General Electronics forum as good as this one?

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Shafto

Senior Member
Since getting into my picaxe project and playing with LEDs I've really started to take a liking to all this electronics stuff :)

I've decided to do a home LED project using CREE XR-E LEDs.. I acquired some warm white (3200-3500k) with a 80lumen/watt efficacy, best you can get on the market at the moment for warm white.

I'm replacing 6 50watt MR16 halogen lights with 9watt LED units (3 LEDs each) running off LM3404 based switching current regs that the national website's web bench tool makes it very easy to design..

I want to figure out the best (cost effective/efficient) way to give this LM3404 HV model a DC voltage supply, minimum 36v, but up to 75v is fine.. if it were regulated to 36-40VCD I could use a lower Vf diode and get 97% total efficiency from the LED driver.. if I go up to 75v I have to use a higher voltage capable diode and I go down to 95%.. not a big hit for a better solution that wasn't so regulated... I only need a 1amp supply. (700mA draw)

I know this doesn't really have anything to do with a picaxe.. hence the topic title.. though I could use one to control/PMW dim and such throughout the day.. I'm looking for a general electronics forum as helpful as this one has been... I thought I'd just blab on about my project for anyone interested..

Where should I sign up to start a discussion about how best to go about this?
 
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moxhamj

New Member
Well if you say you might be controlling the leds with a picaxe then I'm sure we can all help out with some answers :)

Re a power supply 36-75V at 1A, one cheap answer is to get a few plugpacks. Eg if you got 4 plugpacks rated at 12V 1A DC and put them in series. Or you could get a transformer and make your own power supply with a rectifier bridge and a smoothing capacitor. Or there are commercial power supplies available from electronic stores. DC voltages of this wattage are commonly used for power supplies for amplifiers so there are lots of modules out there.

LED lighting is almost certainly the future. Similar brightness and power to compact flouros but never need replacing.
 
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BeanieBots

Moderator
Everything you ever wanted to know about the LM3404 including an on-line calculator for the descrete components.
http://www.national.com/pf/LM/LM3404.html

As it is a SMS regulator itself, there is no need to have a particularly well controlled source voltage. A simple transformer, bridge rectifier and smoothing cap is all that is required.
I would suggest a 40v + 40v center tap torroid for audio ampliers. Then you would only need two power diodes. You could probably find something pre-made cheaper than building it yourself.

Don't forget, there's no point building a complex 50% efficient pre-regulator just so that you can get the constant current regulator efficiency up from 95% to 97%. Sort of defeats the objective!
 
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Shafto

Senior Member
To make sure I'm understanding.. is this a toroid with 2 40v alternating outputs or something? so I don't need a full bridge rectifier, just half?

I searched around on digikey but didn't find a suitable premade power supply.

I've actually already used the web bench tool.. it just gives you all the discrete components and the schematic.. pretty easy.. I just have to get good at soldering these little SMT parts.
 
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moxhamj

New Member
If a transformer happens to have two outputs (4 wires) you can either put them in series for double the volts, or parallel for double the amps. Any transformer will work though - toroids are popular for amplifiers as they have less noise but noise wouldn't be an issue here. You can use one diode for a really horrible supply, two diodes for a fairly noisy supply but 4 diodes in a bridge is the smoothest. Smoothing the AC is kinder to the capacitor. Bridges are only worth a few dollars. You get more volts too when you rectify AC - eg about 1.4 times so a 10V AC output will give 14V DC.

If you are running 1A at 40V and you can get a 40V transformer rated for 2A it will run a lot cooler. You will also need a capacitor - eg 80V 4000uF ballpark. Then a box to put it all in. And mounting hardware and proper connections for the mains. Have a bit more of a search for switch mode power supplies as they will work out smaller and all this is done for you.
 
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BeanieBots

Moderator
Indeed, there are many switchmode power supplies available that would give what you want. Something like a laptop supply would be a good place to start. I'm sure there would be something on eBay.

