PSU for DC motor

Discussion in 'General Electronics Chat' started by scorca, May 12, 2009.

  1. scorca

    Thread Starter Active Member

    Oct 31, 2008
    36
    0
    Hi all,

    I have a 24 V 20 W dc motor which takes 11 A starting current and has max. continuous current of 1.2 A.

    How should I choose my psu for the motor? Should I take 24V, 11A psu or 24V, 5A psu is more than enough?

    Thanks all.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    What is the surge rating for the 5A PSU? Is it 11A or more? If not, it will likely trip a breaker when one tries to start the motor.
     
  3. scorca

    Thread Starter Active Member

    Oct 31, 2008
    36
    0
    so you mean I should take the 24V, 11A? Those values are the max values.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    Must the motor run at once?
    Of not you could try to make a softstart using a PWM sequence that goes up until 100 %.

    Greetings,
    Bertus
     
  5. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    In general power supply can provides over current for certain a transient.

    By the way for short time most of the current will come from the output capacitor which is the one that need to withstand high current. Power supply topologies can also make the difference.

    24V 11A power supply is definitely too much.

    Probably a 3A power supply with the right capacitor will make the job.

    The right capacitor depends also from the current transient.
    The problem is that you should know how long the transient last and the output capacitor that is used within the power supply...
    Which normally you don't know.

    A soft start will solve definitely your problem.

    Ciao,

    Mauro
     
  6. scorca

    Thread Starter Active Member

    Oct 31, 2008
    36
    0
    I definitely don't know about either the topology or the capacitor of the psu. The psu is a ready to use product.

    A soft start will not match my application.

    Also when I see the datasheet of the psu, it says the output current is 10.42 A for psu with fan and 5.63 A for convection-cooled psu. Do they have different topology?

    And the transient time is 500 us and it can reach 25 A
     
  7. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    Hello

    If the psu can withstand

    500 us and it can reach 25 A

    and your transient is shorter...you are fine...
    ...or if it's longer it requires less current...

    if you add a fan you can keep the same circuit, just copy and paste and increase the current (assuming that the devices can withstand the current), the reason is that with the fan you can keep the junction temperature lower.

    ...if you don't have the schematic from the power supply, you could do the following test (I did this in the past for a similar problem)

    You create periodic transients using an active load and you check the power supply output with an oscilloscope.

    ...without any test you can not guarranty that the power supply will last for long time.

    Ciao,

    Mauro
     
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