Parasitic power using split core current transformer

Just a silly idea but how doable would it be to use a split core current transformer like this to provide a small amount of power to charge a battery / capacitor and briefly power an MCU that spends most of it’s time in sleep.

Did you intend to post your question in Bar Sport?

The description does not give any indication of voltage or current output.

Current transformers have large number of wire loops to form a one turn primary to many turns secondary. They are designed to be fed into a load R and have the voltage read.

Think about power transformation for a small current flow through the primary and you will see that the power available for anything below a high current would be negligible.

Weedpharma

[quote author=Coding Badly link=msg=2337974 date=1438301301] Did you intend to post your question in Bar Sport? [/quote] Bar Sport might be a bit to obscure but it is not really a project guidance question. Do you think it is miss posted?

Think about power transformation for a small current flow through the primary and you will see that the power available for anything below a high current would be negligible.

Thanks, the link I posted was just a cheap example but could reducing the number of windings up the potential current flow to a level needed to sustain a MCU in standby and possibly charge something (battery/capacitor) to allow a short burst of activity.

Depends on standby current and how often it wakes.

My thought are that it would not work.

If you have access to the power wire, why can't you use the power?

Give us some more information on your project,

Weedpharma

weedpharma: If you have access to the power wire, why can't you use the power?

Give us some more information on your project,

It's not really a project just an idea on how to power something. To be able to clip onto a wire carrying mains electricity (240V AC) and power a small project without compromising the cable insulation might be useful.

The problem is your supply voltage depends on the current in the wire, not the mains voltage.... CTs must have a burden resistor for safety so you'd have to share your power with that

It's not really a project just an idea on how to power something. To be able to clip onto a wire carrying mains electricity (240V AC) and power a small project without compromising the cable insulation might be useful.

That's called "Piggybacking" in the hacker Sci-Fi movies. It can also be called "Leeching" (for obvious reasons)

If you think about it there is a nefarious element to this concept because it implies that something cannot be simply plugged into an outlet, meaning it is not near an outlet, like hidden somewhere. If prompts the question "why do you need to do this and why can't you use batteries (even rechargable ones) and why can't you power the device from an outlet. It raises a lot of questions and possibly red flags. You might even say it suggests a surveillance device (audio , video or both) powered off the target's house wiring.

The problem is getting a DC supply from the CT. The output voltage from a CT is AC , and usually in the low millivolt range, some range up into the hundreds of millivolts with a high current in the monitoring wire. Converting very low AC voltage into a useful DC voltage is very hard, as its too low to rectify.

The alternating magnetic field around a wire carrying 20 - 30 Amps is far too puny to produce any reasonable power, although I’ve seen a 12 gauge wire carrying fault current (probably > 1000 Amps) jerk like a frog leg before the circuit breaker had time to open the circuit.

Linear Technology's LTC3588 is designed for this sort of thing. It's not designed for the very low ~300mV you'd get from a current transformer but if you absolutely needed to use parasitic power from a cable I think you could manage it with a step up transformer. You still need a high current line - with current flowing - in order to get anywhere.

They have an example in the LTC3588 datasheet where they place two 12"x24" copper panels on each side of a 4' fluorescent tube to harvest energy. I'm trying to imagine what circumstances would exist that could possibly make that route practical :)

A step up transformer may raise the voltage but ot would also consume some of the very low power available.

Weedpharma

raschemmel:
That’s called “Piggybacking” in the hacker Sci-Fi movies. It can also be called “Leeching” (for obvious reasons)

If you think about it there is a nefarious element to this concept because it implies that something cannot be simply plugged into an outlet, meaning it is not near an outlet, like hidden somewhere. If prompts the question "why do you need to do this and why can’t you use batteries (even rechargable ones) and why can’t you power the device from an outlet. It raises a lot of questions and possibly red flags. You might even say it suggests a surveillance device (audio , video or both) powered off the target’s house wiring.

