Diver selection and diode/circuit board wiring help

tags420

tags420

Well-Known Member
I've been running LED's for a while and now I'm trying to learn more about how exactly they work in detail. I have a good understanding of LED's as a final product but I think that doing or at least theorizing about a DIY style project will give me the best understanding of the details behind the designs.

My main question is how do you select the right drivers to handle your selected LED's?
For an example lets say I have 120 cree XT-E's that I want to run at 350mA. How would I wire them(series, parallel, combo)? And how to pick the drivers that will handle it all.

The thing that sparked this in my mind, is that I use apache techs in my garden and they use 2 meanwell plc 100 (pretty sure the 20v+ version.) and power 120 1w diodes at 350mA. I'm not sure what the forward voltage of their diodes are...but it just seems like the numbers don't match up plus I don't exactly know how to calculate the drivers needed correctly. And how would they wire the boards to not go over the voltage. Questions like those are what are bugging my brain lately.

I figure that thinking of how to use XT-E's in the apache design would get me the understanding I'm looking for without going all out and building an actual DIY panel.
 
Alex281

Alex281

Well-Known Member
tags420

tags420

Well-Known Member
mmmmbrownies said:
well led lights are based on some basic analog electronics. to understand i would start with ohms law http://www.ohmslawcalculator.com/ohms_law_calculator.php
i use an led array calculator as well http://led.linear1.org/led.wiz
for drivers i always add up the wattage for the leds i'm useing (40 1w leds 40watts) and look for something a little higher, pay attention to your voltage it will dictate your resistor values
have fun
Click to expand...
This basically cleared everything up for me...Like load current, how many in series then parallel, how voltage is chosen and can make difference in how many in series, and the resistors too. It was nice to see the diagram, it llet me play with it and do some self learning. Thanks

Alex281 said:
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20Binning/XLampXPE.pdf

say you wanted to run 20 xpe reds at 350ma. according to the link, at 350ma a red cree xpe uses 2.1 volts. if u had 20 leds thats about 42 volts total. so you would want a constant current driver rated for 350ma and 48v. then simply wire all the leds in 1 strip in series(+from driver to - of led +-+-+-+-+-+-+ end led chain to - of driver)

thats how i did mine for the most part.
Click to expand...
That's exactly how I was thinking before I posted and the problem is try doing that 6 times(for 120led's). Either the voltage was so high you would need to work for the power company or I would need to use 6 drivers which is ridiculous. I was trying to figure out how apache(and others) were doing it. I was thinking that's not enough voltage...That link from brownies let me see how parallel doesn't use higher voltage just adds to the load current.
 
SupraSPL

SupraSPL

Well-Known Member
One thing to keep in mind if you are planning on large strings (120 XTEs), once the voltage on the string gets above 50v-60v you might have to take extra precautions such as carefully covering the traces or solder points and checking clearances more carefully. Another disadvantage to large drivers is that if something goes wrong with the driver or there is a bad solder joint you might risk burning the entire string.

I use 11 25-30w drivers, soon to be 27. They can be organized by mounting on a board which also makes it easy to remove their heat from the grow room and keeps the AC power connections safely contained in one area. I have never tried parallel strings, that might be a good solution if you can figure out how to keep them balanced. Good luck!
 
tags420

tags420

Well-Known Member
SupraSPL said:
One thing to keep in mind if you are planning on large strings (120 XTEs), once the voltage on the string gets above 50v-60v you might have to take extra precautions such as carefully covering the traces or solder points and checking clearances more carefully. Another disadvantage to large drivers is that if something goes wrong with the driver or there is a bad solder joint you might risk burning the entire string.

I use 11 25-30w drivers, soon to be 27. They can be organized by mounting on a board which also makes it easy to remove their heat from the grow room and keeps the AC power connections safely contained in one area. I have never tried parallel strings, that might be a good solution if you can figure out how to keep them balanced. Good luck!
Click to expand...
My original thought that sparked it all was "What would the output be on an AT120 if they just retrofitted with XT-E's instead of their diodes?" and "How would that even work?". The voltage build up is what was confusing me and made me make the post.
I have learned that with parallel strings it adds the currents of each string, which makes the load current, but only needs the one strings voltage to run them all. So the limit to how many parallel is based on the (drive current of each string x the # of strings) needs to be less than rated current of the driver. And the cumulative forward voltage is the limiting factor on diodes per string.
So say I have 120XT-E's(2.85v@350mA) that I want to run at 350mA with two meanwell plc100 20v driver(60 diodes ea)...
I would need to run (10)strings of (6)diodes with 10ohm resistors on each string per driver...
At 350mA x 10strings=3500mA total load current which is less than rated current of 4800mA.
2.85v x 6led's=17.1v...+8.28ohm=20v for each string
I'm still trying to learn the details of the resistor. This builder http://led.linear1.org/led.wiz says to use 10ohm resistors but technically 8.28 is calculated value needed. Maybe 10 is the closest size available?
 
turnip brain

turnip brain

Active Member
What benefit is there to all this circuit balancing with resistors rather than just running constant current drivers? Then it is just adding up cumulative forward voltage of each string run by each driver.
 
tags420

tags420

Well-Known Member
^^^They are constant current driver of 350mA.
The point of running in strings parallel is that I could run 60 led's with 20v driver instead of 171v driver, which is really high and dangerous...or a bunch of smaller drivers which isn't cost effective or practical IMO.
I think the resistor is so that each string uses all the voltage going through so at he end each string it's 0v, but I'm not 100% on that though. The resistor has to do with voltage if there is a constant current so that is why I think that.
Voltage=Current * Resistance(ohms)...The voltage passed on by the 6 diodes in each of my strings is 17.1, so I need to dissipate that remaining 2.9v of the 20v+/- total with a 8.28 ohms resistor. since minor voltage flux is accepted with constant current that might be why the builder site said 10ohms in stead of 8.28.
If the strings used up all the voltage perfectly and evenly, I don't think you would need resistors.
This is my understanding as of now. I would love for one of the pro DIY'er to clarify if I am on the right track.
 
SupraSPL

SupraSPL

Well-Known Member
If I recall correctly, the trouble is that each string would need to be the exact same vF otherwise one string will hog too much current, potentially damaging that string. Of course even if every LED on each string was the exact same emitter, there will still be slight differences in vF. Adding resistors would of course dissipate heat and reduce the efficiency of the system by a significant percentage.

I agree one large string with high voltage is not a good solution either. Multiple small drivers would likely cost the same or less than one large driver. A few random examples, 17W Mean Well for $12 or the 35 watter for $18
 
S

SnotBoogie

Well-Known Member
+1 for multiple smaller drivers. Its really not that bad to have like, 4 driver boxes for example, and as a small bonus you could easily do a "energy efficient veg" type option by incorporating switches for each driver.

also being able to easily remote my drivers saved my ass earlier in the year :p
 
tags420

tags420

Well-Known Member
SnotBoogie said:
+1 for multiple smaller drivers. Its really not that bad to have like, 4 driver boxes for example, and as a small bonus you could easily do a "energy efficient veg" type option by incorporating switches for each driver.

also being able to easily remote my drivers saved my ass earlier in the year :p
Click to expand...
I do see the benefits of multiple drivers as I am learning. AT only uses two and I wanted to know how. But having more control like power switches is cool. Going remote/external can save a lot of heat issues I am told.
 
SupraSPL

SupraSPL

Well-Known Member
Yes that is a big one. If we assume you are using 40% efficient LEDs with 80% efficient drivers, removing the drivers from the grow room would reduce the total heat by 30%.
 
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