As for the torroid, I was thinking center tap rather than two windings.
Center = 0v. More efficient than single/double winding + full rectifier. Due to higher demand, high power torroids can be cheaper then equivalent laminated soft iron and also happen to give less noise but that would not be an issue here.
Quite frankly, you are spoilt for choice on this one!
 
lbenson

lbenson

Senior Member
Why shouldn't it be a picaxe project? Below are pics from mine 9 months ago.

I made my fixtures from lampholders I got on the web and metal dome-shaped ceiling outlet box covers from Home Depot. The 12-volt bayonet-style LED lamps I used I got here: <http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&amp;ProdID=3091 (Oops, changed link--they may be on that site somewhere.) The people at that site do not know the lumin output of the lamps.

I had 5 fixtures with 1, 2, 3, 4, and 5 led lamps each for testing, mounted on a cherry wood board. I added another 08M which read either IR from a TV-type remote, or serial characters from the PC to turn off and on or dim the lights with PWM.

I didn't use the Cree XR-E LEDs. The 9-LED units I used gave adequate light to read or work from, but they were not of such a brightness or warmth that they would have made a good replacement for regular incandescent or CFL bulbs.

I powered the LEDs with a 12-volt wallwart. With all the lights lit it draws 8 watts according to my KillAWatt meter.

Where did you get your Cree LEDs, and the info on how to power them?
 

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Shafto

Senior Member
I got the CREE LEDs from www.cutter.com.au.. well.. I haven't received them yet but they should be here soon... I already have a 5000k Q5 bin CREE that I've been playing around with.. I received it as a sample.. very bright. They have an R2 flux bin now in cool white that gets minimum 100lumen/watt efficacy and with a 1amp drive current will give 275lumen! but cool white light isn't very appealing in a home.

I can't find any male side MR16 bulb bases for sale.. so I think I'll have to just make some on the mini lathe I ordered... which won't be here for quite a while unfortunately.. and alas I must return to work in the far north for a couple months so I can afford to come back home and play with all this stuff again.. so I won't have it until I'm back in the spring.

Check out this free online LED seminar by national:

http://www.national.com/onlineseminar/2007/led/national_LEDseminar.pdf

That's where I learned all about the different switching current drive options they have... and like I say.. the web bench tool on their website basically designs the whole thing for you... and you can even simulate the operation.

I'll search around for a while to see what I can come up with for some premade option.. because I can't find a suitable transformer to even start from to make my own.. not for less than $30+ which doesn't seem economical once the other parts are added. Whatever I decide on I'd like it to be repeatable though.. a good deal on ebay would be sweet this one time.. but I'm gong to slowly convert everything to LED in the home and I'd like to be able to keep using the same power supply for the LED driver.

Another thing is the life of the PSU, can it last 100,000hours like the LEDs can? I often see life ratings on electrolytics of 2000hours or so.. nowhere near enough.. but then I don't quite understand that.. because if they only lasted 2000hours, wouldn't electronics be burning out all the time because of the caps? I swear my computer has a lot more than 2000hours on it... more like 10,000.

Maybe I'm just looking in the wrong places.. but I seem to be having trouble finding supplies with voltage this high.
 
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moxhamj

New Member
Capacitors should last that long if they are not run right at their ratings - eg a 16V capacitor shouldn't be run right at 16V. Also a bigger capacitor is better than a smaller one. I have a computer that has been on continuously for 10 years - that is 87,000 hours. The main things that die regularly are the fans but not the capacitors/transformers etc.

There might be a solution using old PC power supplies as they are give-away items though you can't put them in series as the earths are connected. How absolutely fixed in stone is the need for 40V to 70V?

