DIY LED driver for reef lighting

[der_wille_zur_macht]

Also, not that I want to shill, but the Thread of the Month poll that Dejavu mentioned back a page closes tonight. So go tell all your friends to vote for their favorite thread!

 

[DustinB]

Some of the maxim-ic ones I saw on mouser appeared to be rated at up to 25mA. They were only single output and, unless I'm mistaken, showed they wouldn't vary a great deal from their rated resistance. ie: 60-100%, not 0-100%

If someone can locate a good option, most of these seemed to have a 128 step range, give or take.

 

[TheFishMan65]

I looked at digital pots and got lost too. It looked to me that they acted more like a D/A and set the voltage between the supply and ground. Which is why I went with the analog pot and PWM dimming.

 

[der_wille_zur_macht]

Dustin, can you post product numbers? I should add that I'm trying to stick with reasonable packages. SMT is fine but I want pitch at least .65mm.

Fishman, it looks like there are a few different topologies for digital pots. Looks like most have a resistor network inside, and switches that control which of the resistors are connected to a "wiper" pot. Some only expose one end of the resistor network and hence would act a lot like a DA I suppose. Others expose both ends of the resistor network and hence truly emulate a "real" passive pot with three terminals - there is no voltage or signal present on the "wiper" unless you connect something to one or both ends of the resistor network. This is my first attempt at learning about/using digital pots though so I'm definitely not an expert.

 

[TheFishMan65]

I guess I did not look into enough of them. Thanks for the information.

 

[DustinB]

This one just meets your size: MCP4018T

You are correct on the currents, I was confused. The ones I looked at only had a 2.5mA rating on the resistor circuits, 25mA on any output pins. The one listed above does have 128 steps and is a full range 0-100% pot. It may be acceptable for current settings up to 700mA or so. RSET should be around 1.75mA at 700mA LED current, but hits the max 2.5mA at 1A LED current.

You'd really think it would be easier to find something like this with a higher current rating...

 

[der_wille_zur_macht]

This one just meets your size: MCP4018T

That's one I looked at. It would work for the application of dimming the CAT4101 but I have another application where I want a digital pot with both ends exposed - that chip only exposes one end and the wiper, it connects the other end to ground or leaves it unconnected depending on which variant you order.

 

[bluebayou]

My planned tank: 180gal or 200DD, both are 1,728" area coverage.
LED Qty: Not totally sure but well over 100. 144+?
I plan on controlling with a Typhon

I would need to solder 24+ 4101 boards. How many power supplies would be required? I am a beginner at all this but I am imagining a big stack of ps's.

Does the new Mean Well HLG drivers make more sense for my build? I'm trying to figure out what makes the most sense. The granularity of the 4101s may or may not be worth it, I don't think I understand all of the ramifications of either solution.

My idea is to have the LEDs on individual heatsinks and sitting on opposing rows of L channels forming slots then making a big panel of slots such as this:
____________________________
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|____________________________|
|____________________________|

Using this method I can slide the individual LCDs all over the place creating concentrations or gradients if necessary as well as individually tilting LCDs to prevent overspill ect. The best thing is that it is completely adjustable with the push of a finger not to mention easy to replace burned out LCDs ect.

What do you all think?

 

[TheFishMan65]

If you can find a 24 amp 24 volt supply (OK a little larger current 28) one would do it. Or if you run at less than 1 amp. You will probably need 2-3 supplies. I am guessing 3-4 HLG
IIRC HLG are close to $100 so $3-400 that way
A Cat4101 circuit runs $3-4 so $72 to 96 here. If you can find power supplies on ebay maybe $40. If not new probably $100.
So I would guess costs are about even.

 

[der_wille_zur_macht]

For 144 LEDs you'd need 24 CAT4101 circuits. No one's putting a single CAT4101 on a board (that I know of). For instance, my design uses 3 of them per PCB, so you'd need only 8 boards. If you stick with LEDs that are on the lower-end of the Vf spectrum, which should be easy-ish to do, you can probably sneak 7 LEDs on each CAT4101 (sum of Vf basically needs to be 24.5 or lower). In that case, you'd need 21 circuits, or 7 3-up boards.

