running a camera off DCC track power

[Tylerf]

Hey guys,
Ive got a rather large question, I just bought a pair of wireless security cameras that i am hoping to place on a modified freight car to have a drivers perspective on my layout. Anyways the cameras send the video signal wirelessly but require power from a wall socket. The cameras run at 7.5VDC and 200mA, so im wondering if my DCC rail power can be used to power these cameras making them fully wireless. First I would need a converter(forget what their called) to change the AC track power to DC then, since DCC track power drops with more loads on it, I would need a way to regualte the voltage and power at exactly 7.5VDC and 200mA, that goes to the camera. Now i have no idea what to use for any of these needs, so im hoping some of you electronics experts can help me out with this one. Oh and one more thing that may be important is that the track power never drops below the 7.5v mark.
Tyler

[rich1998]

first of all, you will be robbing power from your dcc controller. at least 200ma. with a system that is 1.5 amp, subtract at least .2 amp.
I would use a full wave bridge rectifier, a filter capacitor and a lm317 voltage regulator. below is a link to lighting circuits which will be usable if you are comfortable working at a component level.
http://www.awrr.com/lighting.html
as an example, circuit #3, adjust the resistor between the lm317 adj terminal and common for the voltage you want at the out terminal and common. i do this with a variable resistor , then solder in a fixed resistor near the same value. a couple tneths of a volt either way will not be an issue.  i am able to work at the component level.
just ignore the components i did not mention with that circuit.
you need the bridge, .1 ufd cap, lm317, 270 resistor and suitable resistor to set the voltage.

you will need clean track,clean wheels  and good wheel pickups.
good luck
lex

[Jim Banner]

Tylerf,
What you want is pretty simple.  A bridge rectifier will convert your DCC track power to about 12 volts d.c.  Then you need an electrolytic capacitor of about 1000 microfarads rated at 25 volts to take care of any losses of connection between your pickup wheels and the rails.  The + of the capacitor must be connected to the + output of the bridge and the - of the capacitor to the - side of the bridge.  A 1000 microfarad capacitor will keep the camera power at full output for a loss of contact with the rails up to .01 second long, so you might want to use multi-wheel pickup on each rail.  With DCC, the voltage on the rails is constant, usually about 14 to 15 volts but the trick is to keep it constant even when pickup is temporarily lost.

A 7808 voltage regulator connected across the capacitor will give you a constant 8 volts output.  To reduce that to 7.4 volts, use a 1N4001 diode in series with the output.

What you really need is even simpler.  I suspect a single 9 volt rectangular battery will do the job.  For that current, an Alkaline type is recommended.  I am assuming here that the specifications for the camera say something like 7.5 volts minimum.  If they say 7.5 volts, no more, no less, then use a battery pack of 5 AAA cells in series.  Using batteries is not to save track power.  When running with the video camera, I am pretty sure you will be running only the one train.  Using .2 amps for the camera will leave plenty of power for the locomotive, or even two of them.  The reasons I suggest battery power is simplicity and reduced noise in the picture.

Using battery power helps keep track noise from interfering with the transmission.  Track noise will be present from the camera car wheels and the locomotive wheels breaking and making contact with the rails as they roll along.  Some receivers are more sensitive to this than others.  The other problem you may have is image flutter with the picture going black and back to normal very quickly.  This happens when the receiver is in the near field of the camera transmitter and is subject to standing waves (at least I think that is what causes the problem.)  Moving the receiver farther away helps.

I had a lot of fun playing with this in large scale a few years back.  I mounted a camera in a caboose, looking out an end door.  Then I pushed the caboose around our group's large scale portable layout with a locomotive.  The first thing I noticed was that I had to run the train slower, a lot slower.  Running at what we would normally consider a "normal" speed was absolutely frightening as we rock and rolled down the line.  Secondly, in large scale it is possible to see which way the switches are aligned as you approach them.  No more excuses for running a switch, derailling, and shorting out the whole layout.  Thirdly, I noticed that as the train went into a curve, it would be nice if the camera turned to look in the direction of the curve.  I have also noticed the same thing when pushing a flat car with a movie camera on it.  And fourthly, I noticed that after a while, I was no longer noticing the flutter in the picture.  I was so busy having fun that I would have sworn the fluttering had stopped, until someone asked me what was causing it.

If I may ask, what brand and model number is your camera?  Maybe I can find a bit more information about it.

Bottom line - Enjoy Those Cameras!!

Jim   

[Tylerf]

Wow that was fast, I thank you both for your help. Anyways, just for the sake of expiriment I think i'll try both methods of powering the cameras.
Jim, I get what your saying about the noise issue and the fact that no, power pickup wont always be perfect which in the cameras case will end up in allot of fuzzy screens cutting in constantly. The cameras says 7.5v max, also ive done a few tests already at 6v's and got nothing. I think ill go with the 5 AA's method as i would much prefer to be able to recharge them easily without the insane expense of new batteries constantly. The cameras, i got from the source for $129.99, they are Home Guardian #4919542. The cameras can be easily unscrewed from their tripods and become perfect for riding on trains. They also have night vision and microphones, plus the picture quality is great.
You also talked about the cameras direction around curves, im planning on somewhat scratch building a car that will disquise the camera somewhat, plus, mount the camera on the king pin of the trucks so that the camera will turn with the direction of the trucks, hence eliviating that camera straight forward problem were all so familiar with.

[Jim Banner]

If you plan to use rechargeables, either Nickel Cadmiums or Nickel Metal Hydride, you will probably want to use 6 of the.  Alkalines are 1.5 volts each while the Nicad and NiMnH are only 1.2 volts each.

Jim

[rich1998]

make sure you get the 7808 with the to220 case. the 7808 with to3 case is quite larger.
in the lighting circuit link i gave you, there is a large value capacitor used on the output of the regulator. i do not remeber what the voltage rating of the cap is but it is used to minimize light flicker. i use a 0.47 farad, yes farad, cap in a lighting circuit to minimze flicker. look at the lighting circuit again. that is a lot of ufd's.
lex

[Jim Banner]

lexon,
Do you have any trouble with your DCC system stating up with such a larger capacitor?  Or does the regulator limit the current enough?

Jim

[rich1998]

the regulator takes care of the surge. i bought the power kit from a guy on the soundtraxx forum. here is the circuit he uses. jim betz is his name.
http://members.optusnet.com.au/nswmn/flicker_free_JB.htm
i modified mine a little as i like to experiment. the max voltage for the cap is 5.5 volts. sometimes called super cap or memory backup cap. i think there are some caps that are 8 volts max. you would have to look around.
the people on the links usually respond to email if anymore questions.

some people use electrolytic smt caps since they are smaller in size than tubular electrolytics if they do not want to use a super cap.
lex

[Stephen D. Richards]

lexon,  I've used the 9 volt battery for some time and is considerably easier to deal with.  It will run several hours without any video breakdown.  i.e. loss of signal etc.  Stephen

[rich1998]

ok, I will store that information. i would assume there is enough room for camera and battery. i do not plan to ever use a camera though. the battery with regulator could be useful for led lighted passenger cars and caboose lights and not worry about the track pickups. he does have a lot of possibilities.
lex

[tac]

For a number of years now, Aristocraft have been making a miniature colour+sound video camera about an inch cube in size that runs off a single 9V battery and transmits to your TV screen.

Why make things difficult, or try to re-invent the wheel?

tac
www.ovgrs.org