So i'm thinking i will invest in these LED Drivers. Probably will get one or two of this type specifically.
http://www.ebay.com/itm/Mean-Well-LPC-35-700W-LED-driver-awesome-and-cheap-/150408656050#vi-content
Their description states that:
Driver is "perfect for driving ~3 - 14 x 3W LEDs"
700mA constant current
9-48V DC Voltage

but if it's max is 48VDC at 700mA, wouldn't that mean that i would be maxing it out at about 12 LEDs?

On a side note: i would like to add 2 x 12v computer fans, does that mean i need to use a separate power supply for that and have two wires sticking out of my canopy i'm building?

 

but if it's max is 48VDC at 700mA, wouldn't that mean that i would be maxing it out at about 12 LEDs?

On a side note: i would like to add 2 x 12v computer fans, does that mean i need to use a separate power supply for that and have two wires sticking out of my canopy i'm building?

If the LED max forward voltage is 3.4V then with 48V max dc output you can run 14 LED's in series (48/3.4)

If the LED max forward voltage is 2.8V then you can do 48/2.8 = 17 LEDs in series
and on and on based on different forward voltages.

If the combined forward voltages of the LED's is greater than 48V the driver cannot regulate the current properly and you will have problems.

That driver is just fine.. but it doesn't do dimming if you want that. and you can find them cheaper here
http://www.rapidled.com/mean-well-lpc-35-700-constant-current-driver/



And yes you will need a separate "constant voltage" power supply for the fans.

 

If the LED max forward voltage is 3.4V then with 48V max dc output you can run 14 LED's in series (48/3.4)

If the LED max forward voltage is 2.8V then you can do 48/2.8 = 17 LEDs in series
and on and on based on different forward voltages.

If the combined forward voltages of the LED's is greater than 48V the driver cannot regulate the current properly and you will have problems.

That driver is just fine.. but it doesn't do dimming if you want that. and you can find them cheaper here
http://www.rapidled.com/mean-well-lpc-35-700-constant-current-driver/



And yes you will need a separate "constant voltage" power supply for the fans.

Isn't so easy to say as the forward voltage will change a lot with current.

-It will increase due to higher current
-Current itself will raise due to temperature

Depends what you use for regulation but normally either you need a means to adjust the voltage, or you need a few volts reserve. If it is a transistor based regulator, you need 3V just for that, and also some volts to care for the LEDs forward voltage.

Interestingly if you use many LEDs in series, you will also observe the internal resistance of the LEDs adds up considerably.

 

If the LED max forward voltage is 2.8V then you can do 48/2.8 = 17 LEDs in series
and on and on based on different forward voltages.

All that makes sense.. thank you for the info. The last thing i am trying to figure out is when using a driver like this one, why is it OK to wire both for example blue LED (running 3.8V max) with red LED (running 2.4V max). I know that their current is both at 700mA, but when the driver has to adjust the voltages to keep constant current, how does it know which led is maxing out at 2.4 and which is maxing out at 3.8? Doesn't it just balance out the voltage if they are wired in series? I am still uneasy about doing two colors together. I read several places that it is a bad idea to do that, while others say it doesnt matter. Can you give me the details on that?

 

Mcgyvr,

Thanks for link by the way, i just ordered 3 from their site.

 

The LEDs set their own voltage. The driver only sets the current.
You should not operate the LEDs at their absolute maximum allowed current (700mA) unless you have very good heatsinks in open air and have airconditioning.

 

So the forward voltage of power supply doesn't really matter so long as it feeds the stable correct current, then rest takes place on each LED individually... given the 700mA current source, each one sets its own forward voltage of LED. So the reason they write out the typical and maximum voltage of each LED is just from imperfections from wherever or however the LED's are made? correct me if i'm wrong.
You guys are great!

 

Each LED will have a different forward voltage (some will have maximum voltage, some will be "typical" and some will have minimum voltage). The current source must be able to provide enough voltage for them to be in series.

 

I've come across a new question with this project... my drivers just came in and i want to be able to turn them on/off with switch. Where would i need to put a switch, on the ac side before the driver or on dc side after the driver before LEDs?

Also, would a switch like this work with AC? or the 48V DC? if not, any links or suggestions as to which kind will?

 

I've come across a new question with this project... my drivers just came in and i want to be able to turn them on/off with switch. Where would i need to put a switch, on the ac side before the driver or on dc side after the driver before LEDs?