You probably wouldn't get a supply for $30 but you would for $60-$70. Another thought - if you are going to wire the whole house, then in general terms one big supply is going to be cheaper and generate less heat than lots of little supplies. So it could be worthwhile building a big 50V 10A DC supply and running new DC wires round the house. Or indeed some other voltage depending on these leds. 12VDC is a much more common voltage though and lots of transformers/power supplies at this voltage. The LM3404 specs say it will run from 6V to 75V.
 
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BeanieBots

Moderator
Ever wondered how those Beijing electrical products manage to fail within days after the end of the warranty?
Component failure can be quite accurately predicted these days.
If you want an electrolytic capacitor to last for more than 10 years, opperate it at no more than half its working voltage and no more than half its ripple current rating. If the ripple current isn't specified, then it's not suitable for power supply use. Keeping them cool helps a lot.
Longevity is simply a question of over engineering which also means putting your hand in your pocket.

Don't forget, you can keep ripple current down by using a choke:p
 
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Shafto

Senior Member
I'm doing 2 light fixtures with 3 bulbs each.. each bulb will now have 3 LEDs for 9 in total.. and I'm running them all in series because I get the best efficiency with higher voltage and lower current... I already received the LM3404HV samples (they are popular so I had to pay $10 shipping for 5 of them) and they are a 1 amp unit so I can't really go to a series/parallel array now to drop the voltage.. and I'd really prefer not to.

A computer PSU isn't possible either.. especially in series.. Space is somewhat of a concern.. I have to fit the PSUs under each light fixture.. These ones seem to have some more room under them.. but for future projects with these MR16s I'd like to have the PSU fit inside a common junction box. The driver itself is tiny..

A junction box something like this... I can't remember the specs of the ones up there.. I'll check it out in a bit... I just googled this pic so you'd all have an idea.





Another thing I was thinking the picaxe might be able to do.. and would be great.. is the PWM dimming via a regular AC dimmer...

As I understand it.. these AC dimmers chop up the ac wave.. kind of like PWM.. only letting the peaks through, and as you turn it down the time the peaks are allowed through is decreased.. if I could have a picaxe read the signal from a standard wall dimmer.. and then have it give out a corresponding PWM signal to the LM3404 I'd be a pretty happy camper :)

but I might start running out a space for such an operation... as I would then have to power the picaxe aswell inside the junction box.. hmm.. now that I think about it though.. how would I get the dimmed AC signal up the junction box without dimming the AC power to the transformer that powers the LED driver.. Maybe some wireless solution is a better way to go...

I'll put a lot more thought into how I'm going to get a PWM signal to be able to dim the LEDs from the wall switch without running any wires.. I'm sure there's some way a picaxe can get that done... that's not too essential right now though.. I can always add PWM later...


Maybe the best option is just 2 of these wall warts

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=T944-P5P-ND

with 24v input @ 1amp x2 I would have 48w of available power.. and the LEDs themselves only draw 27w with a driver efficiency of 95%.. I don't imagine I'd be pulling too hard on the wall warts.

if I can find a more economical way to get the job done I'd definitely like to.. I'll keep checking around for options.
 
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moxhamj

New Member
So if they are white leds with about 3V each then 9 will be 27V so yes, maybe a 40V supply. Before you do anything just test the colour of those leds compared with a normal light bulb - warm white (yellow) looks great but cool white (a blue colour, also called natural for some reason) is a really horrible colour in a house and makes it look like a mortuary.

If the colour is fine and the brightness seems the same as a light bulb then this could well be a whole house project. (to compare brightness, set up two bulbs a metre or so above the ground and a few metres apart and look at the two shadows cast by something between the lights - the shadows should be equal on both sides.) You would want to make sure the leds really are as bright as normal bulbs.

A single big 40V DC supply to do the whole house could work. It would be on all the time but big transformers that are not using any power don't get very warm. Then the buck modules could be in each light fitting.

Just a thought - a single 100W lightbulb running for its lifetime of 1000 hours uses about $20 worth of electricity. LEDs use far less power. I suspect that even replacing a few lights will pay for the parts within a year or so.

