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Ripple on low voltage

Peterd
I look after a small fairground type railway. It is powered via a transformer and full wave rectifier and runs at around 35 volts. At recent inspections it has been noted that it fails as there is around 24 volt ripple on the 35 volt dc, which is not surprising as there is no smoothing. Apparently according to the person undertaking the inspection, who states it is to bs7671, the ripple should be no more than 10% ripple, however I cannot find any such requirement.

Has anyone got any experience of this type of thing, I am loathe to add a capacitor to smooth the dc - it would have to be probably around 0.1F, and ripple current in it could well be a problem.

Any thoughts on this would be appreciated, is there an actual requirement on ripple, or is it OK to just have full wave rectified dc as long as the peak voltage does not exceed the elv limits of 120v dc or 50 v ac rms .
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    30A is not as much as I was expecting - if you have LT spice, you can experiment with capacitors, series inductance and  and resistors in series with various diode to see what the effect of a smoothing cap would be. (see effect of 10mH below, some way from resistive ;-)  )


    Mike.

    d1f64397bc01a0e5f263f8ee24c5b5a9-original-motor_sim.png

    You need surprisingly little motor inductance to keep the motor current (I(R1)) near constant even though  the voltage goes the full p-p

    If you want to play with the sim yourself the files are attached you'll need to
    download LTSpice too.

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  • 0
    30A is not as much as I was expecting - if you have LT spice, you can experiment with capacitors, series inductance and  and resistors in series with various diode to see what the effect of a smoothing cap would be. (see effect of 10mH below, some way from resistive ;-)  )


    Mike.

    d1f64397bc01a0e5f263f8ee24c5b5a9-original-motor_sim.png

    You need surprisingly little motor inductance to keep the motor current (I(R1)) near constant even though  the voltage goes the full p-p

    If you want to play with the sim yourself the files are attached you'll need to
    download LTSpice too.

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