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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 23rd Jan 2019, 11:22 am   #21
unixmanuk
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Default Re: Electric Shock!

I have seen (and felt) similar effects to this on metal object where the PME neutral bonding to earth at the meter end was intermittent. A quick phonecall and visit from the appropriate supply company fixed it. (that assumes the house has a PME earthing system, as do most modern houses).
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Old 5th Feb 2019, 11:07 pm   #22
Lancs Lad
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Default Re: Electric Shock!

I know it's been a while since I first posted, but I was put off using the radio after the 'incident'.

I had another look at it tonight, and noticed something about the power supply that I think is unusual.

I've looked at the half-dozen other PSUs in use in this house, and there isn't anything like this on any of them.

It's an odd little cylindrical thingy, just an inch or so along the flex from the transformer plug.

Yes! I know! I am THAT unobservant! I should have noticed it and mentioned it earlier.

So what is it? And what does it do?

Anyone?
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Last edited by Lancs Lad; 5th Feb 2019 at 11:14 pm. Reason: punctuation correction
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Old 5th Feb 2019, 11:14 pm   #23
GrimJosef
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Default Re: Electric Shock!

It'll be a ferrite https://en.wikipedia.org/wiki/Ferrite_bead I imagine, there to limit electromagnetic interference.

Cheers,

GJ
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Old 5th Feb 2019, 11:14 pm   #24
The Philpott
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Default Re: Electric Shock!

Has the appearance of a simple 'choke' which is supposed to suppress interference.

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Old 5th Feb 2019, 11:37 pm   #25
Lancs Lad
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Default Re: Electric Shock!

Thanks so much for the prompt replies!

Do 240 volt radios have something similar, then? But just built into the actual internal workings?

I'm afraid I'm not very knowledgeable about radio electronics.

The last time I heard the word 'choke' it was something my 1985 Ford Orion had!
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Last edited by Lancs Lad; 6th Feb 2019 at 12:04 am.
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Old 6th Feb 2019, 12:01 am   #26
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Default Re: Electric Shock!

All things electrical must comply with a number of EU directives to qualify for their CE mark. The EMC directive requires equipment not to radiate too much electromagnetic energy and also to be unaffected by radiation from elsewhere.

To meet the EMC directive most things need filters in their circuits. What you are seeing is a ferrite clamp, so just a chunk of ferrite material around the cable - this forms a common-mode choke which helps to make the cable a less-good aerial. Ferrite clamps are expensive so they typically get used when a design that was expected to pass the tests actually just failed. Adding a ferrite clamp is a quick way to get a few extra dB improvement.

At least they were trying!
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Old 6th Feb 2019, 12:14 am   #27
emeritus
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Default Re: Electric Shock!

Last year there was a letter in one of the IET journals describing how the writer had improvised a very effective suppressor from the wire cage used to secure the cork of a bottle of sparking wine. He crushed the wire cage into a ring and threaded a couple of turns of the DC cable of a wall wart that was the source of the interference through it. He was at a friend's at the time and so didn't have a ferrite ring to hand.
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Old 6th Feb 2019, 12:21 am   #28
Lancs Lad
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Default Re: Electric Shock!

Thankyou GMB.

So is that ferrite clamp actually electrically connected to the PSU wire inside? Or just clamped around the outside insulation?

Would it slide down the wire if I attemped to move it?

I have no intention of trying to move it, by the way!
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Old 6th Feb 2019, 12:30 am   #29
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Default Re: Electric Shock!

Hi LL. Re posts 22* and 25*. Some people are unusually sensitive to electricity. You may be one of them perhaps? Personally I have very dry skin which helps! Most Forum members will have had some sort of a shock in their time but may not have been so disconcerted by it! There are few deaths-so far! It's less alarming if you DO have some knowledge of electronics-easily gained with study! How much do you understand about what is described? It is concerning that you might place yourself at risk

I'm afraid that selecting random components and asking if that might be the cause is not very efficient in terms of gathering knowledge/experience, no matter how helpful Forum people are [and they nearly always do their very best to assist]. Most older members [the majority of us] had to work things out with very little resource. There is a lot you can research for yourself. Then, if you get stuck along the way, the advice will be even more invaluable.

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Last edited by dave walsh; 6th Feb 2019 at 12:38 am.
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Old 6th Feb 2019, 1:57 am   #30
Glowing Bits!
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Default Re: Electric Shock!

Quote:
Originally Posted by Lancs Lad View Post
Thankyou GMB.

So is that ferrite clamp actually electrically connected to the PSU wire inside? Or just clamped around the outside insulation?

Would it slide down the wire if I attemped to move it?

I have no intention of trying to move it, by the way!
It is moulded around the insulated wire, coupling it to any of the wires may cause RF issues.
Do not try moving it, you will literally rip the wire clean out of it, rendering the PSU scrap.
Please stop worrying about a few tingles from the antenna, I get zapped good'n propper when taking a pair of tracky bottoms & hoody (polyester) out the dryer.
If you think a tingle is bad, try grabbing (by accident) something at mains 240v, you'll have the biggest hand-shake of your life!
Rick.
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Old 6th Feb 2019, 2:09 am   #31
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Default Re: Electric Shock!

Those ferrite rings are sold for retrofitting.
Do not try to remove that sealed one. There are plenty of photos of them for you to look at on the web if you want to see what is inside them. There is also plenty of data sheets to read too.
https://uk.farnell.com/c/passive-com...-core-ferrites
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Old 6th Feb 2019, 3:04 am   #32
Lancs Lad
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Default Re: Electric Shock!

No, Rick, I've no intention of trying to move it! I just wondered if it was connected inside.

Thanks, everyone, for all your input.
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Old 6th Feb 2019, 2:32 pm   #33
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Default Re: Electric Shock!

Those little ferrite clamps are not connected to the wires but just clamped around them and clamped VERY firmly possibly also with a spot or 3 of potting compound. My girlfriend asked me to look at her DAB radio as it had stopped working turned out the power supply had died. During testing I did feel a slight tingle from the areal so its not uncommon the replacement supply ( a repurposed mobile fone charger) does not give areal tingle so shes double happy now!
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