Regulated switching supply

[Stuartambient]

First, what I am referring to is one of these http://www.amazon.com/gp/product/B00WW60UKU/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00WW60UKU&linkCode=as2&tag=gre09a-20&linkId=RTE4RFN663Z2CZ7K

12V 5A 60W DC Universal Regulated Switching Power Supply,Power Transformer

Electronics is new to me and have done a few projects to date, mostly in r/c multirotors. So I'd like something I can use with my charger for lipo charging but also a decent power supply for testing things and maybe some small kit projects with my son. 

I've been reading up on converting a PC psu but I'm also feeling cautious, especially after searching through some threads here.  Aside from the noise issues the potential dangers concern me as well.  I've looked at some Mastech's and that maybe the right option but something DIY still interests me.

I found one or two online projects that used the unit I referenced above.  Add ons are the posts, voltage regulator and meters.  So I'm wondering if these supplies are cleaner noise wise and safer making a better option then recycling an ATX?  It states that it has "Shortage Protection. Overload Protection. Over Voltage Protection".  That should cover the safety issue better but I'm still not sure.
 

[Ian.M]

Its probably intended for lighting applications and may well be noisier than a good quality ATX supply would be.  Its certainly more dangerous as it has exposed mains terminals.   It will need a case and may need a cooling fan.

If you are building a PSU based on an ATX supply, DON'T MOD THE ATX PSU, and DON'T CUT ANY CABLES.  Simply plug it's motherboard connector into an ATX PSU breakout board.  That way when you do something dumb and blow the PSU, or it dies a natural death, it only takes 20 minutes to swap in a new one, and if it died on its own and the old one is under warranty you can return it.

[rstofer]

There's probably nothing wrong with that supply.  At the cost, who cares?  Play with it for awhile and see how it goes.  Personally, I don't have much use for such a powerful supply so I would probably put a 1A fuse in series with the output.  But that's just me and my needs...

I hung one of these gadgets on an ATX supply and it seems like a great solution:
https://www.sparkfun.com/products/12867

I haven't used the modified ATX supply but I did remove all the unused cables.  It's a real clean setup.  But, again, too much for my needs.

[Stuartambient]

Yes, a lot of these style supplies say CCTV / Lighting applications.  I've looked at the ATX breakout board but while it keeps me from messing with the internals aren't there other potential dangers? Makes me nervous when I see multiple warnings around in comments. 
Burning a board or motor isn't horrible and that risk I can take it's the fire part.  And of course I have found plenty of comments saying theirs have lasted and worked well for many years.   

I had found the  Sparkfun kit the other day and would have snatched it but it's currently out of stock.  Certainly would make things easier. 

[bitseeker]

If you want to focus on your projects rather than having the power supply be a project and/or cause you to question its condition or safety, you may want to consider getting a linear lab power supply. Even if you weren't a beginner, it's a good idea to have at least one supply that you can rely on. Then, you can use it to design your second power supply.

My first power supply was an HP 6200B. An oldie, but a goodie, and still running in my lab. There are plenty of other quality used gear to choose from without breaking the bank.

If you indicate your budget, what voltage and current requirements you have, and any other special features, if any, folks here can offer recommendations.

Note that linear power supplies generally have much less noise on their output than switching power supplies, but are not as power efficient. Unless you're going to be driving something at high power settings for extended periods of time, I wouldn't worry about efficiency and go with a linear supply.

[Stuartambient]

For my charging needs I can probably be okay 12 - 17v, current would be preferable at 5-10a.  For other things probably 1.5 - 3a. So while I could get a charger ps for $20 that would give me 16a / 240W my idea was to combine the two into one unit, projects and charging.   

Outside of atx being a worse then poor substitute for a lab supply (paraphrasing comments I've read on eevblog) I will still try to work on it even if I go for a linear supply. 
I guess I need to figure out what type of things can cause the atx to be dangerous outside of user error and user design. 

[rstofer]

A couple of simple rules:  Believe only half of what you SEE on the Internet and NONE of what you read - including this!

Here's another version of the ATX power board:
http://www.ebay.com/itm/24Pins-ATX-Benchtop-Power-Board-Computer-Power-Supply-Breakout-Adapter-/262194399981

Note that all of the outputs are fused at 5A.  There are other variants on eBay.

Still, if that 12V 5A supply is what you need, go for it!  You can put a piece of plastic (Lexan) over the mains connections.

[Stuartambient]

That breakout board looks good.  Sadly though I was going to get around to the conversion last year and wound up getting as far as soldering the PS_ON and GND together.  Guess I'd have to get some molex tools to fix the plug.

