LED Lightoard Assembly Guidelines
LED Lightboard Rev.2 Assembly Guidelines
(LED Lightboard ordering info here)
There are many different ways you can connect LEDs using the Lightboard. The simplest is probably to connect them in groups of four so that each group has an accompanying current limiting resistor. For each group you choose to connect, insert a resistor and four LEDs as shown below. There is space for ten groups of four LEDs on each Lightboard.
LED Alignment: The LEDs have a round footprint with a flattened face on one side. Align the LEDS so that the flattened side matches with the pattern printed on the board. You will also note that the lead closest to the flattened face is shorter than the other. This lead represents the cathode, or negative terminal of the LED.
Current Limiting Resistor Choice: The purpose of the resistor is to keep the current going through the string of four LEDs from exceeding the maximum allowed in the LED specifications. Many ultra bright LEDs have a recommended forward current rating of 20-30 ma (or .020 to 030 amps). Finding the optimum resistance value that will permit only this much current to flow through the LEDs requires a little calculating mixed with a little guesswork. First obtain a few pieces of information from the LED spec sheet. You also need to know the total voltage supplied by your power supply.
LED Forward Voltage (Vf) = ______ volts
Total LED Forward Voltage (Vt) = Vf x # of LEDs in the string =________ volts
Supply Voltage (Vs) = ________ volts
LED Forward Current (If) = ________ amps (NOTE: 30 ma = .030 AMPS!)
Do a Google search for "LED resistor calculator" or something similar to find an online calculator that will help you compute allowable resistance values. If you must do the calculations yourself, use Ohm's law to calculate the needed resistance value for your current limiting resistor:
Resistance = (Vs-Vt)/If = ___________ ohms
Here is an example for a string of four LEDs in series, LED forward voltage is 3.2 volts, forward current is 20ma, and power supply voltage is 13 volts:
Vt = 4 x 3.2 =12.8 Vs = 13 If = .020
Resistance = (13 - 12.8)/.020 = 10 ohms
In reality these calculations always seem to be off a little bit because the ratings used in the calculations don't match your LEDs exactly, nor will a resistor exactly match its rated value. If you use the onboard adjustable voltage regulator, you can use a ballpark figure for the limit resistor and adjust the regulator voltage. This has the effect of raising or lowering current, adjusting it so it does not exceed the maximum allowed.
If you use the onboard supply to provide a nominal 12 volts to four LEDs in series, a 10 ohm resistor is a reasonable guesstimate. You can always experiment and optimize values by building the circuit on a solderless breadboard first.
For your reference, here for the specifications of the LEDs supplied in the optional LED kits:
LED Specifications (provided by supplier)
| Absolute Maximum Ratings | Forward Voltage (V) | mcd (If @ 20 mA) | ||||
| Dissipation (MW) | Forward Current If (mA) | Peak Current I(mA) | Min | Typ | Max | Min |
| 100 | 30 | 100 | 2.8 | 3.5 | 4.0 | 14000 |
Powering the LED Lightboard: You may supply power to the LEDs in one of two ways. Either use your own external regulated DC power supply, attaching the positive (at top) and negative leads (black at bottom) as shown in figure A.
Figure A. External Power Connections
Note that the polarity is printed on the board. Note also there are corresponding holes on both the right and left sides of the board. Choose the most convenient. You may use the extra holes to extend power to additional boards that are daisy chained together. Select an external supply that can provide adequate voltage and current capacity for your needs.
Alternatively, put the adjustable regulator circuit right on the board. Solder the components shown in Figure B. Component locations are printed on the board:
Figure B. Onboard Regulator
From top to bottom: MIC 29152 Regulator Chip, 50Kohm trimmer pot, 22uf capacitor, 10uf capacitor. + input voltage (red lead), - input voltage (black lead).
Orient the capacitors so as to observe the correct polarity. The locations of the positive leads are printed on the board. Carefully locate the two holes, near the capacitors, used to supply unregulated DC voltage and solder input lead wires. The polarity is not printed on the board so be sure to match the polarity shown in Fig. B. Before you apply power, turn the trimmer potentiometer fully counterclockwise.
