How much voltage can a DC IR camera take??

[lupy 0]

Just found this forum and wondering if someone has some experiance over volting cameras...

I have a long driveway, about 500ft, and am concerned that someone is messing around at the end of it. I installed a ISC P540X day night camera, and am using cat 5 with a balun. Running 2 pair for power, one for video, and one in reserve for a beam break in the future. After install, I had problems with voltage sag during night operation so that the LED's were very dim. Testing at the camera and feeding it with a lab variable power supply, I see about 3.5 volts drop during day. At night it is much worse, needing about 18v at the source to get 11v at the camera. It's drawing about 500ma at night and ~100 in the day. While the LED's aren't full bright at 11v but it's reasonably usable, and I happen to have a wall wart that provides enough voltage to make it work fine at night.

Problem is that when the current drops at daybreak, the camera will see 15.25v. I realize that these cameras have an internal regulator to compensate for variances in power supplies, but how much can they take before they start to fry?? Adding to the problem is that transformer power adapters drop voltage under load, so the day-night voltage swing is higher than with a regulated switching supply, but switching supplies produce a lot of noise, so what to do??

 

The simple solution is to just use this higher voltage wall wart, it seems like it Will work, but I am hoping for some reassurance the camera won't blow prematurely from the higher than normal day-time voltages. (15.25v DC)

 

Thanks for any experiance you all might have.

[vin2install 0]

Try using a regulated power supply. And try using the last pair to bring your wire gauge to 18awg.

[mike_va 0]

Problem is that when the current drops at daybreak, the camera will see 15.25v. I realize that these cameras have an internal regulator to compensate for variances in power supplies, but how much can they take before they start to fry?? Adding to the problem is that transformer power adapters drop voltage under load, so the day-night voltage swing is higher than with a regulated switching supply, but switching supplies produce a lot of noise, so what to do??

Not all switchers produce noise, e.g. every camera that is dual voltage already has one inside.

 

I would not run it that high. Depending on the camera it may cause reliability issues.

 

I'd use the other pair as suggested to get the drop down, or as sense lines since you have a lab supply (but the first method is preferred).

[Birdman Adam 0]

Yea, use 3 pairs for power. Also, check the voltage at the source of the power supply while it is under load. If the actual supply is dropping a lot (not including v-drop over lengths of line) then you need to find a bigger PSU!

[ljarrald 0]

be very careful! i once accidently put 24VDC through a camera that only wanted 9V. the camera released its magic smoke AND backfired killing ch1 of my dvr. i now have to make do with 15 channels instead of 16 which is a pain because i could do with that extra channel!

[lupy 0]

Wow, that's a bummer. I supose 24 from 9 is a lot more than I am talking about, but it's a good warning. I am thinking about putting a 12v or so zener diode at the camera with a resistor in series across the line. During the day, the diode will leak enough current to drop the line voltage to 13v or so, which should be safe for the camera. at night, the volatage will drop from the Ir's down to 11v or so, and the zener will stop leaking, so all the power will go to the lights.

Thanks for the thoughts so far.

Ken

[ljarrald 0]

Wow, that's a bummer. I supose 24 from 9 is a lot more than I am talking about, but it's a good warning. I am thinking about putting a 12v or so zener diode at the camera with a resistor in series across the line. During the day, the diode will leak enough current to drop the line voltage to 13v or so, which should be safe for the camera. at night, the volatage will drop from the Ir's down to 11v or so, and the zener will stop leaking, so all the power will go to the lights.

Thanks for the thoughts so far.

Ken

 

another option is to get a 24V psu and then at the camera end have something like this (link below) 3AMPS is probably too much so you would need a fuse or a converter that outputs less.

 

http://www.ebay.co.uk/itm/DC-DC-HRD-Converter-DC-24v-36v-48v-step-down-12v-3A-/170689225141?pt=LH_DefaultDomain_0&hash=item27bddee1b5#ht_5283wt_1041

[Soundy 1]

The 3A rating on that is irrelevant; it's only a rating of the maximum it can provide. The load (camera, in this case) will simply draw however much current it needs.

 

A fuse isn't intended to limit the current output; it's intended to melt down if the circuit draws too much current (usually due to a short or component failure), thus protecting the rest of the circuit.

[ljarrald 0]

The 3A rating on that is irrelevant; it's only a rating of the maximum it can provide. The load (camera, in this case) will simply draw however much current it needs.

