Is it possible to use a standard AT (old style) computer power supply just for its +5v out? I have a project and I just need 5v with a beefy amount of amps, and I have lots of AT PS's around that would fit the bill, but I'm wondering if running a computer PS just for its 5v line might damage it somehow? There would be no load on the 12v (and other) lines. Anything I should worry about?
Thanks!
You have to fake out (short??) at least one signal on the motherboard connector for the PSU to continue delivering power. Whether draw on only one rail causes a problem will depend on the internal design. You could hook up a 9V-battery-powered low-voltage alarm to let you know the PSU died if that's a major concern. I'm assuming you aren't going to run out of spare AT PSUs anytime soon ;-). -Adam
On February 15, 2016 3:39:02 PM CST, Trevor Cordes trevor@tecnopolis.ca wrote:
Is it possible to use a standard AT (old style) computer power supply just for its +5v out? I have a project and I just need 5v with a beefy amount of amps, and I have lots of AT PS's around that would fit the bill, but
I'm wondering if running a computer PS just for its 5v line might damage it somehow? There would be no load on the 12v (and other) lines. Anything I should worry about?
Thanks! _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
On 2016-02-15 Adam Thompson wrote:
You have to fake out (short??) at least one signal on the motherboard connector for the PSU to continue delivering power.
Even for AT PS? (*not* ATX)
My plan is to cut off the connectors completely and just wire up the 5V wire(s) to a non-standard connector I need for the project.
know the PSU died if that's a major concern. I'm assuming you aren't going to run out of spare AT PSUs anytime soon ;-). -Adam
Nope, but wouldn't want these things bursting into flames...
I think even the AT spec wanted to see a PWR_OK signal or it could shut itself down. I could be wrong, and I'm too lazy to look it up right now. Worst case, you just need to splice two wires together when you hack off the connector.
Even AT-eta supplies had adequate internal protection against, e.g. bursting into flames, I wouldn't worry too much about that. They did often have big electrolytic caps, though, *those* could potentially be a problem regardless of unbalanced power draw.
-Adam -Adam
On February 15, 2016 3:48:01 PM CST, Trevor Cordes trevor@tecnopolis.ca wrote:
On 2016-02-15 Adam Thompson wrote:
You have to fake out (short??) at least one signal on the motherboard connector for the PSU to continue delivering power.
Even for AT PS? (*not* ATX)
My plan is to cut off the connectors completely and just wire up the 5V wire(s) to a non-standard connector I need for the project.
know the PSU died if that's a major concern. I'm assuming you aren't going to run out of spare AT PSUs anytime soon ;-). -Adam
Nope, but wouldn't want these things bursting into flames...
Yes, those garbage-can-sized capacitors can explode and fill the room with a dense whitish smoke (and stink), and it makes a very loud bang at the moment of explosion. That tends to end your OS session too.
Hartmut W Sager - Tel +1-204-339-8331, +1-204-515-1701, +1-204-515-1700, +1-810-471-4600, +1-909-361-6005
On 15 February 2016 at 15:51, Adam Thompson athompso@athompso.net wrote:
I think even the AT spec wanted to see a PWR_OK signal or it could shut itself down. I could be wrong, and I'm too lazy to look it up right now. Worst case, you just need to splice two wires together when you hack off the connector.
Even AT-eta supplies had adequate internal protection against, e.g. bursting into flames, I wouldn't worry too much about that. They did often have big electrolytic caps, though, *those* could potentially be a problem regardless of unbalanced power draw.
-Adam -Adam
On February 15, 2016 3:48:01 PM CST, Trevor Cordes trevor@tecnopolis.ca wrote:
On 2016-02-15 Adam Thompson wrote:
You have to fake out (short??) at least one signal on the motherboard connector for the PSU to continue delivering power.
Even for AT PS? (*not* ATX)
My plan is to cut off the connectors completely and just wire up the 5V wire(s) to a non-standard connector I need for the project.
know the PSU died if that's a major concern. I'm assuming you aren't
going to run out of spare AT PSUs anytime soon ;-). -Adam
Nope, but wouldn't want these things bursting into flames...
-- Sent from my Android device with K-9 Mail. Please excuse my brevity.
