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Step 6Pick Your Power Supply
This next section on power supplies is a little lengthy. You may be able to skip over most of it, or you may have to read it carefully three times. You already know how much you know about power supplies.
A wire cutter (in a pinch, there's a crude one on a pair of slip-joint pliers) will cut the wires, and a fingernail clipper will come in handy to very carefully strip insulation off the ends. A knife has been known to do both, but it's the sign of a newbie.
You'll have a slider potentiometer to continuously vary the voltage from 1.2 to 3.2 volts (low laser power to high power), and a fingertip trigger switch to turn the LED laser on and off. You should unplug it from the wall when making any changes or adjustments to prevent accidents.
If you want to be totally portable, or you can't scrounge an AC power supply, then use a battery holder and 4 or more AA, C, or D-size flashlight batteries with the voltage regulator.
Three batteries without a regulator will produce 3.75 volts, about a half-volt too much (rechargeable batteries are 1.25 volts), and you'll probably blow up your $15 laser.
Two batteries without the voltage regulator will give you reduced power. A pair of alkaline batteres will turn out 3+ Volts, nearly full power. A pair of rechargeable batteries will produce around 2.5 Volts.
One flashlight battery without the regulator will create less burning power, but the focused beam is still dangerous.
"D" batteries last longer than "C" batteries, and "C"s last longer than "AA" batteries. They power the laser, so batteries will go fast at high power. Better yet, scrounge an AC power supply for full, permanent laser power. See below.
You can get a battery holder at Radio Shack or Mouser.com, or you may already have one. The exact part is not critical, and using batteries makes the whole thing portable -- it's only an inch or two wide. You can use anything between 4.5 and 32 volts of batteries. That's the input range on the voltage regulator, which will then pump out between 1.2 volts and 3.2 volts DC for the laser.
You should avoid a common car or motorcycle battery, as those are really overkill, and actually dangerous because they give off toxic, explosive vapors. They can produce far more than enough current to easily launch your cat at least 10 feet off the ground if he's near (or causes) a short in any wiring, which could then ignite the explosive vapors. Nasty.
Stick with simple batteries, and don't ever short a rechageable battery -- if you short them out they get red-hot RIGHT NOW and may burst. Alkalines just go dead if you short them out.
A laptop power supply brick goes for as little as $10 on eBay or search for 'laptop power supply'.
Better yet, if you've got an old 120-volt AC to low-voltage DC power supply (borrow from your brother-in-law and then forget to give it back, $0) laying around from a laptop, pair of powered speakers, the internal power supply from an old desktop PC (and you don't even have to care if you're using the 12V [yellow] or the 5V [red] line), etc., that's between 5 volts and 32 volts and is rated 1 Ampere or more (or 1A or 1,000 mA -- it's all the same) you can use that. If it's rated less than 1000 milliamps (mA) it will still work, it just won't run the laser at full power. You can replace a small one now with a bigger one later. If the power supply output is over 35 volts, it will destroy your power regulator and your laser. But if it's able to supply over 1,000 mA, it will just run cooler and easier. So, an old laptop power brick rated at 1800mA or at 2.5A and 18 Volts DC is just fine.
If yours doesn't have an Amp or A or mA rating, it probably lists 'Watts' or 'VA' (Volts times Amps equals Watts). The number of watts should be at least as big as the number of volts, and both of them should be at least "5" but see the next paragraph for caveats.
Your supply should output at least as many Watts as Volts. So, a 10 volt DC supply that says 10 watts (or 15 watts, or 20 watts) will be fine. But an 18 volt supply rated at 10 watts won't be big enough to run the laser at full power, and you may overheat (and damage) this power supply if you run it hard enough. You might still use it; check it often for overheating.
If you've got a weird power supply that has an AC output, or rates the output with a ~ (tilde) symbol, don't use it. The squiggly tilde means it's AC, not DC. A tilde on the 120 volt AC input rating is OK.
If you can make up a connector to attach to the end of the power supply's cable (take it with you to Radio Shack) you don't need to destroy the plug on the end if you don't want to -- you could still use it for your laptop, etc.
You'll need to get the wires (polarity) straight. If you don't have a multimeter, skip the next paragraph.