Regarding power supplies, FishMan is about right - you need to budget your LED current plus about 20 - 30 percent. If you target 700mA drive current, you're talking about needing roughly 20A. You'll likely end up with multiple supplies as one single supply that large will be hard to find and/or insanely expensive. You need to decide if you care about power factor correction, as well.

I agree with FishMan on cost as well. The HLG drivers are very good in terms of cost per watt of output, so they're hard to beat in that respect on a large tank. If you go with HLG drivers, the biggest "issue" will be dealing with parallel strings and the fact that you'll only have a few discrete groups of LEDs for dimming. If you go with the CAT4101 design, you'll have much greater resolution for control (smaller groups of LEDs) and won't have to deal with parallel strings, but you WILL have to deal with having lots more "things" involved with driving your LEDs. It's a tradeoff based on your preferences, I don't think there's a clear one size fits all answer.

Back a few posts I was pondering the concept of trying to generate a DIY design that was equivalent to an HLG. I think this would be easy to achieve with one of the high-capacity switching chips from National (LM3409HV for instance).

 

[RCBrooke]

On the 24 volt power supplies, how are you protecting them from salt water drips, splashes etc.? I've been wondering if a meanwell set for constant voltage might make a good option (from a safety point of view not dollars) for driving the CAT4101 boards.

 

[bluebayou]

For 144 LEDs you'd need 24 CAT4101 circuits. No one's putting a single CAT4101 on a board (that I know of). For instance, my design uses 3 of them per PCB, so you'd need only 8 boards. If you stick with LEDs that are on the lower-end of the Vf spectrum, which should be easy-ish to do, you can probably sneak 7 LEDs on each CAT4101 (sum of Vf basically needs to be 24.5 or lower). In that case, you'd need 21 circuits, or 7 3-up boards.

Regarding power supplies, FishMan is about right - you need to budget your LED current plus about 20 - 30 percent. If you target 700mA drive current, you're talking about needing roughly 20A. You'll likely end up with multiple supplies as one single supply that large will be hard to find and/or insanely expensive. You need to decide if you care about power factor correction, as well.

I agree with FishMan on cost as well. The HLG drivers are very good in terms of cost per watt of output, so they're hard to beat in that respect on a large tank. If you go with HLG drivers, the biggest "issue" will be dealing with parallel strings and the fact that you'll only have a few discrete groups of LEDs for dimming. If you go with the CAT4101 design, you'll have much greater resolution for control (smaller groups of LEDs) and won't have to deal with parallel strings, but you WILL have to deal with having lots more "things" involved with driving your LEDs. It's a tradeoff based on your preferences, I don't think there's a clear one size fits all answer.

Back a few posts I was pondering the concept of trying to generate a DIY design that was equivalent to an HLG. I think this would be easy to achieve with one of the high-capacity switching chips from National (LM3409HV for instance).

I did mean circuits, I know there are 3 to each physical board. I'm thinking the same in regards to the HLG's only giving me 2 or 3 large groups of resolution instead of 24 smaller groups. I think I will probably go with the 4101's for many reasons not the least of which is to learn more about EE. Some of the benefits that I can think of for having the greater resolution would be:

Nightlight
Cloud Effects
Color change via ratio's of RB and CW as well as dimming/

I would love to try to come up with a LM3409 solution but know that I simply don't have the background necessary yet. Has anyone tried to create a system that has each LED independently adjustable?

Re: my independent slot mounting setup: What do you think of this idea? One issue I've thought of is that the heatsink is 28mm and the star is 20mm leaving me with ~4mm on either side as a lip to set inside the channel. The most obvious concern with this is shorting, the connections are millimeters away from aluminum channel. Not a good thing. I've thought about a connector solution but don't know enough about what is available to know if this is feasible.

 

[der_wille_zur_macht]

On the 24 volt power supplies, how are you protecting them from salt water drips, splashes etc.? I've been wondering if a meanwell set for constant voltage might make a good option (from a safety point of view not dollars) for driving the CAT4101 boards.

I'm protecting mine by keeping them AWAY from water! On tanks where it's not feasible to literally locate them far away from water, I put them in a large box or cabinet with ventilation, or provide obvious and foolproof shielding from wet areas. You certainly don't want the power supplies OR the driver boards getting wet. You COULD use a sealed power supply, but you've got to protect the CAT4101 boards themselves as well...

