DIY LEDs - The write-up

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I'm looking for a 15k color, I was only planning to do one color per driver so I could have more control for dawn/dusk. So I can do 8 LEDs in 2 series on each driver? That will let me get a few extra LEDs in each fixture, since I was worried about 24 being enough. Since y'all are saying I should mix colors anyway, what do you recomend for 36 led fixtures? I'm going to have two of the fixtures over a 75 gallon and was only planning on going all xr-e because it would be less complicated. If anyone can recommend a combo that uses newer LEDs like xp-gs that will be a 14-15k look I'd appreciate it.
 
widmer said:
Parallel strings is such a trendy question, maybe one of you guys wants to put together a comprehensive post about it (ie pros/cons, how to etc) that we can just point people to?
Click to expand...

Parallel strings done right: http://www.ledsmagazine.com/features/6/2/2

The resistor only method helps, but isn't the most optimal.

look at the final method described, "Over-current protection", a few extra parts, but cheaper than blowing LEDs
 
Thanks that article was really interesting, I definitely plan on doin my build the correct way. Now I just have figure out what these extra parts would be called on mcmaster or mouser
 
rcgates said:
Parallel strings done right: http://www.ledsmagazine.com/features/6/2/2

The resistor only method helps, but isn't the most optimal.
look at the final method described, "Over-current protection", a few extra parts, but cheaper than blowing LEDs
Click to expand...

Depends on your definition of optimal. If finding a bunch of extra parts that in no way present themselves as being easily usable is optimal - then that is definitely optimal.
.

How do you propose this for a non-technical user? It's not trivial to select, mount, hook-up, test, and troubleshoot a current mirror with over-current protection! How does one even mechanically protect it?

How does one even measure the string currents in that design?

I know of no commercial designs using that scheme.
 
kcress said:
That is fundamentally what you need to run.

As drawn, that could work well or be a disaster depending on the luck of the draw.

So yes, do it right and add the fuses and the 1 ohm resistors and plan to check the currents in the two parallel strings once you have it running. Also plan to have to disconnect a few LEDs and move them to the opposite strings and vis a verse to properly balance the strings.

You might want to re-think this and just mix the two colors as depicted above. That will save a bunch of complexity and keep the LEDs homogenized.

If you know what color temperature you want. 8k 10k 15k 20k 500k we can advise on the mix and you could NOT have all the drivers.
Click to expand...

+1x

If you do mix leds in a parallel string they must be balanced. Mixing Blue and White is ok but only if they each are from the same lot and evenly balanced.

Its best to keep each parallel string with the same LED from the same lot. Especially if you drive them hard.

On a side note I was experimenting with a 1 Ohm resistor based on the recommendation of kcress and measured the output of my ELN 60-48D at 1.8A from the source. This is bad if your just hooking it up to XP-Gs and expecting 1.3A max...Always check your driver output...

As far as the 1 Ohm resistor it looks like a trip to Home Depot for another meter to do more measurements. A single meter just wont do it as you need to measure the current through both strings at the same time. Will post the results with and without resistors in the next couple days. So far no harm in adding a 1 ohm resistor or fuses all works well as expected.

I'm 100% positive a disclaimer will be posted tomorrow recognizing that this is an artist rendition simplifying parallel string wiring and does not endorse the use of different LEDs while using parallel strings...

Bill
 
So I can run 16 LEDs on one ELN 60-48 as long as I put them in two parallel series of 8? I will still prob be going with 50/50 all xr-es but I really just need to know if I can run that extra 4 per driver.
 
wld1783 said:
As far as the 1 Ohm resistor it looks like a trip to Home Depot for another meter to do more measurements. A single meter just wont do it as you need to measure the current through both strings at the same time.

Bill
Click to expand...

Bill. Why? You don't need two meters. In fact it's sort of a bad idea. If you have resistors in each string just measure the voltage across the resistors.

