Science, Physics, Math, & Myth

[madin88]

@ Hummina

first decide what top speed you want to have and than choose a battery voltage you need to achieve that speed.
this is usually better as using twice the voltage for instance but only using 50% throttle most of the time.

Just to add info for comparison, At interbike i spoke with the engineer of BionX and they confirmed to me that the stator of their new larger diameter motor is 1cm width. And that most of the motor structure is made of special plastic.

stator made of plastic is no good for cooling. hmmm..
have you asked them if we could buy the motor alone without electronic?

 

[John in CR]

Ugh. Where am I wrong here. A motor produces flux solely based on amps. Voltage will increase the amps going through but it's still just amps moving the motor. The voltage of those amps isn't important at the interface between wound too and magnet when it comes to making flux. Where did the volts go and what are they good for other than giving a higher potential top speed?

John this is/was my question but in your unrelated answer...you bring up a question. Are you saying running more voltsge than the esc can take is good with being easy on the amps? I imagine doing that would be with a specific esc or is it universal in what you're doing? Or maybe I'm wrong in what your saying. I thought there was no change in voltage from battery all the way to the motor regardless of speed it was running and it was just chopped on to off at different frequency.

Unrelated answer??? The motor does not get battery voltage. It gets what the controller steps the voltage down to. As LFP explains, our controllers are buck converters with a variable output voltage that varies as the motor needs for the rpm. Current sent to the motor determines the torque, and voltage determines the rpm. The conversion of DC pack voltage and current to 3 phase AC voltage and phase current takes place in the controller using PWM and switching between the phases. I'm not sure 3 phase AC is the correct term, but that's the result on each phase wire, because the current flows down one phase wire and back up another, and the switching between the 3 during commutation creates the alternating flow at the varying frequency based on rpm and number of magnetic poles on the rotor.

 

[Hummina Shadeeba]

Sorry John my question is the problem not ur answer.

I guess these are different esc than are used with skateboards and they vary the voltage. Wish they had these esc for skateboards.

My main question though has to do with how volts are used by the motor. I only read of induction being produced using amps. So what are volts good for other than increasing amp flow? I mean if there was a type of controller that could feed the motor the wanted amps for the load at a frequency that would vary the speed..not using the voltage..then I see no purpose use for voltage in the motor. (i know brushless motors use voltage in the back emf but forgeting brushless and just speaking of ...maybe just a brushed motor)

I know it's volts x amps is watts but is this synonymous with the speed times torque equation..and if you could vary the speed other than with voltage what would voltage's use in the motor? Voltage will increase the speed in the speed x torque equation possibly, but not necessarily, and therefore volts are not necessarily adding anything. so a battery with 100 volts would be a waste (wasted as what I wonder) when it's connected to a motor and spun at a very low speed as the motor is running on torque from amps and not utilizing the potential speed of the volts.

i guess what I'm wondering is do volts equate to watts if the motor isn't utilzing speed to get the watts, or are the volts just giving the possibility of speed and only therein would they add to the watts?

 

[amberwolf]

I guess these are different esc than are used with skateboards and they vary the voltage. Wish they had these esc for skateboards.

All of these ESC work the same--they all vary the average voltage to the motor.

i guess what I'm wondering is do volts equate to watts if the motor isn't utilzing speed to get the watts, or are the volts just giving the possibility of speed and only therein would they add to the watts?

The only thing that can equate to watts is watts, which is volts x amps. (unless you want to convert to joules, or another unit of energy measurement ).

 

[Hummina Shadeeba]

"All of these ESC work the same--they all vary the average voltage to the motor. "

i read the voltage is kept the same just the period of time it is fed to the motor changes, at least for typical hobby esc. "pulse width modulation"


The only thing that can equate to watts is watts, which is volts x amps. (unless you want to convert to joules, or another unit of energy measurement ).[/quote]

but if you have 100 volts and 1 amp put to a motor from a standstill the motor only recognizes the amps. It can build up speed through the voltage and then potentially have 100 watts of power but putting one amp through a motor at a standstill wont put out 100 watts even if the voltage is 100. right? maybe it could be amps x volts with enough time for the motor to spin up equals watts out. ?

maybe i'm missing something fundamental.

