Does anyone know how much current I can draw from a the 12V pin on a psu without harming it? Can I squeeze 2-4?
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Re: How much current can a 12V psu handle?
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Re: How much current can a 12V psu handle?
It depends on the wire gauge and how much temperature increase you're willing to accept and how much voltage drop your application can handle.
For example, a typical 400-600w power supply will use AWG20 rated cables.
This cable will have a loss of about 0.07v per meter of cable, for each A of current : http://www.calculator.net/voltage-dr...es=2&x=46&y=17
The cable itself is rated according to standard for maximum 11A for chasis wiring : http://www.powerstream.com/Wire_Size.htm
However, you may exceed that but the wire will be hot and the voltage drop will be higher.
That's why PCI Express connectors for video cards use 3 yellow wires to send up to 150w to the video card.... 150w / 12v = 12.5 amps / 3 wires = 4A per wire , well within the 11A value and with just around 0.1-0.2v drop on the length of the cable.Comment
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Re: How much current can a 12V psu handle?
IIRC, Molex Mini-Fit Jr. pins are rated for 5A max, and AWG #20 is also rated for 5A max., But I think drawing more than 3.5A from one pin with that gauge wire is risky.PeteS in CA
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
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To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
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Re: How much current can a 12V psu handle?
2-4a is okay i would say. More can be harmful.Comment
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Re: How much current can a 12V psu handle?
Thanks guys. A lot of useful info there. I will try to use in the future. :-)Comment
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Re: How much current can a 12V psu handle?
I posted in some haste last PM. There are several potential issues that can make drawing the maximum current per pin imprudent.
UL rates AWG #20 for 5A (assuming my memory is correct), but the outer insulation will be hot to the touch. IIRC, the wire most commonly used for PC P/S harnesses, UL 1007, is rated for 85C. So in a bundled harness running through a poorly cooled area (e.g. where the harness exits the P/S case), that 85C rating may be exceeded. I don't think the PVC insulation will turn gooey-melty; instead, I think it will harden and become brittle. Not. Good. AWG #18, rated (IIRC) for 10A, is a better choice for +3.3V, +5V, +12V, and Return wires.
There are two places in a Mini-Fit Jr. pin-socket where there is a mechanical (i.e. not soldered) connection. The socket is crimped onto the wire; the sockets make mechanical contact with the pins. With proper crimping, a near-perfect pin-socket mating, and perfect current sharing among the pins, 4.5A-5A per pin would probably be OK. BUT reality is that pins, sockets and crimps are made by imperfect humans and by machines that have to be adjusted and which wear mechanically. Every slight imperfection - in the pin or socket tin or gold plating, in the shape and size of the pin, in the forming of the stamp-and-bend socket, in the seating of the pin and socket, in the crimping of the socket onto the wire is a weak point that will overheat when operated at or near the maximum rating of the pin-socket connection, and which will mess up the current sharing, causing excessive current in other wires for that output circuit.
I've posted before, in talking of heat sinks, that I believe in
heavy metal . That is true of me for current-carrying wires and connectors. I like to see wire that is heavier gauge than the minimum necessary. I prefer solder connections to crimp connections (and IDC connectors should never, never, never, NEVER be used for more than a few milliamps!). And I like to see connectors used at 50%-75% of their maximum rated capacity, at most.
PeteS in CA
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
****************************
To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
****************************Comment
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Re: How much current can a 12V psu handle?
trying to run something other than a pc with it?
gotta load the +5 on most pc psu to get decent regulation.
and if trying to run a cb or amateur radio rfi is another issue....both ways!
the connectors can get snipped off and all the blacks and yellows used together to eliminate droop.Comment
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