Dumb question about power supplys

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Hi
As you can tell from my question I know nothing about electronics
however that doesnt stop me asking anyway.

I have a small security camera that I want to use in my shop.
I have a capture card in my computer and I will connect the camera to my
computer and capture the video.
easy so far.

The camera requires 12vDC and 150ma.
I understand the computer provides 12vDC on its power connections for
HDD etc.

So the question is can I use connect the camera to the computer's DC
power supply instead of using a power adapter?
If so which leads would i use?
I believe the yellow lead is 12+ and the black lead is earth, so would
these be the ones?
Or am I inviting a big bang?

TIA

Re: Dumb question about power supplys


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You need to purchase a suitable supply , talk to a local installer or
take the camera requirements to jaycar or similar and they will have a
suitable supply in stock .

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Thanks, I have a suitable power supply however if I could do without it
by adapting one of the computers power leads then so much the better.

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How far is the camera from your PC? I cant see any problem with doing
this. The PC PSU is probably more stable than most plug packs you can
buy.

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Yes, there is a configurable power supply that sites on a blanking plate
 and takes powere fromthe PC supply and provides it at a socket on the
blanking plate that will do exactly what you want.


i think I purchased mine from Jaycar.

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Yes, I have one of these and that was my intention also.
Just not sure which wires to connect to the molex connector.

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The PC power supply can handle that easily, it should provide 12v at several
amps.

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No risk of a big bang unless you connect the camera the wrong way around.
Yellow's +12v I'm pretty
sure, but double check on Google.

I've rigged up a cable that connects to one of the spare connectors on the power
supply and runs to
5v and 12v sockets mounted on a spare harddisk-bay cover. Very handy.

Cheers,


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amps.

That is actually something to be wary of. I did something like this
once. The camera had a tantalum capacitor across the supply that
decided to go short-circuit. I don't know why - from memory, the
capacitory was a 16V one, so I'm pretty sure the voltage was not
exceeded. Anyway, the resulting high current through the capacitor
made quite a mess of the camera - I was lucky it didn't catch fire.

So, you may want to include a fuse.


Andy Wood
snipped-for-privacy@trap.ozemail.com.au

Re: Dumb question about power supplys



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amps.
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The fuse is an excellent idea, thank you.

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amps.
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That's good advise, thanks.

I will make some cables with inline fuse holders so I can protect each device
individually.

Cheers,
Sam

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Thanks, do you remeber which wires you used?
Yellow and black?

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Yeah, yellow's +12v and black is ground.

Cheers,

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finger to keyboard and composed:

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I think you're pretty safe. However, as a general rule, whenever I
replace an isolated plugpack supply with a non-isolated PSU, I test
for continuity between supply negative and signal ground. Some devices
(eg DMM) may misbehave if you connect the signal and power grounds.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Dumb question about power supplys



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maybe.

set your system up in the normal way, with the external powersupply
and the connection to the PC in place and

and measure the voltage between the negative terminal of the power supply
and the ground of the powersupply (black wire in the drive power connector)
if you get 0 volts,  switch the meter to ohms and measure the resistance
(it should be near 0)

if both of those tests succeed it's safe to power the camera from the PC's
power supply. 150mA is not likely to overload the PCs PSU.
--

Bye.
   Jasen

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