TheFishMan65
New member
kcress, Where are you getting the 9.87 volts from? So you think that by chance I all the 'high resistance' LEDs made it to the same string and I am just seeing tolerances i the LEDs?
DIY LED driver for reef lighting
- Thread starter der_wille_zur_macht
- Start date
DustinB
New member
They will not carry these SMD resistors. Fry's in general doesn't have a really good selection and their prices are pretty high. $3 for 6 x 1/8th watt resistors. Just order a couple more things and get it from mouser. If you get a few things and order UPS ground you will get it next day. That's what I always do. Even with only a couple things, compared to fry's prices, you will be about the same as mouser with UPS ground.
kcress
New member
Sorry Fish! 19.87V. I dropped the "1", and after adding them up several times to make sure. :sad2:
And, Yes! You have a rogue string there.
TheFishMan65
New member
Well it just happens that I got an order of 24 Royal blue LEDs in today (actually a lot more, but that was my share). I will find a low one and switc it out.
TheFishMan65
New member
I replaced the 3.48 and 3.43 with 3.16s and the current went upto 0.80 amps.
So IMHO if we intend to turn down the voltage supply to be 1/2 volt over the voltage string it would be wise to bin the LEDs. Worst case I would have had 6 at 3.6 volts (18.96 volts) and 6 at 3.48 (20.88 volts) almost 2 volts difference. And that was only at 0.3 amps.
So IMHO if we intend to turn down the voltage supply to be 1/2 volt over the voltage string it would be wise to bin the LEDs. Worst case I would have had 6 at 3.6 volts (18.96 volts) and 6 at 3.48 (20.88 volts) almost 2 volts difference. And that was only at 0.3 amps.
kcress
New member
Yes, you'd want to voltage bin if you wanted the very least supply voltage to successfully supply multiple drivers.
I'd swap with the other chain though - not use the new ones. Otherwise your other chain will always be way lower perhaps, than any other chains.
Seems you now have an understanding of your original issue. :thumbsup:
Just to reiterate: To make any of these binning decisions you need to drive ALL the chains at exactly the same current. Otherwise your LED to LED Vf measurements don't mean a thing. As the current changes the Vfs all change. When you originally swapped around strings across a fixed voltage source, instead of a fixed current source, all the Vfs of the string having aggregate-sum Vf issues hid itself by distributing the available supply voltage across all its LEDs. That shows very similar Vfs between a low string and a high string. Which is confusing.
I'd swap with the other chain though - not use the new ones. Otherwise your other chain will always be way lower perhaps, than any other chains.
Seems you now have an understanding of your original issue. :thumbsup:
Just to reiterate: To make any of these binning decisions you need to drive ALL the chains at exactly the same current. Otherwise your LED to LED Vf measurements don't mean a thing. As the current changes the Vfs all change. When you originally swapped around strings across a fixed voltage source, instead of a fixed current source, all the Vfs of the string having aggregate-sum Vf issues hid itself by distributing the available supply voltage across all its LEDs. That shows very similar Vfs between a low string and a high string. Which is confusing.
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der_wille_zur_macht
Team RC
Wow, I am honored. Thatnks evefyone who has contributed so far and made it a great thread.
+1
My CAT4101 drivers are assembled, still working on my prototype fixture and need to get started on the controller.
der_wille_zur_macht
Team RC
People interested in DIY drivers (or LEDs in general) should check out this magazine from Digi-key:
http://reference.digikey.com/TZ/lighting/2010/WebProject.asp?BookCode=dtz10flx&from=2#
There's an article on page 56 that talks about cap selection for switching regulators used to drive HP LEDs. While the CAT4101 design is not a switching reg, it's still an interesting read.
The article on page 54 discusses analog vs PWM dimming but is pretty short and doesn't go into a lot of detail.
http://reference.digikey.com/TZ/lighting/2010/WebProject.asp?BookCode=dtz10flx&from=2#
There's an article on page 56 that talks about cap selection for switching regulators used to drive HP LEDs. While the CAT4101 design is not a switching reg, it's still an interesting read.
The article on page 54 discusses analog vs PWM dimming but is pretty short and doesn't go into a lot of detail.
SpacedCowboy
New member
(steps out on stage, takes a bow, blushes, steps back into the shadows
)This thread got my vote too, unsurprisingly, but I thought the other two were interesting...
Simon
der_wille_zur_macht
Team RC
(steps out on stage, takes a bow, blushes, steps back into the shadows
And you deserve it! Without real EEs like you, kcress, and stugray to keep me on track early on, this thread would have probably fizzled and died.
