Stumbling around in the dark, trying to decide whether stringing 200 feet of extension cord, or continuing with my wimpy rechargeable light would get me home sooner, was the inspiration for this project. So on completion of the job, I began to contemplate my next build. It could not just be a rechargeable work light, thats boring. More is better, right? So I put together my wish list; AC, DC, rechargeable battery powered. Power efficient LED with good color rendition. Full range dimming. Run time of at least 4 hours on batteries at full brilliance, longer at lower light levels. Charge from AC,DC or solar power sources. Continuous run on AC or DC sources. All cables, chargers and adapters must store internal to the device (I hate searching for power cords with a passion!) Provide 120 Volt AC power for small appliances along with 12 volt and 5V USB charging using any input source or internal battery. Versatile mounting options with a margarita blender and self deploying satellite antenna. Sorry, the last two did not make the cut. Eureka! A rechargeable work light plus the perfect bug-out power box for the upcoming Zombie Apocalypse.
Repurposing is good. In rummaging around trying to find goodies to incorporate into the project I came across a pile of old laptop power supplies that I had lying around. These little gems are 60 to 90 watt rated, but have weird output voltages, 16V to 20V is common. Perfect, now if I could just find an affordable LED module I would have a great start, hmm, the local Costco store had a 1250 lumen, warm white LED can light retrofit module for the incredible price of $12.95. This is equivalent to a 120 Watt incandescent lamp and they produce a great quality light that consumes only about 20 Watts. We gotta use this.
Step 1: Parts List
LED 1250 Lumen retrofit kit Costco
2- 5A constant current/voltage buck module www.nyplatform.com
500ma FlexBlock by LEDdynamics www.ledsupply.com
Potentiometer 20K ohm linear taper www.ledsupply.com
Switch SPST pushbutton on-off
2- Relay SPDT 20A 12V www.digikey.com #255-2220-ND
Circuit breaker/Switch 10A www.digikey.com #PB1033-ND
Thermo switch N.O. 50 deg celsius www.digikey.com #723-1192-ND
3A 20V Schottky diode www.digikey.com #1N5082GOS-ND
2- 1N4004 1A diodes
3- Diode 10A 100V General Purpose
2- 4 terminal mounting strip
Fan 40mmX10mm 12V www.digikey.com #1053-1205-ND
Power resistor 4.7 Ohm 8 Watt www.digikey.com #A102124-ND
2- Resistor 1 K Ohm 1/4 Watt
2- 12V 5AH SLA Batteries www.batterysharks.com #SP12-5 (T1)
Input and output connectors and cables are your choice. Auxiliary input should match your laptop supply connector. 13.8V out should be standard cigar lighter jack. I use 2.5mm X 5.5mm barrel power plugs and jacks as a default standard. This is a very common size.
I used inline connectors for the front panel controls, battery, and LED connections. This is optional but could make your life easier. I used large pin Molex for the battery and small pin for the other two but there are lots of other choices.
75 Watt DC to AC power inverter(with 5V USB) www.amazon.com Bestek #MR1711C
Baltic Birch Plywood .125 18" X 24"
Baltic Birch Plywood .250 24"X 36"
3/8" X 1" Dowel rod
Miscellaneous #4,6 and 8 hardware
#6 X 3/4" self drilling wood screws I use Kreg brand.
2- Tripod mounts. I made mine from a scrap piece of 2 1/2" aluminum round turned down to 2.25" outer and 1.50 inch inner .50" overall depth, .25 for each step. Drill and tap 1/4-20" through the center 6-32" for the mounting holes.
