to 3.6 , I also have some lipos 3.6v to 4.1v, with sensible sizing say a 9 cell panel would safely charge such a cell which I thought could power parallel arrays of leds, no fancy electronics, and it works I tinkered a bit last fall but I did notice the current readings varied a lot, what can I say I am simple but little did I know.

I also caught some bad feedback about transmitting 3.6v over large distances, I knew DC drops more than AC did not think it was proportional to length more than the operating voltage, I don't know the math there but apparently same drop occurs at 3v as it does at 24v so very inefficient I am told, could it work or bad Idea? I honestly only know enough to follow this thread and get myself in trouble.

ok so enough intro, I am glad I came across this presentation, especially on a forum based around renewables, I was recently looking at putting together a small 24v setup to run some powertools, I am looking to build something in the country and thou electricity is available, why bother and not do this the hard way :)

the idea was to start out modest and by the time the house is built I may not even bother and call the utility company

so obviously there are many ways to go about it but what is a proper one?, this last 24v setup was rather interesting, could one squeeze 7 leds in series?. most of your batch tested about 3 v, ( I have to go back ad read it again bit confused now ) 2 low batteries 22v, on the high end 30v, that is a bit of a gap but I guess that is why the circuitry. I was also looking into some sort battery/charge controller for my setup, I've built more complicated boards for lithium ( not of my design, I had help, I just built it, literally as in solder by numbers ), with that said I was looking into proper voltages for long led acid life, I believe 11v is already too low, 12.2v I thought would be a proper LVD, I have to ask that elsewhere but for the sake of conversation, in this instance since power would be disconnected say below 12.2v and LEDs wont work at all, should I than look at building an 8 series array? I read all series is best and the more the merrier why the question.

which than takes me even further to rather arrange my small setup at 48v than and do a 16s array but unfortunately I am not sure how that would work for the rest of my stuff, this all started with repurposing an old set of 24v cordless tools, and make them corded and run off a central battery bank powered by solar, maybe 24v is good enough but either way I like the idea and I'd like to build several such LED arrays and wire the house lighting this way right off the bat ( we'll see how the inspector feels about that, or maybe what he don't know ..............)

also while we're at it wonder if I could pull this off in automotive applications, headlights is a bit ambitious, but maybe dome light and indicator lamps, last I looked it up they were too expensive , maybe this is the way
 
anyway I'll go back and read up again while waiting for some advice

MaryAlana

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Re: Led master class Parts 1 thru 5
« Reply #8 on: March 16, 2014, 02:32:42 PM »
There are commercially available LED power supplies now, no need to invent the wheel. Jameco is one that carries them. Have one per room for all lighting in that area so your low voltage only has to go a few feet and wire the house at your battery voltage.

georgec

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Re: Led master class Parts 1 thru 5
« Reply #9 on: March 19, 2014, 01:49:19 AM »
why not reinvent the wheel? there is no progress without innovation or attempt of, if I run the house at battery voltage, say 24v for example, why not build such a current regulating circuit, could be per light or heck a central one right off the lighting circuit breaker, provided it is suitable for the demand, and build light fixtures of 6-8 leds with the equalizing resistor all in parallel of each other.

If going the commercial route, brings up other questions, what are those drivers made of and how do they drive the lights and cost and what LED fixtures to use with them, if I were considering the commercial route, I could simply run the house on 110v AC, inverted of the battery bank and use commercially available LED fixtures, but where is the fun in that.

my Whole interest in this circuit is the simplicity, I don't see any reason to go from a DC source such as a PV panel, through an inverter, grid tied or not, to a commercial bulb which has a driver built in to step it back to a low voltage DC where I first started with, it's silly I think, but by all means I am no authority just passionate so I wont even attempt to argue because honestly I am not qualified to do so. I could barely follow the thread and somewhat understand the concept, my electronic skills are illiterate at best. which brings me to my second interest in this project, I like to build stuff, and learning something new and I always have a great degree of respect for people such as the OP for taking the time to school others like me, I just got to put it in practice now to graduate the class.

so the question still remains, how to best set this up, I believe 24v DC is pretty common for pv setups the Ghurd controller is capable of 24v, another project I am looking into so I recon no sense in looking at 48v or further at this time, the op chose 6 leds, for the prototype, can it be done with 7?at a low of 11v / battery a total of 22v should drive 7 LED's in series, besides I believe it make a better arrangement with 1 in the middle surrounded by 6, the other question is how much light will it output I believe it was  20 000 mc each for your average 5mm, not sure how that compares to incandescent watts ( my point of reference ) most fixtures hold 3 lights so a total of 18 to 21 LEDs per fixture I figure should light up the room just fine, just lots of questions as to wire gauge and voltage loss per foot ( maybe that is why 6S is better ), can it be done with a main current regulating circuit and have the actual lighting devices made of LEDs and equalizing resistor only, I am most certainly not knowledgeable enough to figure it all out yet, not sure how much current those components can handle or in other words how many strings of LEDs can they power?, I have 8 ceiling fixtures in my current house, say 12 for the new build, at 3 strings each, 36 total, can that circuit handle it, should I split it in halves or maybe 3 strings in max one per fixture?

