maximum length of wire?

The fuse limit for typical insulation on 22AWG wires is well over

2 amps, so PROVIDED WITH A SUITABLE FUSE it's safe to connect it to the 12V battery. Your battery does NOT connect directly to this wire, it connects THROUGH A FUSE (1.5A would be a suitable size).

The important part here, is that the fuse prevents the wire from burning up under ANY fault condition, including higher current than your intended device (the video gear) uses.

There is no maximum to remain safe.

To actually _work_, the voltage drop from the battery to the camera has to be fairly low. Make the cable too long for the wire size and your camera won't work (but nothing will burn up). So try it out...

You can get wire as big as you want and connect pigtails to the ends to step the wire size down for your connectors.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

For some back o' the envelope approximations...

We'll assume that your equipment load is about 1 A, as stated. The battery will really be about 13 V when not loaded but we'll swag the equivalent load resistance at 12 ohms.

AWG 22 cable is about 16 ohms per 1000 feet, so using a 100 ft run, you would add 1.6 ohms on "either side" of your existing load. The total load, which is now about 15 ohms, will draw about 0.85 A from a 13 V battery and you'll have a bit more than 10 V to work with at your load. Your equipment may not be happy with that.

If you follow Tim's recommendation and use heavier gauge cable with short transition pieces to the necessary wire size for the connector, things look a bit better.

With regular 14 AWG zip cord, you're now running only about 2.5 ohms per

1000 feet. That 100 foot run now only adds 1/4 ohm to each leg, so your total draw (with that same 13 V battery) is pretty close to 1 A, with only about 0.5 V lost in the cabling. Happy equipment!

As whit3rd mentioned, fuse it. Preferably run from a polarized aux connector to a spare fuse on the vehicle's fuse box, rather than hook directly to the battery. (Nobody would EVER hook black to positive, red to ground, would they?)

If you ever intend to run from an operating vehicle, be aware that the equipment will see some nasty transients. If the stuff is designed to run from a car's electrical system, you're good. Otherwise, be aware that the magic smoke may come out. See the link for a description of some issues

--
Rich Webb     Norfolk, VA

Good thing he's in N. America (Canada) or he wouldn't have an earthly clue what an AWG is. Does Canada use AWG or have they fully metricated now ?

Graham

One may note that the OP mentioned that the "cable i found with 2 conductors, has 2x 22AWG wires" and infer from that statement that he indeed has some clue (earthly or not, to be determined).

--
Rich Webb     Norfolk, VA

--
Don\'t you have access to Google in the UK on Sunday?

From:

http://www.electrical-online.com/cableandwire.htm

"In Canada and the United States there is a standard by which we measure
wire. This standard is the A.W.G. (American Wire Gauge)." 

JF

The OP wrote: "I need a wire ...2x 22AWG wires"

Says it all.

--
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is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Access, and ability to use are two different things.

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--
Keith

just a quick note, is the equipment designed to run directly off a car battery? or are you powering an item that has a 12 volt DC input from a power adaptor (wall wart)

just that video equipment will be pretty sensative to noise and spikes, and you get a lot of them on a car's electrical system, also the voltage at the battery terminals will vary from 11 volts to 14.8 volts, depending on if the engine is running or not.

i've run my hard drive camcorder fixed to my dashboard whilst driving in my motorhome last year, it too wants a 12 volt DC supply at 1 amp max, but no way i'd feed it with the power directly from the battery/alternator.

i was going to get one of the proper 12 volt camera power supplies to run it, but it was easier for me to run an extension cable from the living area of the motorhome to the dash connected to the main inverter, part of that reason was the 12 volt Dc power supply was about 50 quid, the extension cable was 2 quid, and i use the mains adaptor and that has the neccisary filters to take out any noise on the power.

Go to Radio Shack and pick up a 12V lighter adapter.

Good Luck! Rich