 

A fuse isn't intended to limit the current output; it's intended to melt down if the circuit draws too much current (usually due to a short or component failure), thus protecting the rest of the circuit.

 

so if i give one of my 12vdc cameras 12v at 300 amps its gonna survive?

[Soundy 1]

You can't FORCE current into a load. Ohm's Law: I=V/R, or current = voltage divided by resistance. The camera presents a fixed load (well, two - one with and one without IR). At a given supply voltage, it will only draw whatever current the resistance allows. If the camera presents a 40-ohm load, then at 12V, it will draw 300mA, PERIOD.

 

Current rating on a power supply only specifies the maximum the supply is capable of providing, PERIOD. If the camera draws 300mA, it will only draw 300mA regardless of whether the supply is rated 300mA, 3A, or 300A.

 

This is BASIC electronic theory. I would suggest brushing up: http://www.the12volt.com/ohm/ohmslaw.asp

[lupy 0]

The dc-dc converter is an option, and for the price, I might give it a try, upping the voltage would give a little better efficiency, though at 80% conversion efficiency, I would be burning about a watt at full load.

 

Since this is a switching converter, I suspect it will add noise to the system. I realize that switching power converters are often used in cameras and transmitters, but they have been designed for a specific purpose, and proper filters have been added. I once tried powering my cameras with a 12v switching power supply that looked like a lap top charger. The results were very noisy, even with added caps and ferrite rings. The older heavy transformer wall warts provide much cleaner power, but unless regulated, the voltage floats around with load. Most have an open circuit voltage around 15v, and settle down to 12-14 with load. That's why nearly all security cameras have some sort of voltage regulation built in.

[Soundy 1]

I wouldn't worry about noise - the vast majority of the 12VDC power supplies we use now, whether multi-channel cans or basic wall warts, are switching types. There may be MEASURABLE noise, but I've never seen it have a VISUAL effect. Almost all DVRs' power supplies, whether PC or standalone, are switching types as well.

[survtech 0]

Typical camera voltage ratings are +/-10%. For a 12V camera, that means 10.8V to 13.2V.

 

Your issue is the change in current draw when the IR-LEDs turn on. The problem is due to the voltage drop across the CAT5. There isn't a heck of a lot you can do without either:

1. Running heavier gauge power cable.

- or -

2. Running higher voltage and regulating it at the camera end.

 

The easiest option is probably #1.

[lupy 0]

Well, given that it's a 500ft run, through thick brambles and woods, I went with #2. I did calculate the wire resistance at ~23 ohm, so it's a pretty big factor. I ended up putting a 12v 10w zener and a big 10ohm resistor across the camera end of things. This gives ~13.2V at the camera during the day, well within what most wall warts supply, with a total draw at the wall of 250ma. At night, with the IR's, the camera voltage sags to 10.5V and about 400ma draw, so the Zener won't flow at night. This reduced voltage still gives enough brightness to see with. Actually, this brightness level is better than at full voltage, which tends to light up any mist in the air, making everything look foggy. (It's Seattle The wall transformer, (goodwill find) seems to work fine for the night, and at 400ma draw, it's well within it's 900ma at 16v rating.

 

As far as switching power supplies, I tried a couple for powering the cameras and they all put noise into the picture, even with filtering. I know that the DVR uses a switcher, and that works fine. I am running video baluns (sp?) with long runs of cat5, so that might make them more sensitive to higher frequency noise from switchers.

 

Anyway, it all seems to be working, and I tried all the failure modes I can think of without generating excessive heat, I am putting a small fuse on the camera power, just to be safe, and I mounted a small heat sink to the Zener.

 

BTW, Like your avatar..

"I am not a number, I am a free man !"

[hardwired 0]

Instead of dissipating all that heat in a zener, and loading down the power supply, why not use a LM7812 regulator at the camera end, like this.

[ak357 0]

Instead of dissipating all that heat in a zener, and loading down the power supply, why not use a LM7812 regulator at the camera end, like this.

 

And 7812 without heatsink will also act as heater

[survtech 0]

Instead of dissipating all that heat in a zener, and loading down the power supply, why not use a LM7812 regulator at the camera end, like this.

