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insomniac2k2
08/09/2011, 12:45 PM
I hope that i have a quick question on multiple strings. Heres what I want to do:

I have a frag tank that i want to run off of one driver. The only problem is that Im trying to figure out how to get more "use" out of my XPG crees. My biggest question: Is it absolutely necessary to have an exact match on LED types if I were to run multiple strings?

Im running a Mean Well ELN 60-48 rated @ 1.3A

Is it not possible to run say 12 CREE XPE RB's on one string, and just 10 XPG CW on the other. If I was able to run this way, in theory, I would be able to drive the strings at a maximum of 1.2A. The XPE's @ 1A ea and the XPG's @ 1.2A ea.

What kind of imbalance would this cause? Can i not do this because Voltage is dynamically adjusted, and would fry one string or the other?

I seem to missing something, just cant figure out what it is....

ghellin
08/09/2011, 12:58 PM
In parallel the strings need to balanced.

TheFishMan65
08/09/2011, 01:40 PM
That would not work. 1 amp for the XPE plus 1.2 amps for the XPG would be 2.2 amps and the ELN only supplies 1.3 amps. No if you have two ELN you could set it up for what you want.

Theoretically if you had two type of LEDs.
Type A 4 volts Vf and .3 amps
Type B 2 volts Vf and 1 amp
You could run 10 of type A and 20 of type B, but if they ever started to get out of balance I would be hard to get them back. Theoretically if the Vf of each string is the same they can be run on the same driver. The problem is LEDs aren't all the same and small fluctuations in Vf can have radical changes in current.

insomniac2k2
08/09/2011, 02:14 PM
Thats not exactly what i meant on the strings. I was thinking that if i ran my driver at 1200mA then the 10 XPG's on one string would draw around 1.2A ea and the 12 XPE's on the other string would draw around 1A ea.

I guess i was doing math like the fractional reserve system :). So in my case, I would have to run my driver maxed out at 1300mA. If i have 11 LED's per string, then they would pull 650mA ea string?

I will do some reading on Vf now and get a better understanding on the rest

That would not work. 1 amp for the XPE plus 1.2 amps for the XPG would be 2.2 amps and the ELN only supplies 1.3 amps. No if you have two ELN you could set it up for what you want.

Theoretically if you had two type of LEDs.
Type A 4 volts Vf and .3 amps
Type B 2 volts Vf and 1 amp
You could run 10 of type A and 20 of type B, but if they ever started to get out of balance I would be hard to get them back. Theoretically if the Vf of each string is the same they can be run on the same driver. The problem is LEDs aren't all the same and small fluctuations in Vf can have radical changes in current.

rysher
08/09/2011, 03:16 PM
So in my case, I would have to run my driver maxed out at 1300mA. If i have 11 LED's per string, then they would pull 650mA ea string?

yes, and each string should not exceed your drivers rated voltage.

insomniac2k2
08/09/2011, 06:39 PM
OK, thanks for the feedback. So then my direction now seems to be set. My final question is simply, "can i do this?"

After sorting out placement on my heatsink, i find that optimal coverage will be 26 LED's. 14 XP-E RB and 12 XP-G CW.

I want to run these off 1 Mean Well ELN 60-48. So im getting the impression that I can run the XP-E and the XP-G together in a string?

If so, I would just want to stagger it to something like this right? (CW=XP-G)

String 1 : RB CW RB CW RB CW RB CW RB CW RB CW RB
String 2 : RB CW RB CW RB CW RB CW RB CW RB CW RB

If this is correct, would it be more efficient to run them like this instead since the XP-G and the XP-E's have a different FV?

String 1 : CW CW CW CW CW CW RB RB RB RB RB RB RB
String 2 : CW CW CW CW CW CW RB RB RB RB RB RB RB

If im completely off on this, please slap me around a bit...

TheFishMan65
08/09/2011, 07:46 PM
You can wire them either/any way as long as each string has the same number of RB and CW. You will also need fuses and proferably a resistor for measuring current.

insomniac2k2
08/09/2011, 07:59 PM
Cool. Yep, fuses are definitely going to be used. Thanks for the confirmation!

You can wire them either/any way as long as each string has the same number of RB and CW. You will also need fuses and proferably a resistor for measuring current.