Set your multimeter to the 20 Volt DC range (or the 200 VDC setting if your power supply is over 20 volts). The red + meter lead, when connected to the positive wire on your power supply (and the black - lead to the negative wire), will give a normal voltage reading on the meter. If the wires are reversed, there will be a - (minus sign) in front of the number on the meter. Do not change anything on the meter while it's connected (20VDC to 200VDC and back is OK). Do not use any other range on the meter until you've read the manual and understand how to use it. If you blow your meter up, don't despair; you probably just blew a fuse inside. Replace the fuse EXACTLY with one from eBay or Radio Shack -- this is a safety issue.
If you don't have a meter, look at the power supply label, or the case next to the hole where the power supply (used to) plug into the old laptop or whatever. There's typically a 'circle and tip' drawing of some kind linked to plus and minus signs to signify whether the outside conductor (circle) or inside hole (tip) is which lead. If your plug has some weird 3-hole arrangement, study it carefully.
If you cut the plug off the end of the wire, you'll notice there are two separate wires side-by-side, (like a lamp or extension cord has) or a single round wire (like a satellite or TV cable has, only thinner) between the brick and the end in your hand. If there are two wires, one of them is marked with a stripe or a ridge or lettering or something. That one is usually positive (+) and the unmarked wire is usually negative (-)Usually.
If there are two wires and a braid inside, use either wire as long as the ratings show them to be adequate. More voltage in does not equal more voltage out of the regulator.
If there's only one round wire, you'll find a second wire hidden inside the first. The outside braid wire is usually negative, and the inside wire is usually positive. Usually.
Usually, the positive wire is the one that's marked in some way, and the positive lead on the plug is the one inside. This makes the negative wire unmarked and on the outside (perimeter) of the plug. Usually.
You can always test the polarity of any low DC voltage with an inexpensive LED connected to a 200 to 500 ohm resistor (the slider you bought is 500 ohms). The LED's short leg is negative, next to the edge of the plastic that's flattened. If it's backward, nothing happens. Resistor can go on either leg. If it lights, you can determine the polarity of the wires.
If you still can't figure it out, maybe you should spring a few bucks for the meter, or borrow one.
Enough, already. Let's move on.
A wire cutter (in a pinch, there's a crude one on a pair of slip-joint pliers) will cut the wires, and a fingernail clipper will come in handy to very carefully strip insulation off the ends. A knife has been known to do both, but it's the sign of a newbie.
You'll have a slider potentiometer to continuously vary the voltage from 1.2 to 3.2 volts (low laser power to high power), and a fingertip trigger switch to turn the LED laser on and off. You should unplug it from the wall when making any changes or adjustments to prevent accidents.
If you want to be totally portable, or you can't scrounge an AC power supply, then use a battery holder and 4 or more AA, C, or D-size flashlight batteries with the voltage regulator.
Three batteries without a regulator will produce 3.75 volts, about a half-volt too much (rechargeable batteries are 1.25 volts), and you'll probably blow up your $15 laser.
Two batteries without the voltage regulator will give you reduced power. A pair of alkaline batteres will turn out 3+ Volts, nearly full power. A pair of rechargeable batteries will produce around 2.5 Volts.
One flashlight battery without the regulator will create less burning power, but the focused beam is still dangerous.
"D" batteries last longer than "C" batteries, and "C"s last longer than "AA" batteries. They power the laser, so batteries will go fast at high power. Better yet, scrounge an AC power supply for full, permanent laser power. See below.
You can get a battery holder at Radio Shack or Mouser.com, or you may already have one. The exact part is not critical, and using batteries makes the whole thing portable -- it's only an inch or two wide. You can use anything between 4.5 and 32 volts of batteries. That's the input range on the voltage regulator, which will then pump out between 1.2 volts and 3.2 volts DC for the laser.
You should avoid a common car or motorcycle battery, as those are really overkill, and actually dangerous because they give off toxic, explosive vapors. They can produce far more than enough current to easily launch your cat at least 10 feet off the ground if he's near (or causes) a short in any wiring, which could then ignite the explosive vapors. Nasty.
Stick with simple batteries, and don't ever short a rechageable battery -- if you short them out they get red-hot RIGHT NOW and may burst. Alkalines just go dead if you short them out.
