Mar 09, 2015, 04:26 PM Registered User Joined Jul 2014 249 Posts Discussion voltage equals flux or torque? if you look at the coils in a motor as if they were a transformer, when you supply a given amount of amps they are stepped up a lot of voltage as it's presented in the air gap. given two motors which are the same other than the amount of turns, the one with more turns will produce more torque given the same amount of amps. Cant you therefore say that the motor with many turns is producing a much higher voltage in the air gap and the volts equate to torque?
 Mar 09, 2015, 06:43 PM Condescending Pedant Joined Aug 2013 1,194 Posts The motor torque comes from the amount of current flowing through the conductors and the number of conductors in the magnetic field. Essentially given two motors with the same magnetic properties it is the amperes X turns that determines the torque. So in your example the motor with twice the turns and the same amperage will develop twice the torque of the other motor. There is no voltage generated in the air gap.
 Mar 09, 2015, 06:59 PM Registered User Joined Jul 2014 249 Posts if this more turn motor(which gets more torque per amp) were viewed instead as a transformer, it would be considered a step-up transformer and therefore be converting its fed amperage into voltage. this voltage would go through an air gap to the secondary transformer. cant we say step up transformer produce more flux and voltage than step down transformers?
 Mar 09, 2015, 07:15 PM Condescending Pedant Joined Aug 2013 1,194 Posts In a transformer there are two windings per phase. One winding has power supplied to it from an AC source. If you take the voltage applied to this primary winding and divide it by the number of turns in the primary winding you will have the volts/turn for the transformer. Now on the same iron core of the transformer will be a second winding. This winding will have roughly the same number of volts per turn of the winding. If there are more turns than the primary then you will have a step up transformer. If there are less turns than the primary you will have a step down transformer. Now here is the secret of a transformer. The volts X amps of the primary will be the same as the volts X amps of the secondary. There is no power gained or lost (actually there is a small loss due to iron and copper losses in the transformer) just a change in voltage level. Again there is no voltage generated in the air gap of a transformer either. there are just magnetic lines of force in the air gap. Actually in a transformer there is no appreciable air gap anyway, unless it is a coreless transformer, which would be operated at very high frequencies and would be for use in RF applications. Our brushless permanent magnet DC motors can in no way be compared to a transformer, at least in any useful way. Last edited by Mike Dubovsky; Mar 09, 2015 at 07:22 PM.
 Mar 09, 2015, 07:25 PM Condescending Pedant Joined Aug 2013 1,194 Posts Ooops! Ain't technology wonderful?
Mar 09, 2015, 07:33 PM
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Quote:
 Originally Posted by Mike Dubovsky ...... Our brushless permanent magnet DC motors can in no way be compared to a transformer, at least in any useful way.
I look at a motor as a transformer between electrical power to mechanical. Power in is related to power out (with efficiency in between). That's why for the same stator design, power in is only a function of volts*amps. Kv just allows you to make the transformer primary winding (electrical power in) match the mechanical power out.

Not exactly what you meant--I know-- but nevertheless an interesting equivalent--IMHOQ.
 Mar 09, 2015, 07:54 PM Registered User Joined Jul 2014 249 Posts i know there's no magical energy generated and with a transformer its transformed up or down in voltage. Transformers are AC but if you made an electromagnet, dc, and it had a lot of turns, similar to a step up transformer, instead of equaling a possible change to higher voltage, if the current were constantly switched, you get a stronger magnet. I'm skipping the big important AC part and the transformer with multiple turns will net zero flux as it's constantly switching and reversing polarity. but what's happening in slow mo... I'm imagining with many turns in a transformer, as the coil is building it's magnetic field, which would take a bit of time, all is fine, and then maybe it collapses and has a voltage spike? but it's a sine wave and I dont think that would happen. So imagining a huge step up transformer I think at 60hz maybe it never has time to fully develop a magnetic field and..so...? if you can do the slow mo for me I'd appreciate it Last edited by Hummina; Mar 09, 2015 at 10:44 PM.
 Mar 09, 2015, 09:21 PM Registered User Joined May 2012 166 Posts You can't look at a motor like a transformer. A transformer uses a changing electrical current in the primary winding to generate a changing magnetic flux which couples to the secondary winding to generate an electrical current. The transformer requires a changing electrical current on the input to generate an output. If you put DC in to a transformer you get nothing on the output. The magnetic field generated by the primary has to change to induce current flow in the secondary. In contrast, a motor uses a winding to generate a magnetic field that interacts with another magnetic field. A DC voltage on a motor winding generates torque because DC flowing through a wire makes a constant magnetic field. The AC that actually drives a brushless motor isn't AC in order to excite the magnetic field, it's required to switch the field direction in order to get the motor to turn. To most-efficiently run a brushless motor, the electrical current needs to be sinusoidal. That's because you're driving a coil which has inductance, that's moving through a permanent magnet field that generates back EMF. You can drive a brushless motor with a simple square wave, though. It'll heat up due to the effects that square wave has when it tries to flow through the coil's inductance, but it'll run.
Mar 09, 2015, 09:49 PM
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Cats and oranges

Quote:
 Originally Posted by Hummina if you look at the coils in a motor as if they were a transformer, when you supply a given amount of amps they are stepped up a lot of voltage as it's presented in the air gap. given two motors which are the same other than the amount of turns, the one with more turns will produce more torque given the same amount of amps. Cant you therefore say that the motor with many turns is producing a much higher voltage in the air gap and the volts equate to torque?
An electric motor is not a transformer, and the reverse is also true.

