[NC Cams]

XYZ100: The link in post #17 addresses that issue.

This is also the reason the same post emphasizes "not getting creative - do it as indicated"

Good to emphasize that part about ground clipping no matter what. Hoever, I'm sure SOMEONE will ignore or forget that part of the directive.

Sort of technicaly dyslexia.

[gregsnovas]

i herd somewhere that you can get 24 volts out of a single atx power supply by using the negitve logic instead of the ground

http://www.tc.umn.edu/~beck0778/powersupply.html

[fyffe555]

i herd somewhere that you can get 24 volts out of a single atx power supply by using the negitve logic instead of the ground

http://www.tc.umn.edu/~beck0778/powersupply.html

yeah but the -12v is only rated to 0.5A, so if you need 24v at under 0,5a you're ok..

[NC Cams]

To add to fyffe555's reply, the chain is only going to be as strong as its weakest link...

[Willbird]

I know this is gonna complicate it, but what about a drawing that shows the voltage(s) of the 5 volt outputs on the succeeding daisey chained power supplies ??

Bill

[NC Cams]

The voltage at any succeeding 5v tap depends on what two points you measure the voltage.

The 5v from the "bottom" P/S from where you're referencing ground is going to read 5v.

If you measure from +5vdc on the next one up to the ground on the "Bottom" P/S, it should measure 10vdc. If you measure it to that respective P/S's ground, it should be 5vdc.

If you have at third supply stacked, it will read 5v at its own ground but 15vdc with reaspect to the "bottom" ground referenced P/S.

Still don't understand?

Hook 3 batteries (9v will do nicely) in series. Then measure the voltages at the various terminals and you'll see how the voltages relate. Arbitrarily keep the ground at one point and simple move the + probe.

You'll now understand how a -9vdc is generated from a +9v battery.

[Willbird]

I gotcha :-). Fumbling my way thru this electron bit :-). I had the whole cabinet off a Burgmaster machine at one time, wanted to make a hillbilly garage gun safe from the cabinet, but it slipped away from me at some point, that cabinet had a HUGE DC power supply in it with taps for about every voltage you could imagine...... *sigh* the rash mistakes of youth :-).


Not to hijack the thread, but on the capacitor issue, I have ordered a 20 amp 72 volt power supply from kelinc, I am going to run (3) 1160 oz/in steppers. they draw 4.2,3,or 6 amps depending on how they are wired (uni,bi-series,bi-parallal). I'm going to try like heck to get my power leads under 12" long from the PS to the Gecko 201. But the belt and suspendors approach suggets to me I should STILL use the cap, figuiring at the maximum draw for any wiring method I come up with 18,000uf. Wondering if the cap size is extremely critical, IE with 10" leads would a 10,000uf be good ?? Also does the cap need to be sized for what the setup draws in the real world ?? or what the motor(s) are rated at combined ??

Also I keep seeing refernce to using 5 amp fuses for each DC leg to a Gecko, would you still use a 5 amp if your motor was rated to draw 6 ??

Also NC I really have learned a lot about Ball bearings from some of your posts :-). Thanks for that info.

Bill


Bill

[NC Cams]

Fusing:

Re: the fuse in the 5 amp leg = It depends what the 5v is feeding. If it is only feeding the control circuit for that Gecko, the recommended fuse is adequate.

IF the motor is sharing the 5 v buss, that's a different story. If/when it draws more than 5 amps w/ a 5 amp fuse, probably POP.

IF the motor is fed via the Gecko from the 12 or 36 volts line from the P/S's, the motor never draws current via 5v buss. Thus your question about the motor drawing 6 amps doesn't affect the fuse selection of the 5v buss.

Not at home so I can't provide the link - sorry. You might want to do a "capacitor sizing" search via the search engine. This topic has been discussed and answered MULTIPLE times.

[Willbird]

In the Geckodrives,com stepper motor FAQ they show the 5 amp fuse in the 24-80 VDC leg from the PS to the gecko.(page 10)


http://www.geckodrive.com/photos/Step_motor_basics.pdf

Bill

[NC Cams]

You'll have to check with Gecko on the 6amp motors.

Generally, mosfet based drives are derated so that you can experience some current surges (inrush especially) and still have the drive survive. AT 5 amps, it would seem that the drives are rated for 400 watts continuous max.

