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70W COB LED lamps

Is this power supply suitable for powering these chip on board (COB) LEDs?

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I have an LED project using 100 Citizen CLU048-1212C4 LEDs.

I need to run each LED at 70W, and I want to run every 5 LEDs on 1 power supply.

I was thinking of using the MEAN WELL LSR-350-35 (it takes a long time to show PDF)

Video review of the power supply.

This screenshot is from the LED datasheet

enter image description here

I saw in the power supply datasheet:

INPUT Voltage Range : 90 ~ 132VAC / 180 ~ 264VAC by switch 240 ~ 370VDC (switch on 230VAC)

This screenshot is from the power supply datasheet

enter image description here

Where I live, the electrical power 220V and 50Hz.

I think if I connect the LEDs parallel it’ll be good because the current of the power supply (9.7A) will be divided on the LEDs count so every LED will take 9.7A/5 = 1.94A for each LED DC voltage 36V.

I think that means 1.94*36=69.84W ~ 70W (automatically.)

  • Is that power supply good for this project?

I feel confused from this screenshot from the LED datasheet.

I think I need to drive the LEDs at ~38V to reach 1.9A, I’m not sure about that.

This screenshot is from the from the LED datasheet

enter image description here

ledparallelled-drivercobShareCiteEditFollowFlagedited 21 hours agoJRE47.3k88 gold badges7474 silver badges128128 bronze badgesasked yesterdayYousef JO2711 bronze badge New contributor

  • 1Please note that you can’t directly connect bare LEDs to a power supply. Or at least not to a constant voltage power supply. Or you can, but most likely you would not be happy about the results. You are missing a key component between the power supply and LEDs, and that’s called a LED driver. – Justme yesterday
  • @YousefJO: Do you really need to build the lights yourself? Unless the LEDs you have chosen are special in some way (particular color temperature or something,) it would probably be cheaper to buy 100 LED lamps rated for 70 watts. You can order complete 70 watt lamps (with housing, heat sink, and power supply) for what just one of your planned LEDs would cost. – JRE 23 hours ago 
  • That power supply is inappropriate for your lights. You need constant current. Constant voltage will just blow up your lights. – user1850479 22 hours ago
  • 1@tlfong01: I think you changed the point of the question with your edit. You’ve made it specifically about the current/voltage curve, but the only question that the text directly asks is whether the power supply is a good match for the project. – JRE 22 hours ago
  • @JRE, My apologies for making an edit that miss the important question of whether the OP’s PSU is good for his application. Which PSU to use is a bit complicated. Perhaps I should add an answer later. I am happy that you edit it again to highlight the more important question. Thanks for pointing out my carelessly misleading edit. Cheees. – tlfong01 22 hours ago   
  • 1@tlfong01: Should I change the title to match the text? All I did before was to fix the capitalization and punctuation on your edit. – JRE 22 hours ago
  • @JRE, yes, please go head and edit it again. That is what I just suggested. Cheers. – tlfong01 21 hours ago   
  • @JRE I have also given an update, at the beginning of my answer, on why I cannot decide which PSU, 110/220AC, or 24~48VDC is good for the OP. Ah bed time. See you tomorrow. Cheers. – tlfong01 21 hours ago   
  • 1At 1.9A per LED, you’d probably need to consider some active cooling options as well. Will that be powered by the same PSUs? – Mast 19 hours ago 
  • @JRE the markup on LED lights compared to COBs and heatsinks, particularly for ahem horticultural lighting is huge. I’d go with CREE CXB3590s myself though. – K H 2 hours ago

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3 Answers

ActiveOldestVotes6

7000W of LEDs? Are you lighting a stadium?

Well, since this project will make you blind, it wouldn’t be complete without the risk of electrocution, so let’s wire the LEDs in series.

As you noticed, the voltage across your COBs varies with current (and also temperature, and between each COB). So you can’t drive them with a constant voltage supply, it has to be constant current. You can, perhaps, parallel them, if they are well matched, but that’s pretty hazardous because when one COB fails open, then the driver will send the whole current to the others, so they will also fail in cascade.

