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using PC psu as power source

A

Andy C

Jan 1, 1970
0
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?
thanks !
andy
 
P

Pete D

Jan 1, 1970
0
Andy said:
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?
thanks !
andy
Lots of Pc power supplies need to have some load on the 5V line too and
the oututs are quite noisy
 
E

Eeyore

Jan 1, 1970
0
Andy said:
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?

A PC's power supply is designed to provide much of its power on the 5V supply.
If it's totally unconnected, there may be operational problems. Also, such power
supplies aren't always happy with such a light loading. You'd need to
experiment.

Graham
 
M

Marra

Jan 1, 1970
0
A PC's power supply is designed to provide much of its power on the 5V supply.
If it's totally unconnected, there may be operational problems. Also, such power
supplies aren't always happy with such a light loading. You'd need to
experiment.

Graham

Thats easy to fix, put a resistor across the output and some caps to
get rid of noise.

www.ckp-railways.talktalk.net/pcbcad21.htm
 
C

Charlie Siegrist

Jan 1, 1970
0
Circa Fri, 18 May 2007 19:47:10 GMT recorded as
<[email protected]> looks like "Andy C"
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?
thanks !

I get the impression from your question that you intend to use the 12V from
a functioning computer. If so, forget it. The power supplies are designed
to run a motherboard and a few peripherals, and won't have enough reserve
power to be used for this kind of external load. Others have touched on
the load requirements if the PS is to be run independently.

Stand-alone 12V 5A supplies are plentiful and inexpensive, and far less
hassle.
 
A

Andy C

Jan 1, 1970
0
I get the impression from your question that you intend to use the 12V
from
a functioning computer.

yes, that is exactly what i had planned - we have a dedicated PC to run the
software for the CCTV cameras and i was hoping to run the cameras from one
of the 12v supplies from this functioning pc...
If so, forget it. The power supplies are designed
to run a motherboard and a few peripherals, and won't have enough reserve
power to be used for this kind of external load.

how so ? the computer PSU boasts 500watts - wouldn't 4amps @ 12volts be a
puny external load ?
cheers,
andy
 
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?
thanks !
andy
Hi Andy
I'm a totaly newbie here, but I would find out what uses 12V on this
computer, and if it is things like floppy and CD drives (I'm too lazy
to look it up :) and you are not using these and there is 50W of 12V
power to spare, it might work. But your computer might run a little
hotter (well PS, anyway) so I would be looking for devolution in this
system, ie, having a separate PS for the cameras. Just my idle
thoughts.... jack
 
J

Jasen

Jan 1, 1970
0
hi there,
i need a 12v regulated power source to run approx 10 CCTV cameras (total
should be 3 or 4amps max) which use a dedicated 'CCTV' PC... is there any
reason i can't use a 12volt output from the PC powersupply (inside the case)
for this ?
thanks !

If the cameras need a negative supply that could be a problem.

Check that with the camera running there's no voltage between the
battery negative and the ground of the video output.

Bye.
Jasen
 
J

Jasen

Jan 1, 1970
0
A PC's power supply is designed to provide much of its power on the 5V supply.

Recently there's more power provided on the 12V. Much of it is
downcoverted to below 2V on the motherboard to run the CPU.

there's not much in a modern PC that runs at 5v
If it's totally unconnected, there may be operational problems. Also, such power
supplies aren't always happy with such a light loading. You'd need to
experiment.

this one is going to be running a PC at the same time as the cameras
so that shouldn't be a problem.

Bye.
Jasen
 
C

Charlie Siegrist

Jan 1, 1970
0
Circa Sat, 19 May 2007 00:57:01 GMT recorded as
<[email protected]> looks like "Andy C"
yes, that is exactly what i had planned - we have a dedicated PC to run the
software for the CCTV cameras and i was hoping to run the cameras from one
of the 12v supplies from this functioning pc...


how so ? the computer PSU boasts 500watts - wouldn't 4amps @ 12volts be a
puny external load ?

That rating is for the entire supply. Most of that rating will be for the
5V and 3.3V rails. You have to look at the specs for the individual
outputs. Suppose the 12V output is rated at 15A. That seems like plenty,
but have you spec'd and measured what the MB and peripherals are drawing?
Suppose that total is typically 10A. Now you risk topping out the PS, and
causing a voltage droop under full load.

Furthermore, you will have no isolation on the 12V rail between the
computer peripherals and the cameras you want to use. Noise and
instability from any one device will affect all other devices on the rail.
So you are faced with doing a complete load analysis on the computer and
the cameras in order to find out whether or not this idea is feasible.

All that instead of spending $25 on a 12V 5A dedicated switching supply.
It just doesn't make sense, unless you are more interested in experimental
engineering than creating a workable, stable system. What if something
unpredictable happens with the bus you have routed external to the
computer, and you wipe out your hard drive? To me, the cost-risk-benefit
analysis is weighted very much in opposition to the shared bus idea.
 
C

Charlie Siegrist

Jan 1, 1970
0
Circa Sat, 19 May 2007 00:59:50 GMT recorded as
<[email protected]> looks like "Andy C"

I'm not sure what the point of posting those links is, but what strikes me
from reading the "Discussion:" is that there are a hell of a lot of people
out there playing with electricity who don't know jack shit about it. You
did well to post your question here, and I hope you take the advice you've
been given. I see from other posts that my estimate of $25 for a separate
supply was very much on the high side. That makes the decision even more
of a slam-dunk, IMO.
 
A

Andy C

Jan 1, 1970
0
All that instead of spending $25 on a 12V 5A dedicated switching supply.
It just doesn't make sense, unless you are more interested in experimental
engineering than creating a workable, stable system. What if something
unpredictable happens with the bus you have routed external to the
computer, and you wipe out your hard drive? To me, the cost-risk-benefit
analysis is weighted very much in opposition to the shared bus idea.

yes, that makes good sense, thanks everyone - i will buy an independent
supply for the cameras -
i was just thinking it would be convenient if it was possible as they would
power up and down with the PC, the cables are already routed to the PC and
at face value the '500watt' PC PSU seemed ample-
thanks again,
andy
 
C

Charlie Siegrist

Jan 1, 1970
0
Circa Sat, 19 May 2007 21:50:44 GMT recorded as
<[email protected]> looks like "Andy C"
yes, that makes good sense, thanks everyone - i will buy an independent
supply for the cameras -
i was just thinking it would be convenient if it was possible as they would
power up and down with the PC, the cables are already routed to the PC and
at face value the '500watt' PC PSU seemed ample-
thanks again,
andy

Consider getting a switched power strip, and plug the computer, monitor and
camera power supply into it. Make turning the strip on and off part of the
routine of starting and stopping the computer. Good luck! :)
 
Z

zack

Jan 1, 1970
0
works for me for a 200 watt supply
for no load testing.
i power my ex modom, a hub and some
fans, has run for years now.
 
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