Adjusting Supply Voltage: When LEDs fail it is almost always because they were driven too hard. For long life, it is crucial to make sure you do not exceed the LEDs' forward current rating. You can measure the current flowing through the LEDs by measuring the voltage drop across one of the resistors and then applying ohms law. Current in amps equals voltage drop divided by resistance. Let's say you have a 10 ohm resistor and you want to restrict the current to not more than 25ma (.025 amps). If you're using the onboard regulator, start with the trimmer pot turned fully counter clockwise. With power applied, measure the voltage across one of the resistors as you slowly turn the trimmer clockwise. You will observe an increasing voltage. Stop when the voltage reaches .25 volts (because .025amps = .25 volts / 10 ohms) Got it? Another way to look at it is the desired voltage drop equals the maximum current (.025 amps) times the resistance (10 ohms). The voltage drop therefore, is .25 volts.
Connecting LED Lightboards Together: Consider chaining two or more LED Lightboards together to achieve truly brilliant lighting. It's easy to do. If you use an external power supply, just wire the positive terminal of one board to a positive terminal of the next in the chain. Connect the negative terminals in the same way. You will need to insure that your power supply is capable of handling the current of all the Lightboards. As a conservative estimate, figure that each board, fully populated with LEDs will need about 400 ma.
If you use the onboard regulator, you can put the regulator circuit on one Light board and then power 2-3 additional boards, depending on current, that do not have regulators. A 12 volt dc wall transformer is an adequate source of unregulated dc voltage. These transformers are sometimes called "wall warts" and have a bad reputation for consuming large amounts of electricity because they are left plugged in all the time. Putting a switch somewhere in the ac line so the transformer can be turned off eliminates this waste.
The MIC29152 is capable of handling 1.5 amps. It has several features that make it a very cool regulator. Literally. It is extremely efficient and has very low dropout so you can supply it with voltage just slightly higher than the regulated output. This means there will be very little heat to dissipate. The chip has built-in protection for over current and over voltage conditions, including reversed polarity. It's virtually impossible to blow out this chip.
Endnote About Soldering
Assembly requires soldering components to the board.
- Use a low wattage soldering iron (20 watts or so). Make sure it has a nice long tip.
- Plug the iron in and let it get good and hot. Melt a little rosin core solder on the tip. If it is dirty and oxidized, wipe it on a damp sponge to give it a shine.
- Insert several of the components you wish to solder. Bend the leads a little to hold them in place.
- Rest the tip of the soldering iron so it touches the pad on the printed circuit board and the lead of the component coming up through the hole.
- At the same time with your other hand touch the end of the solder wire to the heating metal.
- Let the solder melt and flow around the contacts before you remove the soldering iron and move to the next joint. 2 to 5 seconds of contact with the hot soldering iron is ok. If it's longer you run the risk of damaging the component.
- When the solder is cool remove excess leads with side nippers.
I hope you find the LED Lightboard to be useful in your highly efficient energy saving LED lighting projects. Please keep me informed of your successes. If you have questions or need more LED Lightboards or components, please do not hesitate to send me an email .
Thank you,
Tom Woods
Parts and Kits For Sale (prices include first class postage!)
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Tom WoodsP.O. Box 64Jefferson, NH 03583 U.S.A.
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Tom,
Got my Hong Kong LEDs today and built up one of your boards. Pretty nifty! I just adjusted the regulator by feel, just a touch brighter than where I could see the LEDs get dimmer. Your current estimates seem really high. I got 45ma total with a conservative pot adjustment and 160ma wide open. That's nowhere near 400ma that you mentioned. Do you know offhand what my current across the 10 ohm resitor should be for these 2000mcd LEDs? My battery is about 12.75V. I suppose I could go look up the specs and calculate but I might as well try and be lazy. Anyway, I left the light going at my shop on a 12AH recargeable Lead acid battery. I'm tempted to leave it for a month or so and see how long it will run
Still haven't decided how to use these yet but at those current ratings, they sure do make a lot of light! I've got some chipped solar cells and was thinking I could make the mother of all garden lights with this battery, the LED lightboard and about 20W of broken solar cells!
