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DPDT switch question

Discussion in 'General Electronics Discussion' started by jim belcher, Feb 7, 2015.

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  1. jim belcher

    jim belcher

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    Jan 13, 2015
    I am replacing the AC motor on my wood lathe with a DC motor with variable speed controller. I have the controller components and motor, but would like to add a reversing switch. I can't seem to find any dpdt switch rated for 90vdc at 15a. Is it possible to use a diff type of switch rated for example 30a 120vac? It doesn't make sense to me to try something like a 30a 12vdc, but I don't know that either.
    I will never be utilizing the switch while the motor is running. the entire system will be powered off before I reverse motor direction.
    Any suggestions and tips would be greatly appreciated.
    ~Jim
     
  2. pebe

    pebe

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    Sep 3, 2013
    Switches are rated at a lower DC current than AC because the arc produced by switching DC current can cause excessive heat. Using AC, the arc is self-quenching as the sine wave goes through zero volts so is not sustained.

    In your case where there will be current as you change over, so only the current carrying capacity of the contacts matters and a 30A a120Vac switch should be OK to switch 15Adc.
     
    drunkseamonkeys likes this.
  3. jim belcher

    jim belcher

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    Jan 13, 2015
    thank you for the detail!
     
  4. pebe

    pebe

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    Sep 3, 2013
    Sorry, Jim. there was a mistake in my reply. It should have said
    "In your case where there will be no current as you change over, so only...."
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Jim, would you please post the schematic of your circuit? I know that you stated that the reverse switch will never be operated while the motor is running but I think many of us would feel more confident about that after we see the circuit.

    I've been turning wood for over 25 years and I can attest to the sequence of events that immediately follow a chuck and wood blank unscrewing itself from the spindle. ... There's a sh!t load of ducking and diving involved. :eek:

    Chris
     
    drunkseamonkeys likes this.
  6. drunkseamonkeys

    drunkseamonkeys

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    Feb 8, 2015
    Cdrive i just did that last week with my homemade lathe lol
     
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