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Author Topic: Lost with 50w LEDs + PWM  (Read 8033 times)
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Madrid
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Hi guys, first of all sorry for my bad english. I'm also a noob so this makes an awesome mix.

I'm a bit lost in my project and I need some guidance.

I'm trying to control 5 x 50w RGB led.



I couldn't find the datasheet and the only info that I have is this.

50W:
Color: RGB
DC Forward Voltage (VF):  Red 22-24V, Greed 32-34V, Blue32-34V
DC Forward current (IF): 300MA
Out put Lumens: Red 400-500LM, Green 600-800LM, Blue 200-300LM
Wave Length : Red 620-625nm , Green 515-520nm, Blue 455-460nm
Beam Angel: 160 degrees
Life span: >50,000 hours

What I want to do is to control each single channel (RGB) of each led (5x3= 15 in total).

I'm gonna use exactly this psu.



http://www.ebay.com/itm/110933317767

Input Voltage Range  90~132V AC/ 180~260V AC by switch; 254-370VDC
Out    32-36V,0-9.7A

I know that I will have to reduce the output voltage more or less for each channel, that's not a problem, the problem that I have is this one.

Will I be able to use PWM through a transistor (one per channel) to control the intensity of each channel? Will I blow up something?

Thanks for the help!
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Use some nice big NMOS transistors, and the slowest PWM you can bear. Might need to drive the gates higher than 5V to avoid heating.
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As those LEDs have only 4 connections, they are either common anode or common cathode. You need to determine which. The connection on the left is probably the common one. To determine the polarity, connect your power supply between that connection and one of the others through a 10K series resistor and see if there is a faint glow from it. If necessary, do it is a dim light and reduce the resistor to 1K.

I suggest you drive them through a mosfet+BJT constant current circuit, because your power supply gives very little spare voltage so a series resistor won't give good current regulation. The details of the mosfet+BJT circuit depend on whether the led is common anode or common cathode.
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Madrid
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Use some nice big NMOS transistors, and the slowest PWM you can bear. Might need to drive the gates higher than 5V to avoid heating.

I'll take it on consideration, thanks!

As those LEDs have only 4 connections, they are either common anode or common cathode. You need to determine which. The connection on the left is probably the common one. To determine the polarity, connect your power supply between that connection and one of the others through a 10K series resistor and see if there is a faint glow from it. If necessary, do it is a dim light and reduce the resistor to 1K.

I suggest you drive them through a mosfet+BJT constant current circuit, because your power supply gives very little spare voltage so a series resistor won't give good current regulation. The details of the mosfet+BJT circuit depend on whether the led is common anode or common cathode.

I completely forgot to check if they are common anode or common cathode (I said I was a noob).

I don't have the LEDs yet, I just wanted to get ready before them arrive.

After a long time of searching I'm still unable to find the datasheet. I finally got to the manufacturer's website but there is not anything similiar to a RGB led so I give up. I'm just ask to the seller, I know it's a long shot but, why not to try it?.

Meanwhile I'm ordering the psu and  I'll test the LED when I got it. I just wanted to know if what I want to do can be done by the way I was thinking of.

I'll post the results as soon as I got it.

Thanks!
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In general the inability to find  a data sheet would personally concern me, but I suppose that is normal for a lot of eBay stuff from ominous sources. Based on a recent post using that same sort of LED for Aquarium lighting, you should be able to find at least a data sheet for the single LED elements that they have assembled in this package.

Also make sure you have sufficient heat sinking, possibly using a fan if you intend to run these close to their max current. The 50000 h lifespan is likely not applicable if you run them at max current and will be definitely many magnitudes smaller if you don't heat sink properly.

A second suggestion is to use a switched constant-current power supply. Most high brightness LED drivers are switched constant-current power supplies for reasons of energy efficiency. Otherwise they would dissipate too much heat and also would need a lot of heat sinking. Energy efficiency is also the reason of a relatively low PWM frequency.

Perhaps if you post a little more about your project you'd also be rewarded with more pointed advice.
« Last Edit: January 19, 2013, 05:01:25 pm by Headroom » Logged


Madrid
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I didn't want to make a long post but I'm happy to share what's on my mind.

I'm going to illuminate a room using these LEDs, (very cheap so not very reliable).

http://www.ebay.com/itm/50W-High-Power-LED-Chip-Full-Color-LED-RGB-Light-Lamp-Bright-Light-/160898806371?pt=LH_DefaultDomain_0&hash=item257650f263

Each one of them (5 in total) will be inside of a ceiling spotlight (plus the heatsink that I'll try to make it as big as possible).

I want to control every channel of every led individually, this will make 15 channels in total.