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
The -5V and -12V are probably fine with no load, but the +12V line should have at least the minimum required load (whatever that might be). Just use a suitable power resistor (power resistor means it won't fry into a molten lump) on the +12V line. In the absence of info on the PS label, I'd go for loading the +12V line with about 10% of its maximum power/amps. Use V = IR and P = IV to do the algebra to get the right resistance (ohms).
Also, along the lines of Adam's reply, you might have to signal back to the PS (by closing a circuit?) that "this motherboard likes you" - otherwise the PS might cut out.
Hartmut W Sager - Tel +1-204-339-8331, +1-204-515-1701, +1-204-515-1700, +1-810-471-4600, +1-909-361-6005
On 15 February 2016 at 15:39, Trevor Cordes trevor@tecnopolis.ca wrote:
Is it possible to use a standard AT (old style) computer power supply just for its +5v out? I have a project and I just need 5v with a beefy amount of amps, and I have lots of AT PS's around that would fit the bill, but I'm wondering if running a computer PS just for its 5v line might damage it somehow? There would be no load on the 12v (and other) lines. Anything I should worry about?
Thanks! _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
I've never used the 5v rail on its own, but I've used the 12v rail for various things. They do make great high amperage supplies. You have to short the green wire in the main 24 pin connector with one of the many black ground wires and then it'll turn on.
-- Wyatt Zacharias (mobile) On 15 Feb 2016 3:59 p.m., "Hartmut W Sager" hwsager@marityme.net wrote:
The -5V and -12V are probably fine with no load, but the +12V line should have at least the minimum required load (whatever that might be). Just use a suitable power resistor (power resistor means it won't fry into a molten lump) on the +12V line. In the absence of info on the PS label, I'd go for loading the +12V line with about 10% of its maximum power/amps. Use V = IR and P = IV to do the algebra to get the right resistance (ohms).
Also, along the lines of Adam's reply, you might have to signal back to the PS (by closing a circuit?) that "this motherboard likes you" - otherwise the PS might cut out.
Hartmut W Sager - Tel +1-204-339-8331, +1-204-515-1701, +1-204-515-1700, +1-810-471-4600, +1-909-361-6005
On 15 February 2016 at 15:39, Trevor Cordes trevor@tecnopolis.ca wrote:
Is it possible to use a standard AT (old style) computer power supply just for its +5v out? I have a project and I just need 5v with a beefy amount of amps, and I have lots of AT PS's around that would fit the bill, but I'm wondering if running a computer PS just for its 5v line might damage it somehow? There would be no load on the 12v (and other) lines. Anything I should worry about?
Thanks! _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
On 2016-02-15 Wyatt Zacharias wrote:
I've never used the 5v rail on its own, but I've used the 12v rail for various things. They do make great high amperage supplies. You have to short the green wire in the main 24 pin connector with one of the many black ground wires and then it'll turn on.
Haha, Wyatt's showing his age! He's never even seen an AT PS! Probably wasn't born yet :-)
back in 'the day' ... i used standard pc power supply to run my old mocom 35 vhf radio ... it needed 8 amps to run at 30watts output -- worked like a charm to run my 1200bps AFSK modem/radio :-) ran for years no problem. just check the specs for current rating and have at'er ...
Dan.
On 15 February 2016 at 16:16, Trevor Cordes trevor@tecnopolis.ca wrote:
On 2016-02-15 Wyatt Zacharias wrote:
I've never used the 5v rail on its own, but I've used the 12v rail for various things. They do make great high amperage supplies. You have to short the green wire in the main 24 pin connector with one of the many black ground wires and then it'll turn on.
Haha, Wyatt's showing his age! He's never even seen an AT PS! Probably wasn't born yet :-)
http://www.playtool.com/pages/psuconnectors/atpic.jpg _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
On 2016-02-15 Hartmut W Sager wrote:
The -5V and -12V are probably fine with no load, but the +12V line should have at least the minimum required load (whatever that might be). Just use a suitable power resistor (power resistor means it won't fry into a molten lump) on the +12V line. In the absence of info on the PS label, I'd go for loading the +12V line with about 10% of its maximum power/amps. Use V = IR and P = IV to do the algebra to get the right resistance (ohms).
Thanks for the tip! The old PS indeed says a minimum on the +12V of 1.3A. I paralleled 2 15ohm power resistors (5%; the big huge white rectangle ones) to approximate a 1.3A or higher (1.6 actually) load. I only had a limited selection of power resistors around here.
