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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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    Thanks to you all who have replied, your input is very helpful and much appreciated. To put the record straight, it is a very simple 2 rail affair, in essence the same as a model railway, but much bigger with the supply to the train via the wheels, with those on one side having insulated bushes and those on  the other side being connected to the engine metalwork. I don't think that either rail is actually earthed, but the rails are not insulated as such from the earth. I hope to be on site next week and will take a scope along to measure the actual voltage.  Sadly 3 phase not available and whilst on-board battery is a good idea, speed is controlled by voltage applied to track and polarity is reversed when train stationary to provide power to lights and therefore a complete redesign would be needed to use that approach. Max current is around 30 amps, but will try and measure this next week.
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  • 0
    Thanks to you all who have replied, your input is very helpful and much appreciated. To put the record straight, it is a very simple 2 rail affair, in essence the same as a model railway, but much bigger with the supply to the train via the wheels, with those on one side having insulated bushes and those on  the other side being connected to the engine metalwork. I don't think that either rail is actually earthed, but the rails are not insulated as such from the earth. I hope to be on site next week and will take a scope along to measure the actual voltage.  Sadly 3 phase not available and whilst on-board battery is a good idea, speed is controlled by voltage applied to track and polarity is reversed when train stationary to provide power to lights and therefore a complete redesign would be needed to use that approach. Max current is around 30 amps, but will try and measure this next week.
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