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 Post subject: Homebrew Power Supply?
PostPosted: Jan Wed 13, 2021 9:59 pm 
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Location: 07960
I checked out the random electronics at my town's recycling center today, and came across what appears to be DIY-ish looking DC power supply. At least that how it looks from the front--inside looks more "produced" than I expected. Anyway, I haven't done anything with it yet, but thought you guys would appreciate some pics.


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PS 4.jpg
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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Wed 13, 2021 10:13 pm 
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Two more pics for posterity.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Wed 13, 2021 10:53 pm 
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Location: S. Dartmouth MA 02748-1225 USA
I kinda doubt a schematic could ever be found. So, check out the caps for leakage, they look like quality, check any devices for shorts, transistors, diodes and what looks like SCRs. If they all appear good, power via a variac and dim bulb. If it comes up with out blowing up. Guesstimate the load and fabricate some load resistors, then cook for a 1/2 hour. If good then go from there. Be great if it was adjustable and it may not be too hard to figure out. Then make it so, add a couple a rectangular panel meters, el-chepos, good bench supply that may well stand the test of time...

I have a couple of vacuum tube supplies real boat anchors, in fact big enough for a cabin cruiser. They work, work good and do so when ever I flip the switch.

That one Sprague cap has a date of 6825, but if it is a quality cap....

None of this switch mode crap for me... :roll:

chas

-------------------------------------------------------------------

How does the town allow taking of the electronics scrap? Oops thin ice?

I can't touch anything at the transfer station, not allowed, period...

At junkyards, depends on the yard generally pay 10 to 50% over the scrap value so the yard makes money. I used to buy shooting lead that way and the occasional small hand bench press or other mechanical junk...

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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 12:06 am 
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That sure looks like a complex circuit to simply provide 3 voltages; are you sure it's just a power supply?

Back in the '80's, my wife was taking an electronics refresher course, and I helped her build a simple power supply. It still works just fine, as I had recently used it to power a solid state car radio.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 1:12 am 
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Location: 07960
chas: We're on the same page. I plan to test the various components before powering up with my variac and DBT. That said, I already have a decent HP power supply for my bench work, so not sure how much effort I'll want to put into it if there are significant issues.

Here in NJ, some towns will let you take stuff from the electronics recycling and others won't. I've gotten some decent things, including an Adcom speaker selector, Denon receiver, and some completely trashed equipment that I was able to scavenge for parts. One man's trash, eh?

fifties: Nope, I don't know for certain that it's a power supply. And you're right that there's a lot going on. For instance, did you catch the line voltage selector switch for 115VAC and 230VAC?


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 1:13 am 
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Location: Dallas, TX
That's how precision solid state linear power supplies were done before there were integrated circuit three terminal regulators were available.
I do think I see a SCR also. That may be part of a "crowbar" circuit. If for any reason the output voltage rose above a certain value the crowbar would trigger and short the output to protect anything connected to it.
Notice each output has a fuse.

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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 1:42 am 
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Location: 07960
Notimetolooz wrote:
That's how precision solid state linear power supplies were done before there were integrated circuit three terminal regulators were available.
I do think I see a SCR also. That may be part of a "crowbar" circuit. If for any reason the output voltage rose above a certain value the crowbar would trigger and short the output to protect anything connected to it.
Notice each output has a fuse.


Interesting. I'll have to pull the board again to see if you're right about the crowbar circuit.

Looks like I'll have to check all of the solder connections. I've already found two that were never done in the rectifier bridge.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 2:20 am 
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Best to heat sink that re-solder job. I suspect that these older tophat rectifiers may not like excessive soldering heat...

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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 4:08 pm 
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Location: 07960
Anyone recognize this plug style?

The hot and neutral pins measure 7.5mm apart, center to center.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 5:54 pm 
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Joined: Dec Sat 28, 2019 4:18 pm
Posts: 563
Location: Corinth, TX
Looks like components stripped out of a commercial PS and stuffed into a homemade case. Two clues: the homemade Dymo labeling (duh!) and the circular, instead of D-shaped, hole for the input power connector.

Chas wrote:
Best to heat sink that re-solder job. I suspect that these older tophat rectifiers may not like excessive soldering heat...

If you wish. I wouldn't bother. A clean, well tinned soldering iron and, as with all solid state components, get on and get off - fast. Those old, top hats are surprisingly rugged.

And I concur. That SCR indicates the presence of a crowbar.

John


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 9:10 pm 
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Joined: Mar Sun 25, 2018 10:50 pm
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Location: 07960
Checked out most of the components, soldered those diodes, and brought it up on the variac and DBT. It lives! The +5V and -5V were both spot on, and the 24V just needed a slight tweak of the trimmer.

Still need to figure out what this type of power socket this is.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 11:29 pm 
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You can always change the socket to something more usable.

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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Thu 14, 2021 11:36 pm 
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What would kinda be appropriate is a IEC 63020 male bulkhead power connector, salvage from an old computer power supply...

Then you will never be short of a power cord. Who hasn't got a computer power cord hanging around...

I think I have a few connectors about if an old computer PS isn't around...

Will need to do a bit surgery is it goes into a round corner rectangular hole... chas

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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Fri 15, 2021 2:57 pm 
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Joined: Mar Sun 25, 2018 10:50 pm
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Location: 07960
Yeah, I'll likely just replace it with an IEC 63020 male. Still, it's weird that I can't find anything on the one that's in there. I assume the "W" in the shield symbol is probably for some kind of certification agency, a la SA?


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Mon 18, 2021 8:41 pm 
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Location: 07960
Ok, wrapping this up. Installing an IEC 63020 would have required a fair bit of cutting around the existing mounting hole, so I decided to install a captive power cord instead. I retained the original D-shaped plastic piece shown in the pics, cut off the two male pins, and widened the top screw hole so that it could accommodate the new cable. Anyway, it does the job. Also: new bulb for the red indicator on the front panel and one new fuse holder. Now I'll put it away and forget I even have it.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Mon 18, 2021 8:49 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 1981
I'm glad it's yours and not mine. I already have too much stuff I don't know about.

Occasionally I take a tour around the closets and garage and see something I don't recognize. I think oh boy I wish I had one of those. Wait, I do have one. And if I do, why? I should sell it. To whom?

It's a disease.


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Tue 19, 2021 3:53 am 
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Joined: Dec Sat 28, 2019 4:18 pm
Posts: 563
Location: Corinth, TX
And a week after you have sold it, "Rats! I wish I had kept it."


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 Post subject: Re: Homebrew Power Supply?
PostPosted: Jan Tue 19, 2021 4:01 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 1981
What strikes me as strange is that hobbyists who have far more money than I and way too much stuff will try to squeeze every nickel out of you if you want something they have. In a few years their widows will give the stuff away.


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