I agree it is hard to find products. I just got lost for 15 minutes in Mouser's catalogue. I am certain they sell the parts but I cannot find them - too many products. Here in Australia we have electronics stores with less products but they sell lots of the ones people want. Eg Jaycar - a quick check finds a toroid 18V-0-18V which is 36V AC which will be about 45VDC when rectified and smoothed. 300VA which is 300W which will run 10 of your strings of 9 leds. (9 leds 27V ?1A = 27W). $75.
 
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Shafto

Senior Member
I've done my calculations on this one.. (it's easy math) I've been planning it a while.. electricity here is quite cheap.. all hydro electric, $0.0615/kWh.

So if it's on for 12h/day for a year:

12 x 365 x 0.3kW x 0.0615 = $80.81/year (6x50watt halogen = 300w, 0.3kW)

That's the lighting for the whole kitchen.. the lights "say" 6000hour life.. but it's more like 4000.. they need to be replaced once a year on average.. which adds another $30/year.

with LEDs:

12 x 365 x 0.054kW x 0.0615 = $14.54/year for 100,000 hours, or 22 years... total cost of ownership for 20 years = $290 + ~$350 install = $640

with halogen 20x ($80 + $30) = $2600

The initial price for LEDs is still steep.. but this is small scale too.. if I bump up production price would obviously go down.. and that's a total estimate as of yet.


They call that very white light "natural" because it's most like the light we get from the sun.. but it doesn't look right in the home I agree.. Halogen is around 3000k, "natural white" is around 5500k, The LEDs I got are 3200-3500k warm white.. they will look much like halogen.. slightly whiter.

As for brightness.. with halogen we can assume around 20w/lumen, for 1000lumen per light.

that doesn't account all the optical losses dealing with a cheap disposable reflector in the MR16 light.. with the light shooting 360degrees from the filament much of it is wasted. With LED you get much better optical efficiency for directional lighting.

These LEDs I have are P4 flux, 71lm/watt efficacy.. I screwed up at first thinking it was 80lm/watt.. it's 80 lumen @ 350mA, (I thought that was 1 watt drive, slight over I suppose)

so at 9w per light x 71 I get 639 lumen each.. since my heatsinks keep these nice and cool I emailed CREE to see if I could up the drive to around 900mA or so and get closer to 4 watt per LED... The cool white versions handle 1000mA no problem.. so I don't see why the same die can't take a little more current if it's kept nice and cool... either way I think the lighting will be sufficient taking into account the better optical efficiency.

oh.. these LEDs run around 3.7Vf

..using 1 big power supply would be nice.. but then I'd have to rewire the whole house.. I'd like to have little Power supplies that can fit into junction boxes for each light fixture.. I know this will cost more, but the easy of use is worth that...

Edit.. noticing now I'm not running quite 3w per LED.. was going on the general 700mA = 3w rule for LEDs.. but the CREE vF is lower than most... I should have the LEDs this week.. and I"ll do some comparisons.

..I just thought of another possible solution? if I didn't need a bulky transformer I could wire it all into the junction box with the switches.. what if I just used a full bridge rectifier with a smoothing cap, and then a voltage divider to feed each separate driver? I dunno if that's an option though..
 
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moxhamj

New Member
I don't think you can get individual power supplies at that voltage/wattage/size at a cost competitive price. 5V/9V/12V/24V are common voltages but anything more than that becomes unusual = expensive.

But you may well be able to make something yourself out of surplus parts. I once picked up a whole pile of 9V plugpacks for $1 each (qty 100) and I'm still using them for all sorts of things eg a 27V supply for a dremel tool using 3 in series.

I also once needed a 100V supply for a US printer and managed to get a whole lot of 24V centre tapped transformers at surplus prices. Put them in series to get 100V. No need for toroids - just ordinary transformers.

