I’m a lighting tech for film and TV and I’m quickly becoming intrigued at the notion of being able to feel whether or not a cable has juice flowing to it.
Exactly how easy would it be for me to sense something like that with a magnet somewhere in my hand?
I’d also love to hear more about people’s experience with such things. I sometimes work around very high voltage equipment (tens of thousands of volts) and wonder about the sensing range and whether it would be too distracting while I was working.
Basically there needs to be a significant amount of current flowing.
Keep in mind it needs to be AC, and current is the only factor that matters:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html
Higher voltage is actually a hindrance because higher voltages require less current to supply the same power. Also, for mains voltage wires, they have a Live wire but also a Neutral wire that is magnetically coupled to it, which contains the field and mitigates sensing. So ultimately it’s not great for sensing live wires. That’s why non-contact voltage sensors use capacitive instead of inductive circuits.
What magnet implants are really good at sensing is transformers and ballasts. No matter how well they manufacture a AC/DC converter, the transformer will always be magnetically very noisy in an area around it. I can hold my finger over my laptop charger and determine roughly how full the battery is by how much current it’s drawing through the transformer. When it’s full and it dies down, I can plug in a USB cable to my phone and clearly detect the change in draw, even though it’s at most 2A on the 5VDC side, which means as little as 80mA going through the transformer.
Very interesting stuff! Basically, amperage trumps wattage? When you say “holding your finger over” how close are we talking? It sounds like you could get some feedback from a full wave rectifier but not a bridge rectifier? I assume the ripple current itself is too small to sense. Thanks for the information!
Yeah, current flow is the only value that has any affect on the strength of a magnetic field. At least for a single turn solenoid (a single wire).
The only effect of voltage is that it allows more current to flow through a circuit that has a higher resistance. So for example in high voltage (32kV+) transformers, higher voltage is helpful because the number of turns on the HV side of the transformer presents a higher impedance (AC component of resistance) to the flow of current. You’ll definitely be able to detect a HV transformer the size of an engine block from half a meter away, but not because of the voltage.
When I detect a laptop charger for example, the transformer is about a 10x step down in a small package, so I can detect it at full draw from about 5cm away. Magnetic fields lose intensity at a rate of about 1/r³ though
The rectification and regulation have no effect on your ability to sense a transformer, because that’s all happening downstream. No matter what kind of load you hook up, the transformer is going to generate a constant very low signal on the HV side, until the LV side starts to draw current. Then you’ll be able to sense a larger field on the HV side as it draws more current from the mains in response.
Well, what kind of amperage are we talking? I’m regularly working around lights that draw 20+ amps, sometimes up to 90 amps.
Assuming it’s 50/60Hz AC, you should be able to tell when those wires are live from a few mm away. Even with the Neutral return path right next to the Live wire, at that current there should still be a big flux bubble around the entire cord.
You can test it by resting a small magnet on your fingertip and holding it next to the wire…
I was thinking more along the line of just rectification rather than a voltage step down followed by rectification so there isn’t always a transformer involved–such as with a bridge rectifier. Obviously I need to do more reading, haha! Thanks again for all the information.
a little while ago I was working in the boiler room of my building and needed to find out which relays were on or of and I forgot my multimeter and I was close with my hand like 2/3 cm and I felt my magnet in my fingertip vibrating I forgot it also worked for that so it was pretty easy for me to tell which ones whare on or off
keep in mind this is a 400-volt system with a bit of juice flowing pretty big pumps
and I can easily feel if an electromotor is running or nog if there is no way to see or hear it
I have a magnet implant from cyberise.me
I can feel currents as low as 10A when I’m almost touching the wire, already pretty hard when it is in a cable though.
All Old style Transformers are easily noticeable, regularly test the power supplies of the most common doorbells/intercoms by holding my magnet to it.
Relays and Contactors are easy to test as well.
Naturally also electromagnets ;p
Sadly can’t feel the current in switch mode power supplies, too high frequency I guess.
Let me tell you that a wire that is loaded at 400A is VERY noticeable xD
WIsh I could compare it to the Titan but I haven’t been able to get one in this far.
Also
First time I used an angle grinder again after the implant I nearly dropped it due to how strong the magnet buzzed the moment it turned on.
Some serious magnetism there.