Inductive current measuring using Raspberry Pi
Vložit
- čas přidán 8. 09. 2021
- Making a coil to inductively sense current flowing through 2-conductor house wiring cables, without modifying the house wiring.
I used a Raspberry Pi and an ADS1115 A/D converter to sense the output from my coil and graphed it using ascii graphics on the Raspberry Pi computer. I also experimented with how much current it takes to instantly pop a breaker.
I have a Ph.D. in electrical engineering and I am very impressed with your knowledge. You really know your stuff! It is so refreshing to see someone who genuinely thinks about things and solves problems in a deep-manner. The more experience I have working with other engineers, the more that I am convinced that these traits are exceedingly rare. Most people do the bare minimum to get things done and are very surface level, making decisions based on their ego rather than focusing on the problem at hand. You are a treasure!
It's not easy to get a job where you're paid to think a problem through well outside academia. quite often more through goes in home made projects than work projects since we're forced to estimate the time necessary to solve a problem. And in that competition, a thinker always looses. They put a poster on the wall that says "Done is better than very good", and I could not disagree more.
@@Muhovc loses*
@@aaronalquiza9680 Engineers dont spell well. 😃
Hey! You're alive. Are you gonna get back to making steam engines and such? Perhaps I've just been missing your videos? Used to enjoy your stuff in the before times. Hope you're well and all. Cheers
@@gregfeneis609 Lol yes still alive. I appreciate you watching my videos! I have been very busy with life. I had two daughters in the time since I last posted a video. Haven't had time to get out in the shop much, and when I do, its been working on my house. I definitely plan on getting back into building the steam engines. But it might not be until my 2nd daughter is a bit older and things are less hectic.
You can estimate how subtle the considerations are in a Matthias explanation by the number of nested "buts".
Alternate title: Man fails to create an electrical fire for 10 minutes
haha
In a workshop made almost entirely from flammable materials
Too clickbaity :D
Add 3x or 4x commercials on top of that
@Bob Dad?
10:30 You should lookup the trip curve for your circuit breakers. For example, if I look at the trip curve for a 'C' curve Eaton Breaker I see that it could let through 9 times its rated current (that's 135 Amps for a 15A breaker) for almost 3 seconds, however at 10 times rated current (150A) it will trip in < 0.02 seconds.
As a retired electrician I found it very interesting and matches up to my real world experiences.
Great video! I love the journey toward simplified solutions.
Depending on the breaker characteristic, it could trip "instantaneously" for anywhere between ~3x rated current to ~20x rated current. Look up the trip time characteristic curve for the manufacturer and part number for the breaker in the panel - there should be a point where it jumps in value from seconds down to milliseconds (it'll be a log-log plot, so it's pretty obvious)
Exactly right Steven. Then Mathias needs to buy a DRLO/Ductor to play with tripping that breaker instead of plugging everything in his shop in lol
True in the UK too. When I first got my table saw, it would trip the breaker in the garage every time I tried to turn it on. Had to replace the 'B curve' breaker with a 'C curve' breaker, which is more tolerant of high inrush currents.
I had the same thing in mind, which type of characteristics is the breaker. In Europe we have B and C type mainly in home appliances
9.06. That is right in line with what we are taught as electricians when calculating fuses for motors.
We are taught that most motors will surge with roughly 6 times the current of steady state. 70A/12A=5.83. So bang on! The same goes for the circular saw
Is this true for DC and AC?
@@jjanderson1987 oh sorry. AC motors. More specifically squirrel cage, asynchronous-and universal motors. Which are a very large part of AC motors used
@@jjanderson1987 I'd say yes, it's the starting that takes the big surge and is the hardest on the wires (regardless of the motor type). At the big saw mills, they turn on the motors sequentially. Turn them all in at once and you could black out half the city to the whole province/state.
@@casperunnerup the exact multiplier may be different for different types of motors, but all motors consume more when starting. Some will take more than 10 times the rated current during start under load.