I can get the whole unit to power on now, and seems to try to boot and blink some LEDs, yay!
BUT the power resistors get REAL hot REAL fast. Like too hot to touch in under 30s. Does that sound right? Not sure I can deliver that to customer like that. Any other ideas? Different resistors? Maybe try a "real" load, but what?
Do the resistors have their power rating on them? 1.6A at 12V is 19.2 watts total. You'll need some hefty resistors to sink that much power into.
Out of curiosity, how much power do you actually need from the 5V rail? Single voltage switch mode power supplies can be had for under $50 with decent amperage ratings.
-- Wyatt Zacharias
On Wed, Feb 17, 2016 at 11:54 AM, Trevor Cordes trevor@tecnopolis.ca wrote:
On 2016-02-15 Hartmut W Sager wrote:
The -5V and -12V are probably fine with no load, but the +12V line should have at least the minimum required load (whatever that might be). Just use a suitable power resistor (power resistor means it won't fry into a molten lump) on the +12V line. In the absence of info on the PS label, I'd go for loading the +12V line with about 10% of its maximum power/amps. Use V = IR and P = IV to do the algebra to get the right resistance (ohms).
Thanks for the tip! The old PS indeed says a minimum on the +12V of 1.3A. I paralleled 2 15ohm power resistors (5%; the big huge white rectangle ones) to approximate a 1.3A or higher (1.6 actually) load. I only had a limited selection of power resistors around here.
I can get the whole unit to power on now, and seems to try to boot and blink some LEDs, yay!
BUT the power resistors get REAL hot REAL fast. Like too hot to touch in under 30s. Does that sound right? Not sure I can deliver that to customer like that. Any other ideas? Different resistors? Maybe try a "real" load, but what? _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
On 2016-02-17 Wyatt Zacharias wrote:
Do the resistors have their power rating on them? 1.6A at 12V is 19.2 watts total. You'll need some hefty resistors to sink that much power into.
10W resistors, 2 of them should take 19.2W. These are the biggest resistors I've ever personally seen.
Out of curiosity, how much power do you actually need from the 5V rail? Single voltage switch mode power supplies can be had for under $50 with decent amperage ratings.
I need 10A 5V. I don't want to use a wall-wart as they don't usually put out very clean power compared to a "real" power supply. As for buying one, the idea here is try the "free" stuff first, buy something second.
On 2016-02-17 Gilles Detillieux wrote:
half the heat of a 40 W incandescent bulb. Any load you use will put out that much heat for the same amount of current.
I thought maybe I'll try putting in a .5A fan to take up a chunk of the 12V output, and have it blow on whatever hot resistors I need for the rest :-)
It seems to me a decent switching power supply should be able to regulate voltage with much less draw than that, though. I'd try a single 15 Ohm resistor and see how well it holds the +12 & +5 V, and if it's good, try even higher resistor values than that. You might be able to get the current draw down below 100 mA (1.2 W) without any loss of stability.
That's voodoo territory for me. I'm not sure what the characteristics of the PS are with different loads on the unused lines. I'm not certain I could a) reliably measure stability in a short amount of time and b) project those results out over the (offsite) usage lifetime of the PS.
What I could easily do is check if I have some other PS's with a lower min 12V rating on their label. Maybe I just picked the wrong one with the initial grab.
I have a whole box full of high wattage resistors (some as big as 25w I think), if you need some more to play with let me know.
Alternatively, if you decide a cleaner solution is needed, here's an example of what's available commercially: http://www.alliedelec.com/mean-well-usa-lrs-75-5/70696528/ 70W 5VDC power supply for under $20.
-- Wyatt Zacharias
On Wed, Feb 17, 2016 at 3:51 PM, Trevor Cordes trevor@tecnopolis.ca wrote:
On 2016-02-17 Wyatt Zacharias wrote:
Do the resistors have their power rating on them? 1.6A at 12V is 19.2 watts total. You'll need some hefty resistors to sink that much power into.
10W resistors, 2 of them should take 19.2W. These are the biggest resistors I've ever personally seen.
Out of curiosity, how much power do you actually need from the 5V rail? Single voltage switch mode power supplies can be had for under $50 with decent amperage ratings.
