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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Mon 26, 2017 3:05 am 
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Jim Mueller wrote:
There are other failures that could cause excessive output voltage (like a sense lead getting disconnected)...
All of the many remote-sense power supplies I've encountered have an internal 1-ohm resistor between each output and sense lead to avoid such problems.

- Leigh

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Mon 26, 2017 5:24 am 
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Hi Jim, and welcome to the discussion...

Jim Mueller wrote:
Quote:
Sounds like the crowbar is more of a compromise and way to reduce costs.

Not true. A crowbar circuit is a safety device. If the output voltage of a power supply exceeds a certain value, it short circuits the output to prevent damage to the load. This is especially important in linear power supplies where the most common failure is a short in one of the pass transistors. This causes the output voltage to go sky high. In switching power supplies the most common failure is the switching transistor going bad. This causes the output voltage to go to zero. There are other failures that could cause excessive output voltage (like a sense lead getting disconnected) but they are much less common. A relay is unsuitable for this purpose because it is too slow; the load will be damaged before it opens.


Hmmm. Okay. Well, scratch that idea. How about this: use the Arduino to cycle the display, showing current, voltage, hours on the internal backup battery, temperature, line voltage, and the number of hours since power-up. Call it 5 seconds before it cycles to the next reading. Leave the sense circuit alone completely. Should the Arduino notice that power has been removed (fuse blown and it's running on the backup battery), then use bluetooth or wifi to transmit an SMS text message of the failure.

Quote:
I don't see computer power supplies as being too useful for a variety of reasons: noise, minimum load requirement, the useful output voltages are usually the low current ones, and the need for additional circuits to turn them on (applying power only turns on the standby supply which allows the computer to "wake up" when something happens, the main supply needs to be turned on by this).


Well, I guess we all know that they are a compromise to save on supply costs, and your comments only prove the situation.

Quote:
On my job I used industrial grade switching power supplies to run low level analog circuits with no problems. The key words are "industrial grade".


Oh, I can see how something like that would be absolutely no problem. You start throwing some serious cash at things, stuff starts to happen very quickly :D.

73,

Randy AB5NI

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 2:02 am 
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Leigh wrote:
Jim Mueller wrote:
There are other failures that could cause excessive output voltage (like a sense lead getting disconnected)...
All of the many remote-sense power supplies I've encountered have an internal 1-ohm resistor between each output and sense lead to avoid such problems.

- Leigh

The ones I have seen have a much higher value resistor, like 68 ohms, but it works the same. I have seen a few, mostly older units, that don't have those resistors.

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 4:22 pm 
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What a bizarre post, full of good and bad info, over and over!
Cheap components? How long would a power supply maker last in the hyper competitive PC world if their stuff didn't last?
Have YOU ever had a PC supply fail in use? I've used them since they came out and have NOT. I know it happens, just at very low probability.
Hundreds of thousands of hams operate the most sensitive receivers next to one, often more, powerful PCs without hash problems!
So how bad can the supplies be?
I use an HP server supply from Ebay ($50) and it's perfect. Been on for years, like the thousands of servers at Google!
There are many articles on using PC supplies, just study them.
On the analog side, learn to prowl hamfests and look under the tables. We just had one and great analog supplies and parts were passed on at giveaway prices, like 2-10 bucks for a chassis and parts weighing 20 pounds! There were several filament transformers, for LV supplies.
Air conditioners and furnaces contain nice little 24 volt transformers, great 24V power relays, and motor starting caps of 30-50 mF.
Wall warts with switching supplies are the most notorious noise makers. You can tell them by weight. A wall wart and adjustable regulator can make a great adjustable supply.
So start scrounging and building. There are parts all around and many are inexpensive.
Locate experienced people who will advise you, join a radio club, READ, READ, READ. The ARRL handbooks cover most of our stuff very well. Used ones are a few bucks and 50s and 60s are my favorites. Later is better for solid state projects.
Electronics by guesswork and rumor is rarely successful!
Wilson
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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 6:01 pm 
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how are the "Meanwell" brand of power supplies? I see them on ebay for $20 and up.
You can get a 24v, 16amp PS for about 30-40 $$.

