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Thread: Back EMF smoke in controll panel

  1. #13
    Registered john-100's Avatar
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    Default Re: Back EMF smoke in controll panel

    now I have had another look , this is what I would build

    Back EMF smoke in controll panel-energy-dump-6-jpg

    the diode D1 has to carry the full load current to all the drivers connected to the circuit
    so I would use a minimum of a 15A diode at least - a 20 or 25A diode could be better option

    depending on your supplier , you may find it less expensive to use part of a bridge rectifier than a single diode !!!
    connecting the two ac terminals of the bridge rectifier to the power supplies positive terminal
    and connecting the bridge rectifiers positive terminal to the driver(s)

    not knowing how long the TIP147 will be conducting
    its not going to be possible to know if the capacitor C2 will be fully charge and therefor how long the LED will be ON

    assuming C2 is charged to 80V , the 39K resistor (R5) limits the MPSA42's base current to 2mA

    as C2 discharges , the MPSA42 will dissipate the most power when the collector to emitter resistance is equal to the 6K8 LED current limiting resistor
    the dissipation at 80V will be 470 mW which is less than the maximum of 625 mW for the MPSA42

    the diode D3 is optional and just speeds up the discharge of the capacitor C2
    when the power is switched off

    if you use a TIP142 Darlinton NPN transistor instead of a MPSA42 then you can increase the resistance of R5 the 39K resistor to 390K , since the TIP142 has a very large current gain

    John

    Last edited by john-100; 08-13-2017 at 08:58 AM. Reason: to add ref to using a TIP142 instead of MPSA42


  2. #14
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    Quote Originally Posted by john-100 View Post
    now I have had another look , this is what I would build

    Back EMF smoke in controll panel-energy-dump-6-jpg

    the diode D1 has to carry the full load current to all the drivers connected to the circuit
    so I would use a minimum of a 15A diode at least - a 20 or 25A diode could be better option

    depending on your supplier , you may find it less expensive to use part of a bridge rectifier than a single diode !!!
    connecting the two ac terminals of the bridge rectifier to the power supplies positive terminal
    and connecting the bridge rectifiers positive terminal to the driver(s)

    not knowing how long the TIP147 will be conducting
    its not going to be possible to know if the capacitor C2 will be fully charge and therefor how long the LED will be ON

    assuming C2 is charged to 80V , the 39K resistor (R5) limits the MPSA42's base current to 2mA

    as C2 discharges , the MPSA42 will dissipate the most power when the collector to emitter resistance is equal to the 6K8 LED current limiting resistor
    the dissipation at 80V will be 470 mW which is less than the maximum of 625 mW for the MPSA42

    the diode D3 is optional and just speeds up the discharge of the capacitor C2
    when the power is switched off

    if you use a TIP142 Darlinton NPN transistor instead of a MPSA42 then you can increase the resistance of R5 the 39K resistor to 390K , since the TIP142 has a very large current gain

    John
    I am using a separate energy dump circuit for each gecko drive, the stepper motor current will be limited to 3.5 amps by the gecko drive, so I believe D1 will be ok it is rated for 10 amps. There are several reasons to have a separate energy dump circuit for each drive, lower current and with each having the LED it let me see each drive seperatly.

    I will use the TIP142.

    Let me know if D1 is ok for just one drive, I will be using a separate circuit for each drive.

    Thanks again

    Joseph



  3. #15
    Registered john-100's Avatar
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    Default Re: Back EMF smoke in controll panel

    one circuit per drive is a detail I did not have (may be I missed it last night )
    with a separate energy dump circuit for each gecko drive the 10A10 diode will be OK



    john



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    Quote Originally Posted by john-100 View Post
    one circuit per drive is a detail I did not have (may be I missed it last night )
    with a separate energy dump circuit for each gecko drive the 10A10 diode will be OK



    john
    I ordered the parts today to build your design, I am making 6 of them, cost about $10 US each.

    Thanks Joseph



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Back EMF smoke in controll panel
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