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DiY LEDs - How to Power Them

Discussion in 'LED and other Lighting' started by SupraSPL, Feb 22, 2014.

  1.  
    SupraSPL

    SupraSPL Well-Known Member

    There are many ways to design a DIY LED but here are the details of the wiring for constant current drivers. If you have no experience working with 120V wiring you should understand that it can be dangerous under certain conditions and you should study and gain a thorough understanding of the dangers before attempting your project or ask for help from an electrician. The most obvious thing is never work on live wires. Once your build is complete, a GFCI can help protect you from electrical shock in our wet growing environments and are available for $7 on eBay. Check your AC circuit for hot spots which is a sign of an overloaded circuit or a poor connection. This can occur in timers and in the connections of extension cords.
    ==================================
    Recommended tools:
    Multimeter with 10A current measuring capability
    Power meter - KillAWatt or EnSupra (no affiliation)
    Wire stripper
    Wire crimper
    Slide Connectors
    Heat Shrink Tubing

    =========
    The AC side

    The AC power input has a hot and a neutral. This is important when wiring an LED driver. If you mix them up, the LEDs can glow a bit during lights out because the timer will cut the neutral instead of the hot and the LEDs may respond to ghost voltages and emf. In most homes the smaller side of the outlet is the hot wire (black) and the larger side is the neutral (white) so it is helpful to use a power cord that forces the plug into the correct polarity. If you install a switch make sure you switch the hot wire or use a double pole single throw switch. The driver should have labeling so you know which is the hot (Line) and which is the neutral. You can make the AC connections using molex connectors although that can get prohibitively expensive if you are making dozens or even hundreds of connections.

    =========
    The DC side

    -Do not apply AC power to a driver that is not connected to an LED string
    -Do not switch an LED driver on its DC side, but rather on the hot wire of the AC side.

    -Constant current circuits operate with the LEDs connected in series.
    -On the DC side of the driver there is a positive and a negative wire. Red is the positive and black or white is the negative.
    -The negative wire of the driver goes to the negative side of the LED. (I find this unintuitive in a series connection)
    -The positive of an led connects to the negative of the next LED in the series until the whole circuit makes a loop.
    -If wired backward the circuit will not function and there is a possibility of damaging the LEDs.

    -The driver will have a certain voltage range that it can operate within and this range may not be printed on the driver.
    -The efficiency of the driver will vary depending the voltage of the LED string.
    -To estimate the total voltage of the string, add the total vF or each LED in the string. If the voltage is of the LED string is too low the driver may flash. If it is too high the driver may flash or it may drastically reduce its current output.
    -Each LED will operate it its own voltage but they will all operate at the exact same current.
    -As each LED warms up its voltage will drop slightly.
    -If you decrease the voltage load on the driver, its current output will rise and vice versa.
    -As the driver warms up its current will drop (unless regulated). LED drivers are typically 75-90% efficient so they will heat up as they operate.
    -As the current drops the LED voltage will drop slightly.
    -Each driver may operate at a slightly different current +/-5% even if they are the same model.
    -Adding a fuse that is lower than the maximum current of the LEDs may help protect the LED string in the event of a driver malfunction.
    -It is critical that all connections and soldering points are secure. Flickering or arcing in the circuit can damage the driver or worse can destroy the entire LED string.

    DSC06859a.jpg

    For the DC connections you can use molex, wire nuts (not recommended), splices, closed end crimp ons or you can solder the connections and heat shrink them. In my case I use .25" bare (non insulated) crimp on slide connectors (quick disconnects) and once I have verified that the connection is very solid, I cover with heat shrink tubing leaving no metal exposed. They are cheap, secure, force the correct polarity, can be color coded and it makes your drivers and LED strings easily swappable.

    LED Driver wiring.jpg

    ==========================
    Choosing a Driver - Drive Current

    LEDs suffer from current droop which means that the harder you run them (higher current), they dissipate more power but become significantly less efficient. They also suffer from temperature droop. As the temperature rises they become less efficient and if run hot they will suffer significant lumen depreciation over time. Because we use our lights for long hours each day, efficiency becomes an even more important factor. Therefore it is recommended to run LEDs relatively soft and use more of them. This increases the up front cost for the LEDs but decreases the cost of drivers, heatsinks and electricity. The value point will vary depending on electrical costs and keep in mind that we expect LEDs to continue to improve in the coming years.

    =========================
    Testing the String - Do this when the driver and heatsink are already warmed up and stabilized.

