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500mA or 1A ? Does it really matter?
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| Smit9352 |
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Posts: 248
Joined: 14 Feb 2008
Location: Louisiana
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Posted: Thu Jul 03, 2008 8:08 am
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| Kiwi wrote: |
| You're not suggesting extra current capacity directly accommodates longer wire runs...?! |
There's a good argument that could be made concerning this as I've seen first hand benefits from running a stronger power supply on longer runs (1000+ ft.) and have had cameras get a voltage/power drop (I know there two different things) over that long of a run which then required a larger power supply to get the camera up and functioning properly.
Maybe it's all in my head?
Thanks,
John
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| Kiwi |
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Posts: 250
Joined: 03 Sep 2007
Location: New Zealand
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Posted: Thu Jul 03, 2008 4:59 pm
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Well, from the theoretical point of view clearly extra current capacity is not going to help directly with voltage drop.
But as you have noticed and survtech has pointed out, 24 VAC transformers and older style (or cheaper) 12 VDC power supplies (based on line frequency transformers) tend to have poor regulation and so often output a higher voltage at lighter loads to make up for it. So that gives you a bit of extra headroom for wire losses.
Modern general purpose 12 VDC switch-mode designs have excellent regulation and normally nothing to allow for voltage drops. Over the entire current range it might not vary more than 0.1 V.
Next to ensuring voltage drops are minimized, the ideal solution is to use a supply with an adjustable voltage output if the wire voltage drop will cut the voltage supplied to the camera below its minimum allowable value.
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| cachecreekcctv |
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Posts: 369
Joined: 11 Nov 2005
Location: California (Northern)
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Posted: Thu Jul 03, 2008 5:27 pm
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One suggestion of mine to you, as not to confuse you any further. Do not confuse voltage , amperage, and resistance. Buy yourself a decent volt/ohmmeter and get familiar with how to use it. I use mine ( and I own several) everyday. Some of my "higher end" Fluke models, actually generate their own milliamp signals, and can check an incoming milliamp signal also ( my Fluke model 744, H.A.R.T. enabled) . Start out with a nice Fluke model, and teach yourself how to check resistance, voltage, and amperage. Will help you out many times over, in the long run. Good Luck !!
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| quaidorsay |
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Posts: 7
Joined: 26 Aug 2008
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Posted: Tue Aug 26, 2008 2:08 am
Post subject: Power problem
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Hi all,
I've installed several dozen, or close to a hundred cameras, and now I have come to my greatest challenge.
I have installed around 12 Mini domes + 4 other cameras plus around 5-6 Audio mics for a large Sydney restaurant and I have been unable to get the Cameras to power up.
I believe at this stage the problem is I have too much current going through the cameras.
For instance, the 12 Mini domes, each dome is rated to take around 300mA to work, and the power supply is a 8amp 9 Channel and even though I double or triple up on each channels, it seems to be consistently delivering 1amp through each connection, and my cameras, through observation is not turning on. Another issue is that I have one starlight dome which does turn on when connected to this panel, and for this matter I believe which is odd, because starlights only need 190mAmps but then again, Starlights having their own power regulation circuitry, whereas the mini domes, although also using Sony Chips are unable to negotiate with 500mAmps +.
This is really an odd situation, because I have tried plug in power supplies and I have been able to switch on the devices before but now, for some reason fuses are blowing up on the panel and there seems to be a short on a few of the channels,
however,
I have used a cheap made in hong kong china Power Supply with 16 channels, with a total of 6 Amps and the cameras do turn on. With that said, this is all weird. I have had the cameras able to turn on with more than 500mA with no probs, but now, they just do not turn on when there is more than 500mA available.
Any ideas?
Cheers,
Joey
Sydney, Australia
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| survtech |
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Posts: 667
Joined: 21 Mar 2007
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Posted: Tue Aug 26, 2008 12:50 pm
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There is no such thing as too much supply current. There can be too little, but never too much. If a device is fed the correct voltage and hooked up correctly, it will draw only as much current as it needs to operate.
You can also have too little (as well as too much) voltage. Too much or the wrong type (DC vs. AC) can cause problems, including frying cameras. Too little will cause non-operation. You should check the voltage at the camera with a good VOM.
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| cachecreekcctv |
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Posts: 369
Joined: 11 Nov 2005
Location: California (Northern)
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Posted: Wed Aug 27, 2008 11:35 pm
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Exactly true. Never "too much current available". Usually too small size wire, too much voltage drop. When you switch on a light in your home, the Power Plant that supplies your city with power, isn't "pushing" it to your home, you are "drawing" it from the grid. When you try to power up that many cameras, are they on the same power feed wire ? I have seen other installers try to wire their customers' cameras in series, believe it or not. The fuses in those ready-made power supplies ( assuming it is 12vdc) are probably in the 1amp range, but check this out for youself. Usually when this many devices ( in this case cameras) do not power up, it is because there are too many things drawing power on a circuit. Check voltage at the cameras, while they are in use.
