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I would be remiss in my responsibilities as a grandfather if I didn't work to ensure my grandkids understood some of the nuances of automotive restoration. Since the entire industry is going more towards electronic solutions, I figured the best way to get them enthused while teaching them something valuable is to get a kit called Snap Circuits Jr. for the younger ones. The problem comes in when you consider the age old problem of AA Batteries. Grandparents all over are purchasing toys with AA Batteries and then when they die, the Parents are not just standing around with a new set of batteries waiting to be installed. (Oh the Humanity!) That's where this weeks Tip comes in...
Most people have power supplies laying around all over the place. Every cell phone you have ever purchased over the years, all the computer routers, that old recharger from your long dead rechargeable drill, if you look around a bit, its likely you have a few. The idea is to make a wall charger that powers anything that takes batteries. Most of them are rated at about 1 amp and able to handle the job. Problem is, most of these power supplies are rated at 5 volts. In our example, we need to emulate two AA Batteries. This means we need about 3.2 volts. The plan is to cut the end off the power supply and reduce the voltage, then put alligator clips on the ends. Then the Parent who is so happy they do not have to worry about batteries will teach the kid how to attach the two leads to the battery box.
To do this, we need to decide what to do about getting the voltage reduced. Enter something called a Voltage Divider Circuit. There is a really nice Calculator here:
https://learn.sparkfun.com/tutorials/voltage-dividers
We will then use 3 watt resistors just to be overly cautious and put them in a voltage divider orientation. Which is one after the other in series. Looking at the site above, we plug some numbers into the calculator and come up with a 150 ohm and a 350 ohm resistor.Then, the black wire on the power supply goes to one end, and the red lead (+) goes to the other end. Then, to get the reduction, we will take another red wire, and solder it to the junction of the two resistors. This is our new Positive. Measuring with a meter, we get 3.2 volts. Now to pretty things up and keep the kids out, we will use shrink tubing to close it up and keep the current flowing. You can get the resistors at Mouser.com or Digikey.com. I got a few rubberized Alligator Clips from Harbor Freight and soldered them on the ends.
Note: The value of the resistors are carefully chosen in one direction you will get about 2 volts. The other direction you will get 3.2 volts. Check the voltage before buttoning it up.
Be sure to look carefully on the outside of your power supply candidate to make sure you know what the Voltage output and Amperage output is, and use the calculator above to determine the value of the resistors. Have fun! I know my grandkids will, even if they have to play near an AC voltage outlet! This is not a good way to reduce voltage in a power supply normally, because of the inefficiency, but in the case of a very low amperage and low wattage, this will get the job done. Use 3 watt resistors just to be safe!
Now if for some reason you do not get enough amperage to run a servo-motor or something more amp hungry, get this instead of the above:
http://www.ebay.com/itm/141249782084...%3AMEBIDX%3AIT
This works with 1 amp supplies like cell phone chargers and still delivers the amps needed. The other great news is, it steps any voltage from 32 volts down to any voltage down to 800 millivolts! 5 Amps too! Seeya Next Week!
Most people have power supplies laying around all over the place. Every cell phone you have ever purchased over the years, all the computer routers, that old recharger from your long dead rechargeable drill, if you look around a bit, its likely you have a few. The idea is to make a wall charger that powers anything that takes batteries. Most of them are rated at about 1 amp and able to handle the job. Problem is, most of these power supplies are rated at 5 volts. In our example, we need to emulate two AA Batteries. This means we need about 3.2 volts. The plan is to cut the end off the power supply and reduce the voltage, then put alligator clips on the ends. Then the Parent who is so happy they do not have to worry about batteries will teach the kid how to attach the two leads to the battery box.
To do this, we need to decide what to do about getting the voltage reduced. Enter something called a Voltage Divider Circuit. There is a really nice Calculator here:
https://learn.sparkfun.com/tutorials/voltage-dividers
We will then use 3 watt resistors just to be overly cautious and put them in a voltage divider orientation. Which is one after the other in series. Looking at the site above, we plug some numbers into the calculator and come up with a 150 ohm and a 350 ohm resistor.Then, the black wire on the power supply goes to one end, and the red lead (+) goes to the other end. Then, to get the reduction, we will take another red wire, and solder it to the junction of the two resistors. This is our new Positive. Measuring with a meter, we get 3.2 volts. Now to pretty things up and keep the kids out, we will use shrink tubing to close it up and keep the current flowing. You can get the resistors at Mouser.com or Digikey.com. I got a few rubberized Alligator Clips from Harbor Freight and soldered them on the ends.
Note: The value of the resistors are carefully chosen in one direction you will get about 2 volts. The other direction you will get 3.2 volts. Check the voltage before buttoning it up.
Be sure to look carefully on the outside of your power supply candidate to make sure you know what the Voltage output and Amperage output is, and use the calculator above to determine the value of the resistors. Have fun! I know my grandkids will, even if they have to play near an AC voltage outlet! This is not a good way to reduce voltage in a power supply normally, because of the inefficiency, but in the case of a very low amperage and low wattage, this will get the job done. Use 3 watt resistors just to be safe!
Now if for some reason you do not get enough amperage to run a servo-motor or something more amp hungry, get this instead of the above:
http://www.ebay.com/itm/141249782084...%3AMEBIDX%3AIT
This works with 1 amp supplies like cell phone chargers and still delivers the amps needed. The other great news is, it steps any voltage from 32 volts down to any voltage down to 800 millivolts! 5 Amps too! Seeya Next Week!
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