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Discussion in 'General Electronics Discussion' started by priit, Aug 11, 2016.

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  1. priit

    priit

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    Aug 11, 2016
    Assuming that this is inductance with ferromagnetic core, how many mH it is ?
    Produced 10 years ago.[​IMG]
     
  2. priit

    priit

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    Aug 11, 2016
    I do not want to say at the moment anything about my opinion. If they are other offers, it would be interesting.
    I have no room for mistakes.

    I was happy to measure Ω, before it got broken. DC resistance was 12Ω
     
    Last edited: Aug 11, 2016
  3. Sunnysky

    Sunnysky

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    Jul 15, 2016
    The value is correct, but other options are DC current , Frequency - SRF and of course DCR.

    If this is critical, we need to know circuit parameters & application

    The red coating was added?
     
  4. Alec_t

    Alec_t

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    Jul 7, 2015
  5. priit

    priit

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    Aug 11, 2016
    [​IMG] You are welcome. Application is robot loader controller part (i/o) card.
    Supply voltage 24Vdc, signals i/0 24Vdc.

    Red coating-warranty ? No, this is not an issue.
    As I do not have wiring diagram of this card, I do not want burn down something and wish to get everything running ASAP
     

    Attached Files:

    Last edited: Aug 11, 2016
  6. Sunnysky

    Sunnysky

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    Jul 15, 2016
    next question is why did it fail? why was it suspect?

    THis choke reduces the current surge charging up the 1000 uF cap to some voltage when switched on. The cap ESR may be lower than the choke DCR of 12 Ohms. thus the current di/dt =V/L where dt is the charge up time.

    This is a basic Current spike decoupling choke where the surge current is limited by V/(R_total)

    Assuming 20V to a 25V cap worst case, and R_total = 15Ω, I max = 2A for a few milliseconds then expected load should be 200mA for decent load regulation . I would choose a higher current rating choke than 200mA as a guestimate as the choke simply acts as a resistor with low L when saturated.
    Even a 12 Ω power resistor might work, but the L reduces pulse ripple current to source supply to triangle waves.

    Risk low. 10% tolerance ok if voltage applied is lower, then lower current rating is Ok.

    Does this drive small motors? then measure DCR of motors and consider higher. current rating.
     
    Last edited: Aug 11, 2016
  7. priit

    priit

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    Aug 11, 2016
    Good question. Burnt inductance was visible fault when I opened box. Why I opened the box ? Because ultrasonic proximity sensor what was one of the inputs in this card, sometimes malfunctioned.Sometimes not. Sensor seemed to be ok, so my next step was to go further. Actually original one was this:[​IMG]

    I had a spare card, but during soldering one leg of inductance brokened.
     
  8. Sunnysky

    Sunnysky

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    Jul 15, 2016
    alec's part seems to be the closest match

    To reduce self heating, I would use 500 uH rated for 240mA with DCR of 7Ω which is two of Alec's chokes in parallel . These are like 1/4W resistors which would burn out with 1/2W.

    A lower DCR of 3Ω would work but increase dissipation power in 1000uF cap with ripple current.
    Often designs like this shunt parallel caps and chokes for redundancy any reliability. Hi Rel designs try to increase the circuit R to limit charge currents to caps.

    These days ICL's are used to perform this better, like a Polyfuse but with NTC instead of PTC.
     
    Last edited: Aug 11, 2016
  9. priit

    priit

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    Aug 11, 2016
  10. Sunnysky

    Sunnysky

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    Jul 15, 2016
    Last edited: Aug 11, 2016
  11. Sunnysky

    Sunnysky

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    Jul 15, 2016
    Last edited: Aug 11, 2016
  12. priit

    priit

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    Aug 11, 2016
    Experimentation with measuring tools is tricky, because card is installed in tight rack.But we will see.

    Anyway, thanks and greetings to you Sunnysky to Canada, I will order some more inductances from Farnell as they dont cost a lot and see what happens. Resistor assortment is acceptable here in local shop.
    Now I have something to think.
     
  13. Sunnysky

    Sunnysky

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    Jul 15, 2016
    twisted pair out from current sense 10Ω R can use two probes in differential mode.
    single end to monitor Vdc.
     
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