Step 2: Hacking a Retrofit LED Module for DC Operation
Ok, pop that puppy open! I will go through the steps you need to perform in case you use a different LED. We need to determine what current level the LED module requires. We will also measure the voltage across the diode string, but you do not really need this info for the build. Gently pry out the power supply and remove the potting compound. It should peel off easily. Unsolder the diode wires attached to the power module and and attach longer wires in their place. Connect your ammeter in series with one of the attached wires and apply 115 volts to the power module input wires. Your ammeter should display 500, 700, or 1000ma plus or minus 20%. These are the most common series currents for most high power LED array. You can also connect your volt meter across the LED string and should see something between 12 and 36 Volts. Each LED uses 3 volts so you can determine the number of series connected LED's in your module. Mine runs at 36V so a string of 12 LED's.
So if your paying attention at this point you are probably wondering how we are going to get 36 volts out of a 12 volt system. Thats were the Luxdrive FlexBlock comes in. This little jewel is a buck and boost constant current power module that will allow our LED to operate over a voltage range of 10 to 40 volts with full range dimming. It comes in all common current flavors, 500, 700, and 1000ma. Makes me feel all warm and fuzzy just thinking about it. You can stop right here and build a nice 12 volt LED flood lamp with just these two parts. But I hope you keep going!
Step 3: Let's Build a Box
So your laser cut parts came out beautifully. You remembered to resize any holes for parts that might have been slightly different than mine. Double checked text alignments for the resized holes. Great! You are way ahead of me, at this point I am usually camped out at the lumber yard waiting for them to open so I can buy another sheet of Baltic Birch plywood and trying to explain to my wife why we have so many strange looking pieces of kindling in the wood box.
Let's start with the main box. I like to lightly sand the exterior faces at this point then install the 8-32 threaded wood inserts into the front panel. If you are using my tripod mount design, counter sink the mounting holes for the 6-32 flathead machine screws. Layout the top, bottom, front and sides as shown in the picture. It is critical that the panels are arranged correctly. There is a lot of glue up on this so have a plan, work quickly, and keep a damp cloth for glue clean up handy. I use Titebond II glue, it is a great product with quick grab and extreme strength but it does not have a long working time. You might want to try a hide glue if you need more time. Brush glue on all of your joints and hinge the outside of all the sides up. Wipe up glue from outside of the box and the inside corners. There is a subframe that will be hard to install if you allow glue to dry on the inside corners. You can set the back on the box to help with alignment, but make sure it will not be glued in place. Clamp and set to dry.
Assemble the two battery boxes, I do not think there is any way to screw them up, believe me, I am always trying. Set aside to dry.
Step 4: Box Interior and Subframe
Install the two control mounts on the back of the front panel. the cutouts in the front panel are down so make sure the text on the mounts are right-side-up. Install the tripod mount on the bottom panel with 4 6-32 flathead machine screws.
This is where the party starts. Dry fit this, then dry fit it again. Lay the subframe out as shown in the picture. there are two sides with legs. the legs are marked with an S for short and L for long. The two short legs must land on the front panel control mounts. The storage box must be on the side opposite of the large side opening. One of the two similar pieces without legs has a small hole in the middle, it must go towards the center of the box. The subframe is installed with the legs pointing towards the front panel. Glue up and insert. Make sure the legs bottom on the front panel and panel mounts. The back edge of the subframe will be level with the inside face of the back panel except where the storage box is recessed by 1/8th inch for the door retainer to sit in. Follow this carefully or you will cry. Trust me on this.
Glue in the two battery boxes making sure the wire access holes point to the large opening on the side. Clamp it up, let it dry.
Step 5: Power Panel
Assemble the cooling tower, it is a simple box that mounts on top of the fan. It is easier to sandwich the fan between the back panel and the cooling tower bottom panel and bolt it together before assembling the rest of the cooling tower. I put hot glue on the nuts to make a poor-mans version of a captive nut. This will allow you to remove the tower if needed. Not shown is the small metal heat sink that I attached to the back of the LED driver module with thermal epoxy. Probably not needed, but more is better. Use any size that does not block airflow or short out the supply modules. The LED driver and DC power modules mount to the cooling tower with a drop of hot glue in each corner. They can be easily removed by warming with a hot air gun if needed. You will notice that my cooling tower looks different than the one you are building. Mine has an offset adapter that was added after I "pulled a Homer" (or a dohhh! as I like to call it) on the initial design. Yours will not require this. Mount the rest of the panel parts. The battery switch and relays will need hot glue to hold them and possibly your barrel power connectors depending on the style. !Important! Mark the input and output connections of the DC module on the plywood where you can see them after installation.
