ATX Bench power supply, ideas and suggestions wanted - Page 1
Forum section: electronics / beginners

author: Ludvig82
author_rank: Contributor
timestamp: November 30, 2015, 10:27:35 pm
content: Hi there, this is my first post on this forum.I have wanted to build myself a bench power supply from atx power supply for a while now. I dont often need something like that, but i am alway up for learning new stuff, and i see that it may come in very handy.In my search for this, i came over this product:http://www.seeedstudio.com/depot/atx-breakout-board-bench-power-supply-p-1222.html?cPath=155. It looks like a nice product and almost excact what i want already done for me. Does it look any good to you guys? If i buy that one, i still would like to add a variable output, but i am pretty green at making these kind of circuits, or circuits at all. I would really love if someone helped me with a suggestion how i could get this made, wich parts i need and how to connect it. To explain a bit more, i read that i can use the range between the -12v and the 12v, so the range of the output would be somewhere like 1v to 24v, depends on what parts you use. I also would love to have a display showing volts on this output so i can adjust it easily without measuring it with an external device.Just to clear a few things up, since I foud this breakoutboard, i wont touch the inside of the PSU. I will make a case to house it all in. Not sure what the case will be yet, but that will come laterHope i made myself understood ok, English is not my language, but i hope i am good enough in writing it

author: Cliff Matthews
author_rank: Unknown
timestamp: December 01, 2015, 01:40:23 am
content: Hello and welcome! I might as well tell you now.. That question has been asked here before and you would do well to use and read the forum searches on just that topic. Here is one such example:https://www.eevblog.com/forum/beginners/beginner-need-advice-on-atx-psu-gt-lab-psu/I love that quote from user Sigmoid, "Converting an ATX PSU into a benchtop lab supply is - quite literally - like converting a Caterpillar hydraulic excavator into a remote surgery robot."

author: MarkF
author_rank: Super Contributor
timestamp: December 01, 2015, 02:03:23 am
content: I have the Seeedstudio ATX breakout board you mentioned. It's okay and you can get plastic cover for the top and bottom. However, I don't recommend it for beginners and you can NOT form a 1V to 24V output from an ATX power supply.I would recommend a proper variable power supply that will provide you with more protection. You can find inexpensive power supplies on eBay that would give you what you want. Look at thisHP 6216A 0-25V DC Power Supplyfor example.

author: moya034
author_rank: Regular Contributor
timestamp: December 01, 2015, 02:09:04 am
content: I did this once. (i used an AT instead of ATX, but still the same bag)I was powering a radio transceiver with it. It worked very well... until the PSU blew up and took the radio with it. I will never do it again. Life is too short to use shitty power supplies.

author: Cliff Matthews
author_rank: Unknown
timestamp: December 01, 2015, 02:23:52 am
content: Here's a great way to spend just $10http://www.ebay.com/itm/Red-0-30V-2mA-3A-Continuously-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-PCB-/221739263622?hash=item33a0b0a686:g:JwQAAOSwymxVJfou

author: crispy_tofu
author_rank: Super Contributor
timestamp: December 01, 2015, 02:38:34 am
content: Quote from: Cliff Matthews on December 01, 2015, 02:23:52 amYou need a transformer though...

author: moya034
author_rank: Regular Contributor
timestamp: December 01, 2015, 03:03:54 am
content: Quote from: crispy_tofu on December 01, 2015, 02:38:34 amA heat sink would be a good idea tooStill a great value I would say!

author: Cliff Matthews
author_rank: Unknown
timestamp: December 01, 2015, 12:48:19 pm
content: Quote from: crispy_tofu on December 01, 2015, 02:38:34 amOops, sorry! I tear so much stuff apart (because I learn and it's fun..) that I always seem to have too many hanging around.

author: MarkF
author_rank: Super Contributor
timestamp: December 01, 2015, 02:28:51 pm
content: For a few dollars more you can have one with more capabilities:http://www.aliexpress.com/item/B3008-precision-CNC-DC-DC-constant-voltage-constant-current-buck-LED-driver-modules-solar-charging/1550355670.html

author: Cliff Matthews
author_rank: Unknown
timestamp: December 01, 2015, 02:55:41 pm
content: Quote from: MarkF on December 01, 2015, 02:28:51 pmAn ideal bench supply needs to have a stable and clean output (low ripple). A 24v 100va transformer with the PCB mentioned would likely prove to be the better option.