Depending on the derating factor that the amp maker used, a bit more curretn may not cause any real problems if the surge is not that high nor that often. Again, check with Gecko.

Chances are that for testing, you could temporarily run a 6 amp fuse for the 5 amp one - again TEMPORARILY.

[Willbird]

Well it only draws 6.0 wired Bipolar parallal, bipolar series draws 3.0 and unipolar draws 4.2. The 5.0 amps makes perfect sense with what the drive is rated for.....I was not sure if the 5 amp value was arbitray and coming from the fact that most motors I see people using here are wee little things.....and it needed to be adjusted according to motor size.

It's all coming clear as mud :-)....just slowly :-)

Bill

[AYahoo]

When you connect the resistors to the ATX (+5V). Don’t use 1 or 2 ohm resistor. I used 2 ohm 25Watt that should be enough (V^2/R = 25/2 = 12.5Watt) but it gets to hot, I think 10 ohm is more than enough current, so I think it is best to use 10 ohm 25Watt (thou 25/10 = 2.5Watt so maybe 10Watt is enough).


Asaf.

[iggk]

anyone messed around with a newer ATX powersupply with 2 12v rails?
would it be possible to daisy chain the 2 rails to get 24v?

[biotech1]

Ok have a couple of questions how many power supplies will i need for this set up 3 nema 23 steppers at 3.6V/Phase 2.4A/phase.
2. each motor has its own driver board that i got from pminmo the http://pminmo.com/forsale/1X279805.pdf

[cts]

I have 3 stepper controllers that pull 2-3A each (3A+3A+3A = 9A Total). I want to use 4 ATX supplies to get 41V (12V+12V+12V+5V) connected to each controller.

Is it correct that I would need a power supplies rated for at least 108Watts for the 12V supplies (9A*12V) and 45Watts for the 5V supply (9A*5V)?

(Note that I am using the 5V to get 41V because I cannot have 48V. It is not to power the controller PICs.)

[PoolQ]

I have just read this thread and some of the links and finished modifying an ATX power supply so I thought I would post what I found. Not only was my chassis ground gonnected to power ground, but the chassis was actually used as a conductor to connect several components to ground. When I unmounted the power supply from the chassis I noticed that at two screw locations the copper around the screw hole also connected to some component leads. When I cut the copper from around the screw holes I had to run some wire from DC ground to the now floating components (caused by the cut traces).

This project is not for the faint of heart. You could not only burn out the power supply, but also your driver board and even your PC.

[rdpzycho]

anyone messed around with a newer ATX powersupply with 2 12v rails?
would it be possible to daisy chain the 2 rails to get 24v?

some of them does have 2 separate converters inside the PSU but the grounds are common. if you cut away the common ground then you can wire it in series.

[rdpzycho]

messing with power electronics is really not for the faint of the heart. already got electrocuted by a few kilovolts during a homebrew ESD testing.

I already did modify a single PSU from 12V to 48V. I rewound both the transformer and the inductor. daisychaining would be easier though.

there are also other techniques to increase the power output from a PSU, but you may be burning lots of transistors in the process.

never mount daisychained PSU's in a metal chassis. most of them use the chassis as ground (either Analog or Earth Ground). insulate them if you should. some cheap PSU's also don't feature current limiting (I don't remember if it's specified by ATX Spec.), overload them then the fuse will blow. mid-end to high-end PSU's would happily accept shorts.

[KLeeper]

• As mentioned before, grounds are the critical part of these mods. Carefully isolate the case from all points of contact with the board and any heat sinks. When assembled, check with a ohmmeter for shorts.
• ATX supplies may require a load resistor on the +5vdc in order to turn on.
• Power on line (green wire) must be tied to ground. http://www.technick.net/public/code/...nmth_atx_power
• Lowest rated supply is maximum rating for series configuration. Add them in parallel configurations.
• For more info: http://www.wikihow.com/Convert-a-Com...b-Power-Supply

[emtffkev]

Hate to revive an old thread, but.....

Is it possible to daisy chain 2 sets of 2 power supplies in series (24v / roughly 3A), and then daisy chain those two sets in parallel (24v / roughly 6A). These aren't ATX supplies they are ones I've scrapped from some OLD dot matrix printers and they only have a 3A output but 12v each. I have 4 of them...