Wiring is simple "dead bug" point-to-point, butt ugly, just follow the schematic. Some things to consider as you wire; There is limited clearance on the panel, bend the lugs of the battery switch 90 degrees to minimize its depth. Keep all parts and wiring dressed down close to the panel. It is a good idea to set the panel assembly into the box before wiring . This will give you a good idea of the clearance issues you will face. I used 16 gauge wire for the battery current paths, 18 gauge for the supply and 24 for low current hook up. The 16 is tough to use and I am sure you could get away with using 18 even for the higher current paths.
Assemble the battery harness, front panel control harness and install connector for the LED.
Step 6: Test, Calibration, and Operation
Those little red meters are basically free, work surprisingly well, and you should have a bunch of them. Thank you Harbor Freight!
Come on, it's not as bad as it looks, lets get started. You can complete test and calibration after final assembly if you like, just do not install the batteries and leave the back panel off.
Turn the battery switch to off. Connect one battery. Press the on-off switch. Nothing should happen. Rotate the dimmer control and nothing should still happen. Abandon project and use as a doorstop..... Just kidding, we need to turn the battery switch on now. Push button switch and dimmer control should work now. Measure voltage at 13.8 V socket, it should be the same as battery voltage. Good.
Remove battery and plug in your laptop supply. Apply AC to the supply and you should hear a click. LED's should be illuminated on both DC modules. The LED switch and dimmer should be functioning. Measure the voltage on the battery harness and adjust the charger voltage to 13.8V. Place an amp meter in series with the battery leads, then short the wires. Really, its Ok. You want to adjust the current control for 1.5 to 2 amps for a dead short. Depending on the capacity of your source supply it may current limit before the charger module does, weird things happen at this point. Don't Panic, just keep adjusting till you get to your set point. Excellent.
Attach your voltmeter to the 13.8V out jack. Adjust the other supply to get an output of 13.8V. You can adjust the current limit down if you wish, but it is not really necessary.
That's it! Told you it wouldn't be bad. You probably will want to check the settings after the modules have aged a bit and I think the setting for the charger can be refined. I just want to let it run for a while before I start to tweak.
Some operational tips
Do not feed it 13.8V and Aux power at the same time. When running on a laptop power supply your 13.8V output is limited by the capacity of the laptop supply minus the battery charge power and lighting power. I.E. with a 60 Watt supply 60 - 22 - 15(Full intensity LED and batt charger)= 23 Watts or about 2A. When fed from 13.8V source (fused at 10A please) you have 120 Watts to play with. On internal batteries, the max draw is limited to 10A by the battery switch/breaker, again 120 Watts. Remember the 120 Watts is the combination of all the subsystems in operation.
A 5 or 10 Watt solar panel equipped with blocking diode can be directly plugged into the solar input jack. Larger panels should use a charge controller.
The unit will function as a power fail light. Operation will automatically switch from an external power source to batteries if the source fails.
The small DC to AC inverter specified in the parts list works well and has two USB charge ports in addition to AC.
Step 7: Final Assembly
Attach the unlock knob and round spacer to the dowel rod. You are going to glue the latch plate to the door being careful not to get glue near the rotating latch assembly. Apply glue to the latch plate and attach to the door again being careful to maintain free rotation of the unlock knob assembly. You can use the template for alignment but it is a little off on one side. Just make sure to keep the sides even and the unlock knob rotating. Align the unlock arrow on the back and the pointer on the knob and hot glue the latch to the dowel rod with the flat edge to the top. Hot glue will allow you to adjust the friction tension on the knob assembly by heating and squeezing. Trim the dowel.
