ATX power supply versus spend on a bench PSU

Just at the stage of building a PSU using an computer ATX power supply I bought. . Will give 22A on 12V.
Reading the wiki
Wiki on ATX PSU build

a bit at the bottom says:

"A computer power supply is fine for testing purposes, or for running simple electronics (eg battery chargers, soldering irons) but will never produce power like a good lab power supply, so if you intend on using your power supply for more than just testing, buy yourself a good lab supply. There is a reason they cost so much."

Doing a print is of couse more than "just testing ", so: How does that square with using an computer ATX running a Prusa for maybe several hours (?)

(It's a splash-of-cash for a decent pre-made bench PSU but is using one of those a better long term thing to do?)

Thanks in advance.

Mike

Edited 2 time(s). Last edit at 11/28/2011 04:23PM by 3D2B.

I use a micro ATX supply which runs a printer with heated bed, AND an entire desktop computer simultaneously.

However, I've heard some tales about needing a decent 5V draw on the supply to keep it from thinking it is shorting out. I have no experience running a standalone supply with a printer, though.

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www.Fablicator.com

Lots of people are running repraps reliably with an ATX supply. You do need a good load on the low V lines though. (like a couple amps at least. ) Gen7 electronics even has ATX and molex power connectors on board.

3D2B Wrote:
> a bit at the bottom says:
>
> "A computer power supply is fine for testing
> purposes, or for running simple electronics (eg
> battery chargers, soldering irons) but will never
> produce power like a good lab power supply, so if
> you intend on using your power supply for more
> than just testing, buy yourself a good lab supply.
> There is a reason they cost so much."

That warning is there because an ATX power supply isn't particularly well suited for the job if you need a proper lab power supply. It'll may get the job done in many cases, but it'll get the job done poorly.

Defining lab power supply needs, however, typically means things like very low noise, very low AC ripple, and be very precise. Basically, in an ATX supply, 5% tolerance is within spec, but a typical tolerance for a good lab power supply would be two orders of magnitude better (0.05%). Comparing a true lab power supply to a ATX supply is no contest.

For just pushing electrons where they need to be, it's fine. Consider how complicated a computer is and that it's still happy with the 5% ATX specification.

There is an alternative. Use a power supply intended for 12V lighting systems. They are readily available and easily deliver 20A.

David

I started to use an ATX power supply for my Prusa build, but then looked at Adrian's Prusa Build notes on the wiki and noticed he uses a nice compact power supply that outputs 12v DC with 30A. I found them on ebay for about 28 bucks each I think, so if you are buying something for power, I suggest those types as they are smaller and require no hacking/modifcations.

I think this is the one I bought: http://www.ebay.com/itm/120692623020

Ostrich99

ostrich99 Wrote:
-------------------------------------------------------
> I started to use an ATX power supply for my Prusa
> build, but then looked at Adrian's Prusa Build
> notes on the wiki and noticed he uses a nice
> compact power supply that outputs 12v DC with 30A.
> I found them on ebay for about 28 bucks each I
> think, so if you are buying something for power, I
> suggest those types as they are smaller and
> require no hacking/modifcations.
>
> I think this is the one I bought:
> [www.ebay.com]
>
> Ostrich99

I was looking at getting something like that, but the price at my local electronics shop was MUCH higher - like $170 for a 240 W model: [www.jaycar.com.au]

I also wasn't at all comfortable with the fact that the live AC terminals are exposed on the back panel - the unit sits on the desk next to my printer, not in an enclosed electrical cabinet, and apart from the risk to myself, there are other people who might want a poke and prod. Live exposed 12V terminals is one thing, but 240V? I don't think so!

For this reason, I built myself an ATX-based power supply for a cost of almost nil (one salvaged 500 W ATX power supply, plus a few binding posts etc): [julianh72.blogspot.com]

If you can get a suitable (SAFE!) commercial model for around $28, then go for it, but if you find (like me) that the available price is too high, then the ATX option is a great alternative.

Edited 1 time(s). Last edit at 11/28/2011 08:52PM by julianh72.

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Follow my Mendel Prusa build here: [julianh72.blogspot.com]

The model that I received has some terminal covers, but yes, they are still slightly exposed so you wouldn't want young kids around them. Although I wouldn't want young kids around any of my 3D printers when they were plugged in as most likely the printer is running at 225C on the extruder and 110C on the printbeds.

I don't have a switch on my power supplies, so they are only plugged in and live when in use and out of the way of prying hands.

I would suggest 3D-printing a safety cover for the high voltage terminals. That's what my team is planning to do.

ostrich99 Wrote:
-------------------------------------------------------
> The model that I received has some terminal
> covers, but yes, they are still slightly exposed
> so you wouldn't want young kids around them.
> Although I wouldn't want young kids around any of
> my 3D printers when they were plugged in as most
> likely the printer is running at 225C on the
> extruder and 110C on the printbeds.
>
> I don't have a switch on my power supplies, so
> they are only plugged in and live when in use and
> out of the way of prying hands.

Agreed, a RepRap isn't really something to leave lying around where unattended kids could touch it - all sorts of pinch points, potential entanglements of hair or clothing in belt drives, etc. However, most such injuries are unlikely to be fatal - even grabbing a 225C Hot End or planting your hands palm-down onto the 110C Heated Bed would only give you a nasty burn. (Heck, just knocking it ff the table onto your foot would be painful!)

Accidentally grabbing a live 240V terminal could kill you.

---

Follow my Mendel Prusa build here: [julianh72.blogspot.com]

julianh72 Wrote:
-------------------------------------------------------
> Accidentally grabbing a live 240V terminal could
> kill you.

The current that actually kills, is DC type (higher voltage than 12v ofc), because once it starts passing through your muscles it commands them to constraint continuosly and cramps them so you cant let go anymore - and likely cant change position to escape it. In comparison alternative current doesnt kill you, it will just make your body shake a little, sort of like laughing. And would be rather impossible to command your muscles to keep the contact with that live ac wire because of the xxHz shaking it induces.

Edited 1 time(s). Last edit at 11/29/2011 05:07AM by NoobMan.

Quote

In comparison alternative current doesnt kill you

DC is more dangerous but plenty of people have been killed by 240V AC.

It needs a printed cover and strain relief for the mains cable, or better still an IEC inlet socket. Also the mains and low voltage wires should be kept apart or have double insulation.

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[www.hydraraptor.blogspot.com]

Adrian Bowyer has already thought of this for us! Here's his cover for 12V power supplies: [reprap.org]

There's also a bracket for a 3-pin XLR plug power connector.

Ok thanks to you all.

Ostrich99, like julianh72 I found those to be much more expensive when I went looking (I'm in the UK).
I think I'll modify the ATX unit I have, but get a larger metal (or ABS ?) enclosure to make the overall thing safer. The main local source for the hobby market to me is a Maplins store.
Understood a metal case will need to be earthed & that I'll need to allow for ventilation.

Any further tips/advice on this welcome.

Mike

If I looked at Lab or Bench power supplies, they were always $150-$300 USD, but when I searched ebay for 12V 30A DC it found a bunch of cheaper ones that looked very similar to the bench top ones.

I'm sure they are made in China though.

I've heard of people being able to find Laptop Power supplies with sufficient AMPs also, although you might end up using a separate one for the heated bed, etc.