Also, would a switch like this work with AC? or the 48V DC? if not, any links or suggestions as to which kind will?

Switch the AC side. (AC is easier on switch contacts)

Any switch that is rated for 1.5 to 2 Amps and 120V (or 240V) will work just fine..

That switch "might" be ok but I can't guarantee that unless we have a part number/spec sheet.. Looks a bit small IMO. I wouldn't risk it. However many times the ratings are molded into the switch body too. Your local hardware store will have a selection of switches like that (toggle/rocker/push button, etc...).. and all will show their ratings.

 

All the power switches I use are not stamped "ALOHA" but instead have the ratings stamped "CSA 250VAC 5A". Don't buy cheep oriental E-Bay junk!

 

These switches i actually got from Radioshack. The only place i know that sells stuff like that locally. And yes you are right fellas, the switches i have are 120VAC .5A.

I'm back to being a little confused and need help. I ran a test of two of the constant current power supplies to power up all the whites. Each one drew about 730mA and not 700mA, is that ok?
Also, each CCDriver rated 48V, max V of each LED was 3.8, but i am getting some that are reaching 4.1V~4.2V. Please advise. Thanks. I appreciate your support.

 

Was eager to see what the blue and red's would do.... They are way under the 48fV max from driver, but somehow, the series runs at 800mA. For the most part, each LED is not getting too much voltage though. Not sure what's going on.

 

Was eager to see what the blue and red's would do.... They are way under the 48fV max from driver, but somehow, the series runs at 800mA. For the most part, each LED is not getting too much voltage though. Not sure what's going on.

White test.. How many LED's in series? and whats their Vf?
red/blue test.. How many LED's in series? and whats their Vf (of each color)?

What were you using for heatsinking?
How are you measuring the voltage drop of each?

If the summed Vf of the series string is not within the drivers DC output range they driver will have trouble regulating the current properly. And also how "exactly" are you measuring current and is your ammeter calibrated to that precision?

Obviously there are driver tolerances associated with the stated 700mA..all covered in the datasheet.

 

These switches i actually got from Radioshack. The only place i know that sells stuff like that locally.

They are gone from Canada because they sold CHEEP (cluck, cluck) oriental junk at very high prices.

I ran a test of two of the constant current power supplies to power up all the whites. Each one drew about 730mA and not 700mA, is that ok?

I did not see what is the maximum allowed current. It might be 700mA then the LEDs will get very hot and will not last long.

max V of each LED was 3.8, but i am getting some that are reaching 4.1V~4.2V.... somehow, the series runs at 800mA.

The "typical" voltage of the blue LED is 3.8v at 700mA but I did not see the maximum voltage. The voltage is higher when the current is too high.
Your LEDs will probably burn out soon.

 

They are gone from Canada because they sold CHEEP (cluck, cluck) oriental junk at very high prices.


I did not see what is the maximum allowed current. It might be 700mA then the LEDs will get very hot and will not last long.


The "typical" voltage of the blue LED is 3.8v at 700mA but I did not see the maximum voltage. The voltage is higher when the current is too high.
Your LEDs will probably burn out soon.

"typical" CREE or other 3W LED's will run at 700mA all day long... IF and ONLY IF your heat sinking is adequate. The last "fixture" I build ran for 12 hours a day for 3 years at 700mA with NO problems at all. I only stopped using it because I needed a bigger fixture.

I'd bet this is all simply a misunderstanding by the OP of #1 how to measure their forward voltage, #2 not understanding the tolerances associated with the driver and #3 related to the number of LED's used for these "tests" and ensuring they the driver is operating in its rated output voltage range.

 

White test.. How many LED's in series? and whats their Vf?
red/blue test.. How many LED's in series? and whats their Vf (of each color)?

What were you using for heatsinking?
How are you measuring the voltage drop of each?

If the summed Vf of the series string is not within the drivers DC output range they driver will have trouble regulating the current properly. And also how "exactly" are you measuring current and is your ammeter calibrated to that precision?

Obviously there are driver tolerances associated with the stated 700mA..all covered in the datasheet.

