Shop OBEX P1 Docs P2 Docs Learn Events
Powering the parallax servo control (PSC) — Parallax Forums

Powering the parallax servo control (PSC)

addaadda Posts: 13
edited 2007-03-18 01:46 in BASIC Stamp
I'm running a BOE on a 9V/300ma and have a PSC connected.· I noticed in the instructions for the PSC that a separate power source is required for the servos running on the PSC.· Can I·share power from·the 9V at the source and run power to the BOE and PSC servos?·(I.e., I would like to·have one power supply and run separate lines from the single power source to the BOE and PSC servos).· ·I'm running 8 standard servo (Futaba) - is the 9V too much?

Thanks.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-02-28 17:27
    Hello,

    Not only is 9V typically too high for servos, but adapter is most likely unregulated, which means the voltage will likely be much higher. Besides that sudden current draw from the servos may cause dips or other problems in the supply. Take care.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
  • dandreaedandreae Posts: 1,375
    edited 2007-02-28 18:56
    One other point is that the servos draw anywhere from 125mA to over·1 amp depending on the torque that is applied.· We recommend using a RC battery pack 7.2v or a DC power supply of at least 1 amp.


    Dave


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Dave Andreae

    Parallax Tech Support·
  • addaadda Posts: 13
    edited 2007-02-28 19:00
    Thanks for the suggestion.· Other than the battery pack, can you recommend any of the 120V AC power supplies on the parallax site that I could use with the PSC to drive the servos?



    Best regards.
  • addaadda Posts: 13
    edited 2007-02-28 19:02
    A clarification - I would use the 120V power supply that you recommend to only power the servos. I would have a seperate power supply for the BOE.
  • dandreaedandreae Posts: 1,375
    edited 2007-02-28 19:04
    Yes, here is a link to our 7.5 (1 amp supply):·

    http://www.parallax.com/detail.asp?product_id=750-00009

    Dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Dave Andreae

    Parallax Tech Support·
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-02-28 21:22
    Please note that if you connect an unregulated wall adapter you could permanently damage your servos. The capacitors inside the servos are usually rated at around 10V while the output of one of our supplies can be as high as 16V when no load is applied. This is enough to destroy the servo. The battery pack on the other hand is usually no more than 7.5V and can be safely used. Even 7.5V is more than most servos are rated and will reduce the life of the servo somewhat. Take care.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
  • randyazrandyaz Posts: 61
    edited 2007-03-01 03:49
    you could always put a voltage regulator between the PSC and the power supply...



    http://www.mouser.com/search/ProductDetail.aspx?R=L7806CVvirtualkey51120000virtualkey511-L7806CV
  • ZootZoot Posts: 2,227
    edited 2007-03-01 16:51
    Running from a single power source (if that's what you want to do) can be a bit tricky. On one of my projects, I used a big 12v battery as the main supply, then 5v regulators for logic and electronics, and well heat-sunk 6v regulators for the PSC.

    The real trick here is to NOT hook up a ground wire to the 5v/gnd/signal side of the PSC -- only the serial signal line and the +5v supply one side, and the beefy 6v and motor ground on the other (the PSC's -Vin and logic GNDs are connected on the board). Otherwise you get a ground loop. A setup like this would work with an external AC-to-DC supply or a battery, etc., presuming you are not overburdening the regulators.

    Here's the discussion when I worked this out with the help of the forum members: http://forums.parallax.com/showthread.php?p=610598

    I would also add that you can use 5v regulators for the servos as well. Just remember your heat-sinking (and it doesn't hurt to measure total current going into the Vin of the PSC before building your power supply circuit so that you know you won't cause regular shutdowns on your regulator).

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    When the going gets weird, the weird turn pro. -- HST
  • addaadda Posts: 13
    edited 2007-03-18 01:00
    To close the loop on this:

    Chris was correct. I fried 2 servos. (Please don't ask why one servo was not enough). Voltage regulation is needed if using an AC/DC power source.
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2007-03-18 01:46
    adda--

    Would someone please elaborate for adda (and me; I could use more lecture on the subject) concerning tieing the grounds of separate power supplies together?

    adda, I commonly run my Stamp/BOE or Stamp/PDB with the proper wall transformer driving the Stamp/BOE or Stamp/PDB·and my motors or servos driven with a regulated variable DC power supply. I tie the ground of the regulated DC power supply to the ground of the BOE.

    The only thing I have fried in my entire (short) microcontroller career is an LED. It didn't really FRY, it went "pop" (lower case). Actually, it was kind of neat. I might do it again.

    --Bill

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    You are what you write.
Sign In or Register to comment.