Mount the front panel controls and cable assembly. Run the battery cables into the battery boxes. Carefully install the power panel assembly into the box and attach it with 4-40 X 1/2" inch screws and nuts. Connect connectors and install LED assembly with 8-32 X 3/4" screws. Install the door retainer plate in storage area, watch the orientation. No need to glue, the back panel will hold it in place.
Place the back panel on the box. Use an awl to center punch start holes in the box frame and drill a 1/16th" pilot hole about 3/4 inch deep for the back panel screws. Install Batteries and close back with #6 X 3/4 self drilling wood screws, I use Kreg brand.
The knobs are made from stacking 3 - 1"X 1/4" sections. The small hole gets the round with the etched top. Glue the three rounds together and attach with a little hot glue. Be careful with the push button switch not to press the knob on too far as it will not allow the switch to cycle on-off.
Step 8: Lessons Learned and Battles Lost
I have missile lock
I used to mercilessly tease my coworkers when they would come to me with an unsolvable problem and I saw the solution to it immediately. It was not because I was smarter, quite the opposite, I always hired people smarter than myself. It was because they became so fixated on the wrong solution that they were unable to look for other avenues. "Missile locked" on the wrong solution. I too suffer from this. The original power panel for this project looked much different. I have a bunch of 4PDT heavy duty slide switches that I have wanted to use in a project for a long time. The original design included two of these. It was a little wonky, with lots of switching paths but it worked OK. Then disaster. One of the contacts became intermittent and no amount of cleaning would restore reliable operation. As I set about the task of replacing the switch, It suddenly hit me. Can anyone actual replicate this circuit? A search of part sources for the switch turned up nothing. What's the point in doing this if it cannot be copied. I scrapped the design and came up with the current one. Simpler, easier, and made with parts that are common. A much better solution.
Parts is Parts
Right? Well sort of. The plethora of electronic building block modules coming from Asia has been a great boon for experimenters but it is not without some problems. Take the DC converter modules used in this project. A great module at a really low price but very poor documentation. I was never able to determine if the modules contained a DC blocking diode for reverse power protection. I incorporated one in the circuit design just in case, but this created an issue with the supplies becoming unstable. This was solved with the addition of a small load resistor. Sure you can grab a data sheet on the main IC and figure out what should be happening, but a healthy sense of the unknown goes a long way when using these modules.
Engineers are evil
Barrel power connectors prove this. I have a big box of power adapters that do not seem to fit anything. When I go to use some device that needs an adapter it is off to the box, were without a doubt nothing fits. For this project, I had two extra laptop supplies with the same connector, so it made sense to make the input connector match. Electronics Warehouse our local parts store and all around cool place has several shelves devoted to the connectors from hell. Luckily, they have samples attached to all the boxes so you can try to find a mate to your connector. Not sure how else you could do it, the size difference between the connectors is in fractional millimeters so its really tough to gauge sizes. It's all a plot, and here is how I see it playing out.
"Mr President, the alien armada has entered orbit around the planet. They are demanding the immediate dissolution of all military forces and and the establishment of a "One World" government consisting of Aliens and Engineers, and oh, they want every Twinkie on the planet piled in the Grand Canyon" "What a vile demand" snarled the President, "they are not getting our Twinkie's without a fight! Defense tells me the BFG9000 space cannon can annihilate anything in near Earth orbit, lets fire it up and give them a good thrashing." "Um sir, there is a problem, it seems the first dog chewed up the power adapter for the control panel, we can't fire the cannon." "What!" barked the President. "Get another power adapter, there must be a 100 of the dang things in the White House alone." " Sir, sir we tried, but it seems the barrel connector on the power adapter is 3.14mm X 6.02mm. There is not another one available east of the Mississippi." President collapses into stunned silence. " Mr President, Um Mr President, would you like the last Twinkie?"