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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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    Default Re: Back EMF smoke in controll panel

    Quote Originally Posted by mirocha View Post
    I ordered the parts today to build your design, I am making 6 of them, cost about $10 US each.

    Thanks Joseph
    Built one circuit to test design. The very first time the stepper motor stopped quickly the LED on the Returned Energy Dump Circuit lit and stayed lit and the 33 ohm resistor started to smoke. This is telling me the TIP 147 is staying on or is shorted. I did use the TIP142 and the 390K resistor and did not use the D3 optional diode. Is the 100uf cap to much added load to the TIP 147, maybe the 100uf cap should be on the other side of the TIP142 somewhere or different resistors?





    Back EMF smoke in controll panel-img_0411-jpgBack EMF smoke in controll panel-img_0412-jpgBack EMF smoke in controll panel-return-energy-dump-npn-jpg

    Attached Thumbnails Attached Thumbnails Back EMF smoke in controll panel-img_0411-jpg   Back EMF smoke in controll panel-img_0412-jpg   Back EMF smoke in controll panel-return-energy-dump-npn-jpg  


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    Quote Originally Posted by mirocha View Post
    Built one circuit to test design. The very first time the stepper motor stopped quickly the LED on the Returned Energy Dump Circuit lit and stayed lit and the 33 ohm resistor started to smoke. This is telling me the TIP 147 is staying on or is shorted. I did use the TIP142 and the 390K resistor and did not use the D3 optional diode. Is the 100uf cap to much added load to the TIP 147, maybe the 100uf cap should be on the other side of the TIP142 somewhere or different resistors?





    Back EMF smoke in controll panel-img_0411-jpgBack EMF smoke in controll panel-img_0412-jpgBack EMF smoke in controll panel-return-energy-dump-npn-jpg
    I don't know maybe I bought bad transistor any thoughts?



  7. #19
    Gold Member TomKerekes's Avatar
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    Default Re: Back EMF smoke in controll panel

    Hi Joseph,

    I wonder if the circuit is breaking into oscillation. Do you have a scope? When the transistor switches on if the supply wiring is long and has any inductance the input voltage may drop making the circuit think more clamping is needed, etc... Or something like that. You might try adding a filter capacitor on the input. Such as a 0.1uF 100V ceramic capacitor. Also possibly the output. Although the output already has a huge capacitor such a capacitor has too much inductance to be effective at high frequencies.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Back EMF smoke in controll panel

    Quote Originally Posted by TomKerekes View Post
    Hi Joseph,

    I wonder if the circuit is breaking into oscillation. Do you have a scope? When the transistor switches on if the supply wiring is long and has any inductance the input voltage may drop making the circuit think more clamping is needed, etc... Or something like that. You might try adding a filter capacitor on the input. Such as a 0.1uF 100V ceramic capacitor. Also possibly the output. Although the output already has a huge capacitor such a capacitor has too much inductance to be effective at high frequencies.

    Regards
    Back to basics, tried the Gecko return energy dump circuit with only adding a 6.8K resistor and an LED as below. Tried it numerous times with the upgraded 70 volt 800 watt power supply and it worked with no problems. The LED flashes when the stepper motor is coming to a quick stop. The LED flashes bright and long enough to see with no problem. This let me know the TIP 147 transistor is turning on and the circuit is working. In my trial and error method I did find out that if the 1000uf cap is bad the circuit will not lite the LED so it also lets me know that the cap is ok by lighting.

    The unit that is working is using a STMicroelectronics TIP147 transistor. I made a second unit using the new TIP147 transistors I bought from China, an off brand and the circuit/transistor failed on the first try and fried the 33 ohm resistor.

    I ordered STMicroelectronics TIP 147 transistors from Digikey and should have them next week, I am now thinking the chinese transistors I bought are all bad and that is what caused the more complicated circuit with the 100uf cap to fail, I used the cheap China transistors.

    Gecko return energy dump circuit with only adding a 6.8K resistor and an LED is actually very nice and I will stick with that design, it works and does what I need it to do, I would have liked to get the LED to stay on a little longer with a capacitor but the added load of the capacitor on the STMicroelectronics TIP 147 fried it and the other circuit with the 100uf circuit failed because of the Chinese transistors and I'm done with trying to get that to work. I could try it with the STMicroelectronics TIP 147 but at this point I don't see any real benefit.

    The TIP 147 is rated at 100 volts 10 amps which I think is a little close to what the circuit is and would like to change the TIP 147 to a higher rated transistor. What I found was a MJH11019 that is rated at 200 volts and 15 amps. I don't know if that would work because the TIP 147 has built in Base-Emitter shunt resistors which the MJH11019 does not have, I don't know if it would work as a drop in replacement and I don't know how I would build an external Base-Emitter shunt.

    Below is the circuit that worked numerous times using a STMicroelectronics TIP147 transistor, however with the issues I have had, it needs to be verified that the 6.8k resistor and LED combination and the way it is hooked up in the circuit is proper at 70VDC.
    I will try the new STMicroelectronics TIP147 transistors but if someone can tell me that the MJH11019 transistor would work I would use it for the higher rating.

