Installation Help and Accessories

24v power supply question

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fas - 29 Jul 2008, 12:00 pm

All of my cameras in this particular system pull between 500 and 1000 milliamps. I am looking at a power supply that has these specs:

Output: 24V AC/ 16 Output
Supply Current: 5amp
Max Amp: 1.1 Amp/Channel

Does that mean each of the 16 channels will support a camera pulling 1 amp?

vin2install - 29 Jul 2008, 01:27 pm

That unit supplies a total of 5 A. So with all 16 channels the load cannot total more than 5A. But you can have 1.1A max on one channel but all other channels must add up to 3.9A max.

survtech - 29 Jul 2008, 02:36 pm

To add to that, I wouldn't recommend connecting a camera that is rated to draw 1000ma to a power supply that is rated at 1.1 amp (1100ma) maximum per channel. That is asking for trouble! Common practice is to never exceed 80% of maximum rating; therefore each channel should be rated at least 1.25 amps (1250ma) and the supply as a whole should be rated at least 1.25 times the total current draw.

One question: Few 24VAC cameras are rated in milliamps and relatively few cameras other than PTZ's or IR cameras with built-in IR LED's draw that much power. Most are rated in VA (volt-amps), which is voltage times current. Usually only DC cameras are rated in ma. Are you certain your cameras operate on 24VAC?

fas - 29 Jul 2008, 05:43 pm

Here is the camera:

http://nuvico.com/downloadfile.htm?id=132

survtech - 29 Jul 2008, 06:25 pm

You might want to double-check the specs with Nuvico.

First, there are no regulated 24VAC power supplies that I know of.

Second, if the camera draws 500ma at 12VDC, that would be 6VA (approximately the same as 6 watts) (0.5 x 12). If it still draws 500ma at 24VAC, that would be 12VA (approximately the same as 12 watts).

So the big question is what happens to the extra 6VA (watts)? It can't just disappear into thin air so something has to dissipate it. While 6 watts doesn't sound like an awful lot when compared to a 100 watt light bulb or a 1,500 watt space heater, it is a lot when it comes to electronic equipment.

If that power is not used by the electronics, it has to be dissipated as heat. 6 watts is a lot of heat to dissipate, especially in a camera.

ak357 - 29 Jul 2008, 09:44 pm

QUOTE:
You might want to double-check the specs with Nuvico.

First, there are no regulated 24VAC power supplies that I know of.

Second, if the camera draws 500ma at 12VDC, that would be 6VA (approximately the same as 6 watts) (0.5 x 12). If it still draws 500ma at 24VAC, that would be 12VA (approximately the same as 12 watts).

So the big question is what happens to the extra 6VA (watts)? It can't just disappear into thin air so something has to dissipate it. While 6 watts doesn't sound like an awful lot when compared to a 100 watt light bulb or a 1,500 watt space heater, it is a lot when it comes to electronic equipment.

If that power is not used by the electronics, it has to be dissipated as heat. 6 watts is a lot of heat to dissipate, especially in a camera.

On 24 V side it does not take 500 ma

fas - 30 Jul 2008, 08:07 am

Do you know what it takes on the 24v side?

fas - 30 Jul 2008, 12:09 pm

Just confirmed with Nuvico it takes 500mA on the 24V side as well.

survtech - 30 Jul 2008, 03:18 pm

Well, 500ma is 1/2 amp. Therefore, each output of the power supply should be fused at 1 amp. If you have 16 of those cameras connected to a single power supply, the supply should be rated at 8 amps total plus at least 20% headroom or 10 amps total. You can get a power supply rated higher than that, but no lower.

fas - 30 Jul 2008, 03:27 pm

I am getting a 24vac central power supply rated at 10 amps.

ak357 - 30 Jul 2008, 06:34 pm

QUOTE:
Just confirmed with Nuvico it takes 500mA on the 24V side as well.

Well, here we go
just for fun

measured DC and AC current for CNB dual voltage D2315 camera
12V---.26A ~ 3wt
24V---.13A ~ 3wt

not to be mean but...

plz call back Nuvico tech support and ask if anybody ever measure
current and at the same time ask if anybody remember Ohm's law
u might be surprise with answer

survtech - 31 Jul 2008, 01:02 am

[quote:4aa4883bda="ak357"]

QUOTE:
Just confirmed with Nuvico it takes 500mA on the 24V side as well.

Bravo!!! :D

Unless they internally drop the voltage from 24V to 12V by dissipating it as heat (I doubt they would use a DC-DC inverter due to cost), the power drawn by the camera should be the same. If the voltage doubles (12V to 24V) the current would be cut in half (500ma to 250ma).

Then again, it doesn't hurt to over-rate the power supply.