45 replies to this topic

[Mr. M]

There is a space next to the AC to DC brick for the control circuit that takes 12V DC and makes the output variable. The brick is a fixed voltage output. I found a voltage regulator and an application note telling how to make it a variable.

The board is from Radio Shack, the parts are from Digital Key, and the heat sink was salvaged from a scrap box at work. The regulators are only rated for 5A, the application note shows how to gang them to make them 10A capable. The wiring of the control board is point to point with no custom circuit board required.

This assembly is not finished. All the off board connections need work to provide a place for the wiring to attach. Building the board is quite unconventional, but should work just fine.

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[anarot]

L  ooks nice and neat. 

[anarot]

Completely off  topic, but do you guys (USA) have on/off switches on your power sockets. Just been watching a couple of TV programs and it looks like they just plugs this in

[Mr. M]

Not typically, but there probably one out there somewhere.

[Bill from NH]

Completely off  topic, but do you guys (USA) have on/off switches on your power sockets. Just been watching a couple of TV programs and it looks like they just plugs this in

 

I have a couple duplex outlets (sockets) in my living room that are split, one has constant power, the other is controlled by an on/off switch. The switched outset comes in handy for turning on a lamp in a dark room as you enter the front door. Today, there might be other means for accomplishing the same thing, but my house was built 35 years ago.

[mdiv]

Very interested in this build!  How is it coming along?

Mike

[Mr. M]

I have made some progress, but have been sidelined with selling a house and getting ready to move. I will update the pictures when I get a chance.

[mdiv]

Cool, thanks Chris!  Getting sidelined these days is easy!

Mike

[Mr. M]

The back panel is wired for the AC plugs and is ready for wire nuts to connect. The front panel AC is wired and also ready to connect. The top cover has the AC plug power indicator light installed. Next are all the DC connections. I put this light on top so that it is visible when looking at the top when on the bench.

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[mdiv]

 

Looking good!

[Mr. M]

These were taken a long time ago and never posted. So here goes.

The module that controls the voltage from the regulated supply is wired and completed. I used crimped lug connectors bolted to the board instead of a connector to get the wires off the board. The module is mounted with spacers to the bottom of the chassis.

The AC power indicator for the power plugs on the back is installed on the top cover.

All the other connections are wired and ready to install with wire nuts to make changes and repairs easy. The sharp eyed reader will note that the connectors to the regulated supply for AC in and DC out as well as the 120V AC power cord are not yet installed.

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[Mr. M]

One of the suggestions from the regulator manufacturer's application sheet that I found interesting is the addition of 2 feet of 18 gauge wire on each output of the LT1083. This is to take into account small differences in the output of the 2 devices in parallel. This is shown in the schematic above. The wire for this is not shown in the pictures above.

[Mr. M]

I have made a couple of updates since this first build and will post them shortly.

[Mr. M]

I didn’t like the way the regulators worked in the 5A range, despite measures they would go into thermal shutdown. So I built an old school control with a MOSFET and NPN transistor. It never did what I wanted exactly, so I have replaced it too.

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[Mr. M]

I replace the controller with a PWM from Amazon 12V 10A for less than $10. It came with a knob and has an on/off switch built in. I ran out of time getting the previous one right and just moved to an off the shelf solution.

[Mr. M]

Back to the original 1981 box. I straightened the case, added a new 16V 10A transformer and the same PWM controller. Rewired everything. Cost was about $30. You can see the PWM in the open photo, the black case with the power supply heat sink.

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[Mr. M]

This is really old school, transformer, diode bridge, big cap, PWM, and gauges. It is not a regulated supply and has all analog displays, but works fine and sits nicely on the bench. I connect everything with wire nuts for easy service. It is a bit heavy compared to modern regulated supplies.

[Clyde Romero]

Very impressive, you're a NASA grade engineer 

[Mr. M]

Hahahahaha!  Kind of you, but in the circles I work with, this is, well, not so impressive. Program Management Aerospace is my comfort and strength compared to this fun stuff.

[Bill Seitz]

I rebuilt a small, 2-amp DIY power supply I purchased from someone at work and turned it into a low voltage supply for testing and breaking in motors. I used the parallel IC regulator approach using two 7-amp regulators similar to the ones used here initially. I think the problem encountered here with the regulators going into thermal shutdown is insufficient heat dissipation. Aside from the block of aluminum, I'm assuming this was attached to the housing. I used much more heatsink area than this and have no problems with thermal shutdown even on motor break-in runs of an hour or more. My supply provides 1.25 to 6.97 volts at 8 amps rms (higher peak), the limits of the transformer I used.

[Mr. M]

Yes, could be, but they were never very warm when they shutdown, so after a bit of tinkering, moved to a different solution.