Question on Voltage Drop

[able1 0]

Hello all,

 

I am presently designing a cctv system but the building size dictates a lot of cable. The longest run will be about 390 feet from the head end. After doing some calculations for voltage drop I can see that I am going to be in trouble at the camera dome location with heater/blower current draw at 24 vac.

 

My plan is to use siamese cable with 16 gage 2 cond. wire. However the volts are just going to be past operation.

 

What would be the recommended options. Place the power supply closer is one choice but that is going to mean new AC circuits being installed. Or is it better to get 115v cameras and run power from the headend???

 

Any helpful thoughts would be appreciated.

 

Thanks,

 

Les

[securitymonster 0]

390ft shouldn't be an issue. I've installed many cameras running 24V AC, heater/blower/camera powered up with homerun cable runs over 500ft.

[able1 0]

390ft shouldn't be an issue. I've installed many cameras running 24V AC, heater/blower/camera powered up with homerun cable runs over 500ft.

 

 

Then what am I missing. I have not had a camera run more than 125' feet before so I never really calculated the voltage drop. So this time I went here http://www.altronix.com/app_notes/calc.php and pluged in the numbers.

 

I double the wire length to 780 feet and get a voltage drop of 14 volts with 16 gage wire and 2.25 amps at 24 volts. Is this calculator broken or something???

 

Even if I don't double the wire length (which should be) I get 7.02 voltage drop.

 

I just noticed that the calculator does not include a cell for volts. So I used another calculator that does request voltls that I have, with the same numbers as above and got a 8 volt drop. Thats a 36% drop in power.

 

Something is wrong or right here and I am not sure what??

 

Any thoughts.

[Lloyd 0]

It all has to do with the amount of load you are going to put on the circuit.

 

You are refering to 24 VAC I believe.

 

You will need to know the total current ( amps ) needed by all devices on the circuit.

I have very little experience in the CCTV area, so I have no idea what the heaters, etc. require.

But all devices will have a watts or amp requirement identified.

 

Example:

 

The power requirement for a Panasonic WV-CP484 is shown as 4.7 watts @ 24 VAC.

 

The power, or watts, formula is P = I x E.

 

Power ( watts ) = I ( amps ) x E ( volts)

 

So filling in the blanks ....

 

Let's increase the power requirement from 4.7 to 4.8 watts .... just to make it easier to see.

 

P ( 4.8 watts ) = I ( .2 amps ) x E ( 24 vac )

 

There, now I know I need .2 amps @ 24 VAC to run the camera.

 

Now go here and find the chart for your distance, then cross reference for the amps and wire size.

 

I see that at 400 feet ( paired conductors ) with 16 ga wire, I can safely run a load of .42 amps.

Only .2 amps is needed for the camera.

 

Find your current draw for each device you are going to power.

Add them together for a "total amps needed figure".

Go to the chart.

 

I see the chart shows info for a 28 VAC tap.

Someone elso would have to tell you if it is standard in the industry to use the 28 volt tap, but it appears from the chart that it is.

If the 28 VAC tap is used, then the load in my example could be increased to 1.67 amps.

 

I hope this helped.

[able1 0]

Thanks for the nice chart. It would seem that this confirms my fears.

 

24vac at 2.25 amps on 16 gage wire 390 feet long will have a bit of a problem. Even at 28vac is still a problem. 8 volt drop is a bit much.

 

With this in mind it would seem that pulling the power from the location of the camera dome would be better.

 

OR

 

Run 120vac to a txfmr at the camera dome would be another solution.

 

Anyone have any other thoughts???

 

TIA

[rory 0]

Power it local, if then you have issues with ground loops, get a ground loop isolator. Look at what it costs to just plug it in local at the camera, as to running 400' of cable (any trenching, conduit, etc?) .. if you have a few cameras in the same location then power them all at a central point to those cameras .. add a UPS with AVR and you are good to go. Ive done a couple hundred feet before, didnt notice any serious power drops .. but never powered anything that far before. Ones I had that were over 200' I powered with other cameras at that distance in the same location.

[kensplace 0]

What equipment are you powering, 2.25 amps at 24vac is a lot of power for cctv stuff.

[able1 0]

What equipment are you powering, 2.25 amps at 24vac is a lot of power for cctv stuff.

 

I am going to be using some Videolarm SWD domes with Heater/Blowers. According to the specs they will about draw 2.25 amp at 24vac. Granted they will only draw that when it gets cold but when it does I beleive that the picture will be gone, gone, gone!!!

 

Question for kensplace or anybody for that matter, any recommendation on a good gound loop isolator??? And what is AVR when it relates to a UPS. All Video Return??? Have not heard that term before and was wondering.

 

TIA

[rory 0]

Ok so its a PTZ? I would power that and especially due to the Amps they use and the distance, near the camera. You can normally get a weatherproof power supply from the manufacturer for the PTZ.

 

AVR = Automatic Voltage Regulation

A Must for all electronics, so that during low voltage and brownouts, your equipment does not get fried. If you dont get much of that where you are located, not so much of a worry. I wouldnt warranty anything without it though.

[able1 0]

Ok so its a PTZ? I would power that and especially due to the Amps they use and the distance, near the camera. You can normally get a weatherproof power supply from the manufacturer for the PTZ.

 

quote]

 

No not a PTZ just a Dome with Heater and Blower. Oh I almost forgot. You have never used an Heater/Blower before have you???

