Benchtop Power Supply Options

Hello again,

It is time for me to acquire a better bench top power solution. Most of the time I will use it to power a breadboard for experimentation. I used a wall wart for awhile until it got super noisy, and batteries are a hassle. I was about to go for something like this:

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And then attach something like this:

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to the leads internally. (and maybe add a power switch, mount it and the breadboard all to a piece of melamine board, etc). I would of course verify output with the DVOM before I trusted the display.

For someone still in the larval stage, do you suppose this would be adequate? Will 15V be enough for future growth? So far I've done mostly

5V logic, 9V guitar stompboxery and small radio. Occasionally I've done some 18V and 24V stuff, though. I see that a lot of other power supply kits say they go up to 30V, but they cost upwards of 4x as much.

Am I being too cheap? I was going to just buy/dumpsterdive the parts and use an online schematic, but I might not know enough to verify a schematic before I fry myself and burn the house down. Therefore I think a kit is the way to go- should be correct, comes with all the right parts, and (hopefully) has instructions that'll teach me a thing or two.

I've looked at a bunch of kits and this Elenco one seems pretty idiot proof, but is there anything else you folks might suggest otherwise?

Thanks.

-J

Reply to
Jurd
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0-30V @ 3 AMps, digital display with current limiting controls for 49 bucks. get two if you can so you can generate dual rails, or look at that site and get a dual supply.

I always send people here when low cost is in their plan!

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Jamie

Reply to
Maynard A. Philbrook Jr.

Your plan is sound, except that you'll find that the case is much too small for the meter.

Look here if you want complete solutions:

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I've found that regardless of whether you're doing a 1-off or production, the box you put the electronics in almost always costs more than the electronics. So you're tossing quite a bit of value along with the box.

You can also just use the power supply as-is, and check the voltage with a meter when you need to. That works well for me.

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Tim Wescott 
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Reply to
Tim Wescott

This costs a little more, but it's a linear, so will be less noisy.

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I use one. It's very stable.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

Some of these little LCD and LED meters can measure their own power supply voltage and some can't. In other words, some of them *require* a 9 V battery to work. It usually says somewhere in the description.

Good idea.

If you have any plans to do audio stuff that requires both positive and negative supplies, it might pay to buy a dual-output supply. You can interconnect the two supplies (either with built-in switches or by applying wires to the outputs) and get both positive and negative. On the fancy ones you can just turn one knob to vary both outputs.

Don't forget that a "power supply" adjustable in 1.5 V increments is as close as all the AA batteries (and holders) you can scrounge. This is not the right thing for 5 V at 10 A but if you need an odd voltage at low current for a little while, it's hard to get anything simpler.

Use the right size fuse in the AC input, be very meticulous with all the AC (120 V) wiring, and unplug the thing from the wall when you're not using it, and you are unlikely to burn the house down. If it develops a bad fault when you're sitting in front of it, it will usually heat up slowly enough that you can either shut it off and investigate, or (in urgent cases) toss it out the window.

General advice: if you buy one, it will probably have a fuse in the AC input. Find out what type and size it is and put a few on your next Digi-Key or Mouser order. You shouldn't blow it too often, but it's a bummer to be out of commission for a 25 cent fuse. (If it keeps blowing and you don't know why, then there is a problem inside the supply. But sometimes you know why, like you accidentally connected that 300 A diesel starter motor to your 3 A supply.)

It may or may not have a fuse in the DC output; most don't. Usually, if you try to draw too much current from the output, the voltage automatically drops lower (as low as maybe 1.5 V) to reduce the current.

That design (or a clone of it) seems very popular. The oval power button and three binding posts are exactly the same on all of them; older ones had LED meters but the newer ones are LCD. I see the same thing sold (for more money) as an "HQ Power PS3003U", and Tektronix even rebadged the older LED-meter version. There is a wider version with dual variable outputs and a fixed 5 V output as well.

I have used the Tektronix LED-meter version, plus someone else's clone of the LED-meter version, before, and they both worked well. The meters on someone else's clone were slightly inaccurate, but those specific units had also had several years of exposure to students.

Personally, I use an 0-12V/6A, 0-24V/3A supply that I assembled from a kit about 25 years ago. It has served for almost all of the trouble I get into. It was designed by Western Electric engineers and I expect it to outlive me. :)

Matt Roberds

Reply to
mroberds

If you've got more time than money, then I like the idea of building your o wn power supply. Either from a kit... or better yet (more learning potenti al) building it yourself from pieces/parts. There are lots of places that will show you how to make a linear supply. ("Art of Electronics", for one. )

And hey you can draw up a schematic and post it here for comments.

If not, I also like the mastech linear supplies that John L. linked to.

George H.

Reply to
George Herold

If not, grab a small transformer out of a clock radio or something and make a little linear power supply for it. The meter won't require much power. I suppose at this point, there are plenty of switching type AC adapters that could be put in a box without taking much space.

Michael

Reply to
Michael Black

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.

Reply to
Ian Field

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).

Reply to
whit3rd

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.

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Reply to
Jasen Betts

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

Reply to
Michael Black

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!

Reply to
Ian Field

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.

Reply to
Cydrome Leader

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

Reply to
Jurd

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

Reply to
Michael Black

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

Reply to
mroberds

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.

Reply to
Ian Field

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

Reply to
Michael Black

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.

Reply to
Ian Field

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

Reply to
Jurd

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