Great video Mathias! I work at a national lab as an EE and I do a lot of hands on stuff like your doing there. It is cool to see how much you think out side the box.
I enjoy watching these types of videos on this channel
And I can tell that you enjoy making them as well
Another great video keep up the good work
fun to watch. love seeing you experiment with building your own stuff instead of always reaching for a COTS solution.
I've been an EE for a LONG time. When I was relatively new at the job, an old timer pointed out that if you want to get rid of "noise" you have have have an energy consuming element. IOW: a resistor. Non energy absorbing elements (caps and coils) merely move the noise energy about.
I've got a spare Raspberry Pi (well, 10-20), an Adafruit ADS1115, and loose ethernet cable...I should give this a try! Well also a chinesium ADS1115 and some split current-sense coils, as I intended to do a similar power-monitoring project already. :D
I enjoyed that video. Watched whole thing in one go. Nice work.
Pretty interesting indeed, Matthias! 😃
Thanks for the lesson!
Stay safe there with your family! 🖖😊
This is so helpful! I'm planning to work out some kind of a current monitoring setup and see how many lines I can monitor off a single Pi. This single quick video covered about a few months of research and experimentation that I would have needed to do otherwise. Bravo!
I used to design inverters. I did similar testing, and the worst load that we had to deal with on an instantaneous basis was a compressor.
Great video. Very interesting. I've been interest in home energy monitoring for a very long time.
Two things: first try to find characteristic (time-current curves) of your circuit-braker, what is important there is to notice that it is just integral from i^2*t on chart. Second measure voltage without and with some restive load (electric kettle is good). Then from current with load and the voltage drop on your cables you can calculate impedance. I don't know exact english transcription but it is something like: external loop impedance. When impedance is high with installation overload (or even shortcircut) you get hot cables (and fire in long time) without breaker trip (because with big impedence, current is not big enough).
I am not sure that your fuses are well chosen....
I like your videos, so if you need something from mechatronic engineer just write me :)
Every time i pop the breaker at home i get pissed and here is Matt trying to pop one on purpose .Love your channels
Wow, what a fantastic video! Great content and so educational!
I had a number of ideas to measure the "mileage" of a thickness planer (or really any of our rotating tools). I think it would be fun to watch how much linear or squared feet of wood I've planed increase over time.
Measuring the current jump with such a coil when the cutting head engages the stock seemed like the best overall method.
What a fascinating video!
Most circuit breakers have a graph of time vs current for it to operate. After many years of electrical engineering, I'd say that a crude rule of thumb would be that a breaker will open when the surge current is 10x the breaker rating. But I have to say again, this is a very crude generalization, consult the manufacturers data, and then add in correction factors for age of the breaker and for the shape of the initial current surge. :-)
Really nice experimentation, thanks for time!
When there is a “dead short” there is a very high fault current. Much, much higher than what there is during an overload condition. Then the breaker will certainly trip.
My question now is why don't they make a clamp on transformer that fits nicely over 12-2 or 14-2 romex? It seems plenty sensitive, and that way most of the branch circuits in a home could be monitored right out of the box.
if you put the clamp ons in the breaker box where the wires are already separated when the hot is going into the breaker you don't need that?
it would need calibrating based on the wire geometry. I think I will make a wooden insert to go I to the hole to clamp it in a consistent position, then fasten it closed with a zip tie.
I would rather not introduce more stuff to the inside of the breaker box. breaker boxes are messy, with exposed line voltage.
@@matthiasrandomstuff2221 In my case, all the wires come out of the breaker box and are exposed to air for at least 6" above the box (which is bolted to my foundation wall), so I have plenty of access without even removing the cover.
I forget that many people probably have boxes that are _inside_ walls, which would make that a lot less appealing.
I'm using some DIN rail mount units I got on eBay for $16 each. They measure current, voltage & several other parameters with the ability to transmit that via a serial RS485 output. The downside is they need to be wired in series with the circuit to be monitored but they work quite well.