If you can get 24V transformers at a good price then put two in series to get 48V, rectify with a bridge, a 4000uF cap and put it in a junction box you could get the price down. I've bought these transformers for $5 in the past at surplus sales though you really need to go looking for surplus electronics. A quick search on ebay finds one for $4 US so they are out there. You could look for higher voltage transformers though often two more standard lower voltage ones work out cheaper than a less standard higher voltage one.

A bit more of a search - am finding lots at $6-$7 and a few at less than this. 24V at 1-2A is a very common size.
 
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leftyretro

New Member
Shafto said:
I'm doing 2 light fixtures with 3 bulbs each.. each bulb will now have 3 LEDs for 9 in total.. and I'm running them all in series because I get the best efficiency with higher voltage and lower current... I already received the LM3404HV samples (they are popular so I had to pay $10 shipping for 5 of them) and they are a 1 amp unit so I can't really go to a series/parallel array now to drop the voltage.. and I'd really prefer not to.

A computer PSU isn't possible either.. especially in series.. Space is somewhat of a concern.. I have to fit the PSUs under each light fixture.. These ones seem to have some more room under them.. but for future projects with these MR16s I'd like to have the PSU fit inside a common junction box. The driver itself is tiny..

A junction box something like this... I can't remember the specs of the ones up there.. I'll check it out in a bit... I just googled this pic so you'd all have an idea.





Another thing I was thinking the picaxe might be able to do.. and would be great.. is the PWM dimming via a regular AC dimmer...

As I understand it.. these AC dimmers chop up the ac wave.. kind of like PWM.. only letting the peaks through, and as you turn it down the time the peaks are allowed through is decreased.. if I could have a picaxe read the signal from a standard wall dimmer.. and then have it give out a corresponding PWM signal to the LM3404 I'd be a pretty happy camper :)

but I might start running out a space for such an operation... as I would then have to power the picaxe aswell inside the junction box.. hmm.. now that I think about it though.. how would I get the dimmed AC signal up the junction box without dimming the AC power to the transformer that powers the LED driver.. Maybe some wireless solution is a better way to go...

I'll put a lot more thought into how I'm going to get a PWM signal to be able to dim the LEDs from the wall switch without running any wires.. I'm sure there's some way a picaxe can get that done... that's not too essential right now though.. I can always add PWM later...


Maybe the best option is just 2 of these wall warts

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=T944-P5P-ND

with 24v input @ 1amp x2 I would have 48w of available power.. and the LEDs themselves only draw 27w with a driver efficiency of 95%.. I don't imagine I'd be pulling too hard on the wall warts.

if I can find a more economical way to get the job done I'd definitely like to.. I'll keep checking around for options.
Click to expand...
"Maybe some wireless solution is a better way to go..."

The Picaxe have such great built in IR commands using standard Sony IR remote codes, I would use that for dimming via PWM output and have the Picaxe save the last setting into EEPROM memory so that when next powered up it would go to the prior last setting.

Lefty
 
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andrewpro

New Member
Check Here

48 volt, 1.35 amp switching PS, 90-240 volt input. A little larger than a junction box though, it's 3x5 inches and 2 inches high. But, ti's only 27 dollars.

--Andy P
 
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Shafto

Senior Member
Awesome find andypro! I think that's exactly what I need.. possibly a little large, but I think I should be able to make it work.

300,000 hour life.. certified everywhere.. looks like a great deal.

80% efficiency with the switching supply.. I imagine that is better than I would get using a transformer with a smoothing cap and rectifier?

Is my rectify and then voltage divide idea a no go? I would end up with a little over 60v a side or so?

Edit: 80% efficiency is spec for all of their switching line-up, but the engineering report shows that the 48v unit (as you'd expect) has the highest efficiency, 83.95%
 
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moxhamj

New Member
Ballpark figure 83% is probably pretty good. Sometimes you see 90% but generally every time you "transform" a voltage you lose 10-15%. I suppose here you are transforming down to 48V in one step and transforming again via a switch mode power supply down to a constant current 27V so there are losses twice there. Maybe there is a way to do it in one step and maybe, maybe a single step and a simple dropping resistor would work out cheaper or more efficient. But one can get caught up too much in the details - I'd be just buying that power supply that Andypro suggests as it looks really good value and then get it working and later maybe do some more maths and see if another solution works out better value.
 