Or even illegal stuff, like leeching power from the live input tail to the meter.

jcallen: The alternating magnetic field around a wire carrying 20 - 30 Amps is far too puny to produce any reasonable power

True if there isn't a magnetic core involved, but with a magnetic core you can extract 1000's of times more than an air-cored transformer

I don't get the whole nefarious argument here.

It's not like getting access to wiring in someone's house is easy... And, more to the point if you did have access to their wiring it is not a monumental task to tap into it directly... All it takes is some sharp needles to pierce the insulation...

People routinely place strips of metal behind the Meter sockets to steal power...

Low tech and more effective... I don't see anything nefarious about this..

I don't see anything nefarious about this..

Just a silly idea but how doable would it be to use a split core current transformer like this to provide a small amount of power to charge a battery / capacitor and briefly power an MCU that spends most of it's time in sleep.

And, more to the point if you did have access to their wiring it is not a monumental task to tap into it directly... All it takes is some sharp needles to pierce the insulation...

Maybe the OP didn't get that memo....

No, I understand that he wants to do it "wirelessly"...

My point was that trying to collect power in this way is not really an indication of something nefarious, because doing it this way requires just as much access to wiring as any other possible meathod...

No, I understand that he wants to do it "wirelessly"...

My point was that trying to collect power in this way is not really an indication of something nefarious, because doing it this way requires just as much access to wiring as any other possible meathod...

Let's say I agree with you so we don't waste any more time on that subject and talk about the OP's request.

First of all, I don't know what your electronics background is but what the OP wants to do is

"inductively" (not wirelessly, which denotes transfer of information , not power)

TV ads touting wireless cell phone chargers use the term "wireless" because 99.9% of the world's population doesn't know what "inductively " means, while probably more than 50% know what "wirelessly" means. A "wireless" device is a device with a transmitter and/or receiver and an antenna.

If you are old enough to remember the pre-cell phone days, you still were aware of radio technology because you saw truckers using CB, Ham operators using HAM radio and Police and Fire using VHF, but if it were possible to go back far enough in time to a time before there was anything wireless (maybe before Marconi), and you approached someone and said "I want to do such & such, but I want to do it "wirelessly", you would get a blank stare and people would think you had lost your marbles. Even though the word "wirelessly" clearly means "without wires", it still would make no sense before the technology had been invented. What the OP is doing is very similar. We are IN that time long ago right now because there currently is NO way to slap a device onto a straight house wiring ac line without making any physical-electrical connection and obtain power to charge a battery to run an MCU.

Stop and think for second. If such a device existed, wouldn't the OP be buying it at Best Buy as we speak ? He is here asking because he thinks we are on the cutting edge at the FRONT of the bus and can see new technology before he does. I don't know about you but I haven't seen that device yet. If you have, I'd love to hear about it.

An inductive device (like a current transformer) is a loop of inductive material with a hole in the middle.

It can also be a flat tranducer (which mates with the coil in the cell phone charging

How it works

Wireless charging as a concept has been around since inventor and physicist Nikola Tesla first concluded that you could transfer power between two objects via an electromagnetic field, said Ron Resnick, president of the Power Matters Alliance, which has a wireless charging protocol.

Essentially, wireless charging uses a loop of coiled wires around a bar magnet — which is known as an inductor. When an electric current passes through the coiled wire, it creates an electromagnetic field around the magnet, which can then be used to transfer a voltage, or charge, to something nearby, Resnick said.

Most wireless power stations nowadays use a mat with an inductor inside, although electric toothbrushes, for example, have long had wireless charging embedded in their bases. Because the strength of the electromagnetic field drops sharply with distance (as the square of the distance between the objects), a device must be fairly close to a charging station to get much power that way, Resnick said.