I used a clamp meter to verify that I was getting high spikes in the electric here. I found out both by capacitors blowing up and certain led lighting having bright flashes. Finally, they fixed the local transformer.
Love the video.
lol. I need to update my periodic table. Chinesium is not yet represented. I had to replay the video.
At the end…I realized you basically recreated THE FLUX CAPACITOR!
You’re a genius Doc!
Very good. This is the necessary part 2.
Very nice... exactly what I was looking for
Great work!
Really great work.🙆🏿♂️
A fun experiment. Thanks.
I wonder if the clone chip is based on the ADS1015 instead of the ADS1115. The 1105 is a 12-bit chip with higher sample rates. If the data interface of both is the same that's what I would bet on.
You can often request a breaker datasheet from the manufacturer. There they show how long it takes for the breaker to pop at a specific current. The graph is hyperbolic and if the current is
Great! Had fun watching it and learned something, thanks Matthias! :)
Interesting video as always. Measuring current is one thing, but you don't know the phase of the current with respect to the voltage. If you measure that too things will get even more exciting. And as for circuit breakers, they are designed to prevent your wiring from burning whilst not nuisance tripping from inrush current. Check out the characteristics for these things, the amount of current needed to trip the breaker is strongly dependent on the amount of time this current flows.
I always though you knew a lot about electricity for a woodworker, then I watched your intervew on WWMM's podcast.
This is some quality content.
I understood temperature sensors and iPad charger from this video.
The look @10:47 - that’s someone in their happy place!!
Haha, nice!
Very good video👌
Wow, really neat. I didn't realize you could do this over the wire pairs, thought you needed a single conductor thru the coil, like that clamp on transformer you showed. I have been curious about Hall effect current sensors too, but have so far been too busy and too cheap to buy one.
Damn cool work.
Interesting video Matthias. I'm always looking for "non standard" Raspberry Pi projects.
Call the fire department... Matthias wants to play with his Raspberry Pi....
If you look up your circuit breaker make and model and find the datasheet - there are trip curves associated with time to trip based on current load. There are levels for May trip, must trip, and never trip. all in one convenient place.
this is good content !
Mrs Matthias: "honey, why is the fuse box on the house on fire?" 🔥. 🙂
Matthias is now a member of the ThinkPad club
All of these experiments demonstrate why you need to understand that I=C*(dV/dt) and V=L*(dI/dt) better than any of my college professors could.
Just note: Breakers, or even old ceramic fuses, are made in my country with various "speed" characteristics. For example 10A normal will hold just a few amps over and goes off almost instantly, while "slow" one (old ceramic ones had snail shell printed on) can take peaks from devices like engines for few seconds and still keeps on without going off instantly.
I like how your brain works!
I have seen breakers stick closed when the inrush current was to great. It makes a terrible buzzing noise. It was a new installation, the neutral was wired directly to load.
I love these videos. It reminds me that I am not as smart as I think I am and that I probably just hang around really dumb people. 🤔
Cool Matthias! You designed a Sense energy monitor! LOL
Raspberry pi ftw
That was fun!
There are $10 smart outlets on Amazon that can measure current and are WIFI enabled. I’d probably try and use one of those with a pi but I love your DIY approach and problem solving. I recently bought an amp meter for the same reasons.
I have one. updates too slow.
Amazingly, I even understood a tiny bit of this....
Ha, me too!
Did you try a hall effect sensor against the wire?
Might want to check the loop impedance on that circuit to get an idea of whether it is limiting your fault current. Would be an interesting detail.
A few months ago my dust collector was failing to start and tripping the breaker. My first check was a current clamp meter over one conductor and it would get up to ~70a (120v) before tripping. And that's with a slow meter without a min/max function.
probably the startingswitch was failing to make contact, or a blown starting cap
Nice home made rogowski coil.
Hi Matthias, excellent work! I would suggest you try a coil transverse mounted to just one side of the romex. Thus trying to only sense the current in say just the black wire. Since the white and black carry opposite currents they are trying to cancel. Wind a coil and place it on the side of the romex.
please learn about electromagnetics, or try out your suggestion.
