Powering a CCTV Camera

Discussion in 'General Electronics Chat' started by BiloxiSam, Oct 30, 2009.

  1. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    I have a small wireless CCTV camera that I need to power from a rechargeable battery pack. It requires an 8v DC source and draws 120mA maximum current, 80mA minimum. It’s currently powered by an AC-DC wall adapter, but I don’t always have AC power available on the jobsite. The camera is used 3 or 4 times a day for about an hour each time. What is the best solution for this?

    I was thinking of using a simple LM317 circuit to build an 8v voltage regulator and powering it with 10 Sanyo NiMH 2700mAh AA batteries connected in series. But is there a better solution?
     
  2. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    Looking around, it looks like I could use a LM2914CT instead and get away with 8 batteries which should supply around 9.6v at full charge and 9.0v fully discharged to it's input. That's still 1v above my needed 8v and 0.5v above the LM2914's drop out. Is that cutting it a bit close?
     
  3. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    use a 7808 Voltage Regulator to get your 8 volts, you can have a supply up to 35 to 40 volts.......
     
  4. creakndale

    Active Member

    Mar 13, 2009
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    For your power source I would use 8 each AA 2000mAh NiMH Low Discharge cells (Sanyo Eneloop or equivalent). The advantages of the Low Discharge NiMH cells outweigh their slightly less capacity.

    For the regulator, I would use an LDO (Low Drop Out) type but I couldn't find any specs on the LM2914CT. The LM2937ET-8.0 is already trimmed to 8.0V or an LT1086CT for an adjustable output voltage.

    You should be able to run for 4 to 5 days before recharging (at 4 hours of use per day).

    creakndale
     
  5. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    Awesome! Thanks for the info. I wasn't aware of the LM2937ET-8.0. Yeah, the eneloop batteries are great. I have a set of them for a pair of walkie talkies I use. I picked the other ones solely on their slight capacity advantage.

    The LM2941CT is a variant of the LM2941 and is adjustable, which I don't need. It was just what I had found. The specs are at http://www.national.com/ds/LM/LM2941.pdf.
     
  6. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    Looking at the LM2937's datasheet, it looks like I'll need a tantalum capacitor with at least 10uF capacitance and a ESR of less than 5ohm. Looking around at Digikey, about the cheapest one I have found is 478-1875-ND @ $0.88. It's a 16v 22uf tantalum with an ESR of 2.00ohm. Is there any advantage in my application for stepping up to a higher uF capacitor with a lower ESR at a premium price? A 100uF capacitor with 0.800 ESR is $7.00, ouch.

    Also, do I still need a 0.01uF capacitor on the input side? The schematic in the datasheet shows a capacitor there, but doesn't list it's value.
     
    Last edited: Oct 30, 2009
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If the camera is sensitive to power, or the system will be in hot/cold environments, go with the higher grade caps. Otherwise, the standard ones will work OK.

    The input cap for the the Regulator should be 0.1uF to prevent oscillations and smooth out any harmonics that made it that close to the chip. Most any 0.1uF "Decoupling Capacitor" for IC's would work.
     
  8. creakndale

    Active Member

    Mar 13, 2009
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    Be sure to put a 250mA to 500mA fuse right after the battery pack positive lead. You wouldn't want to vent the batteries, melt wiring or destroy the regulator if anything downstream of the batteries creates a short.

    creakndale
     
  9. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    Good suggestion, indeed. Another question, kinda off topic but in the same project. I've looked everywhere I know to look and can not find an enclosure with an 8 AA battery compartment. I've looked at Digikey, Mouser, and a few others. I found several 4 cell ones, that I suppose I could bolt together back to back, but that ends up costing $25 or so to house $5 worth of electronics.:) What I'm considering doing is picking up an 8 cell holder and one of the Radio Shack project boxes instead. It will just be a pain to swap out the batteries. Anyone have any other suggestions or a possible source for an enclosure?
     
  10. creakndale

    Active Member

    Mar 13, 2009
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    My suggestions:

    Use one of those 8 cell Radio Shack AA battery holders as you mentioned and wire the leads to a switched Panel Mount DC Power Jack. Put the battery pack and small circuit board (with your LDO regulator design) in the enclosure. Radio Shack has nice ABS enclosures and multipurpose PC boards.

    It's too much of a pain to be removing batteries from the holder every time they need charging. Instead,
    purchase a battery charger similar to this type:
    http://www.all-battery.com/smartuniversalchargerfornimhnicdbatterypack7-2v-12v-01020.aspx

    Put a DC Power Plug on the end of the charger. Then you plug the charger into the enclosure to charge the batteries.

    Put a jack on the enclosure that mates to your camera's power connector. Make sure that the jack for charging batteries and the jack for the camera's power are different sizes so there's no way to accidentally mix up the connections.

    creakndale
     
  11. BiloxiSam

    Thread Starter New Member

    Oct 30, 2009
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    Another great suggestion! I wasn't aware chargers like the one you linked were available and really never even looked at it from that angle. That's a nifty looking charger and should work great.

    The camera is already hard wired with a cable and a female 2.1mm barrel connector on it, so I was going to get a cable with a 2.1mm male connector and put it through the enlosure to the PCB, using a cable grip to secure it. I figure that will be easier than trying to mount a connector on the PCB and have it line up with a hole in the enclosure.

    I can pick up a cable with a 2.5mm male barrel connector on one end and a female on the other, cut it in half, connect the female end to the enclosure the same way as above and the male end to the charger. That way there is no way to confuse them, opposites and different sizes.

    Thanks for all the suggestions, creakndale. You have been very helpful.
     
  12. creakndale

    Active Member

    Mar 13, 2009
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