 

[amberwolf]

"All of these ESC work the same--they all vary the average voltage to the motor. "

i read the voltage is kept the same just the period of time it is fed to the motor changes, at least for typical hobby esc. "pulse width modulation"

Exactly correct, thus the statement I made, which you quoted above.

The only thing that can equate to watts is watts, which is volts x amps. (unless you want to convert to joules, or another unit of energy measurement ).

but if you have 100 volts and 1 amp put to a motor from a standstill the motor only recognizes the amps. It can build up speed through the voltage and then potentially have 100 watts of power but putting one amp through a motor at a standstill wont put out 100 watts even if the voltage is 100. right? maybe it could be amps x volts with enough time for the motor to spin up equals watts out. ?

maybe i'm missing something fundamental.

If you put 1amp at 100volts thru anything, that is 100watts.

If you get less watts, then you are not putting 1amp at 100volts thru it.

If you add time to the equation, you are now dealing with watt-hours, not watts. watts is only an instantaneous power value.

 

[d8veh]

Personally, I think it gives people the wrong idea when people talk about the controller controlling the voltage to the motor. It's not really a buck converter, it's a PWM power controller. Only battery voltage comes out of the controller. It comes in pulses. The amount of power only depends on the pulse width, which you could call current. It's true that the average voltage varies, but the controller is interrupting the current by PWM, so you could call it a current controller, which gives a better idea of what it's actually doing.

What happens inside the motor is different regarding voltage because of the inductance and eddy currents, etc.

 

[ferret]

but if you have 100 volts and 1 amp put to a motor from a standstill the motor only recognizes the amps. It can build up speed through the voltage and then potentially have 100 watts of power but putting one amp through a motor at a standstill wont put out 100 watts even if the voltage is 100. right? maybe it could be amps x volts with enough time for the motor to spin up equals watts out. ?

maybe i'm missing something fundamental.

I don't have enough knowledge for a detailed explanation, only a simplified one, but here goes:

In your example lets assume that the battery is a 100V one and the controller is set up to a limit of 1 battery Amp max and no limit for phase Amps.
With full throttle at standstill (or very low speed), the controller is pulling the maximal 1 Amp from the 100 Volt battery (100 Watt of power), the motor is pulling those 100 Watts from the controller as 100 Amps and 1 Volt and will be able to accelerate using the torque from the 100 Amps. As the speed increases, for example to half speed, the motor will pull 50V 2A and will have much less acceleration. At max speed, the motor will pull the full 100v at only 1A and will not be able to accelerate any more.

The law of energy conservation tells us that if the battery provides 100 Watts then the motor will use 100 Watts (in practice some of that energy will be lost as heat because the system in not 100% efficient). However, if the battery provides 100V the motor won't necessarily get 100V and if the battery provides 1A the motor won't necessarily get 1A.

It is similar to the way a mechanical gearbox acts. If a car's motor spins at 3000 RPM generating 100 foot pounds of torque, in direct gear (lets say 5th) the wheels will also run at 3000 RPM and accelerate a car with 30 foot pounds of torque, but in a lower gear (same motor RPM etc.) the wheels can spin at 1500 and accelerate a car with 60 foot pounds of torque.

Avner.

 

[madin88]

Personally, I think it gives people the wrong idea when people talk about the controller controlling the voltage to the motor. It's not really a buck converter, it's a PWM power controller. Only battery voltage comes out of the controller. It comes in pulses. The amount of power only depends on the pulse width, which you could call current. It's true that the average voltage varies, but the controller is interrupting the current by PWM, so you could call it a current controller, which gives a better idea of what it's actually doing.

