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Powering everything with one battery? — Parallax Forums

Powering everything with one battery?

skatjskatj Posts: 88
edited 2008-02-24 22:28 in BASIC Stamp
If I had a 1,500 mAH 7.2 volt nimh battery plugged into the Board of Education, could I save weight by powering everything from a single power source?

I have a servo controller running two servos, an HB-25 running two 6V motors, and a Parallax GPS receiver. For the PSC and HB-25, I could just wire the power and ground terminals to the power/ground sockets of the BOE's breadboard, right?

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2008-02-18 17:58
    1. Yes, you could run everything from one battery.

    2. You should probably run a separate 22 guage (zip cord) power and ground wire for the HB-25 directly to the battery pack.

    3. You'll probably have to add a few capacitors -- one across each 6 volt motor + and - leads, one at the HB-25 power input, and probably one at the BOE. The 6-volt motor ones should be non-polarized, probably about 100 uF.

    I wouldn't run the HB-25 power and ground wires off the BOE -- the HB-25 can pull some hefty currents, which would damage the BOE board.
  • skatjskatj Posts: 88
    edited 2008-02-18 18:27
    The PSC should be fine though, right?
  • allanlane5allanlane5 Posts: 3,815
    edited 2008-02-18 18:32
    Probably, but if you really want to be sure, running separate +V and GND wires to the battery couldn't hurt.
  • skatjskatj Posts: 88
    edited 2008-02-20 06:00
    Allan, would that answer change if I was also running two continuous rotation servos in addition to the two regular ones?

    [noparse][[/noparse]quote]The PSC should be fine though, right?
  • Mike GreenMike Green Posts: 23,101
    edited 2008-02-20 06:28
    Just keep in mind that servo motors can draw over 1A peak although the average current is more like 1/4A when they're running lightly loaded (and less when they're not receiving pulses). The PSC is made to handle 16 servos, though not all heavily loaded at the same time.

    Be sure to run heavy enough wires from the PSC to the battery pack and it wouldn't hurt to add extra filter capacitors close to the PSC just like for the HB-25.
  • allanlane5allanlane5 Posts: 3,815
    edited 2008-02-20 18:43
    +1 Mike -- both for the wires and the capacitors.
  • skatjskatj Posts: 88
    edited 2008-02-24 02:09
    Mike, when you say to add capacitors, do you mean when I power the PSC directly from the battery pack, or the Board of Education sockets?

    Would it be ok to run it from the BOE breadboard sockets if I add capacitors, and how large should the capacitors be?
  • Mike GreenMike Green Posts: 23,101
    edited 2008-02-24 03:01
    Because of the potential current drain, you really want to power the PSC directly from the battery pack.

    Breadboard sockets are not high current connections.
  • skatjskatj Posts: 88
    edited 2008-02-24 21:48
    Mike, I apologize for my persistence, but I really have no room to add an extra battery pack and running extra wires down to the battery pack will mean logistical complications in charging the battery (not to mention I've already spliced up it's wires significantly).

    What risk do I run if I power them from the breadboard (i.e., will it just not work until the current goes down, or will components be permanently damaged)? How can I minimize this risk (with capacitors, etc)?
  • allanlane5allanlane5 Posts: 3,815
    edited 2008-02-24 22:15
    It's quite simple, really. If you pull too much current (3 amps or more) through the servo's (which is unlikely) the worst thing that could happen is you'll melt some of the traces on the breadboard. If you're good with a soldering iron, you can repair them.

    Most servo's max out at about 1 amp, when 'stalled', so this shouldn't be an issue. And 1 amp shouldn't melt any traces.
  • skatjskatj Posts: 88
    edited 2008-02-24 22:28
    Thanks allan,

    Do you suggest I add capacitors or resistors of any kind to further minimize the risk?
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