Benchtop Power Supply Options

On Fri, 9 May 2014, Jasen Betts wrote:

> On 2014-05-08, Ian Field <gangprobing.alien@ntlworld.com> wrote:
>
>> IIRC - old ethernet cards have a handy switcher transformer, presumably
>> dimensioned for a 5V supply, I think the secondary is about right for 9V or
>> so - that would suit probably most of the commercially available digital
>> display modules.
>
> yeah  it's a dc-dc converter producing an isolated 9VDC from a 5VDC supply
> This is used to power the thinnet tranceiver. so look for cards with BNC
> connectors.
>
That old?  I think I cleared those out, maybe keeping a sample or two.

There was a time when I had all kinds of neat boards, and no computer to 
put them in.  Then at one point, I finally leaped ahead, so I'm not sure I 
have a computer with an ISA bus anymore.

   Michael

"Michael Black" <et472@ncf.ca> wrote in message 
news:alpine.LNX.2.02.1405090208470.12233@darkstar.example.org...
> On Fri, 9 May 2014, Jasen Betts wrote:
>
>> On 2014-05-08, Ian Field <gangprobing.alien@ntlworld.com> wrote:
>>
>>> IIRC - old ethernet cards have a handy switcher transformer, presumably
>>> dimensioned for a 5V supply, I think the secondary is about right for 9V 
>>> or
>>> so - that would suit probably most of the commercially available digital
>>> display modules.
>>
>> yeah  it's a dc-dc converter producing an isolated 9VDC from a 5VDC 
>> supply
>> This is used to power the thinnet tranceiver. so look for cards with BNC
>> connectors.
>>
> That old?  I think I cleared those out, maybe keeping a sample or two.

There's bound to be PSU manufacturers that can supply something suitable off 
the shelf - but waiting for the order to arrive is less convenient than 
raiding the junk box, and I'm really not keen on the paying for it bit! 

Michael Black <et472@ncf.ca> wrote:
> On Fri, 9 May 2014, Jasen Betts wrote:
> 
>> On 2014-05-08, Ian Field <gangprobing.alien@ntlworld.com> wrote:
>>
>>> IIRC - old ethernet cards have a handy switcher transformer, presumably
>>> dimensioned for a 5V supply, I think the secondary is about right for 9V or
>>> so - that would suit probably most of the commercially available digital
>>> display modules.
>>
>> yeah  it's a dc-dc converter producing an isolated 9VDC from a 5VDC supply
>> This is used to power the thinnet tranceiver. so look for cards with BNC
>> connectors.
>>
> That old?  I think I cleared those out, maybe keeping a sample or two.
> 
> There was a time when I had all kinds of neat boards, and no computer to 
> put them in.  Then at one point, I finally leaped ahead, so I'm not sure I 
> have a computer with an ISA bus anymore.

Speaking of ISA cards, I saw a "new" 16 bit ISA card at the "Design 2 
Part" show last week just outside Chicago.

I had to ask the PCB assembler who was showing this board off if this was 
really the best thing they had to ooh and aaah customers with.

A couple other shoddy-ish board assemblers had rejected garbage with 
defective wave soldering on display. I have no idea why these companies 
even bother to bring anything if that's all they can come up with.

The other fun stuff at the show was lots of springs (really it should be 
called the Spring Show), hand grenades (obviousy not primed and full of 
explosives but still fun) and lots of molded rubber parts that didn't 
stink.

On 5/8/2014 8:35 PM, whit3rd wrote:

> For fiddling about, you'll want one or more adjustable supplies.
> If you are comfortable doing the low-voltage parts, it's often
> suitable to pick up a carcass of some disused appliance, and
> adapt its supply to your bench (like, get an old PC power
> supply for gobs of +12 and +5V, or a newer one for those
> and +3.3).
>
> Add indicator lights, at least one for each independent section,
> or you'll not notice an overload/short circuit and shutdown or
> fuse-blowing response.
>
> Variable voltage is nice, and variable current limit is very useful
> (like, for charging batteries); consider a time switch, as well
> (to prevent overcharging batteries).
>
> Both voltage-variable and current-limit-variable supplies benefit from
> a built-in (ALWAYS CONNECTED) meter.   Whenever you adjust the knob,
> you'll want to watch the voltmeter, or (for current limit) you'll
> want to short the output while watching the ammeter.
> Watch for sales on inexpensive multimeters... like at HarborFreight.
>
> If AC power is important in your experimentation, get a GCFI
> module, an isolation transformer, and a variac (variable autotransformer).
>

Thanks a bunch for the tips and suggestions, everyone.  I too like the 
idea of building my own supply from scratch.  I've avoided the easy and 
obvious computer power supply because they tend to be noisy, and (I 
thought at least) the voltage outputs were biased off each other.  I.e., 
the +12V will only give +12V with a proper load across the +5V section 
and vice versa.  I don't foresee the need for an AC supply, and if 
someday I need one I'll make that its own project.