In Australia the short circuit trip current of a breaker is 7.5 times the breakers rated current. So if its a 16A breaker then the instantaneous trip current would be 120A. You should cut a wire to make it short circuit and see what current reading you get. Just use properly insulated tools
This is roughly how the 'Sense Energy Monitor' products work. They develop a sort-of fingerprint for devices that are plugged in and identified on the circuits into your breaker panel.
Yep and it’s also why they don’t work. Device signals change and they can be similar to other similar devices.
@@Mrcaffinebean Mine has been very accurate. It discerns the difference between my iPhone and iPad when plugged into the same charger for example. I think you're just being Mr passive-aggressive-not-so-smarty-pants.
Great video, it had self propelled scaffold levels of evergy and fun haha
How about making a self propelled step ladder for old times sake
in your dark blue coil you're wrapping the turns around the torroid of the loop. this will add noise to your signal. leave those out of the wrapping and use tape or something non-conductive.
Wants to measure current in power lines.
Matthias: Builds a complicated, safe, and effective system.
ElectroBoom: Plugs in cut and frayed wires to the outlet to measure.
Both are equally entertaining to watch.
Aren't ferrite rounds used for cleaning up the electricity? Wrapping the romex around a suitable ferrite donut could help.
I did understand a word you said.....'cept for chinesium.
I'm wondering what mechanism the iVac switches use. I know they clamp on the wire of the tool. I'm guessing it's similar where it's trying to cancel out part of the coil by positioning the clamp next to a single wire within the sleeve. Been wanting to do something similar to automate my workshop without splitting cords or creating my own extension cord with the split-wire. I tried a Hall Effect sensor too, but I got nothing from it.
If you're particularly fond of a spot of electronics development, a Rogowski coil is an interesting project.
Still gotta split the cable, though.
Mathias, wat would happen if you used braided shield, and what are your thoughts about using a ferrite choke shield on your sense coil?
Try two separate coils, one over the black wire edge and one over the white wire edge of the cable. Connect these coils in series in different polarities till you get the highest output.
Yup, your first attempt made a high-pass filter. With a resistor in series and a capacitor in parallel you get a low-pass filter (and the much-cleaner signal on your scope).
Would probably recommend a bandpass if he wanted that 60 hz only... or use a notch filter if he wanted to rid it from the signal
Very useful also if u have a wire like in europe. 3 in a triangle not in line and from exterior is a circle. The current transformer also not possible.
it would take some experimenting to find the best placement, but it would not be as sensitive.
The shield couples just one wire to the coil as long as it does not approach the centre of the current carrying wire. In the diagram the flux should be shown from the second wire going in the opposite direction. You may get better results if you wound the coil around the 'shield' which would then become a transformer core and then put the shield / core a bit less than half way across the wire.
Have you ever seen the sense energy monitors? They are pretty interesting but it is hard to swallow the initial cost. They can take awhile to pick up all your devices but it's awesome when you eventually get a lot of devices.
I don't think Matthias would be keen on their closed-source cloud smarts.
@@MordecaiV very fair point
If your coil had enough loops you could pass its output through a rectifier and filter cap to get a smoothed reading. More loops in the coil means more voltage allowing it to more easily overcome the forward voltage drop of the rectifiers and so it can be measured accurately by a lower-impedance device.
I already do a better job than that with the signal processing in the software.
That spike of current on startup is called inrush current.
I wonder if you could reduce the noise by making a second coil oriented in the opposite direction and connect them to a difference amplifier of some sort...
Instantaneous trip current is 6-10x rated current according to Schneider electric’s datasheet for square D style breakers.
Wow, your shop circuit is only 15A! And all those tools didn't trip it!
Very good measurements. I will say this though, I don’t think the pi setup is quick enough to measure the in-rush current. I went through this on an aircraft in where they use 28VDC but they have a radar system that is powered by 120VAC 3phase. In order for this to work, they use three separate inverters that are synchronized together.