author: macboy
author_rank: Super Contributor
timestamp: December 01, 2015, 04:16:36 pm
content: I amnota fan of using an ATX supply this way, but at least That breakout board includes polyfuses for some measure of protection. As you know, any ATX supply can crank out dozens of Amps on +5 or +12 V rails, which can lead to dangerous situations if you short something out. The polyfuses should at least prevent fires.For a variable output, look for a DC-DC "buck boost" converter. These are a two-stage device, first a boost converter to increase the input to some higher intermediate voltage (maybe around 30 V), followed by a buck converter that reduces that intermediate voltage back down to the desired output voltage. These can output a wide voltage range (e.g. 2 to 30 V) from a wide input range (e.g. 3 to 30 V). If you use just a boost conveter, the output must be higher than the input, and with just a buck, the output must be lower than the input. This is an example of (but not necessarily an endorsement for) such a module:http://www.ebay.com/itm/DC-DC-Boost-Buck-Converter-Step-Up-Step-Down-Supply-Module-3-35V-to-2-2-30V-HG-/271720088700You can then add a 4-digit voltmeter that will show (e.g.) 00.00 V to 30.00 V. Get a 3-wire one (separate input and power supply). Use the +12 rail for the power supply. This is an example (again not an endorsement):http://www.ebay.com/itm/Mini-0-33V-Car-Motorcycle-DC-4-Digital-Voltmeter-Red-LED-Voltage-Panel-Meter-New-/390734584022. You can also get ammeter versions of these.edit: While browsing for "DC-DC buck boost" on ebay, I see a lot of improperly labelled devices, for example, buck (step down) converters being called "buck boost" in the title. If you want a true buck-boost conveter, make sure that the photo of the device has two inductors (they usually look like the round-cornered black thingies in the one I linked to, or distinctly like coils of wire). Most of these sellers do not understand the stuff they sell, and their titles and descriptions are based on popular search terms and/or copied from other listings. Usually, in my experience, the photo is the most accurate part of these listings, so if you understand what you are looking at, then you can and should ignore much of what is written in the title and description.

author: rdl
author_rank: Super Contributor
timestamp: December 01, 2015, 04:53:11 pm
content: For someone's first bench power supply, and one that may be their only power supply for a while, a switch mode type is not a good choice. And for use as a lab power source, a modified ATX power supply is probably the worst kind of switch-mode power supply there is.

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 06:59:45 pm
content: Thansk for all aswers. I was expecting some negativity around this. I know this is not the best bench supply and that many people are against it. Mind you, let me explain my reasons for wanting one a little better. First of all it is the DIY ascpect of it, i love making things and trying new things to learn. So i figured this would be a nice project for me, and it can help me alot at work where i test alot of things with different power input. These things (Stuff for fish farming, controllers for feeding systems and so on) are most of the time not depending on stable voltage or clean power. They are often powered by car batteries or similair. So just for test purposes to see if things work, this would be ok. The stuff i am talking about is often on fish cages out at sea, and therefor often destroyed by water or similair.Second i already have a proper bench power supply, but i would never bring that one at work on sea.Third, i know this may be crude and so on, but still want to try it. So i still would love some more suggestions on what to do to get a adjustable voltage output, and what parts i need for it. I am not very experienced with electronice as is, but very used to power and so on. It is just when i comes to circuits and so on i am inexperienced. Thats what i want to learn. So please explain as i was a kidI have seen people making tutorials where they use -12v and 12v to make adjustable output that gives more than 12v. Can someone explain this?

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 07:04:11 pm
content: Quote from: macboy on December 01, 2015, 04:16:36 pmAlot of interesting reading. Is it ok to pm u for more info?

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 07:05:05 pm
content: Quote from: Cliff Matthews on December 01, 2015, 01:40:23 amThansk for the welcomeI did a search, and already read that post. Wanted my own thread so i can ask all my silly noobquestions

author: macboy
author_rank: Super Contributor
timestamp: December 01, 2015, 07:54:34 pm
content: Quote from: Ludvig82 on December 01, 2015, 07:04:11 pmPost any questions here and I'll do my best to answer them for the benefit of all. That's the beauty of a public forum like this.

author: fivefish
author_rank: Frequent Contributor
timestamp: December 01, 2015, 08:24:47 pm
content: One has to keep in mind there are no power transformers in these things... no galvanic isolation from mains.If there's a catastrophic failure (say a short-circuit on the project you're working on, miswiring on your breadboard, etc... and the ATX failed dangerously... well you get the picture.)Good luck.