So you want to run the COBs at around 2 amps, let’s look for a constant current driver that will do that…

Meanwell ELG-240-C2100 looks like it, it can output 120V 2A so it will power 3 COBs in series.

There are of course many more options regarding output voltage: higher means more COBs in series, and more dangerous.ShareCiteEditFollowFlaganswered yesterdaybobflux43.3k33 gold badges5656 silver badges127127 bronze badgesAdd a comment3

The MEAN WELL LSR-350-36 (there is no LSR-250-35) is not a good match for your project.

  • LEDs need a regulated current to operate properly. The LSR-350-36 is a constant voltage power supply.
  • You can approximate a constant current power supply from a constant voltage power supply, but that requires resistors in series with the LEDs and a voltage source several volts higher than the LED forward voltage.
  • LEDs in parallel without balancing the current is not a good idea. The simplest way is to put a resistor in series with each LED. Without the resistors, the current will go to whichever LED has the lowest forward voltage. It will get all of the available current and burn out. Then the LED with the next higher forward voltage gets all the current and burns out. Repeat until all LEDs are dead. All your LEDs have the same rated forward voltage, but real LEDs are never identical.
  • The 36V output voltage of the LSR-350-36 is too close to the LED forward voltage for it to be used with current limiting resistors.

Resistors waste power as heat, but they are the simplest way to limit the current.

If you can use the LSR-350-48 (48 V output voltage,) then you could do this:

schematic

simulate this circuit – Schematic created using CircuitLab

The way that works is like this:

  1. IfIf = 1.8A (forward current of the LEDs.)
  2. VfVf = 38V (forward voltage of the LEDs at 1.8A from the datasheet chart.)
  3. PLEDPLED = If×Vf=68.4WIf×Vf=68.4W (power to each LED.)
  4. R=Vpowersupply−VfIf=5.4ohmsR=Vpowersupply−VfIf=5.4ohms (series resistor value. Use 5.6 ohm because it is a standard value.)
  5. PR=(Vpowersupply−Vf)×If=18WPR=(Vpowersupply−Vf)×If=18W (18 watts wasted in each resistor.)
  6. Ptotal=4×(PR+PLED)=4×86.4W=345WPtotal=4×(PR+PLED)=4×86.4W=345W (total power consumed is just under the rated 350W for the LSR-350-48.)

The resistors limit the current to about 1.8A. The resistors also balance the current between the LEDs – no one LED can take up more of the current than it is supposed to.

The resistors (in total) also waste as much power as one LED would consume.

That is not efficient, but it is simple. Each of the resistors will waste 18 watts of power as heat – you need big power resistors to make it work.

That wasted power is the reason you should use proper drivers for each LED. Scaled up to your target 100 LEDs, that would be 1800 watts of wasted power.

Total power is something you need to consider, anyway. 100 LEDs at 70 watts each is 7000 watts of power. The outlets where you are can probably supply a bit over 3000 watts each. You’ll need to get power from outlets on separate circuits in your house in order to properly drive all those LEDs without causing a circuit breaker to trip.


Given the size of the project and the cost of the LEDs (I figure close to $3000 just for the LEDs,) and the complexity of building power supplies, I’d suggest you look into purchasing proper constant current power supplies rather than trying to bodge things together.

Mean Well makes many other power supplies that would be better suited for your project.

The simplest (though maybe not the cheapest) solution would be to use individual 75 watt power supplies for each LED. You can adjust them to get the proper power output for your LEDs.

The ELG-85-42 would be the correct model. It will put out 1.8A of current at up to 42V. The voltage is determined by the current – it won’t destroy your LEDs.

The downside is that each power supply costs as much as the LED it drives. The upside is that your LEDs will operate properly and won’t waste a lot of power.


You’ve picked a very large project to start with. 7000 watts is a serious amount of power.

  • You can buy components and get on with reaching the goals of your project, but it will cost you financially and you won’t learn much about the basics of LEDs.
  • You can try to build your own power supplies to save money, but I think you will in the end spend more to replace damaged LEDs and power supply parts than you will save – and it will delay your project while you are learning.

