Have you ever thrown away a laser pointer because the batteries went dead? Well, I have. Who wants to go search down those 3 hard-to-find, expensive button cells? You'd be better off buying a new laser. But:
It is relatively simple to create your own long-lasting battery pack from just 3 AAA, AA, C, or D cells, depending on how long you want it to last. I imagine 3 D-cells will run the thing continuously for a week or so, but I'm not positive. I will measure the current draw on mine, find out the mA/hr rating of the different batteries, and post the results on this page so we will know for sure.
Swap out the 3 original lithium-ion button cells that came with the laser, with 3 higher-current 1.5V batteries of your choice. Of course, you can't cram 3 AA batteries into the actual laser pointer - so it's not nearly as convenient. However, if you want it to lase at full power for a long time, without having to worry about it going dead, this is the way to go.
Complete Materials List:
1. Cheap red laser pointer 2. Either 3 AAA, AA (my choice), C, or D cell batteries 3. Stranded (not solid) hook-up wire (Radio Shack) 4. Solder and relatively powerful (35W) soldering iron (Radio Shack) 5. Small piece of sandpaper (Hardware Store) 6. Small piece of notebook paper 7. Small alligator clip (Radio Shack) 8. Tool to strip wire (wire strippers, razor, or sharp pocketknife) 8. Electrical tape, duct tape, aluminum tape, or nylon-reinforced tape (NOT scotch) 9. Needlenose pliers 10. Cutting pliers, diagonal cutters, or a similar tool.
#1. Finding the Correct Polarity
Before doing anything to the laser, you must find the polarity of your laser's DC input. Unscrew the cap on the end of the laser to expose the batteries, and remove them one by one until you are at the last battery. Remove the last battery, making SURE to note what side of it (positive+ or negative-) was contacting the spring down inside the pointer. Most cheap red laser pointers will have the negative side of the battery on the spring. If the negative is on the spring, then the positive is connected to the metal casing that you hold. And vice versa. If the positive is on the spring, then the negative is on the case (standard of most consumer electronics to have the case grounded)
We want to hook up the new homeade battery pack to the laser in the same configuration as the batteries we just took out.
#2. Making the Battery Pack
Most people will tell you that you can't solder to a battery - because the solder won't stick. But alas: there is a very excellent way to do it. Simply lay a small piece of sandpaper down on a flat surface, and scrub the end of each battery into it until the once-shiny end is now nice and roughed-up. Now you must tin the batteries so they will take solder easier when it comes time to wire them up. Simply fix a battery down to something so it won't move, and apply a *small* blob of solder to each end. "The bigger the glob, the better the job" doesn't apply here!! Repeat for each battery. Notice that if you are using a low-power iron, it takes a long time to heat the battery up hot enough for it to take solder. Maybe a small (cigarette lighter) propane torch would help here.
#3. Wiring the Batteries Together
Now that the + and - sides of each battery have been tinned, we can now begin wiring them up. First, cut each wire to length based on your battery pack. D's will require longer wires than AAA's of course. After each wire has been cut to length, you must strip about 1/8" of insulation off of each end, then tin each end by laying it on the iron and applying a small amount of solder so it flows into the wire strands. Use the picture below for help on wiring.
#4. Finished Battery Pack and Explanation of Voltage and Current Ratings
Here is the end result of what we want with the new source of power. Make your wires going to the laser pointer at least an arm's length (so you can use the pointer with the battery pack in your pocket), and pre-tin the ends for the next step. When all of the wiring is complete, wrap the whole pack tightly with your choice of tape, but don't use scotch tape (it tears too easily).
There are two ratings for a battery. The voltage (in volts) is one, and the current (in mA/hrs. or milliamp/hours) is the other. Configured the way they are in the picture above, the batteries are said to be connected in series. The voltage ADDS together when wiring batteries in series (in line, back-to-back, or chained), while the current stays the same. Since we have 3 batteries here, and each are 1.5 volts, the total voltage comes out to (1.5V + 1.5V + 1.5V) 4.5V. If we were to add more batteries in the arrangment, then we would simply keep adding 1.5V for each new battery. But since the semiconductor devide in the laser pointer requires 4.5 volts - - going much over that would either fry it, or significantly reduce its lifetime. Anyhow, as far as the current goes in the battery pack, it stays the same throughout, and is the same as the current rating for a single battery. Triple-A batteries have a much smaller current rating (less mA/hrs.) compared to that of D-cell batteries. More current will power a device for a longer period of time. Your pointer will last a lot longer using three AAA batteries rather than 3 tiny little lithium-ion button cell batteries!
Connecting a number of batteries in parallel does exactly the opposite of connecting them in series. Batteries are connected in a parallel arrangement when all the positive ends are wired together, and all the negative ends are wired together. In parallel, the currents add while the voltage stays the same. In series, the voltages add while the currents stay the same.
#5. Making Connection to the Laser Pointer Spring
This is the most difficult step compared to the others. First, we must modify a small alligator clip so that it will fit completely inside your laser pointer. Use cutting pliers, and cut as much metal as you can off of each end of the clip. You will have to weaken the metal by attempting to cut it, then bend it back-and-forth until it finally breaks off. Refer to the pictures below.
At the very beginning of this document, we determined the polarity of the laser pointer's DC input voltage. Make sure to get it right. Even a slight tap of opposite polarity voltage, and the laser will fry. The modified alligator clip will get the battery's voltage to the laser. First, solder the correct wire from the battery pack to the end of the clip. If the spring was touching the negative side of the original button cell, then solder the negative wire onto the clip. If it was touching positive, solder the positive wire onto the clip. Once the wire is soldered, use a pair of needlenose pliers to clip the wire onto the spring. Notice that the clip will touch the walls of the pointer, shorting the battery if the other wire was connected. Now: here is the hardest part. Cut out a 1" x 3" rectangle of notebook paper, and roll it up around the wire going into the pointer. Carefully begin working the rolled-up paper tube into the end, bending and rolling it past the clip. The purpose for the paper is to insulate the clip from the case, preventing an internal short up inside the pointer. Another method is to fill the end of the pointer up with epoxy or some other kind of glue, keeping the clip away from the pointer walls while it drys.
#6. Connecting the Other Wire
Simply place the other wire's end on the outside of the metal pointer, and tape it tightly in place. There is now 4.5 volts supplied to the laser, and it should work great when the button is pushed. And it will last! Follow the next step to keep the wires from pulling out from rough handling.
#7. Strain Relief
One last step, and you will have a laser pointer that will operate for at least 5X as long as it did with the original batteries. On the laser pointer end: Wrap the wire around the pointer several times, and tape it in place as tightly as you can. You might want the wire to exit out the end, so account for it. And on the battery pack end: Do the same thing. Wrap the wire around the pack a few times, and tape it in place. This keeps the actual solder connections from being constantly jiggled around during use.
You're finished. Have a good time.