I'm not above dumpster diving and salvaging parts, but I'll suspect most 
transformers in consumer electronics are going to be for 9V-12V output. 
  A ~36V or whatever might be rare.  This is what drove me to start 
looking at kits.  If the Mastech unit that John Larkin posted was 
available in kit form I'd be all over it.

We have two bench top supplies where I work that look very similar to 
that one.  I don't recall the brand off the top of my head (might be 
Tektronix or other badge engineering) but they get abused quite a bit by 
the other folks and yet they're still accurate, reliable and holding 
together when I go to use one.

Meanwhile, I'll look into AoE for linear psu designs.  (I happen to have 
a copy but it can be a little dense for my skill level at times).

Thanks again.

-J

On Mon, 12 May 2014, Jurd wrote:

> On 5/8/2014 8:35 PM, whit3rd wrote:
>
>> For fiddling about, you'll want one or more adjustable supplies.
>> If you are comfortable doing the low-voltage parts, it's often
>> suitable to pick up a carcass of some disused appliance, and
>> adapt its supply to your bench (like, get an old PC power
>> supply for gobs of +12 and +5V, or a newer one for those
>> and +3.3).
>> 
>> Add indicator lights, at least one for each independent section,
>> or you'll not notice an overload/short circuit and shutdown or
>> fuse-blowing response.
>> 
>> Variable voltage is nice, and variable current limit is very useful
>> (like, for charging batteries); consider a time switch, as well
>> (to prevent overcharging batteries).
>> 
>> Both voltage-variable and current-limit-variable supplies benefit from
>> a built-in (ALWAYS CONNECTED) meter.   Whenever you adjust the knob,
>> you'll want to watch the voltmeter, or (for current limit) you'll
>> want to short the output while watching the ammeter.
>> Watch for sales on inexpensive multimeters... like at HarborFreight.
>> 
>> If AC power is important in your experimentation, get a GCFI
>> module, an isolation transformer, and a variac (variable autotransformer).
>> 
>
> Thanks a bunch for the tips and suggestions, everyone.  I too like the idea 
> of building my own supply from scratch.  I've avoided the easy and obvious 
> computer power supply because they tend to be noisy, and (I thought at least) 
> the voltage outputs were biased off each other.  I.e., the +12V will only 
> give +12V with a proper load across the +5V section and vice versa.  I don't 
> foresee the need for an AC supply, and if someday I need one I'll make that 
> its own project.
>
> I'm not above dumpster diving and salvaging parts, but I'll suspect most 
> transformers in consumer electronics are going to be for 9V-12V output.  A 
> ~36V or whatever might be rare.  This is what drove me to start looking at 
> kits.  If the Mastech unit that John Larkin posted was available in kit form 
> I'd be all over it.
>
I don't see that many transformers these days.

But, inkjet printers are plentiful in the garbage, and they seem to always 
have higher voltage power supplies, either internal or external.  I once 
brought home a Powerbook 1400CS, and needed some higher voltage to run it, 
I seem to recall 24V, and I immediately thought of an inkjet printer, and 
the first one I opened, had the right voltage on a board by itself.

Dot matrix tended to need higher voltages too, though I'm not seeing many 
of those these days. Though back then, they tended to have linear 
transformers.

I've also found AC adapters giving off about 30VDC, I think those were for 
lighting.

LCD monitors are become more common in the garbage.  Though those 
generally just need some new electrolytics in the power supply, if that 
doesn't fix them but does get the power supply going, those power supplies 
tend to be on their own board, and have reasonable specs for a lot of 
experimenting. Beats having to hack the switching supply off a single VCR 
board, or some cable box.

If you can find AC adapters of the right current, they'll be inefficient 
again if you use a regulator to drop the voltage, but cheaper than looking 
for transformers.

One thing about the switching supply AC adapters, they tend to not need a 
load to provide the proper voltage, and certainly since most offer only 
one voltage, only need a load on the one output.  That makes things 
simpler.