I need 10A 5V. I don't want to use a wall-wart as they don't usually put out very clean power compared to a "real" power supply. As for buying one, the idea here is try the "free" stuff first, buy something second.
On 2016-02-17 Gilles Detillieux wrote:
half the heat of a 40 W incandescent bulb. Any load you use will put out that much heat for the same amount of current.
I thought maybe I'll try putting in a .5A fan to take up a chunk of the 12V output, and have it blow on whatever hot resistors I need for the rest :-)
It seems to me a decent switching power supply should be able to regulate voltage with much less draw than that, though. I'd try a single 15 Ohm resistor and see how well it holds the +12 & +5 V, and if it's good, try even higher resistor values than that. You might be able to get the current draw down below 100 mA (1.2 W) without any loss of stability.
That's voodoo territory for me. I'm not sure what the characteristics of the PS are with different loads on the unused lines. I'm not certain I could a) reliably measure stability in a short amount of time and b) project those results out over the (offsite) usage lifetime of the PS.
What I could easily do is check if I have some other PS's with a lower min 12V rating on their label. Maybe I just picked the wrong one with the initial grab.
On 2016-02-17 Wyatt Zacharias wrote:
I have a whole box full of high wattage resistors (some as big as 25w I think), if you need some more to play with let me know.
Oh! Those might work better than my 10W. Those must be BIG.
However...
Alternatively, if you decide a cleaner solution is needed, here's an example of what's available commercially: http://www.alliedelec.com/mean-well-usa-lrs-75-5/70696528/ 70W 5VDC power supply for under $20.
Those are neat! Have to find it Canadian or digikey though to be useful, I don't like getting fee-p0wned by the courier companies on US stuff.
But, doesn't matter (probably) as I just dug out an AT PS that claims .4A min on 12V! Yay! That should be no problem to handle.
Funny, but only 2 out of about 15 AT PS's I have show a minimum load at all, the rest just list max. And only some tell me what color is what V (though I could infer based on the std AT power connector location, or use a DMM). It looks like the older I go back, the more info they give me. No one cares about hobbyists anymore!
The one I'm going to use is from '96. (Would you believe I have a few from the 80's!)
Back to soldering...
On 02/17/2016 11:54 AM, Trevor Cordes wrote:
On 2016-02-15 Hartmut W Sager wrote:
The -5V and -12V are probably fine with no load, but the +12V line should have at least the minimum required load (whatever that might be). Just use a suitable power resistor (power resistor means it won't fry into a molten lump) on the +12V line. In the absence of info on the PS label, I'd go for loading the +12V line with about 10% of its maximum power/amps. Use V = IR and P = IV to do the algebra to get the right resistance (ohms).
Thanks for the tip! The old PS indeed says a minimum on the +12V of 1.3A. I paralleled 2 15ohm power resistors (5%; the big huge white rectangle ones) to approximate a 1.3A or higher (1.6 actually) load. I only had a limited selection of power resistors around here.
I can get the whole unit to power on now, and seems to try to boot and blink some LEDs, yay!
BUT the power resistors get REAL hot REAL fast. Like too hot to touch in under 30s. Does that sound right? Not sure I can deliver that to customer like that. Any other ideas? Different resistors? Maybe try a "real" load, but what?
If you do the math, you'll see each resistor should be putting out 9.6 watts of heat. If they're not rated for that high a wattage, they could burn out. I'm not sure, but I imagine it's possible their resistance would drop as they overheat, causing them to draw more than the 0.8 amps they should draw at 12 V, on their way to burning out (which would make them put out even more heat). Even if they're rated for more than 9.6 watts, that's still a pretty significant amount of heat you'd get out of them. Together they'd put out almost half the heat of a 40 W incandescent bulb. Any load you use will put out that much heat for the same amount of current.
It seems to me a decent switching power supply should be able to regulate voltage with much less draw than that, though. I'd try a single 15 Ohm resistor and see how well it holds the +12 & +5 V, and if it's good, try even higher resistor values than that. You might be able to get the current draw down below 100 mA (1.2 W) without any loss of stability.
-
Adam Thompson -
Dan Keizer -
Gilles Detillieux -
Hartmut W Sager -
Trevor Cordes -
Wyatt Zacharias