    Once your driver and LED string is wired it is recommended that you verify the current (amperage) of the string. Very occasionally drivers malfunction and drive at a much lower or much higher current than specified. To check current your multimeter must be in series with the LED string (anywhere in the string on the DC side). Make sure your multimeter probes are plugged into the correct slot for testing current (amps). Make sure you do not apply power to the driver until the multimeter connections are secure in the LED string (slide connectors are helpful here). Record this number (example 700mA = .7A)

    If you are curious about the efficiency of the driver, connect your multimeter in parallel in the LED string to measure voltage. The voltage measurement has to be taken from before the first LED and after the last LED in the string. The easiest place to do this is at the DC side driver connections. Make sure to move your test leads to the correct slots on your multimeter for measuring voltage or else you will short circuit the string. (Yes I have done this).

    Once you have your volts and amps you can calculate dissipation wattage of the string. It is very simple volts X amps = watts. Next check your input wattage from the KillAWatt or EnSupra. Now divide your dissipation wattage by your input wattage and you get the driver efficiency percentage. Keep in mind that if you measure input wattage while your multimeter is in series with the string you will get a slightly incorrect figure. My multimeter adds .2-.3W.
     
  2.  
    SupraSPL

    SupraSPL Well-Known Member

    Recommended tools/supplies

    -Lead solder 63/37 or 60/40 thin wire $9
    -60W soldering iron $8
    -Flux Gel/Paste MG $10
    -Brass wool/stand $8

    Most of this stuff can be found on Amazon or eBay. I like lead solder because it is easier to work with and easier on the LEDs. Just make sure you wash your hands after handling lead solder. Please solder under a ventilated hood or do it outdoors. The 60W iron is an aggressive amount of heat. This should allow you to work very quickly even on a large heatsink, but be careful not to linger with the iron it will melt wire jackets and unseat solder pads. If it is taking too long to melt the solder just clean the tip and it should melt instantly. This is the method I have developed but there are other ways to solder, please share yours!

    -Warm up soldering iron
    -Strip wire
    -Apply flux gel to wire
    -Apply flux gel to the solder pad on the LED
    -Clean iron tip on brass sponge
    -Apply a few dabs of solder to the tip of the iron
    -Tin the wire by touching the tip of the iron to the wire, the solder will migrate from the tip to the wire
    -Make sure the wire is thoroughly tinned but don't melt the jacket
    -Apply more solder to the tip of iron
    -Tin the solder pad on the LED by touching the iron to the solder pad (careful not to touch the LED dome with the iron)
    -Place the tinned wire in contact with the tinned solder pad
    -Touch the solder pad and or tinned wire with the iron
    -As soon as the solder becomes liquid and the wire sinks into the pad pull the iron away
    -Make sure no part of the wire is shorting to the LED star or the heatsink
    -You are done!
     
  3.  
    Abiqua

    Abiqua Well-Known Member

    Excellent post! Great work.

    I was actually working 2nite on coming up with a new light design for myself. I came over to the forums, to scope those drivers you are running as of most recently. Read this first, everyone should read it :peace:

    P.s.

    Have one about heatsinks? I have a few questions, but don't want to litter up this thread....ciao.
     
    salmonetin likes this.
  4.  
    Abiqua

    Abiqua Well-Known Member

    Pro and con's of using switching power supplies and drivers versus just powered drivers?
     
    salmonetin likes this.
  5.  
    SupraSPL

    SupraSPL Well-Known Member

    Junction Temperature
    ================
    The junction temp (Tj) is an important factor in LED design. Modern Cree LEDs are typically measured with a Tj of 85C, which might make sense in a flashlight or automotive application. Because we run our lamps for long hours each day I recommend aiming for a Tj 50C or lower. At 50C most LEDs enjoy a 6% efficiency bonus that translates directly to more buds/W. Tj is based on how many watts are being dissipated in the LED, the thermal path, heatsink surface area, ambient temp and air movement.


    Passive Cooling
    ==================
    The advantages of passive cooling are simplicity, reliability and efficiency.
    IMG_0041a.jpg

    Depending on the efficiency of the LEDs and the ambient temperature, 110sq cm/watt should be enough surface area to get a Tj of 50C or lower. The price of quality extruded aluminum heatsinks has been rising so active cooling is becoming more attractive. Passive cooling still has a place in cloning and vegging lamps where the LED power needs to be spread out more and small fans would consume more power than the LEDs themselves.
    DSC06960a.jpg


    Active Cooling
    ===========
    Now that COB LEDs have arrived we can pack on a lot of power quickly, easily and cheaply. This can allow us to achieve light intensity greater than 1000W HPS and we can scale that down to micro grows. Active cooling is surprisingly efficient for this task. This example is a standard CPU heatsink with a small 60mm 12V fan attached. At 1A the Cree CXA3070 COB dissipates 37W and achieved a TJ of 44C with only .4W of fan power. The fan should blow air into the heatsink.
    IMG_0184a.jpg

