pandimus
Active member
This seems like the best option atm. thank you sir.
DIY LED driver for reef lighting
- Thread starter der_wille_zur_macht
- Start date
This seems like the best option atm. thank you sir.
I could see eagle files for a 5cmx5cm board that can do x number of parallel strings and as the through hole spots for the resistors and fuses plus the screw connectors. This secondary board would go after the LED driver to facilitate safe operation of parallel strings. That way someone just sends the files to seeedstudio to get their boards and populates with whatever values they need for the strings they're doing.
Think if you did it for 4 parallel strings they could go less or daisy chain for more.
ingoh
New member
Sorry for quoting a message from some more days ago, but I'm trying to verify your design, component worksheet and BOM. Shouldn't Coff be C5 instead of C4? In the reference design Coff is between Pin 4+5 and thats C5 in your schematic.
regards
Ingo
regards
Ingo
der_wille_zur_macht
Team RC
Ingo, there is no C5 in my design - are you sure you're looking at the right version?
ingoh
New member
Last evening I was... But after reading back some pages again I know it was my fault:
- I took the terrahz layout/board/BOM from here: https://github.com/TeraHz/I2C-LED-Driver
- Used the dwmz component worksheet: http://code.google.com/p/hpled/source/browse/trunk/lm3409/lm3409_component_worksheet.xls
- then stumbled over this article: http://www.reefcentral.com/forums/showthread.php?p=20004250#post20004250 to assign the named R/C's in the worksheet to the numbered ones in the BOM. As you mentioned above those are different designs :headwally:
Kindly excuse any inconvenience,
Ingo
der_wille_zur_macht
Team RC
The one you linked on the last page looks totally fine. How big is your build though? 12v is kinda limiting, you'll only be able to "fit" 3 or 4 LEDs per string.
Probably 3 best case 2 worst case depending on the forward voltage and driver efficiency.
Here's best case and worse case for standard 1w LED's. Most drivers it's safe to assume 80% efficiency.
3.2v * 3 LED's = 9.6v + 20% efficiency overhead = 11.52v
3.7v * 2 LED's = 7.4v + 20% efficiency overhead = 8.88v
der_wille_zur_macht
Team RC
...but these are DIY drivers, so we don't have to assume. I'm running all of my DIY drivers with way less than 20% difference between Vin and Vout (I'm assuming that's what you mean by efficiency?)
For example, on the LM3409 chip, I've run LEDs with Vin = 28.2v and Vout = 28v. That's less than 1% difference.
Personally, I think putting resistors and fuses for parallel strings "on-board" isn't needed. It's easy enough to buy some terminal blocks and use axial resistors and fuses. They are nice and easy to swap out if you ever have to.
You're correct of course. :fun4: I was just going with a rule of thumb for people that are not as technical so they don't go with too little voltage and wonder why their LED's are flickering, not working, too dim, etc...
der_wille_zur_macht
Team RC
I appreciate your attempt to generalize. Thing is, I really think you HAVE to take the technical route with DIY'd drivers (or, copy exactly from someone who has) otherwise you risk problems. If you used a standard of 20% difference in Vin and Vout at typical operating power levels on the CAT4101 for example, you'd end up with non-functional drivers, since you'd be putting them into thermal overload from too big of a drop.
I am doing 2 strings of leds, one consists of 5 XRE and the other is 4 XPG. Will that suffice if I lower the current on the XREs?
Thanks a bunch for your past and current help, I really appreciate it.
Oh another thing, what's your opinion on Epistar LEDs?
I see 10 watt modules and such for sale, I'm tempted to give one a shot to supplement with sunlight.
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der_wille_zur_macht
Team RC
What driver are you using?
The supply you posted is technically adjustable though IME you can only expect 10 - 20% range on the adjustment. Even at the "big" end with 20% you're only getting up to 14.2v which doesn't leave enough for the strings you're describing at anything anywhere near a usable current, even if you use a driver that can tolerate very small drops.
To put it shortly, I think you'd be better off with a different supply given your planned LED strings. Look for laptop supplies, they are sometimes cheap and usually between 15 - 20v. Or just cave in and get one of the common 24v "industrial" style supplies like everyone else uses. With the LM3409 you'd still get very good efficiency even with the big Vin-Vout delta.
If you're thinking of the CAT4101 you're gonna need different supplies for those two strings, as the Vouts won't be close enough to allow a tolerably low drop running them both on the same Vin.
Crap. IMHO you'd be better off with a smaller number of "known good" LEDs. XP-Es can be had around $3 each these days.
need some clarification please
need some clarification please
Alright looking at the cost of the lm3409 driver vs the cat4101-
so the lm3409 is one driver and costs 12.45 according to the BOM from mouser plus the cost of the board and is capable of running about 15 LEDs
and the cat4101 is 3 drivers and costs 7.23 (according to my hunting for materials) plus the cost of the boards and is capable of running around 7 LEDs per driver for a total of 21 LEDs
Is this right or am I way off?
need some clarification please
Alright looking at the cost of the lm3409 driver vs the cat4101-
so the lm3409 is one driver and costs 12.45 according to the BOM from mouser plus the cost of the board and is capable of running about 15 LEDs
and the cat4101 is 3 drivers and costs 7.23 (according to my hunting for materials) plus the cost of the boards and is capable of running around 7 LEDs per driver for a total of 21 LEDs
Is this right or am I way off?
der_wille_zur_macht
Team RC
I'd say you're probably close on the CAT4101 pricing. The LM3409 pricing sounds good too, but I wouldn't limit it to 15 LEDs if you're trying to figure out a "driver cost per LED" metric. In theory, you could run 40 - 50 LEDs on one, or even more, depending on current level.
I figured 3 volts per led just to estimate. With the LEDs I am using and the current I want to run them at I can get 8 per driver for the cat (total of 24) and 16 for the 3409
Thanks for your help, I limp around when it comes to this stuff..
I am using Cat4101s since I have had the chips laying around for a long time. To fix that voltage interdependency I am thinking I'll make the strings of LEDs even, I'll add a XPG for a fuge or something.
To know how much voltage I need, I just need determine my voltage required per string then add .5 volts for the driver?
The voltage requirements between the XREs and XPGs aren't significant I'm assuming...
I'll avoid the epistar LEDs, with all the chattering on the other forums I was curious on if it's worth it.
I am using Cat4101s since I have had the chips laying around for a long time. To fix that voltage interdependency I am thinking I'll make the strings of LEDs even, I'll add a XPG for a fuge or something.
To know how much voltage I need, I just need determine my voltage required per string then add .5 volts for the driver?
The voltage requirements between the XREs and XPGs aren't significant I'm assuming...
I'll avoid the epistar LEDs, with all the chattering on the other forums I was curious on if it's worth it.
der_wille_zur_macht
Team RC
Check the datasheets to be sure. I can't keep this stuff straight off the top of my head any more but there are definitely significant variations. As long as the strings are within about a volt of each other you will probably be OK. Allow a provision for cooling the CAT4101 chips an you'll be golden.
To be fair, I'm definitely way more "harsh" on less-than-the-best LEDs. Those LEDs will definitely work and could be a great source of light on a fish tank. To me though, it doesn't make sense to go through all the trouble of an LED build and choose LEDs that aren't the best possible, just to save a buck or two (upfront).
would there be any problem in adding a resistor to the cat4101 to limit it to 1 amp and then use a 10k pot to dial in the color plus use pwm to fade the LEDs on and off? or is it best to just find what my personal preference is for driving current on the LEDs would be and then use that resistor?