I once bought some surplus switching supplies, and they actually had load 
resistors built in, which seems wasteful but if the design has power to 
waste, it's a way of ensuring the supply works properly.

IN the old days, it was often useful to grab the transformers out of 
electronics found ont the sidewalk, even if not taking more of the parts. 
They often did have transformers of the right voltage, with a big run it 
was better to have transformers wound and thus have multiple windings for 
all the needed voltages than to regulate one output voltage down to size. 
VCRs, before they moved to switching supplies, tended to have endless 
windings to cover all the needed voltages.


    Michael

Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
> I'm not above dumpster diving and salvaging parts, but I'll suspect
> most transformers in consumer electronics are going to be for 9V-12V
> output.  A ~36V or whatever might be rare.

Look for (solid-state) stereo amplifiers, or tuners with built-in
amplifiers.  These usually have a big transformer with a center-tapped
winding that originally was used to generate +/- 30 to 60 V DC for the
main audio output transistors.  The transformer may also have another
winding in the neighborhood of 12 V that originally ran the tuner, dial
lights, etc.  Look at the AC line input rating (watts) printed on the
back panel to estimate the transformer capacity.  Usually these die
because the audio output transistors give up, or possibly because the
diodes or capacitors in the power supply give up; the transformer is
often OK.

As a bonus, you get a nice case, usually with lots of venting.  It has
an AC cord and possibly a switch you can re-use.  You also may get a
decent-sized heat sink, and you might be able to re-use the diodes and
filter capacitors.  The speaker terminals can get re-used as output
connectors, although you might prefer "real" binding posts.  Replace
the existing front panel with a piece of aluminum with meters, knobs,
etc to taste.

Matt Roberds

<mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me...
> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
>> I'm not above dumpster diving and salvaging parts, but I'll suspect
>> most transformers in consumer electronics are going to be for 9V-12V
>> output.  A ~36V or whatever might be rare.
>
> Look for (solid-state) stereo amplifiers, or tuners with built-in
> amplifiers.  These usually have a big transformer with a center-tapped
> winding that originally was used to generate +/- 30 to 60 V DC for the
> main audio output

You beat me to it!

Salvage transformers are pretty much drying up - some end user disposals 
houses still get the occasional antique computer with linear PSU, you can 
get some really chunky transformers - but it could be a long wait.

Radio hams tend to stick with linear PSUs because switchers tend to be 
RF-noisy, AFAIK - some ham magazines still advertise parts stockists. 

On Tue, 13 May 2014, Ian Field wrote:

>
>
> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me...
>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
>>> I'm not above dumpster diving and salvaging parts, but I'll suspect
>>> most transformers in consumer electronics are going to be for 9V-12V
>>> output.  A ~36V or whatever might be rare.
>> 
>> Look for (solid-state) stereo amplifiers, or tuners with built-in
>> amplifiers.  These usually have a big transformer with a center-tapped
>> winding that originally was used to generate +/- 30 to 60 V DC for the
>> main audio output
>
> You beat me to it!
>
> Salvage transformers are pretty much drying up - some end user disposals 
> houses still get the occasional antique computer with linear PSU, you can get 
> some really chunky transformers - but it could be a long wait.
>
I didn't mention them precisely because I'm not seeing them like I used 
to.

I was thinking recently that some things are disappearing, and I never 
stocked up.  They seemed so plentiful, it seemed impossible that they'd 
all stop.

I needed some UHF transistors for something, and realized I should have 
stocked up when there were endless tv sets being tossed out.  There are 
fewer analog sets in the garbage, and the ones I keep noticing are 
massive, too much trouble to handle to get parts out of.

There was a period when I'd grab variable capacitors out of any radio I 
saw that had no more value (and wasn't worth bringing home for the rest of 
the parts) and those are mostly gone.  Certainly I'm not seeing them.

There was  a time when I was paying a few dollars a piece for clunky early 
generation cellphones, becuase the parts were recognizable and full size. 
But those are gone too, and you can't pull much out of a tiny pocket 
cellphone, the parts are way too small, and the integration means you 
don't find many parts that can be reused.