author: macboy
author_rank: Super Contributor
timestamp: December 01, 2015, 09:58:56 pm
content: Quote from: fivefish on December 01, 2015, 08:24:47 pmActually that is quite incorrect. These do use a transformer between input and output, in a forward converter topology. The ground on the secondary is connected to earth ground for safety purposes, but the secondarycouldbe floated with a little modification (not that I condone that).

author: Paul Price
author_rank: Super Contributor
timestamp: December 01, 2015, 10:02:32 pm
content: Fiveish:Nonsense, ATX power supplies are as much galvanically isolated as any other piece of equipment, such as a lab power supply or a desktop computer.ATX power supplies do fail, but very rarely fail "dangerously." Mostly they just drop dead (no output) and so almost never damage the equipment they are supplying power to.

author: Paul Price
author_rank: Super Contributor
timestamp: December 01, 2015, 10:28:55 pm
content: When my friend wanted a power supply to charge batteries and experiment with electronics, I converted an ATX power supply to a precision lab supply just for the challenge of it.First of all, I was able to find and salvage as many ATX power supplies for free as I could pile up in my lab, so the cost of components to make a nice power supply was close to zero.Taking one of them apart, I was able to salvage a large power toroid (about 3-in diameter) and used this to make a boost converter that transformed the +12V (>8amp rated) output to any voltage from a few volts(loaded) to around 30V. Then I used a LM317 mounted on a heat sink salvaged from one of the supplies to act as a linear regulator for a really smooth output.I used a Microchip PIC18F25Kxx chip to control the output voltage of the boost converter I made with the power toroid that I salvaged. The wire to wind upon the this large core already came free as removed from the junker ATX supply.The PIC18 supplied the PWM drive to a 30-amp power MOSFET (free also from the motherboard of the same PC the power supply was taken out of) to drive the large toroid. The ATX supply conveniently supplied 12V for good gate drive for a power MOSFET.The PICC also provided A2D to monitor and set the input and output voltage of the LM317 and also to drive 7-seg displays.The same chip was used to monitor output voltage and current(With the help of a small valued sense resistor and an op-amp.)So the same chip monitored the output current of the supply and allowed me to run the supply in constant current and constant voltage mode. Since the 18F chip had a built in 64-MHz clock, it was quite quick and able to adapt to change and provide 1024 PWM steps to adj. the voltage supplied to the LM317 and so I could carefully control the voltage difference across the LM317 to achieve maximum efficiency with just a medium sized heatsink. The fan to cool the supply was also free from an ATX, but was also controlled by the same PIC chip and was rarely on unless I was really drawing some amps from the supply.

author: MarkF
author_rank: Super Contributor
timestamp: December 01, 2015, 10:42:14 pm
content: Why not drop the ATX power supply and build a small power supply with a 3-terminal regulator. Something fairly simple with a 1A current capability. Check out circuit diagram. Just add transformer, fuse and heat sink.

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 11:12:52 pm
content: Quote from: MarkF on December 01, 2015, 10:42:14 pmThat looks like a nice project for later. I need some prefabricated boards for now. I dont have the soldering skill or equipment to start solder parts to pcbs yet. I can do some easy soldering like power to a board, and ofc wires. Hoping to get a nice soldering station with time

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 11:17:38 pm
content: I think i got a shopping list put together now. Hopefully this will be a fun projectI got a PSU from an not so old computer.Voltmeter to use on the variable output:http://www.ebay.com/itm/Mini-0-33V-Car-Motorcycle-DC-4-Digital-Voltmeter-Red-LED-Voltage-Panel-Meter-New-/390734584022Buck converter:http://www.ebay.com/itm/DC-DC-Boost-Buck-Converter-Step-Up-Step-Down-Supply-Module-3-35V-to-2-2-30V-HG-/271720088700A nice knob for adjusting the voltage (Will have to find a way to extend the pot on the Buck converter, and make it 6mm shaft.):http://www.ebay.com/itm/New-High-Quality-Control-Rotary-Knob-For-6mm-Knurled-Shaft-Potentiometer-/171474118517?hash=item27eca76775:g:dLoAAOSwd4tUI9vq&autorefresh=trueAt the same time i will order some binding posts, alligator clamps and banana plugsFor an external case for this, i am not sure what i will do yet. Maybe i will go for wood.I will post here when this projects starts

author: Paul Price
author_rank: Super Contributor
timestamp: December 01, 2015, 11:17:49 pm
content: MarkF: Good reasons not to just build a simple LM317 power supply are:(1) You wouldn't learn much about electronics, or op-amps or current sensors or boost supplies or MCU programming, etc.(2) You would have to pay for all the parts.(3) You would need a very large heatsink and a fan.For instance, if you wanted to output 1.6 Amps at 1.6 Volts for an electrolysis experiment, the LM317 would be dissipating around 1.6A*24..say something about at least 40 watts of power. Makes your power supply a nice room space heater.

