Introduction: Variable Portable Power Supply
I was looking around on Instructables and saw this project https://www.instructables.com/id/Pocket-Size-Power-Supply/ which inspired me to do the project below. I decided to create a portable variable voltage power supply so I could go to garage sales and Goodwills to test toys and camera’s etc.… to see if they worked. Usually I wouldn’t care because I am just going to take them apart anyway. However there were a few times I wished I had it. The Pocket power supply was just what I was looking for. I intended to make just one improvement by making it able to adjust voltage anywhere between 1.5v -12v, but I got a little carried away. Lol. This was now more of a clown pocket power supply than a normal pocket power supply. Still it is very useful.
I start by going off of the pocket project instructions then experimented till I found what worked. The reason I used so many resistors. I could not seem to get much amperage out of the circuit. I am not really a hardware guy. I usually buy the boards then just connect wires and do the programming. Since this was all hardware, I knew I would have a challenge. It was fun being out of my comfort zone though.
I did figure out that I had to put a 15 ohm resistor on the voltage in portion of the circuit because before that I kept frying potentiometers. I really do not know why, but I figured if I limited the input with resistors it would fix the issue. I started high, 10k then worked down by halving until I got the result I wanted at 15 ohms. I put 4 resistors in parallel for a better path, granted probably not the cleanest way to go but it worked. My thinking is probably flawed here, but the device works so that is okay.
LED Multi-meter screen:
I knew I would need a way to measure voltage and I did not want to use $50 worth the Arduino products to do so. A buddy of mine found these http://www.ebay.com/itm/DC-0-30V-3-Wire-Red-LED-Display-Digital-Voltage-Voltmeter-Panel-Motor-Motorcycle-/380687977328?pt=LH_DefaultDomain_0&hash=item58a2c58b70 on Ebay for cheap. They work great in the project, no muss no fuss.
LM317T voltage regulator:
The LM317T pinout is kind of confusing. There are several versions of the pinout on the net. The back of the package from radioshack was wrong. These things are pretty tough so if you hook it up wrong just test an led and if it is hooked up wrong you won’t blow it out. I have not found that I need a heat sink for the 317T. It does not get hot at all.
Alligator Clips and switches:
You will need Alligator clips to attach to the end product. However on a lot of the camera’s I found that the clips cannot reach the proper +/- spots. I am changing this to the small clip on leads. But for now it’s still the alligator clips. I put 2 switches on here because I did not want the device to be turned on by accident. It’s just a personal preference. You can get rid of the second switch if you feel like it.
I hooked all the batteries in series. I could have made this look a lot cleaner with 3 batteries. But I really wanted the 12 volt option. So I went with the 4 battery 16 volt configuration. The LM317T will handle much more than this, but I really do not need any more that 12 volts. Maybe in the future I will make a universal portable power supply that can power a laptop for a few minutes to see it the ones at the goodwill would be worth buying. But for now 12 volts is all I need.
1. All parts can be found at radioshack with the exception of the led screen and donuts.
2. 1 x dozen donuts
3. 4 x 18650 Batteries, I get them from old laptop battery packs.
4. 4 x 18650 batt holders
5. A case
6. 4 x 15 ohms resistors
7. 4 x 180 ohm resistors
8. 1 x 3.3K ohm resistors
9. 1 x LM317T voltage regulator
10. LED Multimeter screen
11. Red and black alligator clips
12. 5K potentiometer with knob
13. 2 x Switches