24v A/C supply problem

[Bam_Bam_of_Atlanta 0]

24v A/C supply problem

 

I could have sworn the thing was working right before installing permanently.

But the volt meter is showing about 8 volts difference on phase to ground. About 18volts on one phase to ground and 10 volts on the other. Phase to phase is about 28 volts. A little high for a 24volt power supply. I will have to re-read the installation instructions to see if the extra 4 volts is too much and also see if after about 55’ of 18 gauge copper it drops to 24 volts. I think, its been awhile, the Sanyo camera allows up to 30 volts.

 

But what bothers me is that the neutral is not in the center. Phase to ground should be the same on both phases. The only way I know to get the neutral to shift is to loose the ground on the supply side, but it looks good visually. A floating neutral will defiantly burn up a 240V motor, but a camera? I don’t know.

 

Any thoughts on this? I may have to go get another power supply and see how it does. A $500 camera Vs a $12 power supply is a no brainier. This little job is getting to be a pain.

 

I may run a ground wire to a ground rod about 4 feet away and double ground this thing. It will have to be temporary as the special ground rod is to pull high frequency radio noise from the house wiring that the TIG welder produces to strike an arc. That is the last thing I need messing with video signals.

 

Any other thoughts on this? Bain storm away.

 

Thanks

[CCTV_Suppliers 0]

Who is the maker and what is the model number of your power supply??

[Kiwi 0]

It's not clear to me why you should expect the 24 VAC lines from a low-power transformer to have any relationship at all with a physical ground? I would expect the transformer secondary to be completely floating. There is no safety or electrical reason that I am aware of to ground either side, nor provide a grounded center tap to place each line at the same potential over ground. In fact leaving it floating is likely to be preferred by the camera electronics.

 

When you measured the potential of each wire to ground, did you load each line one at a time to ground with a suitable resistor? My guess is you didn't and are not getting a useful reading from the voltmeter.

 

Sounds like it's just fine as it is.

[survtech 0]

I agree with Kiwi. Since the secondary of the transformer in a 24VAC power supply is completely isolated, both from the supply input and from ground, the only ground reference point would be inside the camera(s) themselves.

 

In fact, I ran into a situation that I thought was a ground loop but was an unused power cable that got crimped between two metal studs during construction, shorting the common (black) wire to ground. That screwed up the video on more than one camera that was attached to that supply until we disconnected the offending cable.

 

And most 24VAC power supplies actually deliver 28-29 volts under low loads. Most cameras can handle at least 30VAC with no problem.

[si_kungs 0]

it depends on the input voltage on the primary side of the transformer. the secondary output is just a ratio of the primary input. so the output is dependent on the input on primary side. unlike in DC where there is a regulator to maintain the voltage.

[Bam_Bam_of_Atlanta 0]

The camera has a ground and two power terminals.

The power supply has a ground and two power terminals.

The wiring diagram shows a ground and two power temrinals.

So I don't understand why the ground would not have equal voltage to each phase? Unless it is not tied to the center of the windings.

To be honest, I have only seen the power transformers to homes. They have the ground connected to the middle of the windings. This gives 240v phase to phase and 120v phase to ground. Are you telling me that this ground is to the house ground and the windings inside this 24v transformer has no ground tied to it? This would make the ground floating.

 

The manual simply says 24v supply with no range.

[Kiwi 0]

Are you telling me that this ground is to the house ground and the windings inside this 24v transformer has no ground tied to it?

 

That is correct.

 

This would make the ground floating.

 

Umm, no, ground on the power supply output is connected to the ground at the input, hopefully then connected eventually to mother earth. The 24 VAC lines however are floating. Just because the ground terminal is next to the 24 VAC output does not imply some relationship.

 

Unlike house wiring there is no reason to go to the trouble of having a center tap (tied to earth or otherwise) as there is no need to derive 12 VAC, nor is there a safety issue with leaving the 24 VAC lines floating.

[cachecreekcctv 0]

Neither Primary nor Secondary windings of transformer have any connection to "ground", and are not "grounded" or "grounding". The input voltage also dictates the output voltage. If you have 125VAC input on the primary, you might get 28-30VAC on the secondary. But if you input 112-117vac, you will get a different output. The transformer is just a fixed set of insulated windings. If any of those windings are going to ground, then you are bound to generate a lot of heat, and will eventually short out the transformer. Take your ohmeter and check resistance of the primary and secondary windings, and keep note of that number.

[Bam_Bam_of_Atlanta 0]

Thanks for the info. I learned a little more.

 

Do to this forum, I got it up and running this weekend.