Question about next meeting...

[zeroinverse]

WCR, for the next meeting, are we doing LED DIY session?
And if so, are we getting RapidLED involved with discounting also?

They wouldn't want to do a BlackFriday style discount would they? (i.e. good discount off)

 

[northbay-reefer]

I will confirm with them on the date, and yes Rapid will be here and Yes they will give us a discount. I will give the full detail when I get them. No black friday discount because I don't think the margin is that great.

I do have a list of questions that I want to ask and it's mainly on how to select the drivers to match with the different leds, forward voltage, current, parallel, series ect.

 

[zeroinverse]

I can help on the "selecting drivers to match different LEDs, etc question... if you or group need.

 

[northbay-reefer]

I am thinking about getting a 100 watt multichips LED to replace one of my halide as a test. Eventually go to three 100 watt LED hybrid chips and want to find a nice dimmable driver to run each led. Even though these leds are rated at 100 watt, you can push then all the way to 253 watt depending on how much voltage and current you set the driver at. There are several drivers out there and I just want to make sure I picked the right one.

I want to use this chip

http://www.ebay.com/itm/EPISTAR-100...1514714856949649640&pid=100011&prg=1005&rk=4&

 

[zeroinverse]

Read below analysis
===================

Color temperature/Wavelength: 40 chips 20500K + 60 chips 453nm Royal blue
Led chips: EPSTAR EDI-EA1143 45mil
Download Manufacturer Data Sheet
PAR reading(Instrument: Apogee MQ-200):
1360 (3A current)
2045 (6A current)
DC forward Voltage: 32-36V
DC forward current: 7A max
Rated power: 252W max
Viewing Angle: 120 Degree
Intensity Luminous (Iv): 4681LM at 3A current / 9362LM at 6A current
Life span 50000 hours guarantee


# of chips = 100 chips

===========
Chip detail
3.15 ~ 3.6 Vf
350mA (with 700mA absolute max)
===========

with 32~36VDC forward voltage
that means about 10 LED chips in series

This means if there are 100 chips, that there are 10 parallel strands (each of 10 LED chips)

In terms of current distribution, this means 350mA down each parallel strand (if all parallel legs are balanced).
350mA x 10 parallel legs = 3.5A
The maximum LED chip current is rated at 700mA which allows you up to 7A maximum.

===========
Here's the problem with PARALLEL string configurations.

IF you drive them at 3.5A
& ASSUMING balanced current distribution across all 10 parallel legs
==> 350mA goes through each leg.

If any ONE LED chip burns out, that entire "parallel leg" will turn off.
The impact is then that the current you are providing must be redistributed to the other 9 remaining legs of LEDs.
In that scenario, the 350mA from that leg will be redistributed to the other 9 legs. Meaning those 9 legs will then run at 388mA.

The end result is that you can have 5 LED chips burn out (which will shut down 5 parallel legs).
This results in the remaining current to get redistributed to the remaining 5 parallel legs.
These remaining parallel legs will be running at 700mA, the absolute maximum rating.
==========


SO depending on how many chips you expect to FAIL, you can power this module between 3.5A to 7A.

==================
Here is a scenario

Run it at 6A. This means 600mA across each leg. Check weekly.
If one leg fails, remaining 9 legs run at 666mA.
If another leg fails, remaining 8 legs run at 750mA (entire array burns out)
This means before #2 fails, you have to lower current down from 6A.

Since most of us don't have time to check if our LEDs are burned out (PLUS, it may be TOO bright to easily see if a leg is burned out)...
YOU WILL PROBABLY JUST RUN IT AT 3.5A

 

[zeroinverse]

NOTE: the EBay seller/manufacturer does not provide information on the ARRAY's long-term reliability & failure rate. This is the main concern. A bad solder connection, or a bump on the array could dislodge/fracture the soldered gold bonds and cause a parallel leg to fail.

 

[northbay-reefer]

I was thinking about running it at 3.5A to be on the safe side. I know these chips are still new so we don't know too much about the reliability. I am thinking about it but not sure I'll do it any time soon. Right now I am just tossing around different ideas. Another option is to run a bunch of 10 watt leds.