Dc voltage from a 9v battery and 9v from mains.

Discussion in 'General Electronics Chat' started by Bod, Sep 22, 2016.

  1. Bod

    Thread Starter New Member

    Sep 18, 2016
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    So I got this big bulky motor out of a 4x4x4 American RC Monster truck (Runs off about 7.2v DC). I hooked it up to a 9v battery worked fine. So I hooked it up to 9v DC converted from 230/240v AC. And it just turned on then off the on then off repeatedly. Is this something to do with different currents or amps or something like that?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    It sounds like you have something other than 9 VDC from your converter. Can you measure it with a DMM or an oscilloscope?
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Sounds like the current rating of the 9V converter is insufficient.
    Do you have a multimeter to measure the motor current when connected to the battery?
     
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  4. Bod

    Thread Starter New Member

    Sep 18, 2016
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    I measured it and the voltage i got was 9.05 V exactly and the thing is, I don't think there is something different because everything else i used that needed 9V worked fine. Its just the motor that does not. There are some photos of it (sorry one is sideways

    IMG_0041.jpg IMG_0042.jpg IMG_0044.jpg
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Was that measured with the motor connected?
     
  6. Bod

    Thread Starter New Member

    Sep 18, 2016
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    When the motor is hooked up to the battery its current is 2.15 - 2.20. Also I would not say it's insufficient because it's a genuine BT (British Telecom) power adapter and every thing else that needs 9 V runs fine off of it.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Just to be clear, you just said the current was 2.2 amps. Is that what you meant, or is that voltage? Your other post was 9.05V, was this under load or no?

    When you say the motor ran fine off a 9V battery, do you mean one of those little rectangular "transistor" batteries?
     
  8. Bod

    Thread Starter New Member

    Sep 18, 2016
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    I meant 2.2 amps because @crutschow asked me what the current was. Pretty sure it was under load and yes one of those 'little rectangular transistor batteries'.
     
  9. MrSoftware

    Active Member

    Oct 29, 2013
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    Connect your volt meter to the motor while it's connected to the wall adapter. Does the voltage drop significantly when the motor is stopped?

    It's possible the motor is drawing more power than the wall adapter can support, and it's possible the wall adapter has a protection feature that turns it off in this case. Eventually it resets and the motor starts again, and the process repeats.
     
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  10. Bod

    Thread Starter New Member

    Sep 18, 2016
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    I sort of think so. The amps peak at 0.15 when the motor is on. When it turns of it drops to 0.00 amps.

    I could change to to 12 V DC if you think that 9 V DC is not enough. But I won't go much higher as the whole RC Car (and the motors) runs of a 7.2V Li-Po battery.
     
  11. Bod

    Thread Starter New Member

    Sep 18, 2016
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    I think I found the problem, but thanks for all the help anyway! It's that my power supply is 'feeding' the motor 9V DC and 0.65 amps. When you hook the motor to a 9V battery you can see the max amount of amps it draws which is 2.2X (x = a number I don't know). So if you do
    0.65 - 2.2x = fail safe! and the motor resets. :(
     
  12. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Didn't you read post #3? Crutschow (and everyone else that replied) beat you to it.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    Those things still use Ni-Cd cells because Ni-Mh can't handle the current draw - your wall wart probably can't either.
     
  14. Tonyr1084

    Active Member

    Sep 24, 2015
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    I didn't know a 9v transistor battery could deliver 2.2 amps.

    When one assumes the power supply is capable just because of its name - one learns a lesson. Your wall supply isn't capable of delivering that much current.

    And a Li-Po battery is capable of delivering a whole lot more current than a 9V transistor battery. (the rectangular battery with snap buttons on the top).

    The dumbest question is one nobody asked. However, when a question is answered, the second dumbest thing is to not listen to it.
     
  15. wayneh

    Expert

    Sep 9, 2010
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    We may still be missing something in this story, but anyway NiCads can sustain crazy high currents, like 15-50C. Enough to glow red before they destroy themselves.
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    The PP3 isn't the only 9V battery ever made...........................

    2 of these; http://www.ebay.co.uk/bhp/3r12-battery in series was the "9V" battery for one of the Philips EE kits I had as a kids.

    They'd probably spin the motor for a few minutes.
     
  17. Tonyr1084

    Active Member

    Sep 24, 2015
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    I suppose. I once had an 80 volt battery that was slightly longer than a PP3 (whatever PP3 is)(I assume it's a standard 9v transistor battery).
     
  18. ian field

    Distinguished Member

    Oct 27, 2012
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    You must be as lazy as me - I could've Googled what the international type designation is.
     
  19. Mark34

    New Member

    Sep 23, 2016
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    Your 9v DC transformer wire is damaged or connection to the car.
     
  20. bertus

    Administrator

    Apr 5, 2008
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