I'm starting to think about drivers for very large tanks, i.e. making a DIY version of the Meanwell HLG series. What features would be important in a driver like that? I'm guessing we want it to drive lots of LEDs, provide for dimming, and operate efficiently. Theatrus contributed a design a bunch of pages ago for a driver like this (and I hope he gives us an update) but I think there may be a gap in terms of a design that's simpler than his (and I mean that as a compliment).
The main thing I'm struggling with in envisioning this design is the DC power source. In very large arrays, power factor correction seems to become important. Do we really want to design an exact copy of the HLG, which has an integrated PFC-corrected DC supply and can be plugged right into a wall outlet? Or, do we continue the trend here of designing a simple DC-DC regulator that requires an external power supply? The catch here seems to be that while you can occasionally grab as PFC-corrected 24v supply for a reasonable price on eBay, that's a pretty low voltage to run a large array with, and finding larger PFC-corrected supplies is harder and very very expensive. Meanwhile if we ignore the PFC feature, there seems to have been a load of 48v, 350w Meanwell supplies on eBay lately for around $40 - $50, which is actually cheaper-per-watt than the beloved bargain-bin 24v 6.5A supplies so many people use.
Decisions, decisions...
TheFishMan65
New member
I have been following the coral growth one and some of it gets beyond me, but very informative for what I follow.. I found it very interesting that two responses in November got the refugium tips on listed as thread of the month (anybody know how they get nominated). I am in the process of reading and find it very interesting.
But you got my vote too.
But you got my vote too.
SpacedCowboy
New member
Oh, I wouldn't claim to be an EE. I'm just an aging physicist
Ok, so let me play devil's advocate a little here: the only real advantage I see to this is to have a smaller (possibly even a single) driver; this leads to less circuitry, and it's possibly cheaper to do. I suppose if you're using a single PSU, it may edge the efficiency too.
On the other hand, there are several drawbacks:
- Dimming controls are less precise
- I really don't like the idea of getting involved with line-level power. It's perfectly safe when it's perfect. It's potentially lethal otherwise, and my track record is *ahem* not exactly 100% perfect first time...
- The larger single PSU means you need to think about power-factor correction, compared to just soft-starting the individual PSUs using a controller{*}
- The single PSU is a single point of failure for the entire system
- The voltages involved with longer strings make the circuit design more complex, AFAIK the simpler drivers won't go that high. Admittedly, it's not significantly more complex
... just off the top of my head. I guess I'm not sure it's worth it (to me), but I guess everyone has their own preferences... Example: I want to do things like sunrise/sunset-across-the-tank (purely for aesthetic reasons, I realise
) by varying the intensity of the strips at lights-on / lights-off.{*} It bugs me that power-factor-corrected PSUs are so expensive. As far as I know they just put an inrush-current limiter immediately after the bridge rectifier and Bob's your Auntie's live-in-lover. Total cost: about $3. A technical-sounding name makes for great marketing... [sigh] It's a pity it has to be done within the PSU circuit...
Simon
kcress
New member
Willie; I can assure you you do NOT want to go anywhere near building a DIY Meanwell. Hideously dangerous and actually very hard. They also require equipment no typical DIYers would possess. They land you in the same place DIYing a 55gal aquarium does - that is, you will pay more for it than if you just bought it, never mind the hundreds of hours you'd spend doing it.
If you wanted to step it up, I'd suggest a multi-channel board with Boost converters. Feed it 24Vdc from a PFC 24V supply, (just standardize on that input voltage), and have it drive many more LEDs - like 12 or 15 to improve on Meanwells. That way you can use a junker 24V supply if someone only wants to run a smaller rig.
Stick with single strings to avoid the balancing requirements.
Include a 0.1 ohm resistor, on board, to end the tyranny of series current meter hook up. Design it with actual test points across the resistor for easy clip-on.
If you want to add nice features, you could add a local supply for dimming, to end the wallwart nuisance. You could also add a fan driver to ditch yet another wallwart. You could consider a temperature monitoring option too. It could control the fan or throttle back the string in a fan failure situation.
SpacedCowboy; Physics.. My favorite subject. I even minored in it. The PFC stuff is not inrush limiting stuff. It can limit inrush if designed to. It is much more than that. Often another active controller is even involved - hence the higher cost.
If you wanted to step it up, I'd suggest a multi-channel board with Boost converters. Feed it 24Vdc from a PFC 24V supply, (just standardize on that input voltage), and have it drive many more LEDs - like 12 or 15 to improve on Meanwells. That way you can use a junker 24V supply if someone only wants to run a smaller rig.
Stick with single strings to avoid the balancing requirements.
Include a 0.1 ohm resistor, on board, to end the tyranny of series current meter hook up. Design it with actual test points across the resistor for easy clip-on.
If you want to add nice features, you could add a local supply for dimming, to end the wallwart nuisance. You could also add a fan driver to ditch yet another wallwart. You could consider a temperature monitoring option too. It could control the fan or throttle back the string in a fan failure situation.