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Shafto

Senior Member
I can't use a dropping resistor though.. high power LEDs like this need a constant current source.. and I would lose much more efficiency from using dropping resistors than the switching LED driver @ 95%.

Thanks for the forum link jmumby.
 
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Shafto

Senior Member
I'm stoked!!!

I got my LEDs from cutter today and quickly soldered up a little trio to run from a linear current reg using an LM317 for trial purposes.. I needed about 13v so I grabbed the 14.4v drill battery and rigged it all up for comparison... I got pics!

I'm ecstatic about the way it looks.. I think the brightness is mimicked perfectly.. and the colour, slightly more white as I expected.. but still nice and warm.. you can see the much higher CRI of the slightly whiter LEDs really bringing out the colour in things compared to the halogen... I think it's going to look great when I have it all done.

I unplugged 2 of the 3 halogens.. to compare 1 to 1.. pics are a little fuzzy because I had to use a slow enough shutter speed to get a life like comparison.. and I didn't want to fish out the tripod..

The LEDs in the pic are running at 700mA, I was thinking about going for more.. but I really don't think I need to now.. it looks slightly brighter than the halogen even... at around 60% of the lumen output.. just goes to show how optically inefficient a filament bulb is shooting light off 360 degrees...

So at 700mA, I'm not actually running at 3w, only 2.45w, or 7.35w per bulb, and 44.1w for the whole shebang... less than 1 original halogen bulb.

I'm no pro at math.. but is this how it works to figure the efficiency? sounds right to me..

if PSU is 83.95% efficient and the driver is 95%...

44.1w x 16.05% x 5% = 53.7w

ok.. here's the pics:



HALOGEN:





LED:


 
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moxhamj

New Member
That looks fantastic. Once it is done, no more changing light bulbs!

Re the maths - 83% on one and 95% on the other = 0.83*0.95=0.78 efficiency overall.
Take the inverse 1/0.78=1.26. Multiply this by the watts consumed 44.1 at the leds=44.1*1.26=55.9W input. How does that compare with the bulb it is replacing?
 
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Shafto

Senior Member
55.9w will be total power consumption in the kitchen for lighting.. compared to right now... 300w. BIG difference!

..so what's that? 55.9/300 = 18% of the original power consumption

Then take the inverse of 18% to get a % of how much more efficient it is? 537% ? that seems high.. hmm I"m doing this wrong again I"m sure.. hah.

maybe... 300-55.9 = 244.1w more consumption, 244.1/55.9 = 437% ?
 
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andrewpro

New Member
wow! That really makes the blues pop. I'm impressed.

And unless I'm wrong (which isn't unheard of!) the halogen really is using 537% of the energy of the LED's. (536.67262969588550983899821109123% to be exact). That's a nice improvement on both power consumption and vivid colors!. I like it.

Edit to Clarify: It's using 537% of the total energy that the LED's are using, but 437% MORE energy than the LED's. It makes more sense when said that way.

--andy P
 
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Shafto

Senior Member
My tendency to overdo things is kicking in again.. Now I'm pondering how I could have a picaxe not only read a signal from an AC dimmer switch (or possibly easier to fit a standard potentiometer to a mount in the junction box.. one with a nice knob) and send a corresponding wireless signal to the PWM input on the LM3404.. but also possibly have the picaxe turn on the lights when people walk into the room.. and turn them out when the room is emty.. that I'll put some more effort in to figuring out later though..
 
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andrewpro

New Member
Shafto said:
but also possibly have the picaxe turn on the lights when people walk into the room.. and turn them out when the room is emty..
Click to expand...