author: Paul Price
author_rank: Super Contributor
timestamp: December 01, 2015, 11:31:58 pm
content: Ludvig82:That boost module will not do the job. Whenever the input voltage to this device is greater than the output desired the output voltage is unregulated and tracks the input voltage. So, if you supply the board with 12V you cannot set the output to less than approx 12V.If you used the 3.3V supply of the ATX supply you could do a little better and have a lower output voltage limit around 3.4V, but higher voltage output voltages around 20V would be not offering much current output.Besides, the module you selected doesn't look very robust and would likely fail easily with a short circuit condition.On the positive side, the knob choice is nice if it will fit the pot you haven't yet located, and the 4-digit LED voltmeter is just fine.

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 11:38:39 pm
content: Ok, to be honest i could do with a step down converter, So i get 12v and under. What would you reccomend to use then?Could this do the job?http://www.ebay.com/itm/5A-Adjustable-CC-CV-Display-Step-Down-charge-Module-LED-Panel-Voltmeter-Ammeter-/381374424481?hash=item58cbafe5a1:g:wfQAAOSwKrhVW~45I could also be brave and try to solder my own board with a kit like this:http://www.ebay.com/itm/1-x-LM338K-3A-Adjustable-Step-Down-Power-Supply-Module-DIY-Kits-Components-SY-/281830066652?hash=item419e6189dc:g:V4AAAOSwo0JWIPP3

author: Paul Price
author_rank: Super Contributor
timestamp: December 01, 2015, 11:48:46 pm
content: If you want a supply with an output of 12V or less, the ATX supply doesn't look as promising. A buck step-down converter requires that the input voltage be several volts above the output voltage..same is true for the LM317 if you go linear with a big heatsink, so you would be limited to a regulated output voltage high limit around 9V or so at full output current.In this case I would acquire(possibly in many cases for free) a laptop power supply, many of these can supply 3 to 4.5 amps at 18 to 21V, depending on the manufacturer. In this case a LM317 regulator on a sizable heatsink would make a nice bench supply with a decent output voltage capability from about 1.2V to about 15 Volts or more depending on output current. Just don't choose a wooden case for the supply if you don't want to burn down the house.

author: Ludvig82
author_rank: Contributor
timestamp: December 01, 2015, 11:58:55 pm
content: Quote from: Paul Price on December 01, 2015, 11:48:46 pmOk, i have several laptop power bricks lying around. Never throw those awayMaybe that is a better idea then, since it is variable, i can use it for all the purposes that the atx PSU would give (3.3v, 5v and 12v.) With the heatsink i understand that wood would be a nogo, would it output alot of heat? I have several hetasinks from different computer pars lying around, never throw them away eitherWith the choice of several power bricks, should i use the one that got highest amp output?

author: Paul Price
author_rank: Super Contributor
timestamp: December 02, 2015, 12:05:24 am
content: The higher current bricks will be more rugged and run cooler. If you want a nice adjustable supply then buy a simple LM317 module to give you really clean output..heatsink required.http://www.ebay.com/itm/5A-Adjustable-CC-CV-Display-Step-Down-charge-Module-LED-Panel-Voltmeter-Ammeter-/381374424481?hash=item58cbafe5a1:g:wfQAAOSwKrhVW~45I haven't any experience with this module, I donno, never dated this girl, but might be worth shaking a stick at.This module, like all the other adjustable modules will have a small trimpot mounted on their PCB. If you wish to use that fancy knob of yours be sure to to try to keep leads short as possible to the module you are attempting to control with pots on the front panel.Some soldering required.

