Introduction: Bench Power Source
This is a Project that I undertook to solve the problem of limited space for my work area (I usually use the kitchen table for a work bench)
Step 1: BENCH POWER SOURCE
BENCH POWER SOURCE
I work with both solid state, and tube equipment on my bench (which isn’t terribly large). So I decided to assemble a power unit which could provide me the power (& safety) that I need without using up a lot of space.
The first thing I did was determine my needs:
> variable DC 0-~15 volt
> Isolated “MAINS” supply
> outlets for soldering iron, and light
Step 2: BENCH POWER SOURCE
The next step was to round up the necessary
pieces for the project:
Ø 120 volt Isolation Transformer “Triad N-68X” (from http://www.alliedelec.com/)
This unit provides aprox. A half of an amp (a larger unit could be used if more current is required, but it might require a larger Case)
Ø 18 volt Transformer “Archer 18 Volt AC, 2-Amp Power Transformer 120VAC input, 273-1515C” (from ebay)
Ø Variable DC supply (see insert after partslist))
Ø 1 section cut from galvanized stud (2 X 4) for chassis (from home depot)
Ø 1 plastic sleeve for 4 X 4 post (from home depot)
Ø 2 Duplex outlets (from home depot)
Ø 4” metal surface mount “wall Box” (from home depot)
Ø 4” box to single duplex reducer (from home depot)
Ø 2 single duplex outlet cover plates (galvanized) (from home depot)
Ø 1 ¾” Romex adaptor for “Surface Mount Box” (from home depot)
Ø 1 1” Romex adaptor for “Surface Mount Box” (from home depot)
Ø 1 SPST toggle switch (from home depot)
Ø 1 Bussmann HTB-44I Fuse Holder, Panel Mount Rear Nut, 3AG, 6.3 x 32mm, 15A (from ebay)
Ø 1 3ag bussfuse 5 amp
Ø 1 500 ohm potentiometer (which I had in stock, to replace the “trimpot” in the variable supply)
Ø 1 miniature dpst (spst could also be used) (from ebay)
Ø 1 0-30 volt digital volt meter (to monitor variable dc supply) (from http://stores.ebay.com/mfreelaa?_trksid=p2047675.l2563)
Ø 3 Binding posts “Amplifier Terminal Speaker Cable Binding Post Banana Plug Jack Connector” (from ebay)
Ø 1 3 wire cord From Computer
The third step was to assemble the “Mains” section:
Ø A 3/8” hole was drilled in two of the “knockout plates” (on the side to be front)
Ø Then the ¾” “romex adapter” was installed on opposite side in the top position
Ø The three wire cord had the female end removed, and about 1½” of wire was left free on each conductor.
Ø ½” was stripped (and tinned) on each conductor for soldering
Ø A spade lug was attached to the white wire, and it was attached to the silver screws on the duplex outlet.
Ø The black wire was attached to the fuse holder
Ø The switch was attached to the other side of the fuse holder, and the brass screw on the duplex outlet.
Ø I then used an 8” length of 14 ga. Romex wire to carry the ac from the duplex outlet into the chassis, and transformers.
Ø I wrapped electrical tape around the outlet to further insulate the terminals, and finished up the “Mains Module”(and carefully [because open wires are very dangerous]tested the unit)
The forth step was to make the chassis, and enclosurefor the
Ø Cut a 16” piece of the galvanized stud, then cut into the 2” sides at 4” from the end, and fold the edge in, and then the 4” piece up to make a “riser” to mount the “mains module” to the Chassis
Ø I used self-tapping screws to hold the end panel vertical, but “pop rivets” could also be used (or spot welding)
Ø Drill a 1” hole ¾” in, and down from top right side of 4” side of chassis
(the enclosure was inspired byHow To Make Cheap PVC Project Enclosures and Boxes by Chuck Stephens. (https://www.instructables.com/id/How-To-Make-Cheap-PVC-Project-Enclosures-and-Boxes/)
Ø Then after placing the pieces on the chassis to determine placement, I cut a 13” piece of the plastic 4 X 4 sleeve, and cut a 2” strip out of one side.
Ø Then I mounted the transformers on the chassis (and connected the “isolated” duplex outlet to the isolation transformer)
Ø Placing the Chassis Assy. Next to the Case allowed me to determine the placement of mounting holes for outputs, and controls.
Ø I then cut away the front side of the Chassis (on the end away from the 4” riser) a ½” by 3 ½ “ piece, to allow for the gnd binding post.
Ø I used the galvanized cover plate to lay out the hole for the outlet on the right side of the front of the enclosure [with the removed section at the back (then carefully enlarged the opening to allow the outlet to set in it from the outside & be held by the mounting screws) (The cover plate will hide a multitude of sins as long as you are reasonably careful)
Ø I then marked out the holes for the three Binding posts (arranged vertically aprox. 2 ½” inches from the left side of the front, and the potentiometer, and switch (aprox. Centered between “gnd. And +5v binding posts” at aprox. 1” centers (moving right)
Ø While drilling the holes (with a ¼” drill because that would fit the parts that I had) I also drilled a 1/8” hole for the wires from the digital voltmeter (aprox. 1” above the switch)
Parts for the low voltage supply ( for variable 0-20 volt,
and 12 volt [primarily for the volt meter, and fan]).
The schematics were already in my collection ( schematic shows 1000uf, but I substituted the 2200uf)
Ø 4 – 1N4007 rectifier diodes
Ø 1 - LM317 voltage regulator TO220 case
Ø 1 – LM7812 voltage regulator TO220 case
Ø 2 – 1uf 35volt electrolytic capacitor
Ø 2 – 2200uf 35volt electrolytic capacitor
Ø 1 – 5k potentiometer (a ten turn Pot can be used for easier adjustment)
Ø 1 – 220 ohm ¼ watt resistor
Ø 1 – heat sink (for the voltage regulators)
I then carefully assembled all the pcs together in the
Plastic Case and put a 3” X 13” piece of Perforated Aluminum on the Back to keep loose items (like fingers) out of the supply, and the 4” fan in the open end (label out and “red to red wiring).
I hope that this project will help others to build their own
“special “ projects.