 

And 7812 without heatsink will also act as heater

Even with a heat sink. Without one, it's likely to fry. With 24V input and the LEDs operating, the LM7812 would be dissipating 12V @ approximately 1/2A, which is about 6 watts. That's a lot of heat!

 

That's the problem with passive voltage regulation. An LM7812 is basically a passive device, consisting of a zener diode (reference voltage), op amp (error amplifier) and a transistor (series pass element). The transistor has to dissipate the current as heat.

 

[ak357 0]

Even with a heat sink. Without one, it's likely to fry. With 24V input and the LEDs operating, the LM7812 would be dissipating 12V @ approximately 1/2A, which is about 6 watts. That's a lot of heat!

 

That's the problem with passive voltage regulation. An LM7812 is basically a passive device, consisting of a zener diode (reference voltage), op amp (error amplifier) and a transistor (series pass element). The transistor has to dissipate the current as heat.

 

 

Yep, agree I just did not feel like it to go in details with my post ( changed enough of them in good old days)

and I am sure Hardwire knows this too

If I remember correct no more then 2 volts difference between input voltage and output

[rory 0]

thats why one should run the correct wire to begin with.

Problem is you probably listened to some clown talking bout use cat5 for power but the fact is most of them dont even use IR or know much about it.

 

[Soundy 1]

thats why one should run the correct wire to begin with.

Problem is you probably listened to some clown talking bout use cat5 for power but the fact is most of them dont even use IR or know much about it.

That's because most of those "clowns" use decent cameras with good low-light performance in the first place, rather than cheap crap that compensates for poor performance with a bunch of two-cent IR LEDs.

[rory 0]

That's because most of those "clowns" use decent cameras with good low-light performance in the first place, rather than cheap crap that compensates for poor performance with a bunch of two-cent IR LEDs.

You must be talking about that cheap CNB crap.

Anyone with sense would know better than to use that rubbish in a low light app.

[shockwave199 0]

cheap crap that compensates for poor performance with a bunch of two-cent IR LEDs

 

Cheap camera compensating for poor low light performance with a bunch of IR LEDs

 

I don't think it always means suck. Sometimes, but not always.

[hardwired 0]

Even with a heat sink. Without one, it's likely to fry. With 24V input and the LEDs operating, the LM7812 would be dissipating 12V @ approximately 1/2A, which is about 6 watts. That's a lot of heat!

 

That's the problem with passive voltage regulation. An LM7812 is basically a passive device, consisting of a zener diode (reference voltage), op amp (error amplifier) and a transistor (series pass element). The transistor has to dissipate the current as heat.

 

 

Yep, agree I just did not feel like it to go in details with my post ( changed enough of them in good old days)

and I am sure Hardwire knows this too

If I remember correct no more then 2 volts difference between input voltage and output

OK, that's what I get for oversimplifying, too!

 

On to the details!

 

I grabbed a sample image for the diagram, not my own drawing. (and yes, I use heatsinks). I do happen to believe in switchmode regulators, but the OP doesn't seem to want that, plus building your own switchmode regulator is quite a bit more difficult.

 

However, even if the OP's application started with 24VDC at the input, the resistive losses on the cable means he will only have about 16 volts at the regulator/camera end with the LED's on, so that would mean the regulator is dissipating about 2 watts (4V x .5A) or so at full load, and getting about 22 volts at .1A load with the LED's off, so about 1 Watt (10V x .1A) dissipation in the regulator during that time.

 

With proper heatsinking, the 7812 is rated for up to 15 watts of dissipation. (AK357, BTW, they need a minimum 2 Volt input voltage differential, not a maximum)- the 7812 datasheet here http://www.fairchildsemi.com/ds/LM/LM7812.pdf lists a 14.5-27V input.

[Numb-nuts 1]

This is BASIC electronic theory. I would suggest brushing up: http://www.the12volt.com/ohm/ohmslaw.asp

 

I'm not too proud to brush up my electronic theory, it can only help. Thanks, very useful site.

[Soundy 1]

BTW, there are some good ready-made regulator boards out there... we use these two regularly (sorry for the sales link, this is the only listing I could find for them): http://www.electronicproductonline.com/catalog/default.php?manufacturers_id=85

 

Supports up to 32V AC or DC input, has jumpers for fixed outputs at 6, 12 and 24VDC, as well as an adjustable output of 2 to 24VDC. This is the 1A version:

 

 

And the 3A model: