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12Volt-batterie convert to 9volts for the Propeller-Chips — Parallax Forums

12Volt-batterie convert to 9volts for the Propeller-Chips

nomadnomad Posts: 276
edited 2007-06-25 08:02 in Propeller 1
Ref: 12Volt-batterie convert to 9volts for the Propeller-Chips
hi
i build a 4 Leg-Bot with 12 servos.
with a 12volt 3.7AH-Batterie
the servos takes 6volt
i convert the 12 volts down to
- 6 volt with a L7806 for the servos
- 5 volt with a L7805 for digital devices
- 9 volt with a L7809 for 3 propeller-chips (PropStickUSB)

now the question:
is this possible for the propeller-chips without dammage???
i ask you before i testing the stuff
thanks for your answers
regards
nomad

Comments

  • cocokiwicocokiwi Posts: 75
    edited 2007-06-24 08:07
    ·just put a 1k resistor in the data line to or from a higher device than the 3.3 volts,that will protect the prop lines from the higher voltages,shocked.gif go look at:



    attachment.php?attachmentid=73927

    ·

    ·in the stickies at the begining of the forum...burger.gif

    ·cheers Dennis


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  • deSilvadeSilva Posts: 2,967
    edited 2007-06-24 10:37
    The PropStick uses an LM2937 to derive 3,3 V; it is specified upto 26 V (and 60 V input transient protection - which you probably might need with the motors smile.gif )
    cf www.national.com/pf/LM/LM2937.html e.g.

    The regulator will become warm of course when directly connected to the 12 V batteries..
    I myself would connect the PropSticks to your stablilzed 5V system

    Post Edited (deSilva) : 6/24/2007 10:48:00 AM GMT
  • nomadnomad Posts: 276
    edited 2007-06-24 12:47
    hi deSilva & cocokiwi,
    thanks for your answers.

    is this correct:
    1) i can connect my 12volt, 3.7AH Batterie directly with the PowerSupply of the
    propeller-chip without the L7809 IC

    or

    2) connect my 12 volt batterie with the L7809 IC,

    the attachment shows the 2 stuffs (powerSupply.JPG)

    excuse my bad english
    many thanks for your answers
    regards
    nomad
    powerSupply.JPG
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  • Mike GreenMike Green Posts: 23,101
    edited 2007-06-24 13:53
    nomad,
    You can attach the PropStick directly to the 12V battery, but it's not good design. You are wasting a lot of power by using linear regulators which convert the excess voltage into heat. I would strongly suggest you use a switching regulator to reduce the battery voltage (which can go as high as 13-14V with a fresh charge). The best setup would use two switching regulators, one to supply 6V directly to the servos and the other to supply 5V directly to the logic and the PropSticks. Several manufacturers (including Texas Instruments) make small hybrid switching regulators designed to directly replace linear regulators.

    I'd be careful about the servo supply. Most servos can draw over 1A under load and most of the linear regulators won't supply over 1A.
  • JoannaKJoannaK Posts: 44
    edited 2007-06-24 15:03
    Mike is right. Considering the fact that Linear Regulator has to spend all excess wattage in heat ... (A quick calculation)

    12V battery regulated to 6V 1A servo .. Say it has 14volts (as they do while full)

    14 - 6 V leads to 8V voltage drop at regulator.. With 1A it generates 8Watts Heat (+ some extra on regulator losses). So in the end you'll end up wasting over half of watts your Battery has due inefficient power regulation.
  • deSilvadeSilva Posts: 2,967
    edited 2007-06-24 15:07
    Mike has a good point here! A switching regulator would also reduce spikes from the inductivities of your motors....

    This will also help stabilize your digital 5V system you talked about, and to connect the Propeller to it is "Solution 3" you did not sketch. And don't take "... 6 to 9 V..." too serious; the regulator on the PropStick will well work between 15 and 4,5 V (see datasheet link)
  • deSilvadeSilva Posts: 2,967
    edited 2007-06-24 15:14
    BTW: I was looking for power supply solutions lately and found the Racing Packs (RC) @ 7,2 V (= 6 Sub-C cells @ 1,2 V) extremely attractive. They are not low cost, but have a capacity of 3 to 5 Ah at the moment; weight is around 300 g, size around 3x5x12 cm.

    7,2 V (starting near 8 and staying always above 6 V) is an excellent behaviour for digital logic...
  • nomadnomad Posts: 276
    edited 2007-06-24 17:29
    hi mike and deSilva,
    thank you verry much for your help

    i have a question:
    i am not a electronic geek, and to buy the switching regulators, at my distributor
    can i have a discription of this switching regulators
    you write:
    < (including Texas Instruments) make small hybrid switching regulators designed to directly replace linear regulators.>

    to deSilva, thanks but for the first tests, i make this with externBatteries.

    thank you for your answers
    regards
    nomad
  • Mike GreenMike Green Posts: 23,101
    edited 2007-06-24 18:13
    Look at TI's PTN78000 series regulators.· You can download a datasheet from their website.
  • nomadnomad Posts: 276
    edited 2007-06-25 08:02
    hi mike,
    thanks for your answer,
    today i am looking for this stuff at my distributor.
    regards
    nomad
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