Low voltage power "distribution" board design

Question

I got a cheap 12 volts power supply (this one specifically) which I want to distribute to several CMOS CCTV cameras (such as this one) which are spread around the house (15m max. distance).

Normally you would connect each camera via its own power supply to the mains, but since I don't have a lot of space for all these individual power supplies, I thought of creating a "power distribution" board with nice connectors to connect all individual cables to the single powerful supply mentioned above.

Now, obviously connecting them all in parallel worked when I tested it, but for a permanent solution I was wondering - should I add some protection to the circuits? Inverse polarity / overdrive / surge etc.?

Answer 1

While you have not specified the power consumed by each camera,it is usually very low unless it is an expensive PTZ type (Pan, Tilt, Zoom). There are some fundamental rules to abide by:

1) Make sure the power supply amp rating exceeds the amp rating of all the camera's combined.

2) Your distribution board will need to have connectors that match those of the camera's.

3) The power feed to each camera MUST have a replaceable fuse rated slightly higher than the camera's amp rating, by 50% at most.

4) The distribution board should have its own replaceable fuse, rated to match all the other fuses combined.

5) Polarity protection is not needed unless your running zip cord with no polarity marking. Bad Idea. Use wire where the polarity is obvious, a colored stripe, etc.

6) Surge protection is of little help because it normally clamps to earth ground. If you use one just buy an off-the-shelf unit that connects to your power supply AC input.

These are just the basics. If you have weird power connectors (multi-pin, etc) or power is shared with your signal (phantom power), then STOP and post us another question, and please add some details.

Answer 2

Reverse polarity at the power supply if you are going to be fiddling with the power supply a lot (R.P. at the camera if you're going to be moving and fiddling with the cameras a lot). Surge and Overdrive protection is always nice as a safety device, especially when dealing with AliExpress products. I currently work for a company that installs cameras and we just run a separate power cable for each camera back to the power supply and join them all with a screw terminal block (for redundancy we only put 4 cameras on each power supply - but that's a personal choice - allocate 1/2 to 1 amp per camera or so). For ordinary figure 8 cable, I've run 50M to a 12V camera and it still had a reasonable voltage margin (keep it above 11 and you should be fine)

Answer 3

Widely distributing final regulated power is generally not a good idea. Since it's a voltage meant to supply power, there will be significant current. This current times the inevitable resistance of the wires causes a voltage drop.

Devices near the power source may be fine, but devices at the end of the chain may get too low a voltage. Even worse, some of this voltage drop will be in the ground connection. That means the various devices won't agree on what exactly 0 V is, and this will change as current draw changes.

Here are some solutions:

1. If all the devices are relatively low current, you can use thick enough wires so that the voltage drop is acceptable. Do the calculations carefully. Make sure not only that each device gets voltage within its range, but that the ground offset is acceptable. Sometimes you have to use thicker ground wire, or double up wires.

2. Adjust the power supply to just below the maximum voltage the devices can handle. The near devices will see close to that, and hopefully the drop at the far devices still leaves enough voltage.

3. Put the power feed in the middle of the chain. That way the power supply is driving two small chains instead of one big one. Not only does that reduce the drop at the end due to half the resistance in the power wires, but also due to less current on each branch.

4. Distribute a volt or two more than you want and use LDOs at each point of use. Note that this takes care of the drop in the power side of the power feed, but not the return side. If the devices draw lots of current, this is usually not attractive due to the dissipation in each LDO. The wasted power isn't usually the issue, but getting rid of the heat often is.

5. Distribute significantly higher voltage and use buck regulators at each point of use. Modern buck regulators aren't really all that big anymore. I have done systems like this where I've distributed 24 and even 48 V when the devices just needed digital logic voltages. 48 V is the highest you probably want to use because regulatory issues kick in above that.

   Like the LDO method this guarantees the right supply voltage at each device. However, in addition it reduces overall supply current, which thereby reduces the ground offsets.