Now with regard to INDUCTANCE

Ideal Transformers[edit] When k = 1, the inductor is referred to as being closely coupled. If in addition, the self-inductances go to infinity, the inductor becomes an ideal transformer. In this case the voltages, currents, and number of turns can be related in the following way: V_\text{s} = \frac{N_\text{s}}{N_\text{p}} V_\text{p} where Vs is the voltage across the secondary inductor, Vp is the voltage across the primary inductor (the one connected to a power source), Ns is the number of turns in the secondary inductor, and Np is the number of turns in the primary inductor.

It comes down to how many turns are in the loop. You can't see the 'loop" with "wireless" cell phone chargers because it is hidden inside the phone.

What the OP wants to do cannot be done for one simple reason. A straight conductor carrying AC power in a house or industrial building is just that, straight. You can see from the equations that the wire turns ratios are a critical factor.

These effects are derived from two fundamental observations of physics: First, that a steady current creates a steady magnetic field (Oersted's law),[2] and second, that a time-varying magnetic field induces voltage in nearby conductors (Faraday's law of induction).[3] According to Lenz's law,[4] a changing electric current through a circuit that contains inductance induces a proportional voltage, which opposes the change in current (self-inductance). The varying field in this circuit may also induce an e.m.f. in neighbouring circuits (mutual inductance). The term 'inductance' was coined by Oliver Heaviside in February 1886.[5] It is customary to use the symbol L for inductance, in honour of the physicist Heinrich Lenz.[6][7] In the SI system the measurement unit for inductance is the henry (symbol: H), named in honor of the scientist who discovered inductance independently of, but not before, Faraday, Joseph Henry.[8]

What does all this mean ? Well , for one, nefarious or benign, the OP is not going to get any power "wirelessly " (if you prefer to use that misnomer) because he is ignoring all the Laws of Henry, Lenz, Oersted, Faraday , and probably Ohm and Tesla as well.

To comply with all those laws he has to use your needles, tap into the power lines , run it through a transformer , rectify it , etc etc etc. It would be much simpler to tap into the power and connect a powerstrip with outlets and an On/Off switch and plug in all the off the shelf components he needs to do the job. End of story.

FYI, all we know is that the CT has a range of 0.01A to 120 A and it has in ID of 16mm (0.639") which would accomodate up to 5/0 (5 "ought") guage wire. There is no information on the output voltage of the current transformer but but using this as a reference

Ranges: 60 to 200A (330mV Secondary)

which is a resolution of 1.65mV/A

Using that as a rough guideline, 1.62mV/A * 120A =0.198V

So the OP may be able to obtain 200mV of voltage at some minute level of current (probably uAs) using the device he linked.

I think he nailed it with his introduction (and maybe this post does belong in BAR/SPORT Topic)

just a silly idea , but ...

FYI, I heard rumors of UFOs hovering over the power station just prior to the great New York blackout so maybe those guys (or things) know how to do that..

I don't know what you are on about. I didn't say it was practical. Or possible. I said it wasn't nefarious, and in fact, unpractical. There are simpler ways to be nefarious.

If it makes you feel special to say inductive, fine by me. You understood why I meant by wireless, so did I. Good enough for me.

Perhaps he can do it with a motor and a magnet.. Low power generator..

If it makes you feel special to say inductive, fine by me. You understood why I meant by wireless, so did I. Good enough for me.

It’s not to please me. It’s to be accurate. It simply is not a wireless application period because it is not about transmitting information. If you don’t get that , fine. You can lead a horse to water…

More importantly, it is not a wireless application because a wireless application uses antennas and transceivers. This is totally dependent upon Inductive-Coupling. If you remove the CT from the wire and try to do it “wirelessly” without getting close enough to couple the magnetic fields , you would understand why it is not a wireless application. it is purely and 100% inductive, but that still only gets you 200mv at almost no current so it’s a NO-GO. If it cannot be done without direct contact on the conductor , then , by definition, it is not wireless because you are on the wire. It’s an inductive coupling application , and a crappy one at that.

And no he can’t do it any other way either . It’s more than impractical (which implies you could do it but it would be too much trouble) . You can’t do it . Period. End of story.