I really...really...and did I mention REALLY hate those things. I deal with them a lot in my job, and they are absolutely terrible for the most part.

They work very well for a room with a lot of people in them, very poorly with few people. I cant begin to count the number of times I've been working in a room that the lights shut off on my at the absolute worst time. If you can flop your arms around enough, or jump up and down, the lights will generally turn back on, but until they do...dark...ick.


Sooo....if you can figure out a reliable way to get the lights to come on and stay on when they're supposed to, and turn off when they're supposed to and ONLY when they're supposed to I think you'll be well set for life :p


I'm not saying anything to discourage...I'm just saying that you need to build a better mousetrap than what's currently available!

--Andy P
 
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moxhamj

New Member
PIR sensors won't work and systems that count people going through a door won't work. But I wonder if there is a picaxe solution? How about a little key fob transmitter that sends a brief chirp every few minutes. Only issue them to people who are meant to be in the room. Burglars will just have to stay in the dark, as will party guests etc...

Reminds me of all those crime shows on TV where the crime scene investigators always wander round with flashlights. A patient of mine is a crime scene investigator and they tell me that in the real world CSI they just turn on the light switch.

I would have thought this is a project to keep simple. The aim is to save power. Leave the switches as they are?
 
lbenson

lbenson

Senior Member
If the aim is to save power, I'm not sure LEDs are quite there yet--relative to halogen, yes, but not necessarily to CFLs, which could make an easy screw-in replacement (tho they have their drawbacks, which have been visited in the past on this forum). Shafto does show that LEDs may be getting close.

Most people aren't going to wire a transformer into their electrical boxes, so I guess most of us will have to wait until GE manages to put one, along with a constant-current regulator, in a screw-in base. Cree says that the rate of improvement in LEDs approaches that suggested by Moore's law--if that continues for about 3-5 years, then we might be there. 15 years ago I paid $20US for early CFLs to put in always-on, hard to reach cannister fixtures. Now similar bulbs approach $1 (but don't seem to last as long as claimed). I guess I'd pay $20 now for an LED bulb I wouldn't have to change for 10 years, and if it saved $$ along the way, so much the better.

Anyway, I've ordered my Cree 7090 XR-E P4s from http://www.dealextreme.com. Fun to play with, and at the very least, good for emergency lighting.

Congratulations, Shafto, on a quick proof of concept. I look forward to seeing where you go with this.
 
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Shafto

Senior Member
For power savings I think LEDs have the lead.. it's the cost that's still the draw back..

I can't find any other CFL MR16 style bulbs other than these:

http://www.landlite.com/CELONA Web/Catalogue2003/Self-Ballasted_CFLs/CF_PAR_Lamps_Page1.3.pdf

only 8000hour life, barely better than halogen, and their 50w halogen replacement is a 15w unit.. almost twice as much power as my LEDs of similar light output.

If I could figure out the cost of these.. it isn't listed, then I could found out how they compare economically..

For 360 degree spread of light CFL is still overall a better solution.. but for any directional lighting, LED is the winner.
 
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Shafto

Senior Member
350mA is half as much as I need unfortunately.. I don't think I could parallel the outputs?

They do have another LED driver for $5 more than could do 700mA, but only up to 6 in series, I'd need 2 of those as well..

It would take up more space overall, and judging by the fat resistor on that board, and the lack of an inductor, this isn't a switching driver, it's linear.. no efficiency listed... I bet it's not very good...

Because I need to buy multiples of 10 of many parts for these divers I'm making, since it's all SMT.. it's quite expensive.. but per unit I think it'll be about $20 or so.. added to the $27 high quality PSU and it's about 50% more than the 2x linear drivers.. but with great quality and efficiency.. (although a lot more work)
 
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moxhamj

New Member
What a great find! That module looks very efficient - the highest power component looks like a 1/2W resistor so the whole thing might only be heating up by 1W. I think we might start seeing these modules included with the leds soon.

