drop volatge from 28 to 24vac

[CCCmarine 0]

I replaced several camera's and the current power supply is a 28vac. The runs are not that long and have ~27.5vac to them. The new camera's are rated at 12vdc/24vac. Camera manufacturer states camera's life will be shorter under that voltage. Is using a resistor an option? If so what am I looking for?

 

Thanks!

[Birdman Adam 0]

If you were to use a resistor, it would need to be gigantic to bring down the voltage by 4 VAC for all your cameras. Plus, it would waste a LOT of power.

 

Since we are talking AC, you can simply get a transformer to convert 28VAC down to 24VAC.

 

I'm not sure where you'd find one with that specific conversion. Also, it must be rated to handle all the current your cameras will need.

 

Alternatively, you could open up the transformer in your power supply and add more turns to the secondary (side where your cameras connect to). This would bring down the voltage for your cameras.

[ak357 0]

If you were to use a resistor, it would need to be gigantic to bring down the voltage by 4 VAC for all your cameras. Plus, it would waste a LOT of power.

 

Since we are talking AC, you can simply get a transformer to convert 28VAC down to 24VAC.

 

I'm not sure where you'd find one with that specific conversion. Also, it must be rated to handle all the current your cameras will need.

 

Alternatively, you could open up the transformer in your power supply and add more turns to the secondary (side where your cameras connect to). This would bring down the voltage for your cameras.

 

More turns to secondary will bring down voltage ?

[Soundy 1]

If you were to use a resistor, it would need to be gigantic to bring down the voltage by 4 VAC for all your cameras. Plus, it would waste a LOT of power.

 

Since we are talking AC, you can simply get a transformer to convert 28VAC down to 24VAC.

 

I'm not sure where you'd find one with that specific conversion. Also, it must be rated to handle all the current your cameras will need.

 

Alternatively, you could open up the transformer in your power supply and add more turns to the secondary (side where your cameras connect to). This would bring down the voltage for your cameras.

 

More turns to secondary will bring down voltage ?

 

Adding turns to the PRIMARY maybe... although would would be tricky as with most transformers, the primary is inside the secondary

 

Either way, physically modifying a transformer would be an iffy proposition - aside from the chance of damaging something, you'd have to know HOW MANY turns to add/remove to get the change you want.

 

A 28-to-24V step-down transformer, IF you could find one, would do the trick (anything with the current capability and 7:6 winding ratio would do)... but a better idea would be to simply replace the existing power supply.

[cglaeser 0]

but a better idea would be to simply replace the existing power supply.

 

+1.

 

Quality CCTV power supplies are cheap.

 

Best,

Christopher

[SEANHAWG 1]

I have been running my 24VAC cameras on a 28 Volt power supply for a little over a year now with no problems.

[Soundy 1]

Really depends on the design of the cameras. The Panasonic CW484 domes list something like 9-30VDC and 12-36VAC as being supported. Some are fussier about overvoltage than others.

[CCCmarine 0]

Thanks all for the input...I think I am opting for replacing the supply.

 

Are those Pelco MCS series worth it or is Altronix the way to go? I like the 24 / 28 option on the Pelco but the enclosures are huge.

[GG CCTV 0]

QUESTION: Have you measured 28V with or without load (cameras) connected?

Sounds strange that you have a 28VAC output power supply, so I was wondering if 28VAC is the output voltage without load, in this case the voltage will drop as soon as you connect the cameras, which is normal when connecting a load to a transformer.

With camera connected you will probably measure less than 24V.

 

Adding/removing turns on a transformer????

[Soundy 1]

28VAC is a not-uncommon option in some power supplies, intended specifically for use over longer runs where voltage drop will be an issue. Usually it's done with a special transformer with a secondary wound for 28VAC with a tap at 24VAC. The Pelco supplies actually have three screws per channel: one common, and one each for 24 and 28V.

 

Keep in mind that that spec voltage is RMS - peak-to-peak voltage at 24VAC will be about 33.7V. Cheaper multimeters will give an average of that, so they may read a little higher than the actual RMS voltage (you need one that actually states "True RMS").

[survtech 0]

We've been running our cameras on Altronix power supplies for over 15 years. They tend to put out 28VAC +/-, even under load. We have hundreds of 24VAC cameras attached to those supplies that have been in continuous use for over 10 years (installed in 2000). I wouldn't worry about the voltage.

 

If you are still concerned, put the power supply on a variac:

 

[Soundy 1]

The only time I've ever actually seen cameras die from overvoltage (when you connect what's SUPPOSED to be the right voltage), is with some cheap board cameras that are rated for 12VDC, when using a non-regulated supply that actually puts out 16-17VDC. In reality though, most cheap cameras are just fine with the extra (as most ship with equally cheap non-regulated PSUs).

 

Dual-voltage cameras should not have a problem with 28VAC anyway, as "dual-voltage" generally implies they have an internal rectifier and regulator that will limit the voltage to what the camera guts can handle.

[CCCmarine 0]

I measured without load, I will try with load as see the results.

 

Great info, thanks again!