author: Ludvig82
author_rank: Contributor
timestamp: December 02, 2015, 12:10:01 am
content: Yeah, looked at several of these now, and i guess i can change to a bigger heat sink if i want toFor the sake of making it a bit easier in myself, i looked at some with potmeters with axle. I'll link to some of them, and would really appreciate if you could give me your 5 cents in themhttp://www.ebay.com/itm/DC-AC-LM317-Adjustable-Voltage-Regulator-Step-down-Power-Supply-Module-LED-Meter-/391251584891?hash=item5b1869677b:g:kEcAAOSwMmBV7CPshttp://www.ebay.com/itm/New-LED-Display-LM317-Adjustable-Voltage-Regulator-Step-down-module-AC-DC-Hot-/252108685154?hash=item3ab2d93f62:g:wwYAAOSwiLdWCmdthttp://www.ebay.com/itm/LED-display-LM317-Adjustable-Voltage-Regulator-Step-down-module-updated-lastly-/291523096161?hash=item43e0216e61:g:z~gAAOSwu4BVsucC

author: Paul Price
author_rank: Super Contributor
timestamp: December 02, 2015, 12:19:33 am
content: The modules you've presented do not have more than one protruding control..means no control of current.The one I presented doesn't have external pots but could be adapted to front panel controls easily and you have voltage and current metering.Some soldering in any case.To play with anything electronic you will need a soldering station of some type, might as well start to use one to assemble your power supply.

author: Ludvig82
author_rank: Contributor
timestamp: December 02, 2015, 12:21:34 am
content: OK, easiest way to adapt them is to get external pots then?Sent fra min London via Tapatalk

author: Paul Price
author_rank: Super Contributor
timestamp: December 02, 2015, 12:22:17 am
content: Yeah, but pots are not as easy or cheap to buy or as nice to me as my own digital controls with a MCU, but you might not be ready for that challenge yet.But you can find them cheap enough on ebay et al.

author: Ludvig82
author_rank: Contributor
timestamp: December 02, 2015, 12:31:57 am
content: Sounds interesting with the digital controls, but I think it may be for later. What do I have to look for when buying pots then?Sent fra min London via Tapatalk

author: Paul Price
author_rank: Super Contributor
timestamp: December 02, 2015, 12:44:58 am
content: Very important: Match the resistance value and taper (linear in this case) to the ones on the module, and oh..make sure it fits your knob.In some cases, to be properly shafted, some sawing required and someway to drill a hole for the shaft.Look for ones that are sealed against dust, and wirewound pots might be troublesome with your module's circuitry, while some 10-turn pots might be a fancy option for high resolution setting of output voltage.

author: MarkF
author_rank: Super Contributor
timestamp: December 02, 2015, 04:27:25 am
content: Quote from: Paul Price on December 01, 2015, 11:17:49 pmAnd what do you learn from plugging in a pre-made module? NOTHING.Yet a few posts later you suggest getting a LM317 and doing almost the exact thing that I have!Quote from: Ludvig82 on December 01, 2015, 11:17:38 pmThe DC-DC buck module I pointed out has Constant Voltage select, Constant Current select and voltage, current and power measurement via the buttons. Everything that all your modules together provide. I saw a video with the same or similar module. Please do a little more research before deciding.http://www.aliexpress.com/item/B3008-precision-CNC-DC-DC-constant-voltage-constant-current-buck-LED-driver-modules-solar-charging/1550355670.htmlHere is a second video by the same gentleman:

author: jmegar324
author_rank: Contributor
timestamp: December 02, 2015, 01:20:23 pm
content: Any specific applications you are using it for? It may help people recommend something better suited

author: Cliff Matthews
author_rank: Unknown
timestamp: December 02, 2015, 02:36:29 pm
content: These SMPS bench threads go on..On that $10 kit (sans brick or transformer), the most needed upgrade seems to be fine adjustment. Since the controls are ergonomically too close together, I'd short jumper them to a front panel and parallel-wire the wipers to another 20k pot with 47k resistors linking the outside contacts. AFAIK, this should add about 4% (+-) adjustment without PCB changes. Perhaps that part was what was missing? Or maybe metering.. like this:http://www.ebay.com/itm/DC-100V-10A-Voltmeter-Ammeter-Blue-Red-LED-Dual-Digital-Volt-Amp-Meter-Gauge-/131577787046?hash=item1ea2a5b2a6:g:lFcAAOSwMmBVzF8~Once again, don't cook your projects or feed them with dirty power, check the linkhttp://www.ebay.com/sch/i.html?_nkw=Continuously+Adjustable+DC+Regulated+Power+Supply+DIY+KitCall now, operators are standing by...