Skip to main content

Lab Power Supply


This entire time I've been using the PC power supply just by sticking wires in the ATX plug. Not a great solution as the wires have a habit of popping out. To turn on an ATX type power supply you need to short the green and ground (black) wires. ATX powers supplies are the most common type. The only other one I know of are Dell's, which have a special configuration for the 'ATX' plug. Same style of connector, completely different voltages at each pin. This is why your nice new motherboard explodes because you used your old Dell power supply when building a new computer. My friend knows this from personal experience.

Lab Power Supply Formerly of PC

I have managed to take that old PC power supply and make a proper lab power supply out of it. It's a rather simple setup. You can find out how to do this yourself on http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/step2/Planning/ and you can find all sorts of other odd do it yourself projects on Instructables. I took several binding posts and attacked each seperate set of wires to a seperate post. The wires are:

Orange = 3.3V
Red = 5 V
Yellow = 12 V
Blue = -12 V
Black = GND
Grey = PwrOK
Purple = Stby
Green = PwrON

The grey wire you use to indicate, using an LED, that the power in on and the purple wire is hooked up to another LED for stand by power. Stand by power is the power that is still left inside the capacitors. If this LED is on then it is dangerous to touch anything inside the power supply. 

There is also a power resistor in there as most power supplies only work correctly when constantly loaded. In this case I have a power resistor on the 5V rail. In the picture below there is a variable 0 to 500 Ohm, 25W, power resistor (set to 10 Ohm). I later replaced it with a 10 Ohm 10W resistor. I also kept the two 12 V rails seperate. If you make a lab power supply you may or may not have an extra 12 V rail. 

For the ON/OFF switch I had to make a 0.5 inch diameter hole in the case. For this you need a step drill as regular bits typically are not that large. Also, regular drill bits make ugly holes and leave burrs. Canadian Tire has a step drill set that goes on sale for $10 bucks down from $35 every now and then.

Lab Power supply opened.
Labels:

Comments

Post a Comment

Popular posts from this blog

MOSFET Driver Board

Final version?  I hope so.  I have gone back and redesigned my solenoid driver board several times.  In previous versions I attempted to offload some of the logic from the microcontroller.  For example, I used a Schmitt-Trigger [74HC14] with an RC network to provide a single pulse to the solenoid.  Also, I added in a PWM signal to set the average voltage 'seen' by the solenoid.  This worked but was very limiting to have the pulse length hardwired in and it was difficult to adjust without more expensive precision potentiometers. I chose to simplify my circuit to make it a general MOSFET driver for flexibility.  Since I have more than enough space inside my pinball cabinet, it was not a problem to have the extra boards.  The boards were designed to have 4-channels since by default I would get a minimum of 10 boards for the same price from Seedstudio.  Also, the cheapest board option was restricted to 10cm x 10cm otherwise the price balloons quickly. Driving 48V from a separa
3 comments
Read more

Pinball Cabinet Beginnings

I was getting to the point where I really needed to build on something. I have numerous pinball parts but have nothing to attach them to. I managed to find some pinball plans for a Williams Widebody pinball machine. All the measurements are in mm sadly even though all pinball cabinets are in inches. I converted and change it all to the nearest quarter inch. Well sort of. The guy who measured this was intending on using 45 deg cuts in the corners. My skill saw is too cheap for that so I changed the measurements for butted joints. The interior is set for a 23.5" wide playfield. The length of the cabinet is 51.5" in total. I used 3/4 inch plywood so the bottom would be 50" long for example. You can pretty much dimension the rest from there.  I did get a little chipping of the plywood but I went out and bought a blade with more teeth for finer cuts. It's a 60 tooth saw blade and my skill saw doesn't really have enough power for it so I have
Post a Comment
Read more

Pinball Solenoid Control

Pinball solenoids come with designations like 23-800.  The first number, 23 in this case, represents the American Wire Gauge (AWG) used.  The second number, and the more important number, is the number of windings which is related to its power rating.  A solenoid with less windings, say 400, is more power and is used for such applications as actuating the flippers.  These solenoids get very hot very quickly, which increases the resistance of the solenoid thereby decreasing the current and therefore the power.  To avoid overheating, these high powered solenoids will have two coils.  One for the main actuation of the solenoid, and another to maintain the position.  The second solenoid will have a smaller wire gauge and more windings.  In example, my flipper 'coils' are 15-411, 15 AWG and 411 windings.  They are quite strong and found in some of the latter Williams pinball machines such as the popular Adams Family machine.   You can find a lot of good additional information
3 comments
Read more