I think there is an inductor - the yellow component in the middle. I think it would be switch mode, probably very high frequency 100Khz to 1Mhz. It has an 8 pin chip - might be the same one used in PC power supplies. Generally these circuits simply rectify 240V to about 350VDC (or 120VAC to a lower voltage) then run it through a simple buck converter. The output is either adjusted via volts, or amps by converting to volts through a sense resistor. A clever circuit but I wouldn't suggest anyone build one from scratch unless they really know what they are doing - very high voltages.
 
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lbenson

lbenson

Senior Member
>no efficiency listed... I bet it's not very good...

Right. With LEDs at this point, after long life, efficiency is the name of the game. Are you looking to make your own board or use what National Semiconductor offers, along with all the parts, after you design your board with WEBENCH?
 
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BCJKiwi

Senior Member
Had issues with some LEDS from BestHongKong.

I ordered a number of LEDS of four different colours including orange and red and really could not tell the difference between them despite the pictures on their website showing a big difference.

They were most unhelpful and did not reply unless prompted repeatedly then just went around and around in circles. This went on for months in total with them demanding photographs (which I had already sent to begin with so sent them again), then they said they weren't taken the right way so I took more the way they wanted (didn't make any difference). This just went on and on without any resolution until I gave up.

It was very clear that their strategy was to ignore, then obfuscate, then delay, then go round again and again until you gave up. It was a massive waste of time and money which they could have easily resolved by sending a few LEDs of the right colour!

So I certainly won't be buying anything from them again!
 
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S

Shafto

Senior Member
I've seen their drivers fail before.. I know the site well. I have some white LEDs from ebay that I'm pretty sure are the same as their 100mA 5chip LEDs. I am pleased with those but I dunno about the drivers.. that looks like a 1.5ohm 2 watt resistor to me.. 1.25Vrsns to convert voltage to current... just like I use on the LM317 to make it a linear current driver, but I use a 1.8ohm for 694mA, a 1.5ohm is 833mA, that must be the "3 or 5watt" unit pictured.. and they just pic a value in the middle of both.. hah.. pretty cheap... overdrive your 3watt LEDs or underdrive your 5watters. The LM LED driver chips are specifically designed, they use 0.125Vrsns.. much less waste. It looks like a switching PSU, and the chip looks like a PWM chip you see in a computer PSU.. but the LED current driver itself doesn't look like a switcher to me..

I plan to use exactly what web bench tells me too.. etch the boards myself and have fun soldering tiny little components.. then feed that with the PSU suggested by andy.. 48v switcher.

I've looked around.. there are many more reputable companies than BHK that sell LED drivers.. like xitanium made by philips:

http://www.luxeonstar.com/xitanium-120v-drivers.pdf

But none of them suit my specific needs.. and it's cheaper to build my own using what I believe to be even higher quality parts... check out the engineering tests on that PSU... it's very high quality, exactly what I was looking for.

The efficiency on those xitanium drivers, which are the highest end I can find... is %80... mine will be 83.95 x .95 = 79.75%.. I do like the fact they they are smaller though... if there was one that I could do 3x3 @ 700mA or 1x9 @ 700mA I'd be in... I'll keep checking around though.

I just found another datasheet for the xitanium drivers.. "long life" 50,000hours... that's not long enough for LEDs.. I prefer the 300,000 hours of the other PSU.. I dunno about the driver I make.. I guess we'll have to see, but I'll be using the highest quality parts for it.. for longevity and efficiency... it's possible to get the efficiency of the driver to 97% using much larger inductor thereby giving me 81.4315% efficiency = 54.2w total consumption compared to 55.3w with a 95% driver.. I'll weigh the cost and space when I'm ordering the parts.

At 9w with efficiency factored in per "bulb" these brighter than 50w halogen replacements, I'm happy to say.. blow away CFL competition @ 15w..
 
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