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Topic Title: Switching power supply
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Created On: 05 September 2013 05:12 PM
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 05 September 2013 05:12 PM
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mrcornbeef

Posts: 245
Joined: 05 December 2005

Hi
After bit of advice regarding a switching power supply it is for a cctv system there is a fault the 12volt dc supply switches the power off to the cameras rapidly, i disconnected all the cams it is steady 12v put one cam on and it just say works but dips voltage , any more than one it rapidly turns off
i suspect it is faulty unit any info appreciated especially what is switching supply does it sense current then power up ?
 05 September 2013 05:28 PM
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AJJewsbury

Posts: 10977
Joined: 13 August 2003

It might be a faulty PSU, but the symptoms are what might be expected if the output was overloaded or there was a short somewhere.

Has the unit worked OK with that number of cameras before?

Others will probably be able to give you a better description of a switch mode powersupply, but as I understand it, the basic principle is that mains is taken in, rectified to d.c. and then controlled by an electronic switch to charge a capacitor. The voltage across the capacitor is monitored, when too low the switch closes and the capacitor is charged, when it's high enough the switch opens. The load is the supplied from across that capacitor. Extra circuitry looks for overload and shuts things down and so on.

- Andy.
 05 September 2013 05:30 PM
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Fm

Posts: 585
Joined: 24 August 2011

Power with a 12 volt battery to prove the issue is with the power supply
Is the power supply designed for multiple cameras?
What type of cabling for the cameras. Coax and 2 core shotgun?
Local power supply for camera or central power supply
 05 September 2013 06:24 PM
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mrcornbeef

Posts: 245
Joined: 05 December 2005

yes the system was working so they tell me , yes shotgun cable , 1 psu near cctv dvr , i will try and get a larger psu
thanks
 05 September 2013 08:01 PM
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AlanKay

Posts: 232
Joined: 09 July 2002

Guessing its an old switch-mode power supply, been running for a while somewhere nice and warm?
Likely that its capacitors have developed a high ESR (effective series resistance). You *could* open it and replace them, but probably best to replace with a shiny new one.

Alan

-------------------------
Alan Kay, CEng MIEE
 05 September 2013 10:03 PM
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davezawadi

Posts: 2582
Joined: 26 June 2002

I agree with Alan, it has probably failed (end of life!).
You could measure the current with a DC clamp meter, but my first job would repalce it.

-------------------------
David
CEng etc, don't ask, its a result not a question!
myurl
 05 September 2013 10:23 PM
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Fm

Posts: 585
Joined: 24 August 2011

Google system q for a selection of cctv tat
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