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 6:32 pm 
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Howdy Infomet, and welcome to the conversation...I think :D.

infomet wrote:
What a bizarre post, full of good and bad info, over and over!


Glad you're having fun :D.

Quote:
Cheap components? How long would a power supply maker last in the hyper competitive PC world if their stuff didn't last?


Not very long, and a lot of them go out of business quite often, actually.

Quote:
Have YOU ever had a PC supply fail in use? I've used them since they came out and have NOT. I know it happens, just at very low probability.
Hundreds of thousands of hams operate the most sensitive receivers next to one, often more, powerful PCs without hash problems!
So how bad can the supplies be?


As a matter of fact, I've seen numerous supplies fail. When you do any type of IT work in industry, you run across this quite often, actually.

Quote:
I use an HP server supply from Ebay ($50) and it's perfect. Been on for years, like the thousands of servers at Google!


Unfortunately, you are being a bit self-centered here and are only seeing things from "your" point of view. "If it works for me, it must work for everyone else." You really, really need to read, dude, and look up something known as "Mean Time Before Failure" in the engineering world. Also, I worked in the oilfield, and the absolute worst AC power you can imagine was supplying electricity to our electronics and PC's. Most cheap supplies failed miserably.

As an interesting aside, the only consumer-grade UPS' that could take rig power and keep on ticking were built by APC. All others cratered.

Quote:
There are many articles on using PC supplies, just study them.


And who says I haven't? That's the main reason I've asked this question. From perusing the forum posts here, I realized that I was being surrounded by very learned engineers and technicians who would have knowledge in this area. So, if they say avoid them, I say, "Thanks a ton, guys, and I will."

Quote:
On the analog side, learn to prowl hamfests and look under the tables. We just had one and great analog supplies and parts were passed on at giveaway prices, like 2-10 bucks for a chassis and parts weighing 20 pounds! There were several filament transformers, for LV supplies.


Yet again, who says I haven't? You sure are making a ton of assumptions here to try and defend your argument.

Quote:
Air conditioners and furnaces contain nice little 24 volt transformers, great 24V power relays, and motor starting caps of 30-50 mF.
Wall warts with switching supplies are the most notorious noise makers. You can tell them by weight. A wall wart and adjustable regulator can make a great adjustable supply.


I actually did refrigeration work as a kid. Neighbors I grew up with owned a big airconditioning company. We did this as a summertime job and on the weekends to buy our minibikes, motorcycles, 4-wheelers, hunting and fishing equipment, cars, beer, and chase women :D. Fortunately, I have a few 24-volt relays in my junkbox somewhere in the attic because of this, and if I make a phone call, I can have any of the devices you've mentioned in a heartbeat.

As far as wall-wart's go, I've actually designed and built a "wall-wart conditioner" that takes the input of a wall-wart, runs it through a full-wave bridge rectifier, with each diode bypassed at RF to avoid common-mode hum, and it's filtered very, very well. From that point, the B+ is fed to numerous 3-terminal regulators, such as the 7805, 7806, 7809, 7812, AND the LM317 series put out by Fairchild.

Quote:
So start scrounging and building. There are parts all around and many are inexpensive.


Yet again, who says I do not do this already? Oh, it's you, the guy that doesn't know jack crap about me. Never mind.

Quote:
Locate experienced people who will advise you, join a radio club, READ, READ, READ.


For the record, I'm an avid reader, studying electronics since I was very, very young -- six-years old, to be precise. My Dad was a ham and educator, and he taught me electronics so I could be like him and become a ham. I haven't quit reading about it and studying it since. Also, what the hell do you think I'm doing here on these forums? I know electronics decently, but I also know there are folks out there that will always know it much better than I will. I'm a programmer -- software engineer -- and I do know it well enough to design and build stuff with them in a working environment, where they take care of the hardware, and I make my firmware and UI code work on the devices we build.

Quote:
The ARRL handbooks cover most of our stuff very well.


