RE: CCTV

["Keith Doxey" <ukha@xxxxxxx>]

Hi Brian

> > Depends on the camera. If it has onboard voltage regulation
> then it should
> > be OK. If not you may kill it. Als  even if it has onboard
voltage
> > regulation, dropping the extra voltage willl generate quite a bit
> > more heat.
>
> Is there anyway to tell this? s  by dropping the voltage it generates
more
> heat? even just 3v?
> is the opposite true as well? give it more voltage and it turns int  a
> fridge..............
> complicated this lecky stuff........
>

Quick example.

Although the original PSU is 12V @ 300mA, the camera is possibly a 9V
camera
drawing 300ma which will have a built in voltage regulator. The Voltage
Regulator will be dropping 3V @ 300mA which is 0.9W or 900mW of heat
disipated by the regulator. If you use a 15V power supply then the
regulator
will drop 6V @ 300mA  = 1.8W Whilst the actual regulator may be rated for
that power the heatsink may not be able to dissipate enough of the heat and
the whole camera will run hotter than it should. Heat is the biggest killer
of electronics.

> Could I therefore take a feed from the PC PSU and feed it t  all
> the cameras
> at the same time?
> I was originally going to put an extension lead with all the PSU's
plugged
> int  it and use an appliance module to switch the extension lead but
not
> sure if it will all fit in the same case, heat might als  be a problem
> although I could fit a high-speed cooling fan, I have another tray to
try
> just this.
>

A typical PC power supply can supply over 8A @ 12V. Thats enough for at
least 24 cameras.

> What is a wall wart? is it just slang for all PSU's that plug
> int  the wall
> and look hideous?
>

You got it :-)

> Would it be a good idea t  buy a PSU for this job?
>
> What fuse should I use? presumably in line with the power cable in a
> in-holder?
>

Neatest way if you are rack mounting is to fit panel mount fuseholders on
the front panel.
If you put an LED and resistor across the fuse it light if the fuse blows
indicating a fault, or you can put an LED on the outgoing side of the fuse
to show the supple is present.


FUSE BLOWN INDICATOR
+ve --------fuse------------------device--0V

--LED--Resistor---

or

SUPPLY HEALTHY
+ve --------fuse------------------device--- 0V

--LED--resistor-------- 0V


>I have als  bought a 4U case to try and fit my Server int , but this
needs
a
>lot of thinking, something I am loathe to d  on a hot day like t day.

My original thoughts for doing this were get a Minitower. Remove the cover,
lay it on its side inside the 4U case. Slide the CD & Floppy forward,
draw
round them to mark the rear of the front panel, cut the holes and bolt it
all together. By fitting a "normal" chassis inside it it means
any PC config
changes are easy to d .

I have now decided to use Desktop cases and just use Aluminuim angle as
rails to support it in the rack. Short pieces of angle ali as fixing
brackets pop riveted to the sides of the lid will hold it in place in the
rack as the weight would be taken by the rails fixed to the sides of the
rack. My Jukebox is a desktop machine and just measured it.... 17.2 inches
wide so it will fit snuggly between the 19" rails, 5.25" high so
its 3U.

> Sorry for all the questions but you guys are soooooooooooo clever!
>

We've als  learnt a LOT from past mistakes :-(

Keith