Help with power supply

Discussion in 'The Projects Forum' started by Toby Craig, Nov 24, 2007.

  1. Toby Craig

    Thread Starter New Member

    Nov 24, 2007
    2
    0
    Hi,

    I am -very- new to electronics, and I have what I think would be a fairly simple question about powering some kits I intend to build.

    Each kit requires 7-12V DC @ 250mA and there are 3 that need powering. I want to connect them all to one power supply so I don't have to have 3 separate wall warts all plugged in taking up space etc...

    Am I correct in thinking that I can use a power supply that puts out no less than 7-12V DC @ 750 mA ?? Ie adding the mA's up ? Does the voltage need to be increased also ? How to I calculate what sized power supply I will need? Should I use a switched mode p/s ??

    Also, I'll need the kits to be 5 meters away from the power supply. Will I loose power by using a cable thats 5 meters long ? If so, how can I fix this problem?

    Thanks in advance for your help and I'm sorry if this seems like a dumb question. :D

    Cheers!

    Toby
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Give yourself some overhead by finding a regulated wall wart rated at 9 -10 volts and one amp. Are you prepared to get the two extra power supply connectors and slpice them into the output line? You shouldn't have to worry about IR drops with only 250 ma.
     
  3. eeboy

    Active Member

    Sep 27, 2007
    90
    1
    Toby,

    You are correct. You need to find a supply which can deliver the required current for all 3 kits (750 mA). As beenthere mentions, there will be very little voltage drop across the 5 meters of conductor (assuming it's a reasonably sized conductor). There's no reason to purchase a switchmode power supply for this. A cheap wall wart will do just fine. I would find a common wallwart capable of delivering >750mA at 9VDC or 12VDC (probably the most common output voltages). These could probably be salvaged from old equipment you have laying around.

    I don't know anything about your kit, but given the input voltage range it sounds as if there is some on-board voltage regulation. So, your device probably isn't too sensitive about the input voltage provided it meets the minimum.

    Good luck!
     
  4. Toby Craig

    Thread Starter New Member

    Nov 24, 2007
    2
    0
    Hi guys,

    Thanks so much for your quick replies and the great info! I'll grab a cheap wall wart :)

    As for splicing the power connectors together... I assume its just a case of joining them with solder and sealing the cable back up with insulation tape or heat shrinks ?

    Cheers!
    Toby
     
  5. eeboy

    Active Member

    Sep 27, 2007
    90
    1
    You got it... Sounds like you'll need to solder 3 conductors on to both the positive and negative.
     
Loading...