A laptop power supply brick goes for as little as $10 on eBay or search for 'laptop power supply'.
Better yet, if you've got an old 120-volt AC to low-voltage DC power supply (borrow from your brother-in-law and then forget to give it back, $0) laying around from a laptop, pair of powered speakers, the internal power supply from an old desktop PC (and you don't even have to care if you're using the 12V [yellow] or the 5V [red] line), etc., that's between 5 volts and 32 volts and is rated 1 Ampere or more (or 1A or 1,000 mA -- it's all the same) you can use that. If it's rated less than 1000 milliamps (mA) it will still work, it just won't run the laser at full power. You can replace a small one now with a bigger one later. If the power supply output is over 35 volts, it will destroy your power regulator and your laser. But if it's able to supply over 1,000 mA, it will just run cooler and easier. So, an old laptop power brick rated at 1800mA or at 2.5A and 18 Volts DC is just fine.
If yours doesn't have an Amp or A or mA rating, it probably lists 'Watts' or 'VA' (Volts times Amps equals Watts). The number of watts should be at least as big as the number of volts, and both of them should be at least "5" but see the next paragraph for caveats.
Your supply should output at least as many Watts as Volts. So, a 10 volt DC supply that says 10 watts (or 15 watts, or 20 watts) will be fine. But an 18 volt supply rated at 10 watts won't be big enough to run the laser at full power, and you may overheat (and damage) this power supply if you run it hard enough. You might still use it; check it often for overheating.
If you've got a weird power supply that has an AC output, or rates the output with a ~ (tilde) symbol, don't use it. The squiggly tilde means it's AC, not DC. A tilde on the 120 volt AC input rating is OK.
If you can make up a connector to attach to the end of the power supply's cable (take it with you to Radio Shack) you don't need to destroy the plug on the end if you don't want to -- you could still use it for your laptop, etc.
You'll need to get the wires (polarity) straight. If you don't have a multimeter, skip the next paragraph.
Set your multimeter to the 20 Volt DC range (or the 200 VDC setting if your power supply is over 20 volts). The red + meter lead, when connected to the positive wire on your power supply (and the black - lead to the negative wire), will give a normal voltage reading on the meter. If the wires are reversed, there will be a - (minus sign) in front of the number on the meter. Do not change anything on the meter while it's connected (20VDC to 200VDC and back is OK). Do not use any other range on the meter until you've read the manual and understand how to use it. If you blow your meter up, don't despair; you probably just blew a fuse inside. Replace the fuse EXACTLY with one from eBay or Radio Shack -- this is a safety issue.
If you don't have a meter, look at the power supply label, or the case next to the hole where the power supply (used to) plug into the old laptop or whatever. There's typically a 'circle and tip' drawing of some kind linked to plus and minus signs to signify whether the outside conductor (circle) or inside hole (tip) is which lead. If your plug has some weird 3-hole arrangement, study it carefully.
If you cut the plug off the end of the wire, you'll notice there are two separate wires side-by-side, (like a lamp or extension cord has) or a single round wire (like a satellite or TV cable has, only thinner) between the brick and the end in your hand. If there are two wires, one of them is marked with a stripe or a ridge or lettering or something. That one is usually positive (+) and the unmarked wire is usually negative (-)Usually.
If there are two wires and a braid inside, use either wire as long as the ratings show them to be adequate. More voltage in does not equal more voltage out of the regulator.
If there's only one round wire, you'll find a second wire hidden inside the first. The outside braid wire is usually negative, and the inside wire is usually positive. Usually.
Usually, the positive wire is the one that's marked in some way, and the positive lead on the plug is the one inside. This makes the negative wire unmarked and on the outside (perimeter) of the plug. Usually.
You can always test the polarity of any low DC voltage with an inexpensive LED connected to a 200 to 500 ohm resistor (the slider you bought is 500 ohms). The LED's short leg is negative, next to the edge of the plastic that's flattened. If it's backward, nothing happens. Resistor can go on either leg. If it lights, you can determine the polarity of the wires.
If you still can't figure it out, maybe you should spring a few bucks for the meter, or borrow one.
Enough, already. Let's move on.
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