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the toss

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Posts posted by the toss

  3. Posted

    Your not going to feel a zap from 24Vac however the best policy is to turn the power off simply to protect everything in the event of you doing something silly. I've been doing this stuff for 45 years and still do the occassional silly thing.

    The other thing is that some power supplies have a soft power up and dont like a sudden change in load which would happen if the power is left on and other devices are connected especially if they draw a bit of current

  6. Posted

    Joe before you sell them off you may want to reconsider. Hi def is certainly the way to go, It maybe better to sell off your analogue cameras & DVR & upgrade to a CVI system. A 4 chan CVI DVR can be had for as little as

    $180 aus and cameras for $60. Get on to Rhino Technology for exact prices

  9. Posted

    It doesn't really matter as long as it is not more than 300 meters or so. We are talking about baseband video here

    (the same as comes out of the camera) nominal level of 1V, transmission distance 300m on RG50 coax.You only need to modulate it if you want to move the signal to the RF band thence to a VDA and then demodulated at the TV. This was easy to do in the old analogue TV days but now in the digital TV eara it is not usually viable because of the cost of digital modulators. If the DVR is only equiped with HDMI & VGA outputs then you might have a problem if the feed is to go some distance. But why would you separate the DVR and monitor. It would make searching for footage near impossible unless you have multiple monitors but then that is an entirely different situation.

  13. Posted

    Your problem is the mounting position of the camera. You are getting IR reflected off the ceiling tiles. That camera is designed to be mounted horizontally. I know in many cases it can be used in the vertical plane but (as you have seen) there can be problems. Either remount it to the ceiling ( and fix the wall) or get an L shaped wall bracket to use.

    The same problem is often experienced by novice installers who mount a similar camera under an eve. They invariably mount it as far back towards the wall as they can to keep it out of the weather and end up with the same reflection problem from the eve.

  15. Posted

    I could be wrong but I'm guessing you haven't done a lot of cabling. Here is a little experiment to try. Hang your conduit down the side of the building and feed your cable in until it comes out the bottom. Fix it at the bottom so it cannot move and then keep feeding the cable in from the top until it stops falling in from its own weight. When this happens note that there is NO weight now pulling the cable in. This is because instead of the cable being pulled by your 3Kg weight it is now under compession by the weight of the cable above. Most of the load being taken care of by frictional contact with the conduit.

  16. Posted

    What is wrong with putting it in conduit ?

     

    Hahhahahahahhaha !

     

    Why the *** would you think I wouldn't use conduit ?

     

    Ke ?

     

    Can you read the question ?

     

    I want to know how far apart I should space supports to prevent cable damage.

     

     

    SORRY - missed that bit , but I'm still unsure if you are talking about supporting the conduit or supporting the cable. You are talking about cable damage but as long as the cable is fixed at the bottom where it exits the conduit it becomes self supporting within the conduit. If you are talking about the conduit then there are probably guidlines for your area. I saddle it every metre vertically or at 600mm horizontally

  19. Posted

    I got 4 analog cameras 1 that has the longest wire is losing image at night time approx. 6pm - 6am, but works fine during the day, wire was cut in couple places then stripped and joined by hand and taped with electric tape, i wonder if that's the reason and soldering it together would fix it?

     

     

    I had this issue before, but now i have even longer wire i noticed that disconnecting power from all the cameras and then connecting only that camera having issue fixed it, but now as wire got even longer it does not work anymore.What causes this issue, does it have to do something with humidity change at night?

    Will using more expensive wire fix the issue?

     

    This screenshot was taken in the morning just before it started to work again.

     

    While it is better not to have any joints in the cable, if it is done then it should be soldered. The highlighted part above gives you the clue as to your problem. The power supply is not up to the task of supplying all your cameras. Either it can't supply the current that is needed or the voltage drop on that long run is too great when the IR comes on at night. You will need to determine which one is your problem to determine your course of action.

  23. Posted

    I think you should get a better working knowledge of Ohms Law. Voltage drop does indeed depend (to a degree) on supply voltage. Lets look at two examples.

    A) DC resistance of a cable run = 2 ohm (this is a fixed value in this example)

    DC load (ie camera) = 100 ohm (this is a fixed value for this example)

    Total DC resistance = 102 ohm

    If DC supply voltage = 12V then current will be 12v/102^ = 117.64 mA

    Therefore the voltage drop over the cable will be 117.64 mA X 2^ = 0.235V

     

    NOW keeping everything the same but reducing the supply voltage to 5V we get -

     

    DC current now will be 5v/ 102^ = 49 mA

    therefore the voltage drop over the cable will be 49 mA X 2^ = 0.098V

     

    All three operators ( supply voltage , load resistance and current ) will affect the transmission line voltage drop.

     

    The voltage drop depends ONLY on current draw (and cable resistance, of course)!

    You made a mistake, electronic device (including camera) is a non-linear load and can't be represented as a resistant load so you can't use Ohm's Law that way. Usually, there is a voltage stabilizer inside (for instance, 12V powered device works on 5V internally with stabilizer at input to allow wider supply voltage range) which makes it draw the same current in allowed supply voltage range ( 10,5 - 13 V or so).

    Next, your example is wrong. You can't supply 12V device with 5 V, it won't draw expected current , and if you connect 5V device to 12V source you may burn it.[/quot

     

    Lets make this simple.

    * As I have show the voltage drop may depend on the current draw BUT the current draw depends on the supply voltage (assuming the total resistance [load + cable doesn't change])

     

    * Any load offered up to a DC supply will present as a DC equivelant load. For a given supply voltage it will present as a particular DC load. Things are completely different if the supply is not DC.

     

    * The internals of (most) cameras are 12V NOT 5V and will have the normal operating dynamic range of 20%. 24Vac cameras operate in the fashion you describe. Their internals are the same as a 12Vdc camera but have a 24Vac - 12Vdc rectifier/regulator built in. This is why they are used in long (power) cable runs

     

    * Your last point seems to contradict everything you have been saying and confirms everything I have been saying. The current depends not only on the load (+cable) but ALSO on the supply voltage.

     

    * I have never talked about running a 5V camera on 12V. I have talked about dropping the supply voltage from 12V to 5V and seeing the current change as a result.

     

    Hope this is helpful

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