look forward to hear back even if its geared towards a commercial application, I can keep an open mind

George

OperaHouse

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Re: Led master class Parts 1 thru 5
« Reply #10 on: March 19, 2014, 06:32:04 AM »
There are plenty of small buck converters on ebay for less than $2 shipped.  There is a KSS version for even less than a buck.  The one idea I would like you to consider is using a BOOST converter to increase LED string voltage to greater than the battery.  most regulators have a sense voltage of 1.2 to 1.7 volts.   If you string all the LED in series, you can have a sense resistor create that voltage at desired current with acceptable loss.  That voltage can be fed directly into the sense pin of the chip.

MaryAlana

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Re: Led master class Parts 1 thru 5
« Reply #11 on: March 19, 2014, 06:35:58 AM »
I was thinking along the lines of dc to dc converters that are setup as led drivers with a constant current output. The last is something leds like for long term life.

georgec

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Re: Led master class Parts 1 thru 5
« Reply #12 on: March 19, 2014, 08:28:24 AM »
There are plenty of small buck converters on ebay for less than $2 shipped.  There is a KSS version for even less than a buck.  The one idea I would like you to consider is using a BOOST converter to increase LED string voltage to greater than the battery.  most regulators have a sense voltage of 1.2 to 1.7 volts.   If you string all the LED in series, you can have a sense resistor create that voltage at desired current with acceptable loss.  That voltage can be fed directly into the sense pin of the chip.

I am somewhat familiar with boost/buck converters at least I read into it once, I gathered from previous posts that higher voltage all in series would be better, but how could that be practical for the entire house, you would only have one light switch all on or all off plus the voltage would be pretty high,

maybe each fixture could have all LEDs in series say for the sake of conversation 18 of them which would demand something like 72 v DC, now again I am not very familiar with electronics, and if there is a boost converter available to step up from 24 to 72v would be worth considering to be used as a central source, I assume transmission losses decrease as voltage increases, obviously current regulation I learned is more important for long life.

I best check ebay than get an idea of what is available

OperaHouse

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Re: Led master class Parts 1 thru 5
« Reply #13 on: March 19, 2014, 04:26:21 PM »
Seventy volts is certainly taking my advice to extreme.  Because they use the more common lower voltage  parts most boost converter
on ebay are limited to about 35V.  One I like is about $7 and can be found by searching 150W boost converter.  It has a one inch toroid
that you can wind more turns of wire on.  I have an 18W ceiling LED that requires about 43V to operate.  About eight extra turns, a high
speed diode, and a 2200uF electrolytic form a 15V boost circuit.  That is placed in series with the boost converter to get me to 45V.  It
is unregulated, but the LED acts like a zener anyway.  This is installed in the bathroom and only operates at about 6W.  More it would be
just too bright.  I just got a 32W Philips DLM that operates at about 60V.  I will be building the same type of system for that.

When you say 17 LED in series aer you talking about small ones?  I have given up buying anything other than the 10W LED modules. 

joestue

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Re: Led master class Parts 1 thru 5
« Reply #14 on: March 19, 2014, 07:26:08 PM »
whatever happened to OP?

last active  November 02, 2012, 12:17:32 AM

Bruce S

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Re: Led master class Parts 1 thru 5
« Reply #15 on: March 20, 2014, 12:17:05 PM »
She is a very busy person. Doesn't visit here much anymore.

A kind word often goes unsaid BUT never goes unheard

georgec

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Re: Led master class Parts 1 thru 5
« Reply #16 on: March 20, 2014, 10:45:30 PM »
I am referring to the 5mm LEDs, I may have some other application for your Idea, my car has some fake LEDS I was considering at some point drilling them out and replace them with 5mm, there is more than a dozen on each headlight so a boost converter you speak of might do the trick there, I assume they work from 12v to 35v. at 3 v each should be able to run 11 LEDs, something to look into.

as for the initial project I was looking into, was to wire up the whole house in such manner directly off the solar panels/batteries, that be the case if 48v is to be desired I guess I could set up the system as 48v in the first place, I am curious thou as far as DC appliances weather 24v is not better suitable as there are other appliances available that run on 24v thou that is for another thread.