    Michael

> Radio hams tend to stick with linear PSUs because switchers tend to be 
> RF-noisy, AFAIK - some ham magazines still advertise parts stockists. 
>

"Michael Black" <et472@ncf.ca> wrote in message 
news:alpine.LNX.2.02.1405131946280.23300@darkstar.example.org...
> On Tue, 13 May 2014, Ian Field wrote:
>
>>
>>
>> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me...
>>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
>>>> I'm not above dumpster diving and salvaging parts, but I'll suspect
>>>> most transformers in consumer electronics are going to be for 9V-12V
>>>> output.  A ~36V or whatever might be rare.
>>>
>>> Look for (solid-state) stereo amplifiers, or tuners with built-in
>>> amplifiers.  These usually have a big transformer with a center-tapped
>>> winding that originally was used to generate +/- 30 to 60 V DC for the
>>> main audio output
>>
>> You beat me to it!
>>
>> Salvage transformers are pretty much drying up - some end user disposals 
>> houses still get the occasional antique computer with linear PSU, you can 
>> get some really chunky transformers - but it could be a long wait.
>>
> I didn't mention them precisely because I'm not seeing them like I used 
> to.
>
> I was thinking recently that some things are disappearing, and I never 
> stocked up.  They seemed so plentiful, it seemed impossible that they'd 
> all stop.
>
> I needed some UHF transistors for something, and realized I should have 
> stocked up when there were endless tv sets being tossed out.  There are 
> fewer analog sets in the garbage, and the ones I keep noticing are 
> massive, too much trouble to handle to get parts out of.

Last night I found a WW power resistor with wire just right for rewinding 
(expensive) E-cigarette cartomisers, I might get as many as 20 rewinds out 
of that resistor. At one time I had a large box of resistors salvaged from 
scrap CTVs, they became less common as TV designs became more energy 
efficient so I binned loads of them - I wish I still had them now!

DVB tuners still use UHF transistors - they're just PITA SMD packages. The 
old pill style transistors were easy to use but the leads were very fragile.

For prototyping with the SMD dual gate MOSFETs, I scribe a 2x2 bit of 
Veroboard to make 4 lands, the pins just about straddle the lands. and if 
you centre it neatly don't foul the holes so you can solder in 4 bits of TC 
wire for connecting to the outside world. 

On 5/13/2014 1:52 PM, Ian Field wrote:
>
>
> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me...
>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
>>> I'm not above dumpster diving and salvaging parts, but I'll suspect
>>> most transformers in consumer electronics are going to be for 9V-12V
>>> output.  A ~36V or whatever might be rare.
>>
>> Look for (solid-state) stereo amplifiers, or tuners with built-in
>> amplifiers.  These usually have a big transformer with a center-tapped
>> winding that originally was used to generate +/- 30 to 60 V DC for the
>> main audio output
>
> You beat me to it!
>
> Salvage transformers are pretty much drying up - some end user disposals
> houses still get the occasional antique computer with linear PSU, you
> can get some really chunky transformers - but it could be a long wait.
>


My city has a pretty comprehensive electronics recycling system in 
place.  It's good for the big picture and all because it keeps 
recyclable resources out of landfills, but for guys like me it means 
that 95% of 'broken' electronics go to a 24/7 monitored dropoff site 
instead of to the curb.

However, it's the insult to injury that makes it the worst-  As I 
mentioned previously, I work for an electronics recycler so I get to see 
(literally) hundreds of thousands of pounds of this stuff on any given 
workday.  The caveat: I can't have *any* of it.  I can't even *buy* it 
at all.  There's a complex pile of reasons why, most of which I 
understand and agree with, but you've got to understand my frustration.

The small comfort I try to retain is that at least I get to see the 
stuff, and that I get to see things that I otherwise wouldn't have.  One 
of the local universities did a lot of RnD during the beginning of the 
Microcomputer era, so occasionally they'll clear out some old bunker of 
shit from the 1960s and we'll get loads of tube-fired oscilloscopes, 
nixie tube counters for who knows what, big panels of circuits 
prototyped with wire-wrap, reel-to-reel tape drives, the oldschool hard 
disk packs with stacks of 14" platters and neat, vintage test equipment.

One time we got in a bunch of 60s or 70s looking radio stuff (as in 
radio broadcast transmission) and with it was about 150 circuit boards, 
each board having networks of logic gates built up with metal can Ge 
transistors and carbon comp resistors.  Probably 400 components per 
board.  I'm no doctor but I didn't see anything other than the radio 
itself that looked like it dealt with analog signals.  I can only 
speculate what was communicating over radio with digital signals in the 
1960s and 1970s.

Stuff like this hasn't really been 'around' for decades, and since I 
have a fascination with electro-archeology and lore, I feel lucky that I 
have a chance to see these things and look at them once in awhile.

Even if I can't play with it.  :-/

-J