Dual Power Ac 24v Or Dc 12v - Which Is Better?

[luggsey]

No, it won't matter. It probably won't even be a problem taking the mux supply (e.g.) from the house, and the camera supply from the garage - unless the two are on seperate phases.

Assuming the electrican understood the earthing requirements of BS7671 correctly in any case, and the installation isn't sat on a TT supply.

Regards,

It can and does cause ground loops when using two different PSU's without a comman ground refrence which is why so many "humbugs" and the like are installed. TT earthing with it's floating neutral is always going to cause more problems then a TNC system but a great deal of equipment is now double insulated and earth free so the earthing has little effect here.

[Bill]

will only get problems at 240 v level if on different phases and doesnt come from same source consumer unit.

No. Not quite.

Potentially, any AC source can introduce problems with the video image being transmitted, irrespective of the size of the voltage.

The issue with taking power from more than one phase has to do with the fact that the ground on each of those phases is actually sitting at different voltages - and hence any clock timing will become unreliable, since no "fixed" reference is now available.

Consumer units are irrelevant - the phase is the issue such as it actually exists.

There are far more likely issues with an AC supply than phasing however, such as induced AC voltage on the video (co-ax), EMF, noise (harmonics), and so forth.

Regards,

[Guest anguscanplay]

No, it won't matter. It probably won't even be a problem taking the mux supply (e.g.) from the house, and the camera supply from the garage - unless the two are on seperate phases.

Assuming the electrican understood the earthing requirements of BS7671 correctly in any case, and the installation isn't sat on a TT supply.

Regards,

thanks Bill - thats why I said " ..........(probably)" best at the O/P`s level to stick to DC so it isnt a possible problem

[Bill]

It can and does cause ground loops when using two different PSU's without a comman ground refrence which is why so many "humbugs" and the like are installed. TT earthing with it's floating neutral is always going to cause more problems then a TNC system but a great deal of equipment is now double insulated and earth free so the earthing has little effect here.

Okay, here we see the problem which arises when discussing a specific situation in general terms - the topic discussed here is a specific situation of one camera and one mux - and I gather you are making a more general statement to the effect of ground loops).

My comment concerns the specific situation discussed, and is not a generalisation.

Generally, yes - as I think is evident from my other posts here, supply is an issue, and one which is and can be a big industry headache. Most of your ground loops, however, are probably not caused by the the supply directly, but by the fact that the installer hasn't taken care to keep the supply seperate from the video feed and has induced an AC signal onto the co-ax. This more so with modern double insulated equipment.

Installations which have to rely on a supply without a bonded earth should, IMO, ALWAYS, be earthed locally to a ground spike dedicated to that purpose.

How many cabinets have you seen, camera housings have you seen, with a one or two amp block psu (normally with the plug top cut off and the tails wedged into the housing heater supply terminals) to feed a low voltage camera? Cable management? That's where you wedge the 0.75mm 3 core in with the co-ax to get it all up to the housing in a single 20mm copex, right? Wrong - that's where your video problems start.

Seriously, removal of shoddy installation practices would stop the sales of humbugs and other ground loop isolators dead.

I inherited a project a couple of years back which involed a total of around a hundred and twenty cameras spread across ten sites, all linked to Adpro FastScans. The video received at the central station (the eleventh site) was appalling. The video on site was appalling. I still have a collection of about eighty humbugs from that project - which I removed!

Oh - the sites themselves? Electricity substations - each handling anything from 11 to 132kV via rather a lot of open harmonic frequency filters. Not a nice place for any video to live in. The bulk of the problems we found had to do with the quality of installation, rather than any supply issue. That said I had one camera on each of two sites which refused point blank to generate clean video without a humbug in play.

And finally, all that said, I think we remain in basic agreement that generally, it is bad practice to use different source supplies within a single instalaltion where a single source can be obtained.

Regards

[kuchars22]

Okay, here we see the problem which arises when discussing a specific situation in general terms - the topic discussed here is a specific situation of one camera and one mux - and I gather you are making a more general statement to the effect of ground loops).

My comment concerns the specific situation discussed, and is not a generalisation.

Generally, yes - as I think is evident from my other posts here, supply is an issue, and one which is and can be a big industry headache. Most of your ground loops, however, are probably not caused by the the supply directly, but by the fact that the installer hasn't taken care to keep the supply seperate from the video feed and has induced an AC signal onto the co-ax. This more so with modern double insulated equipment.

Installations which have to rely on a supply without a bonded earth should, IMO, ALWAYS, be earthed locally to a ground spike dedicated to that purpose.

How many cabinets have you seen, camera housings have you seen, with a one or two amp block psu (normally with the plug top cut off and the tails wedged into the housing heater supply terminals) to feed a low voltage camera? Cable management? That's where you wedge the 0.75mm 3 core in with the co-ax to get it all up to the housing in a single 20mm copex, right? Wrong - that's where your video problems start.

Seriously, removal of shoddy installation practices would stop the sales of humbugs and other ground loop isolators dead.

I inherited a project a couple of years back which involed a total of around a hundred and twenty cameras spread across ten sites, all linked to Adpro FastScans. The video received at the central station (the eleventh site) was appalling. The video on site was appalling. I still have a collection of about eighty humbugs from that project - which I removed!

Oh - the sites themselves? Electricity substations - each handling anything from 11 to 132kV via rather a lot of open harmonic frequency filters. Not a nice place for any video to live in. The bulk of the problems we found had to do with the quality of installation, rather than any supply issue. That said I had one camera on each of two sites which refused point blank to generate clean video without a humbug in play.

And finally, all that said, I think we remain in basic agreement that generally, it is bad practice to use different source supplies within a single instalaltion where a single source can be obtained.

Regards

Think I'll stick to 12vDC! Just bought an adapter from Maplin and working fine.