Electrics - relays.

Hi all,
We've heard of two relays being used for drive before - one as a 12v starter circuit and the second as the full power 24v circuit.
However, whenever our electrical team has tried this (they're simulating using Crocodile Clip software) they seem to get a short circuit. They believe that a 3-pole relay is the only solution, but getting one rated to a high enough current to stop it melting is... interesting.
Would someone be kind enough to explain their solution to this problem?
Thanks

Comments

  • edited February 10
    Hi Sam,

    It should be possible to switch between 12V and 24V using two SPST relays: you will need a SPDT switch to select which voltage to use, as well as an SPST switch to turn the motor on and off. A circuit is shown below demonstrating this

    image

    You'll need to make sure the SPDT switch you use is a "break-before-make" type changeover switch to prevent both the relays activating at once.

    Perhaps a more robust solution would be to use an SPST relay in conjunction with a SPDT relay such as this one (link) this gives the advantages that there will be no possibility of a short circuit and the changeover could be electronically controlled.

    image

    Using a current sensor like ACS758 (L1 in diagram) a microcontroller could be used to set the point in the accelleration at which the voltage should be increased to remove the dependency on the driver remembering to change the voltage.

    image

    Dan

  • Thanks Dan.
    It all seems so simple when you think about it!
    This should be perfect for our budget...
    Thanks
    Sam
Sign In or Register to comment.