How to Power a 100W LED

How to Power 100W LEDs
How to Power 100W LEDs

I have really become interested in LEDs since they have improved a lot and their price has come down so much and I like to find ways of saving money.  I had seen 100W LEDs available and wanted to buy one and try it out for myself.  I finally got around to it and here is how to power a 100W LED…

100W LED
100W LED Powering a Radiometer

How to Power a 100W LED

Parts Needed:

Tools Needed:

Alternative Things I Use:

  • Radiometer (it was fun to have this thing spinning on the power of the LED light–movement makes things look cooler!)

Step 1: Collect all the components.

I ordered my 100W LED and the DC-DC Boost Converter Power Transformer off of Amazon using the links I share above but all the other parts I had laying around my workshop.  I always save old power supply cords for such a time as this and I had a 12V 2.9A DC power supply that has 2Wire written on it so it must have been from someone’s DSL modem.  I had a big CPU heatsink I had saved from disassembling an old computer, and I used a small 12V fan from a computer I had torn apart some time ago too.  I also had the thermal paste left over from an x-box repair I did a long time ago.  Try to reuse what you can!

Step 2: A Cautionary note about handling a 100W LED.

Do not press on the yellow substrate area–you can destroy the LED.  Also, once we get it turned on, it is going to get hot, so don’t burn yourself and touch the LED surface!

Step 3: Determine the polarity of the LED connections.

The LED has a + and – marking on the top left and bottom right but they don’t help you know which of the two metal tabs on the right and left to connect to though AND the documentation given on Amazon seems to be backwards to me.  On the physical LED there is a positive and negative symbol, but they give you NO CLUE as to which of the two tabs which goes to:

100W LED Up Close-What is the Polarity
Which tab is positive and which is negative?

So I decided to do some checking with my Fluke 177 Multimeter to see what connects to what.  With the multimeter in the diode testing setting, which plays a sound when a short circuit is found, I started checking to see which tab was connected to which side (top or bottom).  What I found was that, when oriented as seen in the pictures above and below, the right tab is connected to the exposed metal plate on the bottom, by the + symbol, so the right tab must be the positive:

100W LED-Checking Connections-Positive Found
Finding the polarity of the LED–Right Tab is Positive

I went ahead and checked the other tab and it was consistent, and the top exposed plate and the left tab are shorted together, so the left tab must be the negative terminal.

100W LED-Checking Connections-Negative Found
Checking the negative terminal too

This is BACKWARDS from what they tell you on Amazon, so beware:

100W LED Amazon Diagram--Polarity WRONG
The Amazon Diagram is labeled WRONG

Step 4: Attach the 100W LED to the heatsink.

This LED cannot be run without a heatsink of some type!  Don’t ruin yours by powering it up without one.

There are four screw holes in the LED, made for mounting it tight but my heatsink didn’t have corresponding holes and I didn’t want to drill holes in it at this point since I’m just messing around.  I’ve seen heat sinks held into place by metal springs and I thought I could hold the LED down on the heatsink with some heavy wire, actually a coat hanger I had laying around that I had used earlier to dig hair out of one of our sink drains.  I bent two M-shaped pieces, except the bottom legs of the M’s bent in to hook onto the heatsink.  This is what they looked like:

100W LED Heatsink Spring Wire Bracket
Bracket I made to hold the LED onto the Heatsink Tightly

I then put thermal compound on the back of the LED.  Thermal compound is critical to make a good thermal connection between the LED and the heatsink.  If you don’t put it on there will actually be an air gap between the two because the surfaces are not perfectly smooth and air doesn’t conduct heat like thermal paste or aluminum does.  Without thermal compound the heatsink will not pull the heat away from the LED effectively.

100W LED With Thermal Compound Applied
Thermal compound applied to back of 100W LED

Then I took my wire brackets and clamped the LED to the heatsink.  I shaped the wires to they are pressing down on the heatsink, so it makes a good thermal connection.

100W LED Held on HeatSink With Wire Brackets
100W LED held onto Heatsink with Coat Hanger Brackets

Step 5: Familiarize yourself with the Step-Up Voltage Regulator

3.5V to 30 V DC Boost Converter Voltage Regulator

Step 6: Connect the LED, cooling fan, and power to the Step-Up Regulator

Solder a wire to the now-known positive and negative terminals of the LED.  I’d encourage you to color code it so you can easily tell which is which.  I used the typical red for positive and black for negative.  What we are going to do, since the cooling fan is 12 Volts and the power supply I’m using to power the Step-Up regulator is 12 Volts as well, I’m going to connect the fan to the same input connections on the Voltage regulator.  The input and output connectors are a little weird on this regulator in that there are pairs of negative inputs and pairs of positive inputs and the same goes for the output.  It works good for powering the fan, because we can connect the fan to one set of inputs and connect the power supply to the other set:

100W LED Boost Converter Fan Schematic
Schematic of How I Wired the 100W LED

I cut the end off the 2Wire power supply and there were three wires: yellow, white, and black.  I used my multimeter to determine which wire was which.  It turns out the yellow was 12 volts, the black negative (of course), and there was no voltage on the yellow–it must be some kind of feedback wire, who knows.

And here’s what it looks like in real life all wired up and ready to go:

100W LED Wired Up and On Heatsink
It’s all ready to go now!

Step 7: Power it up.

I have to confess that when I first powered it up, nothing happened.  The problem was that the output of the step-up regulator was set too low for the LED to come on.  I found that the voltage must be at least 21 volts before any faint appearance of light shows up on the LED:

100W LED First Signs of Light at 21 Volts
The first signs of light came on at 21 Volts

At 25 volts it begins to get bright:

100W LED at 25 Volts
At 25 Volts all the individual LEDs are showing up

At 30 Volts, it is BLINDING:

100W LED at 30 Volts
At 30 Volts it’s really unbearable to look at for long

Step 8: LED Power analysis.

