500mA or 1A ? Does it really matter?

[quaidorsay 0]

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

[survtech 0]

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.

[dcam 0]

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

[mr.surveillance 0]

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.

[CraigVM62 0]

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.

[kensplace 0]

I would fit a inline fuse in the cable, rated to blow before the cable overheats..

 

What I tend to do at home when I need several outputs from one DC power supply is build a small distribution board (just on veroboard) that takes the main DC output, and splits it X ways, with each way having its own fuse, rated at what the camera needs.

 

So a 4amp single output power supply could have 8 individual 500ma outputs. Although I tend to leave spare capacity by not using them all, so that the power supply runs cool.

 

Usually also, they are a mix of milliamps, I fit the fuse to the output needed, label it and forget it (but keep a spare sets of all fuses).

 

The fuses are in fuse holders, and the inputs/outputs on terminal blocks on the board. The board then gets bolted inside the power supply box.

 

I also stick a label inside clearly stating max 500ma fuse per fuse holder in case I drop down dead tommorow (so if someone else gets the power supply they dont go sticking 4amp fuses in each holder and putting the cables at risk.)

[cachecreekcctv 0]

Fuses, instead of circuit breakers, will always "blow" (open their filament) upon a short circuit. An "overload" can be different, depending on the design of the fuse ( i.e. slow blow) . No overcurrent device should be rated higher than the current-carrying capacity of the conductor (wire). One reason that "dual element" fuses are used in industry , mostly to protect motors. So, if your positive and negative (assuming 12vdc) come into contact, and everything is workly as designed, the fuses will "blow". But your camera might have to "draw" more than 1 amp for a little while, in order to "blow" the 1 amp fuse, especially if it is the smaller AGC style.