No matter how you power your LEDs, keep in mind that each of them is going to need a heat sink to keep it cool.

This is a 100 watt LED work light that I use around the house:

enter image description here
enter image description here

The housing is basically one enormous heat sink. It is made of aluminum, with the LEDs solidly attached to the back plate to carry off the waste heat from the LEDs.

Your 70W LEDs will require a large heatsink. Not quite as large as on my 100W light, but not small at all.ShareCiteEditFollowFlagedited 22 hours agoanswered yesterdayJRE47.3k88 gold badges7474 silver badges128128 bronze badgesAdd a comment1

Update 2021apr14hkt2008

The OP has not yet given a user requirement of the venue for the 100 sets of COB LEDs, each set of 70W. This is easy to do, as we can easily find 12~24VDC 70W LED lamps. The following is an example.

AliExpress 70W DC 12V Dimmable COB LED Light with Controller Strip Board Outdoor Camping Lights DIY Fishing Rod – US$10 ~ 12


70W LED

Notes

  1. If the OP has a very large camp site, we just get as many as 100 such 70W COB LEDs.
  2. We can use 12V car batteries for outdoor, and 12V bench PSU indoor.

Update 2021apr13hkt2221

I confess I have not answered the OP’s question of whether his suggested PSU is good. Below is my reason.

There are three options for the OP:

(a) 110VAC/220VAC power LED lamp, say 70W, or 35W x 2, if 70W is not available. This is quick and dirty, but perhaps also a clean solution, as the OP is going to make as many as 100 sets for his project. 

(b) 110VAC/220VAC LED driver, eg Meanwell ELG-240-C2100, as suggested by #bobflux. This gives some flexibility of the COB LED configuration.

(c) 220V to 36VDC~48VDC PSU. I am not sure if the OP prefers low voltage PSU. I prefer low voltage PSU because I doing smart home light project, and I want to choose my CCS (PT4115E) for which I can fine tune the dimming/fade in/out to 1/5000 resolution.

Each of the above three options has its pros and cons. Perhaps the OP can tell us more of his requirements, and we can give more suggestions.


1. About COB LEDs’ V-I Characteristics

Well you LED module is COB (Chip On Board), which means the many LEDs are serially squeezed within one module. You might like to read this tutorial The Basics of Chip on Board (COB) LEDs – Rich Miron, Digi-Key Electronics 2016aug03 for more details.

Usually one LED taking 1A has a voltage of approx 3V. So your module has approx 36V at 1A, implies there are 12 LEDs in series inside the module.


2. About COB LED’s input voltage

You might like to read my answer to the following Q&A:

What’s the voltage used to power LEDs inside an LED light bulb? Asked 2 months ago Active 2 months ago Viewed 170 times

My answer explains that special AC mains to DC conversion uses the “Capacitive Dropper” accepts AC input in a range of 185 to 150VAC, like many smart phone chargers accepting 110VAC or 230VAC.


Update 2021apr13hkt2018

3. Using a CCS (Constant Current Source)

You are asking two questions, one on AC mains input. which I said it can be a wide range.

You other question is related to the DC voltage of the COB LED module (about 30V DC for a series of 12 LEDs at 1A).

Suppose now you want to use a DC voltage source to power the LED module of 12 LEDs, the standard trick is to use a CCS (Constant Current Source) of 1A, and the voltage source can be, a couple of Volts higher than 30V, perhaps 36V to even 48V. This is a bit confusing. You might like to get a rough idea by reading my answer to the following Q&A on how to use a CCS:

How can Rpi Python PWM GPIO pins control and dim LED strips of 1W 350mA?

This is also a good newbie friendly tutorial on power LED.

1W LED Tutorial (On why use a CCS) – Components 101


ShareCiteEditDeleteFlagedited 4 mins agoanswered yesterdaytlfong011,77811 gold badge66 silver badges1212 bronze badgesAdd a comment

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