Remote (portable) power supply for 24vAC cameras

[surveillancetech]

I install and service CCTV systems and occasionally find myself installing a (24VAC) camera where I don't yet have a power supply in place. I have a portable monitor, so if I was able to power the camera I could set the camera and then come back later, put power to it, and have it all ready to go. What I need is a way to convert DC battery power to 24VAC. Most of the cameras that I use draw between 3 and 6 watts, and I would only need to power them for a few minutes, so portablility is more important than power capacity.<p>Thanks for any help,<p>surveillancetech

[Edd]

Jim (Mr surveillancetech):<p>Since I'm "blind" to your equipment I'll just
assume the ordinary.E.G. Your video out is coaxed out....or remote possibility of RF carrier utilization..... unless you have many units.Common 24v ac control line used for all of the units power supplies. And with your power consumption specs sounds like up to date specs on cameras.Seems like they would just take the 24v ac into a full wave bridge ckt then regulate it down to the required voltage(s).If this is the case see if you can confirm this is their technique on a schematic of a camera.If this is the case a 24v DC supply should just steer itself right thru the bridge and power the units up just like ac had been doing.Research this out and see if its not true.If not 'mo info
is needed.<p>Tnx 73's de Edd

[ian]

Hey man, go get a cheap, low power inverter 12V to 120AC, then plug one of your 24VAC transformers into that. Done.

[Chris Smith]

Check for Pico power suplies on the web for step up invertors/power supplies etc. 5v to 12, 24, & 36 volts.
The fact that you use a 24 volt AC wall transformer at 1/2 amp in, means that DC might also work because the ac is rectified into DC already inside the camera unit. Two small motor cycle batteries will equal 24 volts but Im betting your cameras will start to fire around 14 to 16 volts one amp DC, If they are like some of the ones I played with?

[ian]

Some are suggesting these cameras don't require an AC signal. While that may be true for newer cameras, my understanding is that older (and possibly still some newer) cameras use the AC signal for phasing. Maybe I'm wrong. Maybe not.

[Chris Smith]

Some cameras do set their timming cycles by the AC power cycles. You will find out when you plug in DC? If this is true then any variation in the 60 hz will cause the camera screen or out put signal to "Roll" like a old tv set going from frame to frame or even a "Z" like patterns. However, most Cameras have a local oscillator to set this frequency. The small invertor idea might be your best method if this is a problem, but Then I would use a sine wave invertor over the step wave model.