Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why doesn't converter operate pump?

  1. Jul 25, 2015 #1
    I connected my 12 volt 3 amp bilge pump to a 36 watt 3 amp 110v ac/12v dc power converter. The impeller blade vibrates but does not spin so it can pump. The pump operates ok when connected to a 12 volt 3 amp/hr battery. What's the problem?
     
  2. jcsd
  3. Jul 25, 2015 #2
    I think the first thing you should do is verify that your DC power supply actually is producing 12v DC.
    You can use a cheap test meter, or just see if it will work for any other motor or device which requires 12v DC.
     
  4. Jul 25, 2015 #3

    rbelli1

    User Avatar
    Gold Member

    The 3Ah specification tells how much energy the battery holds not how much current it can output. You need to make sure the pump is only drawing 3A. Plus there is going to be a huge inrush current when the motor is switched on. Many battery chemistries will do just fine with the inrush currents that are common with motors. What type of battery are you using?

    BoB
     
  5. Jul 25, 2015 #4

    russ_watters

    User Avatar

    Staff: Mentor

    This:
     
  6. Jul 25, 2015 #5

    meBigGuy

    User Avatar
    Gold Member

    Where did batteries come in? where is 3Ah from? The OP didn't mention batteries or Ah

    Setup was
    "I connected my 12 volt 3 amp bilge pump to a 36 watt 3 amp 110v ac/12v dc power converter."

    It should work fine if (as said in previous posts)
    1. The converter is actually outputting 12V DC when 3A is drawn
    2. The pump is only drawing 3A

    An old pump may have bearing issues, causing it to draw more current, for example.

    As also stated previously, it is possible that the pump may draw a lot more when it is first switched on. The current surges, drops the voltage, the motor stalls, continues to draw too much current, and continues to stall.

    But, that is not terribly consistent with the impeller blade vibrating and not moving (could be though).

    If you connect the pump to a 12V battery, does it work? (maybe the pump has an issue, which would be more consistent with it vibrating).

    If you (very carefully) assist the motor, does it get started?
     
  7. Jul 25, 2015 #6

    russ_watters

    User Avatar

    Staff: Mentor

    Two sentences later.
     
  8. Jul 25, 2015 #7

    meBigGuy

    User Avatar
    Gold Member

    I'm still learning to read. Sorry

    It's probably the startup surge.
     
  9. Jul 25, 2015 #8
    The pump is new and so is the converter. I checked the converter output voltage and it is less than 1 volt. The pump works ok when connected to the small 12 volt starter battery. So is the converter defective?
     
  10. Jul 25, 2015 #9

    nsaspook

    User Avatar
    Science Advisor

    I assume it's 1 volt when connected to the pump. Most modern AC-DC converters have over-current protection that drops the output voltage to a low level to protect the circuits inside without just blowing a fuse.
     
  11. Jul 25, 2015 #10

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    maybe, but more likely mis-applied.


    Some "Smart" ones shut down when they sense overload, then try again to see if the overload has gone away, over and over .
    That could explain why your pump flutters. A three amp pump might need a brief burst of ten amps to start and a smart supply will declare that an overload. It'd probably run your pump fine after it got started.

    Have you searched for a datasheet on your supply ? Look for a term like "Foldback".

    A transformer based "dumb" supply would be more tolerant of overload.
     
    Last edited: Jul 27, 2015
  12. Jul 26, 2015 #11
    No
    No, the reading was taken with nothing connected to it.
     
  13. Jul 26, 2015 #12

    NascentOxygen

    User Avatar

    Staff: Mentor

    That doesn't sound promising. Have you a 12v bulb (under 1 amp) or a 10 ohm 10 watt resistor that you could try on the converter, to see whether it needs to output some current before it will work properly?
     
  14. Jul 26, 2015 #13
    Yes, tried a 12 v bulb and it didn't light. I'm returning the converter as defective.
     
  15. Jul 26, 2015 #14

    NascentOxygen

    User Avatar

    Staff: Mentor

    The bulb was rated under 1 amp, was it? If you use a headlight bulb it will try to draw more than 3A and the converter will reduce its output to zero anyway.
     
  16. Jul 26, 2015 #15

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Yes. A cold filament has about 1/10 of the resistance of a hot one. That means a brief period of very high current at switch on. Your converter may specifically and intentionally shut down when this happens (as Jim has said, in another way). Have you (gmagic) any detailed spec for this converter? There may be some 'small print' that would resolve the question.
     
  17. Jul 26, 2015 #16

    russ_watters

    User Avatar

    Staff: Mentor

    It is possible that you destroyed the converter by connecting it to the pump. They may or may not be able to tell when they examine it.
     
  18. Jul 27, 2015 #17

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    That's not the way that things are dealt with, these days, though. :frown: They will probably just give you a replacement and dump your failed on in a bin.
     
  19. Jul 27, 2015 #18

    russ_watters

    User Avatar

    Staff: Mentor

    Awesome...to be connected to the same pump and fail again. I wonder how many they'd replace for free before getting suspicious that faulty application is what is killing them?
     
  20. Jul 27, 2015 #19

    rbelli1

    User Avatar
    Gold Member

    gmagic, Can you share some part numbers or spec sheets of the converter and pump?

    BoB
     
  21. Jul 27, 2015 #20

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I suspect that, after you sent the next one back, they'd offer you your money back and say go away.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why doesn't converter operate pump?
Loading...