Take care,
Bob
Bob W
Bob, 20 watts of LEDs would would make one big garden light. It's more like
a street light, I'd say! Don't blind yourself!
I was making a very conservative estimate when I said that current consumption of a fully populated board would be 400ma. I doubled a more realistic figure of 200ma to allow for users who push the envelope. If your LEDs have a forward current of 20ma then you should adjust the voltage regulator until you observe a voltage drop of 0.2 volts across a 10 ohm resistor. This would equate to a total current consumption by 10 LED/resistor strings of 200ma. The low current consumption you observe even when the regulator is "wide open" may be due to your feeding the regulator 12.75v. Try running it on a slightly higher voltage and see how it changes the board's behavior. Total consumption of 160ma is a good "safe" figure. You could probably go a little higher if you want, but it is at the risk of shorter LED life. --Tom
Anyone's input much appreciated. I'm obsessed with air-conditioning my
camping tent. Don't laugh until youve spent 3 summer days/nights at East
Cape Sable (southern most point on the continental U.S. in the Everglades
National park. Plan to purchase Panasonic window unit. draws 480 watts
continuous, surge? not sure. Have Small gas 2 cycle generator 500 watts
max continuos 1000 watt surge. But I plan to use it to charge deep cycle
125 amp/hr battery that will in turn power the air unit via a(plan to
purchase) 1000 watt rated continuos power inverter (2000 watt max.) Any
other configs or suggestions welcomed. Limited by boat size (the only way
to get there) and weight. Thanks! any idea how long the battery will run
the air conditioner @ 480 watt load? thru a power inverter? Math wasnt my
strongest subject. Thanks again.
Paul,
Thanks for noticing that your question is not on topic, but that's
ok. I can delete it after others who wish to respond have a chance to do
so. My estimate is you will need to run your generator pretty much
constantly when your air conditioner is running. The battery is not
designed to be completely discharged. The most you should safely try to get
out of it before recharging is about 25 amphours. That equates to 300 watts
or half an hour or 45 minutes of run time. You will need a lot more battery
capacity and generating capacity. Maybe solar or wind would be helpful in
that regard.
Very good work. There are some very poor sites available. This is not one
of them. Being ion Australia ready made boards etc are not so simple to
buy. I think I will hjave to start putting a photographic arrangement to
commence making PC Boards for my own use
Regards from Bill P.
Bill Pilgrim [billypil@bigpond.net.au]
I'm interested in purchasing some of your kits, but I have a couple of
questions:
You could run directly off the battery, but in that case, I'd advise using
a larger current limit resistor to handle the extra current you will get
when your batteries are fully charged and the voltage is up. You really are
better off using a regulated power supply, either the on board regulator or
your own separate regulator, because your batteries can fluctuate in
voltage depending on their state of charge. Remember, you don't need a
regulator for every board. You only need one for every 3-4 boards. Hope
this helps. --Tom
Chris, Sorry, I did not look at question number 2. The answer is in the
affirmative as long as you stay within the current parameters of the power
supply you use.
i really have no comment other than to ask for the full detailed design of
a 220/240v solar system.
i need something that will help me with my science project on alternative
energy that is like almost free
Hi Kiara,
I suggest you look for info on building a solar collector, one that will
collect the heat from the sun. You can build simple ones that work well for
very little money if you used scrap and recycled materials. Ask your
librarian to help you look up information about solar panels or solar
collectors or solar heat. Good luck! Write back and tell about your project
when it is finished. --tom
I would like to have the LEDs connected to some lithium rechargeable
batteries , charged by solar panels on top, in a small package say 6" by 10
" approx.. Can this be done?
It must be a very portable all- in- one unit. Do you know how to do this?
Costs for all parts or partly assembled kit? Need help! Thanks.HTR If you
would like to E-mail me it would be appreciated.
Awesome site! Keep it up, I have something to play today:)