Off course I will use an arduino to control the LEDs and enable some modes such as:

- Presence detection
- Ambient light detection.
- Gentle light increasing activated by time. (I think that 250w of LEDs will be enough to wake me up in the morning).
-  Whatever else.

Everything can be controlled by software, I don't know yet how to but probably from the browser.

The total theoretic power will be 250w but  I don't want to put all the LEDs working at full power so I'll define the maximum brightness that I want to have in the room and set the maximum that the user can input, so there is no way you can put the LEDs working at full power. For example, a 100% set by the user will be a x% (0<x<100) of the maximum power available. I think is gonna be around 40-60% but I don't know it yet.

This will reduce the power consumption and the heat and increase the reliability because it is suppose to last for years (I really doubt it).

As I said, I couldn't find the datasheet, but I just find something similar (see the attachment).

The 50w LEDs is an array of 16Red 16Green and 16B. In the poor datasheet of above you can find the specs for every single led .I just multiplied the power dissipation of every single led and the result is almost 50w so I think that we have something that we can use.  

My problem is to know how is the best way to get them working with PWM, dc42 and macegr gave me good hints.

The psu that I will use is NES-350-36 (right side in the specs table), stepping down more or less the voltage depending of the channel (R,G or B).


* 20121126194938448[1].jpg (321.67 KB, 1464x2000 - viewed 99 times.)

* S-350_W_3[1].jpg (151.17 KB, 786x738 - viewed 56 times.)
« Last Edit: January 19, 2013, 06:17:45 pm by Hinjeniero » Logged

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You should use a piece of paper as a lamp shade to difuse the light. Then it would look nicer. Try not to make it la spotlight.
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I'm going to illuminate a room using these LEDs, (very cheap so not very reliable).

The total theoretic power will be 250w but  I don't want to put all the LEDs working at full power

I wouldn't run eBay LEDs at anything like their full power. The numbers they give are for perfect laboratory conditions using huge, active heatsinks. Under any real conditions they're going to get HOT if you try and run them at the quoted power.

Aim for 50-60% of those numbers and you'll be a lot happier/safer. 150W of LED is still an awful lot of light.
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good info,Aim for 50-60% of those numbers and you'll be a lot happier/safer. 150W of LED is still an awful lot of light.
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Madrid
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I'm going to illuminate a room using these LEDs, (very cheap so not very reliable).

The total theoretic power will be 250w but  I don't want to put all the LEDs working at full power

I wouldn't run eBay LEDs at anything like their full power. The numbers they give are for perfect laboratory conditions using huge, active heatsinks. Under any real conditions they're going to get HOT if you try and run them at the quoted power.

Aim for 50-60% of those numbers and you'll be a lot happier/safer. 150W of LED is still an awful lot of light.


I know and that's why I need to know if enabling PWM will be as easy as BJTransistor + MOSFET, also there is not too much space inside of a ceiling spot light and I will have problems to dissipate 50w per led. Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.



Anyway before installing them, I will run some tests to see what could I expect in every single situation so I'll be sure that I won't blow up something or set my house on fire.
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Valencia, Spain
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I know and that's why I need to know if enabling PWM will be as easy as BJTransistor + MOSFET,

It should be that simple, yes...

The amperage of those LEDs isn't too bad (300mA), that should make the PWM switching easier on the PSU than low-voltage/high-current LEDs. If you want to be extra sure you could add some extra capacitors on the power lines near the LED. Get come big ceramics.

also there is not too much space inside of a ceiling spot light and I will have problems to dissipate 50w per led. Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.

Fans will make a big difference, yes

(if the noise doesn't bother you...)
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At first glance that heatsink/fan looks small for 50W... think they're for 5-10W LEDs. THere are some nice big, round LED heatsinks on ebay that should work without a fan. Is there good airflow in those ceiling fixtures?

http://www.ebay.com/itm/20W-30W-High-Power-Led-Heatsink-Aluminium-Cooling-For-20-Watt-30-Watt-Led-Light-/190774600422?pt=LH_DefaultDomain_0&hash=item2c6b0d62e6

If you want 15 separate PWM channels then you'll need some sort of multiplexer since Arduino only has 6 PWM channels... or you can run all the reds together, greens together, and blues together so only need 3 PWM channels.

Does the suggestion for "NMOS transistors" really mean NMOS FETs (N-channel MOSFETS)? Look for devices with low drain-to-source resistance (Rds) otherwise you'll waste power in the FETs and may need to heatsink them too. If driving the gate with a transistor (recommended since they'll drive the MOSFET gates with sharper-edged signals that minimize heating) you won't need "logic compatible" devices.
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Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.