SpacedCowboy; Physics.. My favorite subject. I even minored in it. The PFC stuff is not inrush limiting stuff. It can limit inrush if designed to. It is much more than that. Often another active controller is even involved - hence the higher cost.
der_wille_zur_macht
Team RC
Ouch! I've been shot down! :lol: Honestly I appreciate the honest feedback. It strikes me that there's a void in the sense of driving large arrays "conveniently," but maybe it's not worth the effort anyways. I guess I feel like with the CAT4101 design "done" and so widely used, I'm looking for the next logical step in terms of our DIY driver efforts.
kcress, I like the idea of some of the functionality you're describing. I have to admit I'm hitting another wall in terms of my understanding of switching regulator topologies. You may recall that the NCP3066 design I started this thread with was a boost topology. I had a major complaint with that design, which was that the dimming performance sucked. It basically acted like it could only dim down to a power level equal to Vin, if that makes sense. When the dimming signal was full off, the array still remained brightly lit. Thing is, I don't know which of the following caused that:
1) Was this simply a problem with my implementation or use of the chip? i.e. did I have some stupid flaw in my design?
2) Was this a problem unique to this particular IC? i.e. does it just have terrible dimming performance when used in a boost topology? I actually tried the same IC in a buck mode and it worked just fine, and would dim to true zero (the LEDs would turn off with a zero duty cycle PWM signal).
3) Is this problem going to be present in any boost design? Can a properly designed boost regulator being controlled with a PWM signal actually dim in a nice smooth linear fashion all the way down to zero?
Regarding the other features you suggested, maybe I'm taking a unique approach to this, but I'm completely used to having some form of an Arduino on any tank I'm working on, so stuff like fan control I'd just do there. I do like the idea about actually generating the voltage to drive the fan on the LED driver board though, for just the reason you said - it eliminates the nuisance of having yet another wall wart on every single tank. What do other people think about these functional ideas? Which of them would be ideal to have incorporated with the driver(s) vs. built into some separate control unit?
kcress, I like the idea of some of the functionality you're describing. I have to admit I'm hitting another wall in terms of my understanding of switching regulator topologies. You may recall that the NCP3066 design I started this thread with was a boost topology. I had a major complaint with that design, which was that the dimming performance sucked. It basically acted like it could only dim down to a power level equal to Vin, if that makes sense. When the dimming signal was full off, the array still remained brightly lit. Thing is, I don't know which of the following caused that:
1) Was this simply a problem with my implementation or use of the chip? i.e. did I have some stupid flaw in my design?
2) Was this a problem unique to this particular IC? i.e. does it just have terrible dimming performance when used in a boost topology? I actually tried the same IC in a buck mode and it worked just fine, and would dim to true zero (the LEDs would turn off with a zero duty cycle PWM signal).
3) Is this problem going to be present in any boost design? Can a properly designed boost regulator being controlled with a PWM signal actually dim in a nice smooth linear fashion all the way down to zero?
Regarding the other features you suggested, maybe I'm taking a unique approach to this, but I'm completely used to having some form of an Arduino on any tank I'm working on, so stuff like fan control I'd just do there. I do like the idea about actually generating the voltage to drive the fan on the LED driver board though, for just the reason you said - it eliminates the nuisance of having yet another wall wart on every single tank. What do other people think about these functional ideas? Which of them would be ideal to have incorporated with the driver(s) vs. built into some separate control unit?
I'm an EE! Computer design specialization, to boot.Oh, I wouldn't claim to be an EE. I'm just an aging physicist
No education in power, tho. I had to do some research to understand how to build my own power supplies for LV DC circuits. (And those are really pretty simple circuits.)
Bawwwwwwwwk bawkbawkbawkbawk!SpacedCowboy said:
Just kidding. :bounce3:
I've done some line-level design as a part of my homebrewing stuff. It was pretty straightforward stuff, tho, since it's basically just controlling SSRs. I would be willing to look at this idea, despite not having a lot of experience, except for the fact that I'm broke right now AND moving to a new house (and selling my condo) this winter. What can I say - I love DIY. The journey is as important as the destination.
kcress
New member
Willie; Probably the issue with dimming your boost driver was that there are buck, boost, and buck-boost drivers. In some cases the topology completely bars the driver from ever shutting the supply off entirely. The whole point is dedicated to elevating the output 'above'.
It may be you need a buck-boost controller because, by definition, they have to be able to shut it off entirely (the buck aspect).
You should do another driver chip survey as many more have appeared since you did that last one.
It may be you need a buck-boost controller because, by definition, they have to be able to shut it off entirely (the buck aspect).
You should do another driver chip survey as many more have appeared since you did that last one.
