dividing 24vac to 8 devices evenly. . .

Discussion in 'General Electronics Chat' started by orionrush, Mar 25, 2009.

  1. orionrush

    Thread Starter New Member

    Mar 24, 2009
    3
    0
    So Ive run into a problem. . .

    I'm trying to power these 8 24vac cctv cameras for an art project - the technician at my school instructed me to daisy chain the cameras in series - explaining that in this way each camera would receive approx 30volts each (UK mains at 220vac) - we speculated that this should be well within tolerance for the cameras. So being as trusting as I am - whole hog went for it.

    One pop later :eek: - and I think a few of these cameras have bitten the dust - never mind that my multiplexer now also seems to be on the fritz.

    the question is - what SHOULD I have done? Running them parallel was clearly not an option - running them in series seemed to make sense. . .

    Taking a multimeter to the mess indicated that current from the first to the second camera was hot at about 140vac, second to third at about 47vac and then things went down to about 3vac afterward. . . I don't really want to recheck those numbers as you can well understand.

    Any ideas? - I clearly only know enough to get myself into serious trouble. . . :D

    Cheers - ben
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You may be lucky and had one or two die horribly and so save the others. You simply cannot do a series chain like that. They have to be supplied with the correct voltage on an individual basis - essentially in parallel with one another.

    The correct method would have been to have obtained a 24 VAC transformer with the ability to supply that voltage to all 8 cameras. The calculation is simply to add all the currents together to see what the transformer had to be able to supply in the way of current. Having a transformer that can supply above that level of current is actually a good thing.

    Very bad advice from that technician.
     
    Last edited: Mar 25, 2009
  3. orionrush

    Thread Starter New Member

    Mar 24, 2009
    3
    0
    Wow thanks for the quick reply,

    I think this is what I was inclined to do from the beginning. Tell me if this is what you were suggesting:
    My initial instinct was to buy a 24vac 3amp power supply and run the cameras in parallel off of it - My guess, based on a 4 watt spec on the camera was that each was pulling about .1666 amps, about 1.3 amps with all 8 together. - I figured that the power supply I was looking at had enough headroom to do the job.

    Was I on the right track there? Is that what you were meaning?

    The technition is a frined of mine and he just seemed so sure - I started to doubt myself. This was a hard lesson. :(

    But given what I've just learned - how come the first light bulb a series Christmas tree chain burn up faster or burn brighter then the rest?:confused:

    Thanks for all your help - Ben
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    The problem isn´t exactly in connecting the cameras in series. That would work, but ONLY if they were wireless. The signal wire on each camera has a GND terminal, which was on diferent potential on each. But beacause they were connected to the multiplexer, which has all the grounds connected together, it made a big short and big currents were going in and out of the multiplexer.

    Yes you are right, any 24VAC transformer with at least 1.5A secondary current will work.
     
  5. orionrush

    Thread Starter New Member

    Mar 24, 2009
    3
    0
    Thanks a lot kubeek & beenthere -

    Now- Im not really a betting man - but given what kubeek has said about the line out grounding - anyone want to wager on how many of the cameras are still working????

    No way I would have known about line out grounding. I was completely confused as to why the multiplexer had shorted as well.

    My next question is super simple - what is the easiest way to divide in parallel the current coming out of the power supply 8 ways? I've been looking at terminal blocks but clearly the ones Ive seen only patch through and don't split the current. Surely someone manufactures something that will do this cleanly. I just cant see trying to butt splice 9 wires together!

    I'll post an update to as to how many survived in a few days. I have a power supply on order, could be very disappointing. . . . :D
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    To connect in parallel, a large transformer, to convert supply to 24VAC. "Call" one leg of the output ground, the other hot. All cameras connect between ground and hot at one terminal block in the power supply unit. i.e. One wire from camera to multiplexer for power and video for each camera. I'm not sure how the power is set up now, but new wires might have to be run.

    They have RG-xx coax with 4 wires bonded in sheathing to carry power, audio, and the video signal by pulling one cable.

    The multiplexer is dead because it received 48+VAC on it's input from the camera that worked for a while. It may only be a few channels, it may be the entire unit.

    Also, double check that they all run on 24VAC, and there isn't a switchover to DC anywhere, the last one I dealt with had 24VAC for everything, except the recorder, which needed a different power supply.
     
Loading...