Converting a PC power supply. With custom kill switch!

Hi folks!

I tested my tech zone remix electronics kit today, and everything worked well. The motors moved as expected, the opto endstops triggered and the construction held up. The Z axis jammed now and then though, but all in all, a successful first test!

To supply 12v I wired up an old 250w power supply I had lying around, and during the testing process nearly tripped and ripped everything down several times. A paperclip to connect power on to ground was also a bit unreliable, so I figured I needed a more permanent solution, which I will present to you now:



Features:
Duck tape.
Big dual kill switch, one lead connects power to ground, the other one is on the 12v line to the molex plug for (hopefully) instant power off.
Molex plug for connection to the machine.
Cables (the ones which is spared as they might be needed later) hidden in a metal box which originally contained some lemon-flavoured sweets.
Extra duck tape padding in case it falls off the workbench.
Low footprint.
A hidden power on led.
It goes to 11!
Did I use enough duck tape?



Edited 3 time(s). Last edit at 06/21/2010 07:04PM by Nudel.

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-Nudel
Blog with RepRap Comic

Needs more duck tape.

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Tony Buser http://tonybuser.com * http://reprap.org/wiki/User:Tbuser#Projects

i can still see bare metal needs more duck tape

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[mike-mack.blogspot.com]

LOL

And put the results up on the wiki so the next person will know. ;-)
Excellent!

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

Quote
Tony Buser
Needs more duck tape.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Thanks everyone! I'll incorporate more duck tape in version 2.0

As I feel I now have to stand by my new signature, I've made a small wiring schematic for the wiki. But before I put something wrong up there I'd like to know if the wiring even makes sense. I'm especially thinking about the switching of the 12v wire. My limited electronic understanding tells me the power supply hold the 12v charge in capacitors, which will continue to supply power for a second after the main 220v power is switched off. There also seems to be a tiny delay when the power on is triggered. I know it doesn't hurt to do it like this, but there's no need to make other people do extra work if it's useless.

I didn't time the delay before I did the change, but it feels a bit faster. Am I utterly and totally mistaken?



Edited 1 time(s). Last edit at 06/22/2010 08:33AM by Nudel.

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-Nudel
Blog with RepRap Comic

Yes you are right that it will switch off a bit faster. The output capacitors are not that big though on a switch mode PSU because it works at high frequency, so they don't hold much charge, so you may only make a few milliseconds difference. Not significant when the switch is operated manually.

The input capacitors hold a lot more energy because they are charged to about 310V and energy is 0.5CV^2. So after switching the mains off the PSU will run for 10's to 100's of milliseconds depending on the load.

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[www.hydraraptor.blogspot.com]

Thank for the explanation nophead! So the only reason for connection it like this is if you have several RepRaps connected to the same PSU, and want to switch them off individually. I'll look into something more elegant later on, when I actually have more than one RepRap running.

Here's the wiki entry so far.

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-Nudel
Blog with RepRap Comic

nophead Wrote:
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> The input capacitors hold a lot more energy
> because they are charged to about 310V and energy
> is 0.5CV^2. So after switching the mains off the
> PSU will run for 10's to 100's of milliseconds
> depending on the load.


IIRC, part of the ATX specification is that the psu must supply full output power for 500ms with no mains input, although I suspect many fail this particular test

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Wooden Mendel
Teacup Firmware