Came for the oscilloscope measuring a capacitor charging, but couldn't resist listening to the song. RU-vid is a strange place where some things have just 68 views after 18 months.
Most informative! Your 10 yr old video provided more insight on how to use an oscilloscope than the dozens of recently posted videos that I have watched!
Why can't I get this to work with two motors connected in series, and the bases of all transistors connected to an arduino. If I only have one half of the bridge connected to the arduino it will work, but if I have both halves connected, it doesn't work. Using a 9v power supply connected to the collectors. Am I pushing current into the arduino somehow? Pretty new to electronics.
Ah ha, I see. So the back EMF is not visible to a multimeter because it is buried in the incoming voltage. It doesn't add to it, in a way similar to the way parallel batteries don't add voltage. Current driven in by a voltage source has a balancing effect on measured incoming voltage. Now I need some help to understand why with AC current and a start winding with a series capacitor, the voltage across the start windings is wildly greater than incoming voltage. I assume its visibility has something to do with the phase shift of voltage across the upstream capacitor? To balance, so that net phase is balanced, there needs to be a phase shift across the motor so the sum of the two is equal to overall incoming voltage.
There are two sources of current here: (1) the voltage applied to the motor by the power supply; (2) the Faraday/Lenz's law counter-EMF voltage created and increasing when the motor windings are passing through (rotating through) the magnets mounted inside the motor's casing So there is one "on purpose" current flow in one direction, and one "Faraday/Lenz's Law" current flowing in the opposite direction The second current is NOT on purpose. Nature forces that issue (Faraday/Lenz's law) because you're passing a coil through a magnetic field. So the currents DO ACTUALLY ADD. They are added together, as follows. A) assume the first current, put into the motor on purpose, is 2 amps (paid for on your electric bill) B) and Nature's response - the Faraday/Lenz's law counter EMF current - is (-1.9) amps. That's *_negative_* 1.9 amps THEY ADD TOGETHER AS FOLLOWS: 2 amps + (-1.9) amps = 2 amps - 1.9 amps = 0.100 amps, ie. that's 100 milliamps The 'on purpose' current and the counter EMF current always add together. It's just that Nature's current stiff-arms the current you pay for on your electric bill, and the addition becomes subtraction. The clarification added by this author is valuable -he shows with complete clarity that the counter EMF is subtracting from the EXPECTED current. This is valuable because it is not often made clear, even in formal courses in electricity/electronics. .
@@Greg_Chase I like the way you use current rather than voltage. What makes me confused is the way voltage measurement in AC motors with a start capacitor shows wildly higher voltage than incoming voltage. For example in a typical air conditioning motor, incoming voltage from source is fixed at 220V AC, but voltage measured with a multimeter across the start windings is typically 440V. It's reproducible enough to design a "potential relay" to cut current to the start windings after the motor spools up. I assume that the effect is purely in AC motors with capacitors inline, caused by the phase shift induced by the capacitor/inductor series pair, since a DC motor could not have higher than incoming voltage. Otherwise net current would move backwards into the battery, which is not sustainable! It's easy enough to model that AC voltage spike by considering the way induction of the motor coils increases as rpm increases. RLC circuit analysis can model those kind of voltage spikes. However conventional thinking would say that back EMF is more than simple passive induction. After all, hook it up properly to a source of outside mechanical power and you've got a generator. Or, is it?
@@spelunkerd Back EMF, whether DC or AC, easily exceeds input voltage. An example is a neon bulb - those require 90 volts to fire the plasma to light the bulb. But you can: 1) hook a 9 volt battery to a coil 2) let the five L/R time constants pass by (the magnetic field in a coil reaches near maximum after five L/R time constants have passed) 3) quickly disconnect the battery and allow the magnetic field of the coil to collapse, at which time it will create the Back EMF spike 4) it is common to use a 'snubber' or 'flywheel' diode across a coil to allow the Back EMF to quench 'peacefully' but if you have a neon bulb instead of a snubber diode - assuming the coil is big enough (ie. assuming a large enough magnetic field built up), you can fire the plasma in the neon bulb I have no experience with A/C systems though, have not looked at those circuits. Here is a common use though of Back EMF spikes: 1) create a primary winding coil of say 20 gauge wire 2) create a secondary winding of say 28 gauge wire, with 10x or 100x the number of turns in the primary winding 3) provide DC to one side of the the primary winding only 4) connect the other side of the primary winding through a MOSFET so that, when the MOSFET is turned on, a ground is supplied to that side of the primary winding 5) now, drive the gate of the MOSFET with a square wave from a signal generator The square wave will toggle the ground on/off at the square wave frequency. In other words, you allow DC to the primary winding then shut off the MOSFET to create the Back EMF spike. That large Back EMF spike is electromagnetically coupled to the much larger secondary winding, creating an immense voltage step up. There is a huge ecosystem of experimenters who use Back EMF for all types of circuits, including ionic lifters.