Anyway before installing them, I will run some tests to see what could I expect in every single situation so I'll be sure that I won't blow up something or set my house on fire.

You should also plan for the Arduino crashing and leaving all the LEDs at 100%, eg. Add a fuse that can't handle that much power.

Fuses are cheap and might save you from killing some expensive LEDs due to a software glitch.

PS: Be sure to test it to see if it blows!

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It should be that simple, yes...

The amperage of those LEDs isn't too bad (300mA), that should make the PWM switching easier on the PSU than low-voltage/high-current LEDs. If you want to be extra sure you could add some extra capacitors on the power lines near the LED. Get come big ceramics.

Fans will make a big difference, yes

(if the noise doesn't bother you...)


I was thinking to add the capacitors between the psu and the MOSFET, because if I put them between the MOSFET and the LED, the final wave would be shark type or even almost linear. But in the other hand I think that the wave doesn't matter as long as the average voltage is the same so probably would be better as near to the LED as possible.


At first glance that heatsink/fan looks small for 50W... think they're for 5-10W LEDs. THere are some nice big, round LED heatsinks on ebay that should work without a fan. Is there good airflow in those ceiling fixtures?

http://www.ebay.com/itm/20W-30W-High-Power-Led-Heatsink-Aluminium-Cooling-For-20-Watt-30-Watt-Led-Light-/190774600422?pt=LH_DefaultDomain_0&hash=item2c6b0d62e6

If you want 15 separate PWM channels then you'll need some sort of multiplexer since Arduino only has 6 PWM channels... or you can run all the reds together, greens together, and blues together so only need 3 PWM channels.

Does the suggestion for "NMOS transistors" really mean NMOS FETs (N-channel MOSFETS)? Look for devices with low drain-to-source resistance (Rds) otherwise you'll waste power in the FETs and may need to heatsink them too. If driving the gate with a transistor (recommended since they'll drive the MOSFET gates with sharper-edged signals that minimize heating) you won't need "logic compatible" devices.

The problem with the heatsink is that I don't have too much space for it. The spot light has 50mm diameter so would be impossible to fit a 10cm diameter heatsink but there is enough space above the light to provide good ventilation.

I will use an arduino mega which has 15PWM so I could avoid multiplexing.

Since I don't know yet if the LED is common anode or common cathode there is not much I can do to find the transistor that I need but of course it has to be high efficiency because otherwise it will waste a lot of power. The lights will be on at least 7 hours every day so I need the system to be as efficient as possible.


You should also plan for the Arduino crashing and leaving all the LEDs at 100%, eg. Add a fuse that can't handle that much power.

Fuses are cheap and might save you from killing some expensive LEDs due to a software glitch.

PS: Be sure to test it to see if it blows!



That's a very good idea, I was thinking how was the best way to reduce the maximum that the psu can supply in case of system failure and a fuse is just perfect.
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Madrid
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The seller has answered, seems to be an expert about his products.

Code:


hi?dear,
but?i?don't?understand?your?question.
sorry
?
?
2013-01-22
xiangpailighting
?
發件人:?eBay Member: rexaviis
發送時間:?2013-01-21?23:33
收件人:?xiangpailighting
主題:?有關物品的細節: rexaviis 就 10W 30W 50W watt RGB Changing LED Bright Lamp High Power Chip For flood light,編號為230827659562 的物品寄出訊息
xiangpai-lighting,您好!

Hi, is it common anode or common cathode?

Thanks!

- rexaviis


I made a quick schematic (considering that is common anode) to have a visual reference, this is just for one the LEDs.

Is there anything wrong? Notice the resistor after PWM2, the red LED should work at less voltage than the other two so the resistor drops the input voltage in the third transistor. I prefer do this by hardware instead of setting a different PWM for the red LEDs by software, but I don't know if is the best idea.

PD: The voltages in the schematic are random, I don't know them yet.

PD2: I'm thinking to use this MOSFET (15 in total).

http://www.irf.com/product-info/datasheets/data/irfz44n.pdf

Code:
Manufacturer: IR
Manufacturer Part No: IRFZ44N
Package / Case: TO-220
RoHS: Yes
Datasheet: Click Here

Specifications
Transistor Type: MOSFET
Transistor Polarity: N Channel
Drain Source Voltage, Vds: 55V
Continuous Drain Current, Id: 49A
On Resistance, Rds(on): 17.5mohm
Rds(on) Test Voltage, Vgs: 10V


* Capture.PNG (15.65 KB, 897x620 - viewed 165 times.)
« Last Edit: January 21, 2013, 01:39:06 pm by Hinjeniero » Logged

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