[rory 0]

Oh, well never used a Heater/Blower .. but most fixed domes dont need more than 500ma. I cant speak for the Heater/Blower part though.

[able1 0]

Oh, well never used a Heater/Blower .. but most fixed domes dont need more than 500ma. I cant speak for the Heater/Blower part though.

 

If anything you should be installing small central air units in your domes. Will help the electronics from overheating.

[kensplace 0]

Guess if its outdoors it could suck up power with a heater on top of the motors, course if its installed indoors in a normal room, then the heater should never actually come on, as the room temp + heat from the dome electronics/motors itself should keept the thermostat from kicking in.

 

Not sure about what makes of ground loop isolators are available in the usa, as Im from the uk, and the only one I have tried is a tecton humbug, which works ok. Searching for humbug will probably bring up loads of results, the main thing to watch out for (other than getting one from a reputable company, not some taiwanese fly-by-night) is the bandwidth, you need at least 5mhz+ bandwidth in general for a average 500ish line pic (for pal it works out as around 100 lines or so of resolution per mhz bandwidth, ballpark figures, cant be bothered to do the maths).

 

Get one with too little and you lose resolution...

[rory 0]

LOL .. small AC units. .

 

As for Ground loop gear .. Pelco has one of those.

http://www.pelco.com/products/default.aspx?id=230

[kao 0]

Sometimes the math and the real world don't agree.

 

Just for fun, I took a spool of 1000ft siamese cable (coax + 2 cond 18ga wire), terminated the ends and hooked up a camera and power supply.

The picture was clear as day.

 

According to the altronix calculator, I should have been dropping 3.81 volts.

Camera = 24v .3 amps

Lens takes up minimal power - like .023 amps at 4v

Power supply (simple wall transformer) = 24v .800 amps

I tested the voltage at the end of the spool and it was ~25 volts.

The actuall output of the 24v transformer was 27 volts. All of them seem to kick out between 26.5 and 27 volts.

 

So I'd recommend two simple solutions:

1. Take 400ft of cable and connect your heater/blower box, camera, lens, dvr - all in the shop and see if it works. Remember to put the heater box in a cooler or freezer to make sure it kicks on.

Keep in mind the heater and blower should never be on at the same time as one is for cold weather and the other for hot.

If you get a crisp clear image, youre in business.

2. Run additional wire with the coax pull - either another pair of 16ga or use cat5 and some baluns.

 

I've run 400'+ runs with just coax and 18ga wire and the video is crisp.

[able1 0]

Kao, thanks for the testing, good information.

 

First, I am convinced that the Altronix calculator uses a un-defined voltage for its calculations. I believe it is 24 volts but not sure.

 

Thanks for doing the calculation with the 1000 foot spool. What would be real interesting is checking the actual amp draw with a digital meter. Place the meter in amps switch the leads to the proper jacks and place the meter in line.

 

Doing it with out the 1000' spool and then with the the spool. There should be an increase in amp draw thus a voltage drop. Wish I had a 1000' spool in stock to try.

 

I agree that you may have a good picture but it may be that the camera can actually work with some lower voltage than 24vac due to a voltage regulator. The question is what is the bottom threshold voltage where the picture suffers and/or gone altogether.

 

Also I agree that a given txfmr will normally give an output greater than the specified. ie. 26-27 volts on a 24 volt txfmr. What will happen is that when you approach the VA rating of the txfmr the voltage will drop and the txfmr will heat up until such point that the txfmr will fail or a fuse will blow.

 

A camera load of .3 amps is a bit insignificant to .8amp transformer, since it is not even working hard yet.

 

I have found a common point that I can place a multi camera power supply that will shorten the longest run of cable to about 180 feet. That will make me more comfortable. The video will remain at the 390 feet but I don't see that being a problem.

 

Again thanks for the efforts. This is all very interesting.

[able1 0]

Ok, I think I got a good handle on this voltage drop issue and thought it would be helpful to others here so I decided to share.

 

The Altronix calculator is good. It is based upon resistance of the wire and current draw. If the wire run is a give length ie 400 feet it doubles this length to 800 for the calculations since the wire resistance is for the full length out and back.

 

So if you plug in your numbers and see that you will have a voltage drop of 7.5 volts this is 7.5 volts no matter if you are using 24 volts or 32 volts or even 120 volts. Badda Bing!!!

 

Now some may wonder if you have 7.5 volts worth of drop on a 24 volt source which give the camera a voltage of 16.5 volts how is it you get a crisp picture. Well the answer is that some cameras allow for a wide voltage range. Such as the Bosch LTC's The voltage range is 12-24 vac. Others like the Honeywell HCCM474M has a voltage range of 21--26 vac.

 

The other point is that if you see your voltage is going to be a little low for a given camera then you can pump up the voltage on the source to say 28vac. But becareful, the camera runs that are closer to the source will not have the same voltage drop and you don't want to over power them.

 

So on the given camera location the Bosch will be just fine but the Honeywell will be suffering. Badda Bang!!!

 

The problem as I see it is all the variables involved with the various manufactures it is very important to read all the specs and do the calculations before you just lick and stick. Badda Boom!!!

 

Thanks for all the added input, it really did help me to see that I needed to spend some additional time and did a little deeper.

 

Hope this helps someone else should the challenge come up in your project.

 

Later,