Need help to create a 24v 20amp limiter

Discussion in 'The Projects Forum' started by Ronald Lin, Oct 2, 2015.

  1. Ronald Lin

    Thread Starter New Member

    Oct 1, 2015
    Hi Guys,

    Currently I have an input of 24v DC powering an inverter running a 3 phase motor. Recently my fuse of 20 Amp running the inverter keep blowing which is kind of frustrating as accessing the fuse is not easy (kind of a design flaw by certain people) and I'm offsite most of the time.

    Any way I can't manipulate any of the the programming in the inverter itself.

    So I was thinking of using sort of a BJT transistor circuit to sense the current to the inverter and if it exceeds 20A it will divert off the excess Amp while maintaining the 20A to the inverter.

    My knowledge of transistors are not that great so hopefully some
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    How do you propose to "divert off the excess Amp while maintaining 20A to the inverter"?
    If the load on the inverter is causing it to draw more than 20A and the fuse is blowing, you need to reduce the load.
  3. Ronald Lin

    Thread Starter New Member

    Oct 1, 2015
    Well the reason why the load is high is due to that the motor is jammed some times. And why it is jammed is due to some OEM programming issues in some areas which I cannot tinker with. I have feed backed to the software engineers on the matter but their solution is kind of slow or not working.

    So I'm thinking while waiting for a good solution from them, I hope to limit the current drawn until the inverter senses that it is taking too long to turn the motor and goes into "timeout error" mode. Which in this case I can remotely reset the inverter to return to normal.
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    It is not your lack of knowledge about transistors that is the problem. The problem is basic thermodynamics. To reduce current into the inverter, you must reduce the voltage into it. The nature of such inverters that if you reduce voltage going, they compensate by drawing more current from what supplies them...

    The basic problem is that you are overloading the inverter. You need a bigger inverter! Or you need to make the motor do less mechanical work (slow its rpm, put a gear box between it and the final mechanical load, change a sheave on a v-belt, etc).
    blocco a spirale likes this.
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    I see no reason why you shouldn't be able to apply a current-limiter to the output of your 24V supply.
  6. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    Or a fast-acting electronic circuit breaker. I have designed them into several MIL projects, some latching and some auto-resetting. LTC controllers, great parts.

    The following comment is inserted to meet the mandatory Arduino/555 quota:

    And you can connect the fault signal to an Arduino and have it send you an email when it trips. Or connect the fault signal to a long-time-constant 555 to let things cool down a bit before restarting.

    InspectorGadget likes this.
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    And then what? It will still shut down the motor, and the motor will have to be mechanically un-jammed, and then the current limiter will prevent the motor from restarting due the supply now having no ability to supply the motor starting inrush.

    Better just put a reset-able circuit breaker on the supply in-lieu of the fuse...
  8. ScottWang


    Aug 23, 2012
    So you need an automatic in parallel shunt load as big resistor or heater?

    Normally like this situation will shutdown the load or limited the current, not just let the current exceed and try to using shunt load to solve the problem, because the shunt issue is a big issue, how to keep the motor only draw 20A and other false load take others, when over 1A, 2A, 3A, etc..., it may breaking down the ohm's law.