If they're 1 ohm the voltage you measure is the current.

That's the whole point of adding the resistors, to allow instant current checks of the various strings.

cjones1344; If you're looking for 15k and you're not using XGs for the whites I think you want about a B:W ration of 60:40.

Hopefully someone will confirm that.

If you understand paralleling and do it as described in a dozen places here you can run two strings of 12 or 13 LEDs for a total of 24 or 26 on a single ELN60-48.

If you want to use xpg's and xre's you need about 35% white 65% blue.
 
The boss (wife) finally gave me the green light to set our 90G (48"x18" surface area) display up for reef, which I interpret to mean "go ahead and put LED lighting on it". :)

Is the general consensus right now to go with the Cree XP-G for the white and XP-E RBs for the blue? I'm questioning the benefit of going with the higher-priced units instead of staying with the XR-Es albeit the XP-Gs provide a few more lumens.
 
cjones1344 said:
So I can run 16 LEDs on one ELN 60-48 as long as I put them in two parallel series of 8? I will still prob be going with 50/50 all xr-es but I really just need to know if I can run that extra 4 per driver.
Click to expand...

Yes, you can do that, as long as you understand the implications of running parallel strings. The strings MUST have the same voltage drop, else you will have issues. Ensuring the strings have the same drop is a two step process. First, build them from the same model/bin of LEDs, or equal numbers of different LEDs (i.e. you CAN NOT have one string of royal blue XR-E and another of cool white XR-E, but you can have two strings with 4 each). This is because different LEDs have different specified Vfs under different conditions. Second, once you have built your strings, you MUST test them to ensure they actually do have equivalent voltage drops. If they do, you're all set. If they don't, you have to swap LEDs around until they do. LEDs can have significant variation in Vf from the specified value (the manufacturers acknowledge this, it's not a conspiracy). You can determine if your strings are balanced by putting a 1 ohm resistor inline with each string and measuring voltage drop across each resistor (while running your LEDs at a safe low voltage).

Besides balancing the strings, you need to protect them from a fault - if an LED in one string fails open, the other string will instantly get twice the current you designed it for, which can obviously be bad for the LEDs in that string - the most common method of protection is installing a fuse inline with each string, rated above the designed current for that string but below the value it would get if the other string failed.
 
rguyler said:
Is the general consensus right now to go with the Cree XP-G for the white and XP-E RBs for the blue? I'm questioning the benefit of going with the higher-priced units instead of staying with the XR-Es albeit the XP-Gs provide a few more lumens.
Click to expand...

Yes, that is essentially the typical build right now. Of course, your choice will depend on your own criteria.

Personally, a big part of the reason why I'm in this is efficiency. Hence I feel it is important to be relentless about efficiency. An increase in cost of the build to get more efficiency can easily be offset by lower operating costs over time - the XP-G may seem more expensive, but if you intend to keep your LED rig for more than a year or two, they'll pay for themselves.
 
kcress said:
Bill. Why? You don't need two meters. In fact it's sort of a bad idea. If you have resistors in each string just measure the voltage across the resistors.

If they're 1 ohm the voltage you measure is the current.

That's the whole point of adding the resistors, to allow instant current checks of the various strings.
Click to expand...

kcress

Thanks

I cant believe I missed something so obvious but then again its been a few years since high school electronics shop.

Bill
 
Just to update everyone...

I am going to pull my hair out! I tested for everything and anything and I still can not get this to fire! The worst part is I hooked up my LPC-35-700 in a parallel with 2 strings of 12 and EVERYONE worked fine. Needless to say I looked at the HLG drivers and considered doing the peoples elbow on them.

I'll have to wait until next week to test the drivers with how busy work will be ( Yahoo retail! ). Again I thank everyone for there input and help. I will have these working sometime!

-Dave
 
Digi-Key has 1 ohm 2w resistors right. I was trying to find them on their site with no luck. Anyone have a link to them please?
 
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