New wiki article: Current activated switch

In article , fred scribeth thus

Of course lot of things could go wrong. The whole thing could be cursed by a witch !. It could be crashed into by a UFO, a lot of things could go wrong.

But less chance should there be an insulation breakdown or leakage or creepage between a conductor that for a lot of installations will only be a few volts above earth or two and a half hundred?..

Reply to
tony sayer
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Nothing in Arfa's circuit had a direct connection!.

The one was alluding to is contained in a lockable earthed steel case with some other high volt power.

Its a method that was used in high power TV Tx's years ago before most all of this semiconductor measurement stuff just wasn't that robust or reliable...

Reply to
tony sayer

There might be, I suppose, but the reed switches are not exactly 'bristling out' at you. They are contained inside a moulding that keeps them away from investigative fingers ... :-)

Arfa

Reply to
Arfa Daily

Are any changes needed to get it to work for other AC voltages? I could use something like that here for logging on-time of the house electric heat, but as I'm in the US it's all ~120VAC Mickey Mouse electrics :-)

Anyone know what the transformers look like internally? Are they wound parallel to the wire that they're sensing, or at right angles to it? Lots of turns typically, or just a few? (I'm just wondering if I might have something suitable already in the junk pile to do some testing with, before ordering a batch* of the real thing)

  • I think the heaters are on five or six different breakers, and then it might be nice to monitor the water heater and well pump, too.

cheers

Jules

Reply to
Jules Richardson

No it's detecting the current flow rather than voltage.

At a guess around the hole through which the wire passes. Looking at the specs the other day the turns ratio tends to be 500 to 2000:1 depending on the sensitivity required. Higher turns ratio will detect lower currents. It's this high turns ratio that makes an open circuit current transformer a bit nasty...

Think you might be better off with a box full of small mains coil relays. Like what I'm probably going to do.

Reply to
Dave Liquorice

Ah, but logically you've turned that bit of mains cable from being just a wire to half a coil of a transformer, and that transformer half coil is now in series with the rest of the wire :-)

Reply to
Alan Braggins

You can also increase the sensitivity by looping the sensed wire through the CT a number of times, rather than just passing it through once.

MBQ

Reply to
Man at B&Q

I've got a multimeter with a current clamp. I used it to tell whether a pump was being switched when it should be by putting it around a three-core flex, then wondered why that was working....

Reply to
Alan Braggins

Asymmetry.

Reply to
The Natural Philosopher

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works from the wiki page.

Reply to
Dave Liquorice

Nothing to stop you using a straight wire! ;-)

Reply to
John Rumm

I use a current relay and a delay off relay to ensure that our kitchen hob hood extractor fan runs whenever the electric hob is used.

Reply to
Michael Chare

but thats still in series with the rest of the wire

Reply to
The Natural Philosopher

It's all about the current, so voltage is of no consequence. I've had a second one here on the bench sensing down to a few watts of load, so you should be ok. I wouldn't like to say if you could make it work with a different sensor. The one that I specified was one that I originally had left lying around from another project, which is why it got pressed into use for this one. It is actually a very high ratio one at 2000:1 and I have designed with that in mind. They are readily available and cheap. The postage is free, so you could order just one to play with. The only downside is that they ship surface mail for the most part, so you have a 10 day wait ...

Arfa

Reply to
Arfa Daily

Indeed - this was how it was tested with "big" loads without needing a big load ;-)

Reply to
John Rumm

10 days surface from Hong Kong? That's going some... The voyage time is of the order of 19 to 24 days and I doubt they run a boat every day, so the post may well will be sat on the dockside for a week or more.

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Chinese train system is pretty good but I'm not so sure about the "Orient Express" line that's normally over a week from Beijing. Hong Kong to Beijing is a day or two by train.

Other half sent something to Austraila surface mail, ISTR it took about 6 months to arrive.

I'd almost put money on it being Air but not with any sort of priority, gets left behind once the plane has it's x Kg of (higher priority) mail loaded.

Reply to
Dave Liquorice

Yeah, you're probably right. I thought that after I posted the comment. It's probably a cheapo non priority air service.

Arfa

Reply to
Arfa Daily

How much???

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plus various others.

MBQ

Reply to
Man at B&Q

That's actually about the best price that I've seen them in this country. All of the ones in that series seem to be 1000:1, but I reckon my little circuit would be quite happy with that. I might order one in and give it a try ...

Arfa

Reply to
Arfa Daily

and the current transformer should be driving a current sensing (low impedance) input. Actually, the manufacturer suggests a

300 ohm load. The load is currently 2k7 for half a mains cycle, and (without R5), pretty much infinite for the other half mains cycle. A current transformer driving an infinite load is a definite "no" - in theory there's nothing stopping the output voltage going extremely high, quite likely very much higher than the PIV of BAT85, and might well be enough to give someone a shock. If someone uses a larger cored current transformer, it could be quite serious.
Reply to
Andrew Gabriel

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