I would love to try to come up with a LM3409 solution but know that I simply don't have the background necessary yet.

User theatrus came up with a driver based on the LM3404 a few pages back. The 3409 is similar but has more capacity, iirc. I started playing with it in Eagle a few days ago but don't think I am going to pursue the design at all - I have too much else going on and no immediate need for a driver that "large" and I don't have enough LEDs laying around to test one anyways!

Has anyone tried to create a system that has each LED independently adjustable?

This would not be challenging but it would be expensive in many ways. Firstly, you'd be building/buying circuitry for EACH LED instead of for a group of LEDs. Secondly, regardless of if you're using a switching or a linear driver, there's pretty much always a static efficiency loss per driver circuit. If you have a driver that's 90% efficient with 6 LEDs, you may only hit 70% efficiency designing with the same IC for one LED. So you're spending a lot more up front, AND taking an efficiency hit which translates into dollars lost longterm as well.

Re: my independent slot mounting setup: What do you think of this idea?

I think it sounds interesting but I don't know if I'm following your description well enough to critique it. One comment though - typically I like to experiment flexibly then design solidly. By that I mean that I build experimental builds to be flexible in as many ways as possible - repositioning LEDs, changing their height and angle, and so on. Then when I build something "final" that I want longterm, I often find it's simpler and cheaper to design in a fixed format, instead of designing with the same level of flexibility. It's hard to get flexibility, low cost, and long term reliability at the same time, IMHO. You want the flexibility when experimenting so you can determine what you want, but then once you know what you want, you don't need the same flexibility. Just something to think about.

 

[RCBrooke]

Thanks For the reply, yup don't mix water and electricity - Check, been there done that.

I was planning to mount the CAT4101 boards in one of the aluminium boxes attached/near the heat sinks, so unless I drop the whole thing in the water I should be OK (It only happened once I swear!

I was under the impression the, oh say potrans (sp?) needed to be left out of a box - that is to say well ventilated. Unfortunately I'm going to have to keep the power supply in the 24" space I left behind the tank so I was thinking I might be best served using one the water resistant meanwells (IP67 ?) to run for example 2 meanwells each 21.5v at 2.1a for the 6 CAT4101's (6 LED's each).

Thought I'd run it by ya'll to see if there's aspect I overlooked. I think to get a quick start, I'll use 3 ELN-60-48D's and convert to the CAT4101's after I can get the parts/boards.

 

[TheFishMan65]

IMHO the CAT4101 can't be placed in a box. Maybe it is just my design, but they get very warm.

 

[RCBrooke]

In Eagle is there a way to turn on visible rule / measurements. For example If I wanted to change the CAT4101 board to something other the 2"x2".

This probably should be posted as a separate post but I was looking at the CAT4101 board. Great job and thanks for all the help you give!

 

[RCBrooke]

Good thing I asked. Fishman65 how did you mount / place yours?

 

[der_wille_zur_macht]

You can turn on a grid of dots or lines. Click the little icon in the upper left that shows dots in a grid and you can specify a main grid and a secondary grid, as well as toggle the dots or lines on or off.

That said, that's only going to give you a visual representation of the grid, which is active even when it's not visible. Secondly, you can click the info tool (the little i) and then click on any object and view or edit it's position relative to the origin. So, for instance, you could click on the board outline and change it's position that way, instead of using the move tool and lining up with a grid.

It's also worth noting that if you're changing the board outline to a larger size, you'll probably want to move other components, make the ground layers larger, and so on...

 

[RCBrooke]

Smacking self upside of head. The info button of course! I used it to reposition the via's, don't know why it didn't occur to me to use it for the board's size. Eagle takes some getting used to! kept giving me "can't back annotate" error until if figured out it was trying to use the wrong tool.

Switched to a double CAT4101 and added a LM317 & pot to hit that +0.5v sweet spot with mix LED's better (thinking of the soon to be out XM-L's with XP-E's). Mostly just practice - I used spice (p_spice?) about 20 years ago.

Thanks.

 

[TheFishMan65]

I will be mounting mt driver with the LEDs about 2 feet above the tank. I hope this is above the 'splash zone' as I am planning no special protections. They are mounted such that I have good convection current and I am hoping that will be enough.