I'm usually pretty good about skepticism and the internet but add some lcd screens and blue led's and I'm in 110% 

[Ian.M]

You can bodge the plug, and Molex tooling doesn't come cheap - one flywire for PS_ON soldered direct to the back of the board at the cnnector pin isn't too bad.  If the PSU ever dies, just snip off the wire right at the joint to remove the bodge and plug in the next unmodified PSU.  Alternatively, if you've got a scrap PSU to nick a contact from, extract the female contact complete with enough wire to splice, do a neat job of splicing and sleeving it, then insert the replacement contact in the good PSU's connector.

[Stuartambient]

You can bodge the plug, and Molex tooling doesn't come cheap - one flywire for PS_ON soldered direct to the back of the board at the cnnector pin isn't too bad.  If the PSU ever dies, just snip off the wire right at the joint to remove the bodge and plug in the next unmodified PSU.  Alternatively, if you've got a scrap PSU to nick a contact from, extract the female contact complete with enough wire to splice, do a neat job of splicing and sleeving it, then insert the replacement contact in the good PSU's connector.

Excellent, great to know. I wonder what the viability is of adding a step up down converter to the board. 

[Ian.M]

The classic way to build an adjustable switching supply on the cheap is to take an old laptop power brick, anything over 18V is good, between 3A and 5A then use a CC/CV buck (stepdown) converter module off EBAY,  removing the current and voltage presets and fitting front panel pots with a resistor added to one end of the current pot track to limit the maximum current to 1/2 the module's nominal rating^* or to stay within the current rating of the laptop PSU, whichever is less.   There are a few other 'wrinkles' and the result is nowhere near as good as a proper linear bench PSU, but its good enough to get started with.   

* Chinese Watts are like Sears Horsepower - purely a marketing number.  If you don't derate the module generously it *WILL* *NOT* *LAST* and the failure mode will probably involve letting the full input voltage through to the output.

[ez24]

The classic way to build an adjustable switching supply on the cheap is to take an old laptop power brick, anything over 18V is good, between 3A and 5A then use a CC/CV buck (stepdown) converter module off EBAY,  removing the current and voltage presets and fitting front panel pots with a resistor added to one end of the current pot track to limit the maximum current to 1/2 the module's nominal rating^* or to stay within the current rating of the laptop PSU, whichever is less.   There are a few other 'wrinkles' and the result is nowhere near as good as a proper linear bench PSU, but its good enough to get started with.   

* Chinese Watts are like Sears Horsepower - purely a marketing number.  If you don't derate the module generously it *WILL* *NOT* *LAST* and the failure mode will probably involve letting the full input voltage through to the output.

Not a bad way to go.  Do not use Dell (has 3 wires and not common plug).  Cheap ebay bricks not good.  You can find good used Toshiba ones that use 2 wires and common plugs.  Then cheap bucks to get to your voltages.  This way you get to keep AC main voltages on the floor.

 I once was at a Chinese factory and asked how many watts an amp had.  They said whatever I wanted they would write it on the amp, so I could have gotten a 10,000 watt audio amp for $1 (really 2 watt).   I suggest using 25% reduction on those Amazon power supplies.  It will certainly over heat if run at rated power.  In other words, you cannot believe Chinese ads.

[Stuartambient]

I've considered a laptop brick but the last one I had ran for about 2 hours and died.  Got that one off of Amazon.  Saw one the other day, recommended by a 'maker' on YT but it had horrible feedback on Amazon that echoed a quick death as well.  Usually they run between $10-$20 so replacing them frequently is not cost effective.  My wife says she has a pile of bricks at work so we may find something salvageable.  I have a feeling by the time I'm done there will be 3 ps on my bench.

[Stuartambient]

I had come across this Hobby r/c power supply http://www.hobbyking.com/hobbyking/store/__76186__Turnigy_Reaktor_Pro_240W_16A_Power_Supply_100_240V_AC_.html

Wouldn't it be similar to a laptop charger. I think it is a switching supply though.

[ez24]

I've considered a laptop brick but the last one I had ran for about 2 hours and died.  Got that one off of Amazon.  Saw one the other day, recommended by a 'maker' on YT but it had horrible feedback on Amazon that echoed a quick death as well.  Usually they run between $10-$20 so replacing them frequently is not cost effective.  My wife says she has a pile of bricks at work so we may find something salvageable.  I have a feeling by the time I'm done there will be 3 ps on my bench.

Like everything, there is good and there is sh**.  In general ebay and Amazon Chinese crap is sh**.  Look for the real deal like these

http://www.ebay.com/itm/OEM-LOT-3-Toshiba-45W-Laptop-AC-Power-Adapter-Charger-ADPV16A-ADP-36CHA-/381659729075?hash=item58dcb14cb3:g:DbAAAOSwiYFXEP8E

Look for one that has a laptop makers name on it.  Dell is good but not standard.