When the operators would enable radars their monitors in the back would turn off and after a second or two turn back on. We did numerous load analysis tests on the aircraft and everything looked great, until we pulled out a more modern oscilloscope and tested across the main DC bus. When the radar was enabled, the 28VDC bus would drop to 0.0 VDC for 3 milliseconds.. yes, three milliseconds. The load analysis equipment we had would take at max 4 samples per second and didn’t see it. This short power interruption was caused by the capacitors inside the inverters. When first turned on, they act like a dead short across a circuit until they charge and therefore build resistance.
I’d be willing to bet that circular saw alone would be 150-200 amps for that 0-5 millisecond range until it spins up and induces its CEMF (counter electromotive force) or back EMF into the windings.
As always, I enjoy seeing your videos and it’s crazy what you have done with that Pi. It makes me want to get one lol.
I’m building a project van and should get something like this or a DC clamp meter so I can do load analysis and such for figuring out what my load is on the alternator to make sure I’m not going crazy. Shouldn’t be too bad as I’m switching out to LEDs and whatnot.
Keep up the great work!!
Yes, it may have peaked higher briefly. But the saw is an inductive load, not capacitive, so that inrush won't be as bad. Also, it's DC resistance is more than 1 ohn, so it couldn't take more than 100 amps.
@@matthiasrandomstuff2221 that’s smart. Didn’t think to consider the resistance of the windings themselves. You’re completely right. With that, as it spins up, the CEMF will further lower current as well. Thanks for the info and reply!!!
if you power your electronics connected to the Pi with a separate power supply it will help with noise a ton. Running them off batteries will work best for eliminating noise. The Pi has very dirty power.
👍
Have you looked at using a hall effect device to measure current? I would be interested to see if this would work?
Wouldn't that make it extremely difficult?
Hall effect sensors can only give proportional voltage by magnetic strength.
Magnetic strength is dependent on mu the permeability constant x the medium of travel multiplied by B field and dI/dT times the number of turns, which I assume is 1 in a single coil.... but then again stranded wires effect that too
Hey matthias, do you have any good resources about GPIO controlling with C in the raspberry pi?
This is great stuff. I'm just beginning to dip my toe into some of this.
Do you think the analogue to digital converter in a pi pico would work in place of the ADS115?
You need the circuit breaker manufacturers tripping curve.
Would hysteresis matter for an AC signal of constant frequency? (7:48)
Curious what the sample rate was of your A/D was and if the scrolling graph was a one to one in step? It looked to slow to be accurate to capture the spike loads.
If you kept reducing the sampling time, the instantaneous current would ideally keep increasing till it hits V/(impedance of transmission line). At that point neither the load nor the source affect the measurement. Surely that’s not what you wanna measure right?
4:11 and 12:03 what is the clamp on current transformer? I need one of those. where did you get it? how does it interface with the raspberry pi?
Damn, i'm too dumb for this video. I'm a woodworker, not an electrician or engineer and wish I understood these videos from matthias as well as I do his woodworking videos.
The white is neutral wire and connected to the ground in the breaker box. The alternate electric flows on the black wire from the breaker.
The alternating current flows on both the black and the white when a circuit is completed.
@@bradley3549 your right I'm just getting old.
I'm glad you shared this. I was curious how you had it set up. Did you consider using a commercial line splitter? I just looked them up (on Amazon) and noticed they are pretty expensive for what they are. I've thought about wrapping wire around one side of mine to sense current but I don't know the specifics of setting up the electronics to log it.
Why buy a line splitter when you can just split the line with a knife?
@@matthiasrandomstuff2221 For use in a commercial setting, a hand-made, short "extension cord" with loose wires would surely be frowned upon, over a commercially sold device. Also if you're demonstrating for friends/family, or checking in their home, they may feel more comfortable with a plastic encased unit.
For home use? Bring out the knife!
Can you tell me a good search word to find the small clamp on transformer?
current transformer