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| VST_Man |
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Posts: 1314
Joined: 16 Oct 2004
Location: St. Helena Island, South Carolina
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Posted: Thu Aug 28, 2008 12:05 am
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now if you want to get really serrious..think about paralle & series circuits and the different effect that has on the current & resistance.
I never triple up cameras, just bouble up if last resort. I always plan one for one.
later........
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"you get what you pay for"
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| survtech |
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Posts: 667
Joined: 21 Mar 2007
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Posted: Thu Aug 28, 2008 7:50 pm
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How do you bouble up cameras?
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| ak357 |
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Posts: 277
Joined: 16 Nov 2005
Location: Canada
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Posted: Thu Aug 28, 2008 8:41 pm
Post subject:
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| survtech wrote: |
| How do you bouble up cameras? |
I guess bouble up = double up = 2 cams per output right ...? 
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| cachecreekcctv |
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Posts: 369
Joined: 11 Nov 2005
Location: California (Northern)
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Posted: Fri Aug 29, 2008 10:57 am
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Or run a 3 conductor cable, 16/3 for example. Each camera has a fused "hot" or "positive", and use one common wire for "neutral" or "negative" , if two cameras are in the same physical location. Only for 24vac or 12vdc . I have never done it, but just a thought.
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| quaidorsay |
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Posts: 7
Joined: 26 Aug 2008
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Posted: Sat Aug 30, 2008 11:09 am
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| VST_Man wrote: |
now if you want to get really serrious..think about paralle & series circuits and the different effect that has on the current & resistance.
I never triple up cameras, just [d]ouble up if last resort. I always plan one for one.
later........ |
Thanks fellas for the tips. Yeah, I think I better just keep one camera per output. That could be why they won't turn on. If I double up I'm in effect making it a parallel circuit.
I'm getting a 9channel 5amp 12v dc power supply coming in soon, hopefully it will turn it on, but I'll fill you in on whether I can get this working or not.
Cheers
joey
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| survtech |
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Posts: 667
Joined: 21 Mar 2007
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Posted: Sun Aug 31, 2008 11:48 am
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| cachecreekcctv wrote: |
| Or run a 3 conductor cable, 16/3 for example. Each camera has a fused "hot" or "positive", and use one common wire for "neutral" or "negative" , if two cameras are in the same physical location. Only for 24vac or 12vdc . I have never done it, but just a thought. |
That is not the best way to do it since power requires both a "hot" line and a return line to make a complete circuit. The advantage of running 3 conductor cable would be that each camera is on its own fuse, since most power supplies have a common ground for the outputs, but separate fuses for the "hot" wire.
The disadvantages would be that you couldn't use 3 wires if the power supply has isolated outputs for each camera and that the common wire still would have to handle the current for both cameras. That means the distance limits for the power wire would have to factor in the current draw for both cameras.
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| dcam |
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Posts: 66
Joined: 23 Mar 2008
Location: Nederland
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Posted: Sun Aug 31, 2008 1:17 pm
Post subject: 500mA or 1A ? Does it really matter?
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A good analogy for this power supply problem is, if you compare electrical power to a water supply.
Water pressure is voltage.
Water flow is amperage.
You can get big voltage through a small cable (high pressure through a small pipe), But the only way to transmit big amperage is through a big cable (big flow through a big pipe)
HOWEVER If you are transmitting this power over a long distance, and you are only using 12 v. its not sufficient to overcome the resistance of the small cable, so the only way to overcome this is to increase the size of the cable. You can also increase the voltage but is risky and difficult to calibrate, because the cameras use exactly 12 v.
Remember when you check the voltage at the end of a very long thin cable, you always get 12 v. When the camera is connected, the current begins to flow and you will see a voltage drop
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| mr.surveillance |
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Posts: 117
Joined: 10 Apr 2007
Location: Alameda, Ca
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Posted: Tue Sep 02, 2008 3:27 am
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As a general rule I try to use a power supply that is rated at least double the maximum camera draw. Don't forget cameras with IR illumination draw more current at night! In past experience if the power supply was rated at the same or close to the cameras current draw I would be out replacing power supplies within 6 months.
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| CraigVM62 |
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Posts: 162
Joined: 27 Jan 2005
Location: Pacific NW
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Posted: Sat Sep 20, 2008 2:10 am
Post subject: Maybe...
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Maybe it is the electrician in me that makes me think this way ... but ...
I think my major concern would be a that my power supply will not trip via it's internal breaker / fuse before the current exceeds what my conductors can safely carry before becoming a fire hazard. Should the wires carrying that current get damaged and shorted.
Perhaps those who are much more "DC Savvy" can elaborate on when one might be concerned when working with common 18 gauge wire as often found with Siamese Cable.
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