For descriptions on how our brushless motors work, here is some information.

Microchip ESC Info
 Brushless DC Motors & Control - How it Works (Part 1 of 2) (10 min 33 sec)

And, something I did awhile back, showing our brushless motors can be either a three phase synchronous motor, or three phase alternator. FYI, our automotive alternators have three phase windings inside them.

 Three Phase Alternator and Motor (0 min 23 sec)
 Mar 09, 2015, 09:57 PM Registered User Joined Jul 2014 249 Posts I appreciate the help But I know how a brushless motor works I think u can look at a motor in some regards like a transformer. They're both inductors. They both have an output based on turns. They both operate with flux. The only difference is one ac and the other dc. That difference is a lot though. The only real difference is time maybe as ac is the same thing but just for shorter intervals. A transformer on for half a cycle is..pretty much a motor. My question is what is happening in those tiny fractions of a second which include maybe just one cycle of the current. It's a sine wave so no collapse which would cause a voltage spike, and that's the only thing I know about it. What about at 1hz what would happen to the voltage/amp ratio? The only variable I can think of is the time it takes to develop the magnetic field in relation to the speed of the switching cycles Is flux just flux and independent of volts and amps and only perceivable as volts/amps when it transforms back to an emf? Last edited by Hummina; Mar 09, 2015 at 11:11 PM.
 Mar 09, 2015, 10:48 PM Condescending Pedant Joined Aug 2013 1,194 Posts Really, the discussion of how a transformer works is not within the scope of what we are discussing in this particular forum. A motor is often called an electrical machine, because as the videos above illustrate it can both consume and produce electrical power. I would not call it a transformer. Perhaps a converter as it converts electrical power to mechanical or vise versa. But the accepted term is either motor if it is consuming electrical power or generator if it is producing electrical power. If you start throwing out your own terms for what it is it only adds confusion and contributes nothing toward anyone's enlightenment.
 Mar 09, 2015, 11:10 PM Registered User Joined Jul 2014 249 Posts I'm not saying any homemade terms and just trying to figure how one coil of wire is different or similar to another . Is this the wire coil section or what? We could argue about if it's even a ac or dc coil forum as well. A transformer is a close cousin and I'm trying to figure where the split happens I'm on wiki trying to put my mind at rest but was hoping one of the people here could put it in dumby-speak. They are very similar obviously and the only real difference I've come across so far is the time variable which comes with ac. And they're sine waves solely but motors will do that too. Will u get a specific voltage if you physically pass an electromagnet with a certain amount of coils past another? Maybe an ac current works effectively as a constant hand passing an electromagnet past a second. I have no multimeter and must work solely in the theoretical! Will one pass of an electromagnet past a second coil produce a voltage and current with the same results as an ac current? I'm not trying to confuse but I think it's fair to say throwing light on a transformer further explains a motor.
Mar 09, 2015, 11:56 PM
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Quote:
 Originally Posted by Hummina I'm not saying any homemade terms and just trying to figure how one coil of wire is different or similar to another . Is this the wire coil section or what? We could argue about if it's even a ac or dc coil forum as well. A transformer is a close cousin and I'm trying to figure where the split happens I'm on wiki trying to put my mind at rest but was hoping one of the people here could put it in dumby-speak. They are very similar obviously and the only real difference I've come across so far is the time variable which comes with ac. And they're sine waves solely but motors will do that too. Will u get a specific voltage if you physically pass an electromagnet with a certain amount of coils past another? Maybe an ac current works effectively as a constant hand passing an electromagnet past a second. I have no multimeter and must work solely in the theoretical! Will one pass of an electromagnet past a second coil produce a voltage and current with the same results as an ac current? I'm not trying to confuse but I think it's fair to say throwing light on a transformer further explains a motor.
Yes, any magnet moving past a conductive material will generate a voltage in that conductive material. The more turns that conductive material has, the more voltage will be developed. Adding steel to the combination results in a stronger magnetic field, winding up with more voltage generated.

As an extreme, I've got some very high powered samarium magnets that will lift 400 pounds on a steel block. If you place that magnet along side of a piece of aluminum plate 3/8 inch thick and two feet long, then rapidly slide it down that plate, you will feel a lot of resistance to moving that magnet.

What is happening is, that magnet is generating voltage and current in that aluminum sheet. I actually measured it, the voltage is miniscule, but the current generated was some 1000 Amps in that piece of aluminum plate.

You will get the same effect if you drop a high powered magnet down inside a copper or aluminum pipe. That magnet is generating short circuit currents in the pipe, and will really slow down the magnet falling down through the pipe.

So, any magnet moving through a coil of wire will generate voltage in that wire. The magnet has to be moving. If not, you get no voltage. Or, any current passing through a coil of wire will generate a magnetic field. If you rapidly move that magnet in and out of that coil of wire, you will see AC voltage on the coil of wire's terminals.

FYI, if you'd have known this in the early 1800's or so, you would have been a genius!
 Mar 10, 2015, 01:20 AM Registered User Joined Feb 2015 23 Posts AC induction motors can be and often are modeled in a similar way to how transformers are modeled. And intro to electric machine textbooks very often start off by teaching about transformers before they get to motors. But I have never in my life seen a brushless motor modeled in a similar way to how a transformer is modeled. It just isn't done (because they aren't that similar). To answer your first questions ... there is no "voltage in the air gap." That isn't a correct way to think about motors.
 Mar 10, 2015, 08:42 AM Dieselized User Chicagoland Joined Feb 2000 7,533 Posts