@@Greg_Chase You make a good point, intermittent DC is the basis of the spark plug coil. When supply current turns off, the coil becomes the primary voltage source, and coil polarity reverses to maintain current flow in the same forward direction. This inductive effect seems very different compared to back EMF and backward current in an electric motor.
@@spelunkerd It's a subtle issue, agreed. Because if you are applying the 9vdc battery to the coil, and suddenly disconnect it, it's as follows: 1) the magnetic field is reducing, suddenly 2) Faraday's law of induction + Lenz's Law means that the coil magnetic field will induce a current opposite the current causing the magnetic field change The magnetic field is falling. It could be falling for 2 reasons: 1) reduction of the original DC supply and DC current 2) or, a newly-introduced second DC supply and current that is opposite the original DC, and is mathematically thus subtracting from the original DC supply Both of those cases will make the original magnetic field decline. And the problem is, the magnetic field has no way of knowing: 1) "Am I declining, suddenly, because that original DC supply is declining?" 2) "Or am I declining because a second DC supply and current in the opposite direction was hooked into the circuit?" The declining magnetic field only knows that it is declining, and it responds with Faraday's law of induction + Lenz's Law and induces a current opposite the first, original current that is declining (reversing). In the case of a motor: 1) an original current created a first magnetic field in the rotor coil 2) this first magnetic field experiences torque against the magnetic field of the stator permanent magnet and the motor starts rotating 3) now we have a coil of wire rotating in a second magnetic field (the stator magnetic field) 4) and Faraday + Lenz will induce an opposite current + magnetic field in the coil So there are three magnetic fields in the motor: 1) a first magnetic field created in the rotor by the power supply 2) a second magnetic field - the permanent magnets in the stator 3) a third magnetic field - a subtractive, induced magnetic field in the rotor coil that subtracts from the first magnetic field So you're right, the mechanics of the Back EMF of a coil, compared to the Back EMF in the motor, are different, mainly due to the rotation of the rotor in the motor, which is not a factor in a standalone coil situation.. In the end, Faraday + Lenz behave the same - seeking to oppose the current and magnetic field that were initiated by an external power source.
At 7:15 it says _"Because we have a coil rotating within a magnetic field, a voltage will be induced across the coil which is in opposition to the supply voltage."_ I agree with the first part of the sentence, but should the latter part not read this: *_... a voltage will be induced across the coil which is in opposition to the supply CURRENT._* Hence the back-EMF _impedes_ the current. The total load on the supply voltage (being a 'voltage' source) is the DC resistance of the coil plus the back-EMF equivalent _impedance_ that determines the current. The 'voltage' source of the supply does not change. We do end up with a voltage across the DC resistance R*I=V and as you say, that is the 'real' voltage. We can also calculate the heat being dissipated here, that smaller V, V*I. Which view is correct, or are they both depending on how you look at it?
Well done. You should try that same concept, except to have the solenoid move in more steps, using something like percentage of a range, so the warmer it gets, the more it opens a window... or so that a servo could be used to move a needle on a mechanical temperature gauge.
@@diegoespinoza3492 I have set a link to the sketch in the description, sorry it took so long but I have other priorities these days :) Hope it works out for you.
Just picking up the piano after the death of my mother used to play Boogie woogie and Rock n roll piano, but I can't now so thank you very much for your version of Love on the Rocks it's got me back on the keys cheers Paul, Nice piano sound to.
Not everyone knows what minor and majors are. He FAiLED to NAME EACH keynote / CHORDS by letters! He DUB his voice in LAST recording, that sounded better. Neil's voice is actually Baritone range.
I tried this method on an outrunner bldc motor without removing the housing. I wasn't getting anywhere trying to reach a common voltage. I suspect it could be because of the magnets still attached to the housing. Anyway thanks for the video!