If your questioning my edumacation on this... maybe i'm wrong but here are the details
The spec sheet, straight from Mean Well
http://www.meanwell.com/search/lpc-35/LPC-35-spec.pdf
The specs sheet states that the output of the CCdriver should be +- 5% Current accuracy. Meaning it should be between 665mA - 735mA.
I followed the instructions in this youtube video
http://www.youtube.com/watch?feature=endscreen&v=TGbi1LelOOI&NR=1
Correct me if i'm wrong. When measuring voltage you use the anode & cathode probes while everything is wired together (dont know if that makes sense), but measuring current you run the DMM with the line (i used the cathode side from the LEDs).


But as requested, here are the details to the three series
White1 = 10 White LED in series
(Anode) - 3.79V - 3.48V - 3.89V - 4.03V - 4.26V - 4.00V - 4.03V - 4.04V - 3.98V - 4.12 - (Cathode)
Making total: 39.62 Volts (well below the rated 48V Max on CCDriver)

White2 = next 10 White LED in series
(Anode) - 4.24V - 4.13V - 4.20V - 4.26V - 4.25V - 4.39V - 4.26V - 4.34V - 4.52V - 4.68 - (Cathode)
in total: 43.27 Volts (also below 48V)

Red&Blue = First 8 red, then 5 blue
(Anode) - 2.57V - 2.54V - 2.52V - 2.55V - 2.60V - 2.57V - 2.64V - 2.61V - 3.86V - 3.76V - 3.82V - 3.83V - 3.87 - (Cathode)
in total: 39.74 Volts (below 48V max)

You also emphasize on the heat sinks i am using. Well, i am using (3) 10Inch X 7Inch X 2Inch tall 3/16thick aluminum heat sinks. yes, 3 of them. I will apply thermal compound to the stars when this is regulated as needed and i am finished. Since they will be enclosed as a canopy for aquarium, i am also installing 2 80mm case fans which is why i was asking about that. Will do push/pull. (i have pictures in this thread on previous posts i think).

I'm not sure why, but it appears the current grows pretty slowly. All three of the setups are doing above 800mA and it just keeps growing slowly. My DMM is pretty old and been used around between my dad and bro but it never seemed to lie to us. Maybe it's not 100% detailed but it should do the job.

Patiently awaiting your reply. Meanwhile, i will email the seller or mean well directly and see what they have to say.

 

"typical" CREE or other 3W LED's will run at 700mA all day long... IF and ONLY IF your heat sinking is adequate. The last "fixture" I build ran for 12 hours a day for 3 years at 700mA with NO problems at all. I only stopped using it because I needed a bigger fixture.

What rating did your driver have?
How hot did your heat sinks get? and how fast did they heat up?
Were you running them indoors or out? How much heat did you have to work with when they are on 12hrs/day?
I think if i left my current setup on for 30 minutes, the heat sink will be almost hot to the touch.
Side note: when i ran the led's using resistors, the heat sinks were not heating up at all the way they are now.

 

What rating did your driver have?
How hot did your heat sinks get? and how fast did they heat up?
Were you running them indoors or out? How much heat did you have to work with when they are on 12hrs/day?
I think if i left my current setup on for 30 minutes, the heat sink will be almost hot to the touch.
Side note: when i ran the led's using resistors, the heat sinks were not heating up at all the way they are now.

2 x ELN-60-48D drivers (12 x Cree XPG's on one driver and 12 x XRE's on another)
Temps measured on the star PCB as close to the LED as I could get did not exceed 70deg C. It typically takes 1 to 2 hours to thermally stabilize. My new fixture using 50W multichip LED's runs at 38deg C using Nuventix Synjet 60W heatsinks/PWM coolers..<< I love these but they are sort of pricey..$55 per kit (heatsink/pwm cooler) per 50W LED.. I have 4 x 50W over my 6ft 120G reef without optics.
Indoor (reef/aquarium application)
Hot to touch as in you can keep your hand there?..Should be fine.. BUT only though thermocouple measurements would I sleep right at night.

I think your meter (out of calibration/readings are off) is causing the confusion.. maybe.. Shouldn't be outputting 800mA. 750 max.
I always order dimmable drivers too..

 

I think that even if the meter was out of calibration, it would only be off by milliamps. But anyways... i will try to find someone else who i can borrow one from.
You said you had 700mA running on your canopy over 2 years?

If i have my lights setup on heat sink like in image above with thermal compound, do you think there will be any problems? There will also be two fans (push/pull) inside canopy. If they are running at the rates they are now supposedly.

On a side note, i dont think my drivers have a SVR2 throttle to control current, anyway for me to know for sure? Is there any that i can install externally from the driver unit?