I have been reading the handbook and studying it since the 60's. I've also read, "Solid State Design For the Radio Amateur" when it first came out, and I have 3 dogeared copies to boot. I've also read, "Radio Frequency Design", "Experimental Methods in RF Design", "The Art of Electronics," and other books and periodicals too numerous to mention.

Quote:
Used ones are a few bucks and 50s and 60s are my favorites. Later is better for solid state projects.
Electronics by guesswork and rumor is rarely successful!


And who says I'm guessing at any of this, Wilson? Look, you seem to be a decent sort of bloke -- although a bit feisty -- trying to direct me in how I must educate myself, scrounge parts, and learn electronics. For that, you have my thanks and utmost gratitude! Please keep me informed of any other misgivings you might notice. I'm here to learn, after all.

73 my friend,

Rand AB5NI

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 6:50 pm 
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infomet wrote:
Have YOU ever had a PC supply fail in use? I've used them since they came out and have NOT. I know it happens, just at very low probability.



YES, we replace PC power supplies all the time, from all brands. And I work on printers, not computers, but PC's are a part of the
system that I have to support. This has been true for Xerox, Oce' and Canon gear I work on. NOT office equipment, I work on production systems that run 24/7. I'd say the "probability" is higher than "very low"
I replaced my 1st PC PS about 3 years after the 1st PC came out. They did not last forever then and not now. Manufacturers have cut costs everywhere, including the PS.
How else do you think you can buy a complete PC for under $200?

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Tue 27, 2017 7:03 pm 
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Howdy glue,

glue_ru wrote:
how are the "Meanwell" brand of power supplies? I see them on ebay for $20 and up.
You can get a 24v, 16amp PS for about 30-40 $$.


Not really sure. OTOH, I can tell you that most of the supplies that come out of Taiwan are semi-decent, but the ones made in China aren't on my invitation list to power any PC I'll ever own :D.

I do know one thing: these supply manufacturers will pop up and disappear quite frequently, selling them until we zero in on them and know that they're junk. No problem. They'll just use another company and supply name and do the same thing, over and over. This tactic is quite prevalent in China and Taiwan, actually.

73,

Randy AB5NI

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jun Wed 28, 2017 6:57 am 
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glue_ru wrote:
how are the "Meanwell" brand of power supplies? I see them on ebay for $20 and up.
You can get a 24v, 16amp PS for about 30-40 $$.

This brand has been around for a while but I haven't used them. One brand I avoided was Cosel, not because they are bad quality, but because their products all seem to have weird dimensions so that it is difficult or impossible to find a second source.

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jul Mon 03, 2017 2:58 am 
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Rich, W3HWJ wrote:
2N3772 = much better pass transistor. Higher gain (easier on your regulator IC) and bigger chip (should be more reliable).

Rich, is there a PNP complement to the 2N3772?

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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jul Mon 03, 2017 6:56 pm 
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Hello guys,
the powersupply that have in my computer is Enermax brand it would be nice to find som e cheap ones of them


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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Jul Mon 03, 2017 8:03 pm 
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Quote:
Rich, is there a PNP complement to the 2N3772?


Not that I know of. Most series/pass transistors were NPN.

People like to do this:

Image

But not many big PNPs were available. I am sure you can find small TO-220 in the TIP series.

Or... there is a work-around using a PNP to drive a big NPN.

Image

Rich


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 Post subject: Re: Computer Power Supplies and Powering Homebrew Stuff
PostPosted: Nov Fri 10, 2017 4:25 am 
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I use these things all the time when I need a quick regulated source of 5, 12vdc. I use one to power the added fans (also pulled from roadside PCs) on finals, boat anchors, and other utility stuff.

I also use one to power arduino projects once they're completed. Yes, you could use an arduino with some sensors to do power monitoring...tons of cheap sensors available at SparkFun or on ebay and many code samples online. Tons of arduino ham projects to be found online.

Yep, could be noisy, although I haven't experienced that yet. They are just very handy. Clip excess leads, add a toggle switch and you're in business.

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