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DC supply on AC CCTV camera

Hi,

I have a bunch of (identical) CCTV cameras that I've been asked to set up for a group, here. They require "24VAC" as power. Of course, it is MUCH easier for me to provide a

*DC* supply (lots of "bricks" to choose from).

Conceivably, a DC supply *should* work -- half the internal bridge would simply be superfluous.

*But*, I wonder if the camera is also expecting timing information from the AC supply? I.e., to synchronize it's field/frame rates.

I can always try a DC supply and examine the video output. But, what would I be looking for to indicate that the camera was "craving" this timing information? Slow vertical roll? etc.

Thx,

--don

Reply to
Don Y
Loading thread data ...

But why, 24VAC is just a transformer, with nothing else.

Reply to
edward.ming.lee

Google funny business: There is a "translate to English" button, which translate the above statement to:

But why, 24VAC is just a turn, with nothing else.

If "turn" is English, what language is "transformer"?

Reply to
edward.ming.lee

Den mandag den 6. oktober 2014 18.44.29 UTC+2 skrev Don Y:

Many modems require an AC supply because they have an internal doubler to get a +/- supply

-Lasse

Reply to
Lasse Langwadt Christensen

Use the AC. It'll save you ground loop worries, for one thing. Hum bars, you do not want. You probably have a bunch of old modem wall bricks in a box someplace--they work fine.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

You could try the 32v dc and see.

NT

Reply to
meow2222

Try will ikely release the Magic Smoke :-?

Lots older devices used AC to get the voltages theyneeded oth posative and negative.

Do it the correct and simple way, 24volts AC

--
John G Sydney.
Reply to
John G

I wouldn't.

Are there PTZ motors? Aren't there always?

60Hz is gonna be completely useless for video sync. 

--
Les Cargill
Reply to
Les Cargill

why, what input circuit would be unable to survive dc in?

NT

Reply to
meow2222

32 volts is likly too high and if it has a transfomer input to get required voltages then SMOKE. B-) 
--
John G Sydney.
Reply to
John G

On a sunny day (Mon, 6 Oct 2014 16:10:25 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

Transformer?

:-)

Reply to
Jan Panteltje

  1. 32v is less than 24v ac peak, so its not too high.
  2. I've never seen an LV appliance with a transformer input
  3. Transformers survive dc in no problem, they just pop a fuse or the psu goes into limiting.

NT

Reply to
meow2222

On a sunny day (Tue, 7 Oct 2014 02:21:13 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

That is right, all else being as you think.

Maybe you never seen a leopard, does not mean those do not exist.

They do not always have a fuse.

Reply to
Jan Panteltje

If it's two half-wave rectifiers on for +24V one for -24V, or a doubler.

The capacitors are probably 35V so you put 24V DC in and there's not enough between + and -, put 50V DC in and one of the capacitors explodes

--
umop apisdn
Reply to
Jasen Betts

Just follow the rules and stop pontificating about that which you know not. :-@ After all you are only guessing what is inside the box :-?

--
John G Sydney.
Reply to
John G

It does mean the odds of encountering one are miniscule. And since such an arrangement in a camera also makes no sense from a design pov, its worth be

u goes into limiting.

The psu either has a fuse, current limiting, foldback limiting, thermal cut out or less likely an mcb. Ones with no such protection are unsafe, illegal and rare, and again worth the miniscule risk of failure.

NT

Reply to
meow2222

snips

Why do you say that? Analogue tv was always synched to mains frequency to a void hum bars. Zero crossing is a short event that could be fed through a p ll (or oscillator) to get a more stable output that will match on all camer as, and be simpler to implement than putting sync pulses into the video sig nal, so I wouldn't rule it out. Testing will tell.

NT

Reply to
meow2222

On a sunny day (Tue, 7 Oct 2014 04:20:36 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

I try to avoid betting in electronics.

The question is simply will the fuse go, or the winding in the mains transformer without a thermal fuse go. Of course in a situation like this any of us here would open the 'camera' and have a look at whats in there. Without doing that, damaging it would not create a greateful person I'd think.

Thre is a small change there is a leopard in the camera and it will jump at you, but .. OK,., I will stop here.. :-)

Reply to
Jan Panteltje

On a sunny day (Tue, 7 Oct 2014 04:25:54 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

Not really, the studio was 50 Hz, but free running here, when color came the V was derived from H, and H from the Fc, and that perhaps from some atomic clock.

CCTV cameras are not normally synced to mains.

No, for superinpose you need to be in sync in H and V, and if color also in Fc, and even PAL phase (8 frames sequence IIRC). Of course the days its done digital.

Reply to
Jan Panteltje

an =

be=

That strategy loses out over the long run.

ps=

cut=

gal=

sformer

That's not the question really. When you look at the possibilities and assi gn realistic odds, the chance of something going pots up this way is I'd sa

on a new psu to cover such a miniscule risk, let alone the real cost of on e. Hence I'd be thinking more about what might happen in the other 999,999 cases.

and have a look at whats in there.

hink.

at you, but ..

hehe

NT

Reply to
meow2222

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