Can anyone help pls? 12v motor psu / speed control problem

Discussion in 'General Electronics Chat' started by dave87, Jan 15, 2017.

  1. dave87

    Thread Starter New Member

    Jan 15, 2017
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    I have got a car radiator fan 12v (cant find the specs for it) and a Dell 7000814 psu.
    I have taken my 12v supply off of the rails in the psu 12v at 57.3A max the issue is that it is switching itself into safety mode unless i get the motor up to speed off of a battery before switching it on, i am looking at the following pwm: http://www.ebay.co.uk/itm/162179562778 as im looking to control the speed of the motor but was wondering if this will also reduce the start ampage so i can start off of the psu or if i need some sort of capacitor or resistor to reduce startup ampage on the motor? thanks in advance :)
     
  2. Bernard

    Expert

    Aug 7, 2008
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    No start at 57 A ? , maybe try a different motor or look at Post by Hamlet, PWM pump driver... under Chat. Cap. might be large, somewhere around 20,000 uF, & a really beefy FET.
     
  3. dave87

    Thread Starter New Member

    Jan 15, 2017
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    It moves for a split second and then the psu cuts out ive done some research and it appears it can draw much higher amps to get started once running its only drawing 16Amp so i need away of cutting the startup current so the psu dosent trip :(
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    This may be of interest.
     
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  5. Bernard

    Expert

    Aug 7, 2008
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    You do not need all of the circuitry of the solar motor control. As a trial try adding capacitors to the psu output.
    Turn on psu first then after a few sec. turn on motor. A condition could possibly be reached if added capacitors
    would force a shutdown of psu due to excessive charging current.
     
  6. MrSoftware

    Senior Member

    Oct 29, 2013
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    If that's a computer PSU, it's not unusual for them to NOT be able to deliver max current through a single output. Sometimes the manufacturers will list the maximum power or maximum current as the sum of all the outputs, not the max that you can get from a single output. Double check that the single output that you're using can deliver enough current to start the fan.

    Also if you can get your hands on an ammeter with enough capacity, see if you can figure out the startup current for that fan when starting it from a battery. Maybe it's drawing more than you expect.
     
    Last edited: Jan 17, 2017
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  7. dave87

    Thread Starter New Member

    Jan 15, 2017
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    Thanks for all your suggestions, i am drawing power directly off the 12v rail inside the psu before its split into separate channels with heavy gauge cable so should be getting close to the 57 amps the psu can output (i have tried starting the fan off of a 6v motorcycle battery it startups up more slowly but gets up to speed after 3 seconds so what i would like to know is weather a pwm curcuit would reduce the current demand on the psu and allow the fan to startup more slowly or weather i need capacitors to hold the current required to get the fan started? ty
     
  8. Bernard

    Expert

    Aug 7, 2008
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    I believe PWM should work from past experience with a 20 V, 12.5 A motor using PWM. If I advanced the duty cycle slowly all was well, but when I advanced to fast, 3 paralleled, 30 A FETs bit the dust.
     
  9. dave87

    Thread Starter New Member

    Jan 15, 2017
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    Ok thanks bernard will give the pwm a try i have got some large thin heatsinks which i should be able to fit to the fets with a bit of machining and i will put the board in a fan cooled enclosure, i only needs the fan running at around 30% speed so hopefully will be ok :)
     
  10. rthomas12

    Member

    Dec 6, 2016
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    I'm working on something very similar and I was hoping to use a psu as well. I needed 24 volts and could not use it due to the low amps on the -12. I did buy a cheap power supply and a rfp30n06let mosfet. Pwm is working great with Arduino or a pot. It is a 24vdc 10.8 amp right angle gear motor. The only load so far has been my hand with a glove on.
     
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