[Stuartambient]

Sorry, because this thread took a turn from its original question.  All great responses though and I really appreciate the ideas and help.

That said, with the power bricks / laptop bat charger, wondering if I can use a step up on them.  Perhaps 18v out of a 12v output?

[Ian.M]

You can, but that wouldn't let you go below 12V unless you use a more expensive buck-boost module.

Ideally for a buck module based PSU, one would want a higher input voltage than a 19V laptop PSU provides so one could get up to 24V or even 30V similar to a proper bench supply, but surplus 19V laptop PSUs are far more readily available than anything else suitable and 18V out is enough for most educational and hobby uses.

Depending on your interests, an auxiliary 5V output using another buck module may be useful and it may also be worth adding an inverting buck-boost module (or a LM2596 buck module hacked for negative output), though generally I would prefer a linear dual supply for OPAMP experimentation to minimise noise.

[Stuartambient]

.....Do not use Dell (has 3 wires and not common plug).

Is Dell absolutely not an option? I found a LA65NS0-00 10 19.5v and 3.3a.  Doubt I'll find a female pigtail for it though. 

I was going to pair it with one of the  Drok's stepdown

DROK® LM2596 DC Buck Voltage Regulator 36V to 24V 12V 5V 3.3V 3V Converters Constant Volt&Amp 5-36V to 1.25-32V 5A 75W Step-down LED Driver Switch Power Supply Digital LED Voltmeter USB Output

ahh http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed
So it's a no go it seems on Dell adapters.  They have some kind of 3rd wire which is some sort of Onewire ID to the laptop along with a transistor at the other end.  Sounds like Dell adapters will only work in Dell laptops.   

[bitseeker]

That article talks about how Dell adapters identify themselves to Dell laptops in order to validate the charger before initiating battery charging. Unless the adapter is also checking for something Dell-specific on the laptop before turning on, it should work like a normal power supply. Replacing the connector with one that fits your needs should be pretty straightforward as you don't care about checking its ID.

[Stuartambient]

That article talks about how Dell adapters identify themselves to Dell laptops in order to validate the charger before initiating battery charging. Unless the adapter is also checking for something Dell-specific on the laptop before turning on, it should work like a normal power supply. Replacing the connector with one that fits your needs should be pretty straightforward as you don't care about checking its ID.

I was mostly going on ex24's comment but yes I guess it should work. Thanks!

[Stuartambient]

I peeled things back and guess I'm not familiar with these ac adapters.  The center wire (id wire) is insulated, and then the positive wire is with the center wire with insulation around both.  The ground was wrapped around that insulation but outside of some heat shrink near the joint it is stripped wire. 

[ez24]

So it's a no go it seems on Dell adapters.  They have some kind of 3rd wire which is some sort of Onewire ID to the laptop along with a transistor at the other end.  Sounds like Dell adapters will only work in Dell laptops.

Dell is good quality and if the center wire does not matter go for them, but adapters are hard but not impossible to find.  I got one on Aliexpress but considering the difficultly in finding them I gave up and got a Toshiba. Sorry I do not remember the plug size, but you can find it by looking at them on ebay.

 But again if you have a Dell and the center wire does not matter go for it.  I think they have bigger supplies (watts) than Toshiba.  Since I have about 20 Dell's, it is good news for me to know the 3rd wire can be ignored  .  I always thought it had to be connected to something.  For me jacks are cheaper than Toshiba's. 

[Stuartambient]

All I have are Dell adapters so glad it works. Measured correct voltage so it's good to go.  What I found though looking on Amazon and Ebay is that if you want a name brand adapter there is a premium to pay. Some of the Toshibas run $20+ compared to no name brands that are somewhat less or half the price. 

[Ian.M]

The difference is the lifespan and the probable mode of death.   Leading brand PSUs go on and on and on, and usually die fairly quietly.   I've got a 19V 2.4A Delta Electronics one here that's got a date code of 1996.   It came with some second tier brand name laptop, cant remember which, and has outlasted a succession of netbooks and small laptops for the past 20 years.  For a good part of that time its been on machines with weak batteries being run as substitute desktops, some 24/7.  I'd give even odds a cheap clone or off-brand PSU from EBAY used for that sort of duty, not even making its first anniversary, and I'd also give you even odds that it would fail with catastrophic loss of regulation due to the usual crappy corner-cutting type of design you get at that price-point, and the tendency to under-rate the output caps for the expected ripple current and even replace smoothing chokes with pieces of wire and omit one output cap from each pair,

[bitseeker]

Good job, Stuart. Looking forward to your future posts about your projects.

[Stuartambient]

Good job, Stuart. Looking forward to your future posts about your projects.

Thank you.  I appreciate the encouragement.