Just out of curiosity I wanted to know how much current the system was using.  The heatsink wasn’t even getting warm so it didn’t seem to me like we really had this LED running at 100 watts.  Just FYI, power is calculated by current times voltage: P = I x V.

The Power supply was pulling 2.1 amps at 12 volts, 25.2W.  I tested it by moving the lead on my multimeter to the 10A connector and putting it in series with one of the wires coming from the power supply.  By “in series” I mean I disconnected the negative leg of the power supply from the regulator and hooked up one multimeter probe up to the negative connection of the voltage regulator input and the other one to the negative on the power supply (which I just disconnected) so the current is passing through the multimeter):

Power Supply Pulling 2.1 Amps at 12 Volts
Power Supply Pulling 2.1 Amps at 12 Volts

With the multimeter in series with the positive connection to the LED I found out that the LED is only pulling 700 mA:

100W LED Drawing 700mA at 30 Volts
The LED was drawing 700mA

What’s happening is that this step-up converter is not capable of supplying the full 100W of power needed by this LED.  The heat sink doesn’t even get warm at only .686 A x 30 V = 20.58 Watts.  I figured out that the power supply was using 25.2 W total, so knowing what we know now we can calculate the actual power being used by the DC Step-Up Regulator: 25.2-20.58=4.62W.  And you can feel the heatsinks on the regulator get warm (where some of the power is going–heat).  Oops, I forgot one thing–the fan.  This isn’t taking into consideration the fan’s power usage.  I put my multimeter in series with one of the fan’s leads and found out it is pulling about 30 mA, or .03 Amps of current.  This means the fan consumes 360 mW of power, not that much, but some, from the 12V power supply we have, that only is capable of 25.2W.

We need a power supply that is capable of more amps.  This makes sense because the power supply I was powering this system with is rated at 12 volts at 2.9 Amps, this is only 12*2.9=34.8 Watts.  You can’t get 100 watts out of a system when you are only putting in 34.8 Watts and the step-up converter is getting hot, i.e. wasting 4.62W of power in the step-up process.

Lessons Learned

A Fan is CRITICAL on the heatsink (if you use one similar to the one I used)

I kept feeling the heatsink and it hardly gets warm at all so I began to think that the fan may be unnecessary.  To test out my theory I disconnected one of the leads on my fan and let it go fanless.  I should have watched it closer because I forgot about it and went about my business and when I went to check and feel the heatsink, it was SUPER HOT to the touch.  I quickly turned on the fan and got it cool again.  I cannot see that I damaged the LED but that would not be good to let it go for long.

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    • Glad to be able to help. If you take pictures of all the steps, take notes of what worked, what didn’t, and how you were able to work around the issues then we could add an article to showcase what you built. That’s why I named this site Share Your Repair! If you do, please let me know: Contact Me

  • Thank you for the quick response and yes it does answer the portion on the power source from the vehicle.

    I would like to confirm the step-up converter you suggested is capable of reaching 100 watts as well.

  • If I were to get my power supply from a running vehicle (12 volt system) to include the alternator output (13-14 volts) would this give me the power I need to get to 100watts? My purpose for using the vehicle power is a powerful light for roadside repairs.

    When you stated “What’s happening is that this step-up converter is not capable of supplying the full 100W of power needed by this LED.” was this because of the power supply or the step-up converter? I think you explained it later (still a little fuzzy to me) in the power supply portion. I just don’t want to buy the wrong step-up. Nice article by the way.

    • Thanks for the question. Power (measured in watts) equals current (measured in amps) times voltage (measured in volts) or as P=I*V. You can re-arrange the equation however you like with algebra and calculate the current required to supply 100 watts at 12 volts: I=P/V or I=100/12 and therefore I=8.33 amps. Now any car battery will be able to provide 8 amps because a starter for a 6-cylinder gas engine is in the 200 amp range. Albeit, you don’t run your starter for long. So, if your vehicle is running, you should be able to power a 100 watt LED long-term because it only pulls around 8 amps. If you power a 100-watt LED on a battery without the vehicle running (and the alternator recharging the battery) you will drain the battery. You could theoretically calculate how long using the amp-hour rating of the battery. You Does that answer your question?

  • Hello John ~

    Thanx For Sharing This … I’ve been interested as well in putting together something with one of these 100 watt LED’z for quite some time, but i know even much much less about these things than you by far …. so this was very helpful for me …
    Quick question for ya;
    Being that your unit was only running on 34.8 watts, or was it 24.8 watts? You kinda confused me on that last paragraph … however, if i were to gather materials for this project, would i instead want to acquire a power supply that is rated more like 12volts 8amps? … would a 12volt 10amp power supply burn out the LED or something due to it being over 100 watts?
    I’d love to know these things and whatever else you could possibly add to help maximize the potential of my unit … also i was hoping to build it into a mega flashlight of sorts so if i should do anything different because of that, i’d love to know as well ~

    Thanx again John >


    JeSse BLakTi

    • Jesse, thanks for the comment. Yes, you are right–that was confusing because I had a typo in that article. Both numbers should be the same, 34.8 watts and I have now corrected the article. Thank you for pointing that out. Yes, the power source you use must be capable of sourcing 100 W in order to get 100 W out of the LED. The power supply must be able to put out the optimum voltage for the LED and the current to make the power be 100 watts where Power = current x voltage. There are many tutorials out there on youtube where people are showing their 100W LED flashlight builds. I haven’t been able to find a good real-life practical application for my LED yet honestly. In regard to a flashlight, you need the battery power to source the power supply and 100 W will burn up a bunch of batteries fast. Thanks for commenting, John.

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