    Back EMF smoke in controll panel-img034-jpg










    Back EMF smoke in controll panel-img034-jpg

    Attached Thumbnails Attached Thumbnails Back EMF smoke in controll panel-img033-jpg   Back EMF smoke in controll panel-img033-jpg   Back EMF smoke in controll panel-img034-jpg  


  9. #21
    Registered john-100's Avatar
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    Default Re: Back EMF smoke in controll panel

    Hi Tom and mirocha


    parasitic oscillation a possibility especially if the connecting wires are long

    0.1 uf capacitors across the input and output terminals and the TIP147's base collector terminals could help



    I thought I find I am going back to is the original current dumping circuit would have been helped
    by the other axis drivers taking some of the returned energy


    with this version only being connected to one axis

    Back EMF smoke in controll panel-return-energy-dump-pnp-npn-darlingtons-jpg

    the 33 ohm resistor could be dissipating 175W when the TIP147 switches on

    if it takes too long to switch off the 33R 10W resistor is going to have a short life


    the other possibility is the heat sink is too small
    and the TIP 147 over heating when the base current drops and is no longer saturated

    when the collector current is about 1A and the collector emitter voltage is 35V
    you need to have a heat sink big enough to dissipate over 35W ! ( so will the 33 ohm resistor )



    John


    PS
    unknown Chinese TIP147's could be rejects or fakes - cheaper transistors that's been re-marked



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    Default Re: Back EMF smoke in controll panel

    Quote Originally Posted by john-100 View Post
    Hi Tom and mirocha


    parasitic oscillation a possibility especially if the connecting wires are long

    0.1 uf capacitors across the input and output terminals and the TIP147's base collector terminals could help



    I thought I find I am going back to is the original current dumping circuit would have been helped
    by the other axis drivers taking some of the returned energy


    with this version only being connected to one axis

    Back EMF smoke in controll panel-return-energy-dump-pnp-npn-darlingtons-jpg

    the 33 ohm resistor could be dissipating 175W when the TIP147 switches on

    if it takes too long to switch off the 33R 10W resistor is going to have a short life


    the other possibility is the heat sink is too small
    and the TIP 147 over heating when the base current drops and is no longer saturated

    when the collector current is about 1A and the collector emitter voltage is 35V
    you need to have a heat sink big enough to dissipate over 35W ! ( so will the 33 ohm resistor )



    John


    PS
    unknown Chinese TIP147's could be rejects or fakes - cheaper transistors that's been re-marked
    Just talked with the founder owner of Gecko, he walked me through every thing. The original circuit with adding a 6.8k resistor and an LED will add about 10 milliamps and the circuit will shunt about 2.18 amps so the TIP 147 at 10 amps is more than adequate. The problem was my originally using the 1000uf Capacitor which drew enormous current.

    We did calculations on everything, running a single stepper motor return energy could raise the voltage on the 70 volt power supply as much as 10 volts. Running several stepper motors, the other motors will absorb return energy.

    I will build the original circuit adding just the 6.8k resistor and an LED using a quality TIP 147, no more Chinese crap.

    I think this the way for me to go. Thanks for every ones help and input.

    I will post how it works out once I get the new transistors.

    Thanks again

    Joseph Mirocha



  11. #23
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    Quote Originally Posted by mirocha View Post
    Just talked with the founder owner of Gecko, he walked me through every thing. The original circuit with adding a 6.8k resistor and an LED will add about 10 milliamps and the circuit will shunt about 2.18 amps so the TIP 147 at 10 amps is more than adequate. The problem was my originally using the 1000uf Capacitor which drew enormous current.

    We did calculations on everything, running a single stepper motor return energy could raise the voltage on the 70 volt power supply as much as 10 volts. Running several stepper motors, the other motors will absorb return energy.

    I will build the original circuit adding just the 6.8k resistor and an LED using a quality TIP 147, no more Chinese crap.

    I think this the way for me to go. Thanks for every ones help and input.

    I will post how it works out once I get the new transistors.

    Thanks again

    Joseph Mirocha
    Installed new transistors, using the original gecko return energy dump circuit only adding an LED and 689k resistor and the circuit worked with no problem. The LED is off and when the stepper motor quickly slows down the LED turns on briefly letting me know the return energy dump circuit is working.

    New problem, each drive has a separate return energy dump circuit and a separate LED for each for each return energy dump circuit. I extended with wire and mounted the LED to the control cabinet door. When the LED is mounted directly to the circuit board the LED works perfect when mounted to the cabinet door by wire the LED is always glowing not in the off state.

    The wire length from the circuit board to the each of the LEDs is between approximately 30" and 46". The LED with the longer wire leads flows the brightest and the LED with the shorter wire leads glowing significantly less.

    I mounted terminal blocks in the circuit board to connect the wire leads to the LED. If I connect the LED directly on the circuit board the LED is off and turns on when there is return energy as it should, when I connect the LED with 30" or longer wire leads the LED is always glowing and flashes brighter when there is return energy.

    I also swapped the return energy circuits from one drive to the other to see if the problem moved to see if it was the circuit board causing the problem. Board one with the longest wire leads to the LED had the brightest glowing LED, I swapped it with board four which had the shortest wire leads and the problem did not move so it appears the problem is the wire, I don't know what to do to fix it, just be capacitance or inductance problem I would think.

    Asking for help in how to solve this issue.

    Thanks joe



  12. #24
    Gold Member TomKerekes's Avatar
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    Default Re: Back EMF smoke in controll panel

    Hi Joseph,

    I still suggest adding bypass capacitors to your circuit. In my experience a high speed switching circuit like that will often do bizarre things without them. Those big capacitors will not act like capacitors at all at high frequencies.

    Let us know what you find.

    Good luck and Regards

    TK
    http://dynomotion.com


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