    In this example (4) CXA3070s are dissipating a total of 100W and using only .5W of fan power achieved a Tj of 37C. Without the fan Tj was 76C.
    IMG_0169a.jpg


    Powering the Fans
    ============
    Fan size and fan speed will depend on the size and shape of the heatsink and how much difference there is between the heatsink and ambient temperature. Large fans are very quiet at 5V and consume very little power. You can use old cell phone chargers, printer adapters or small computer power supplies. Unfortunately most of the these adapters are only 50% efficient but there are some switching power supplies available that are 80% or better.

    Heatsinks are Not Flat
    ==============
    Unfortunately aluminum heatsinks and LED stars need significant work in order to achieve significant metal to metal contact. Thermal paste can fill this gap but the question is how much does this affect Tj in practice? Testing is in order here because flattening the heatsinks and stars is a lot of work especially in a large build.
    DSC06848a.jpg DSC06557a.JPG
     
  6.  
    Abiqua

    Abiqua Well-Known Member

    Simple ways to find needed surface area and fan size for both methods actually.....?
     
  7.  
    Mellodrama

    Mellodrama Well-Known Member

    Thanks very much for taking the time to distill so much of the info from your previous threads into one short read. This is very awesome. I'm gonna print it out so I can refer to it at the bench.
     
  8.  
    WDIK

    WDIK Active Member

    Great info as always Supra.
     
  9.  
    PetFlora

    PetFlora Well-Known Member

    Supra, sorry for the jack, seems you would be a proper source to answer my Q


    I ordered 2 multi-chip/Reflector lights said to be 75w, but the specs say 48w +/-

    I imagine they are driving them low, hence the differential

    Thinking at some point to pop the OEM chip and replace with either cob ,or better multichip

    Any thoughts/411 is appreciated

    Here's the link


    http://www.ebay.com/itm/Reflector-C...1524750?pt=US_Hydroponics&hash=item2c7599098e
     
  10.  
    Mellodrama

    Mellodrama Well-Known Member

    Pet, you don't even have them in your hands and you're contemplating dismemberment? What about that 3 year warranty? ;)
     
  11.  
    midgetaus

    midgetaus Member

    Would the fan you have in your grow tent not be enough to cool the heatsinks down...
     
    Levradus likes this.
  12.  
    Gaius

    Gaius Active Member

    This thread should be stickied.
     
    fearnoevil, PerroVerde and salmonetin like this.
  13.  
    WDIK

    WDIK Active Member

    like_share.jpg

    I've learned more in just this "LED and other Lighting" section than I have on any other forum. I love this kind of thing. :)
     
    Kjudah420 and Ronin-indi like this.
  14.  
    wyteberrywidow

    wyteberrywidow Global

    Please threads that the community finds informative and should be stickied bring them to a mods attention. If it's worth it it will get stickied.
     
    Path of Light and salmonetin like this.
  15.  
    WDIK

    WDIK Active Member

    Haha. That didn't take long.

    Congrats on the "sticky" Supra. Well deserved.
     
  16.  
    Gaius

    Gaius Active Member

    Thank for the fast response Wyte!
     
    salmonetin and wyteberrywidow like this.
  17.  
    PetFlora

    PetFlora Well-Known Member

    Well, in this case, they are so simple that they lend themselves to a COB/MC upgrade. Might require upgrading driver, too, but again cheap enough

    Not planning on doing it for first go round


     
  18.  
    Gaius

    Gaius Active Member

    I think Supra is working on a grounding and fuse tutorial. Stay tuned. I'm interested to hear about it too.
     
    salmonetin likes this.
  19.  
    SupraSPL

    SupraSPL Well-Known Member

    Petflora, replacing the chip might work well if the driver can provide the correct vF range and if the current output is at the level you want it. Do you have the tools to test the voltage, current and driver efficiency?

    Mello, the diagram is a great idea. I sketched one up in paint and updated the thread, switched the AC and DC side.

    Gaius most drivers have over voltage and over temp protection, but a fuse is a great idea on the DC side. I will update the thread with some fuse info. As far as grounding, it is a good idea to carry it as far into the circuit as you can. For example if you are using an extension cord make sure to use a heavy duty grounded one.
     
  20.  
    Gaius

    Gaius Active Member

    Makes sense. I'm going to wire the ground cable to one of the metal sliders, then run small wires from that first slider to each of the other 3. Should help prevent accidental shock. Fuse should be easy to add to the line side.
     
    salmonetin likes this.

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