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Removal of ferrite cores..


gordon s

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I have bought a couple of 12v regulated power supplies from RS and the lead is a standard 1m long. One end is moulded into the power pack and the other has a moulded on power connector and a few inches from the end, a moulded on ferrite. I don't need the connector and want to shorten the lead to a few inches long and this will mean cutting off the ferrite.

 

I have an idea these are only for EMC control, but just to be certain, could someone please confirm they won't impact the output of the 12v regulated supply?

 

If it's critical, I'll have to cut the lead in two and rejoin, which I'd rather not do..

 

Many thanks.

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Simple answer: The ferrite cores are to prevent the cable from acting as an antenna, for either transmission or reception. If you're chopping the cable down, then it's unlikely to be a practical problem.

 

More complicated answer: Chopping the cable would shift the problem up to shorter wavelengths, as shorter wires support higher frequencies, but these frequencies are in general less of a problem due to lesser radiated energies and less tendancy to produce problematic interference.

 

Even more complex answer: Nah, it's too early in the morning to go there! :)

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I've finally got my head round it's not a race to the finish, just a gentle amble, taking each day as it comes. I've now been retired two years and really enjoying the new pace of life.

 

The layout thread is here as I can't get my head round blogs at all. I've rewired the main bus and built my first control panel to handle the reverse loop. I'll post a couple of pics later today. Also picked up a whole stack of buildings from Great Northern, so I have no excuse at all to get this one moving...

 

Thanks again for your help.icon_thumbsup2.gif

 

Eastwood Town

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This is not for Gordon s, but for all other RM readers, and the advice is to leave well alone for several reasons, the ferrite cores are there for RF suppression, and for the unit to match it's electrical acceptance tests should remain in place. These days all units require to meet higher and higher standards, and the cables have become part of the system.

There is no law to say that you cannot re-wire it for a different plug, which is what shortening amounts to, but it may break regulations, and with an exhibition layout the re-wire would have to be examined in any electrical safety assessment.

 

Shortening a lead is basically no more than fitting a plug, which any competent person should be able to do, and is allowed to do, but believe me there are others who's electrical knowledge borders on lethal.

 

This is why so many items come with moulded on plugs and lead entries, to prevent such problems, and to re-wire to simply lose a few feet of cable may be overkill, when all it requires is one of the coiled sleeve cable tidies added to the folded lead. ( By the way these should not be used with power hungry fires etc., to much power in a looped/coiled cable is potentially dangerous).

 

The golden rule is to ask for assistance if you are at all unsure, and this is exactly what the poster has done. As a qualified electrician I have spent many merry hours un-picking trully awful wiring in houses, believe me some were disasters about to happen.

 

Stephen.

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Just to clarify Stephen, the ferrites were on the output side, so only 12v, not the mains side. I certainly agree you should never play with the mains side, unless you know what you are doing.

 

Thanks for posting a warning to others.

 

Just to add to your comment re coiled extension leads. I happened to see the results of such an occurence at a neighbours house. The whole plastic centre drum had virtually melted.....

 

I wouldn't have believed it possible had I not seen it myself...icon_eek.gif

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Guest RAFHAAA

Apart from the fact that a coiled cable can't dissapate heat there is also the inductance effect generated by one loop of the cable being next to another which aggravates the problem.

Answer is to use a shorter lead or unroll it all.

Rob

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