What happens inside the motor is different regarding voltage because of the inductance and eddy currents, etc.

we should speak of VRMS and ARMS (root main square values). if we would do some measurements with an oscilloscope on the motor phases i think it will show pretty smooth values but this depends on inductance and probably other things (the motor should work pretty much like a coil in a buck converter)

 

[Hummina Shadeeba]

but if you have 100 volts and 1 amp put to a motor from a standstill the motor only recognizes the amps. It can build up speed through the voltage and then potentially have 100 watts of power but putting one amp through a motor at a standstill wont put out 100 watts even if the voltage is 100. right? maybe it could be amps x volts with enough time for the motor to spin up equals watts out. ?

maybe i'm missing something fundamental.

I don't have enough knowledge for a detailed explanation, only a simplified one, but here goes:

In your example lets assume that the battery is a 100V one and the controller is set up to a limit of 1 battery Amp max and no limit for phase Amps.
With full throttle at standstill (or very low speed), the controller is pulling the maximal 1 Amp from the 100 Volt battery (100 Watt of power), the motor is pulling those 100 Watts from the controller as 100 Amps and 1 Volt and will be able to accelerate using the torque from the 100 Amps. As the speed increases, for example to half speed, the motor will pull 50V 2A and will have much less acceleration. At max speed, the motor will pull the full 100v at only 1A and will not be able to accelerate any more.

The law of energy conservation tells us that if the battery provides 100 Watts then the motor will use 100 Watts (in practice some of that energy will be lost as heat because the system in not 100% efficient). However, if the battery provides 100V the motor won't necessarily get 100V and if the battery provides 1A the motor won't necessarily get 1A.

It is similar to the way a mechanical gearbox acts. If a car's motor spins at 3000 RPM generating 100 foot pounds of torque, in direct gear (lets say 5th) the wheels will also run at 3000 RPM and accelerate a car with 30 foot pounds of torque, but in a lower gear (same motor RPM etc.) the wheels can spin at 1500 and accelerate a car with 60 foot pounds of torque.

Avner.

I'm wondering what happens when the motor is fed one amp at 100 volts, from pretty much a standstill.

you can get watt hours with a different equal combination of amps and volts and it is the measure of stored energy of the battery but how does a motor utilize a volt. I only ever hear of inductance being produced from amperage. Or is an amp under high voltage different than not?

 

[flangefrog]

I'm wondering what happens when the motor is fed one amp at 100 volts, from pretty much a standstill.

you can get watt hours with a different equal combination of amps and volts and it is the measure of stored energy of the battery but how does a motor utilize a volt. I only ever hear of inductance being produced from amperage. Or is an amp under high voltage different than not?

You might have 100V at 1A on the battery side, but if you measure a motor phase you'll find you have 30A at 1V (ok, voltage probably won't be this low but you get the point). Here is a good link explaining how a buck converter works: http://www.learnabout-electronics.org/PSU/psu31.php The circuit in a ebike is very similar but the inductor (motor phase) itself is the load and the output capacitor is usually omitted.

 

[markz]

deleted

edited
Here is a good video, from timestamp 1:38
https://youtu.be/c96n0Ma2rLY?t=5891

Also 2:16 timestamp
https://youtu.be/c96n0Ma2rLY?t=8172

https://endless-sphere.com/forums/viewtopic.php?f=3&t=111422&p=1650979#p1650979

https://endless-sphere.com/forums/viewtopic.php?f=3&t=111422#p1651119


-----------------------------------------------------------------------------------------------------------

The Myth continues online............
https://www.electricbike.com/modified-hub-motor/

Eric Hicks

What are “motor winds”, and what does it have to do with anything?

In general, hub motors are either wound for torque, or wound for speed. It will act like a type of gearing that will decide if your hub motor is fast or its torquey. Motors wound for torque hold up a lot better when hot rodded, because in general, when you raise the voltage (which should raise the top-speed) and then the motor starts to bog down on a hill… the controller will start adding more amps to try and get the motor up to the higher speed you are commanding. The extra amps will mean more heat, and if the motor and controller get too hot…they will be fried.

If your system gets up to top speed rapidly, the controller will have only sent as many amps as needed to do that, and the “high amp” phase of your acceleration will be short.

The pic above shows two stators from the same model of RC motor. There is only so much room for “copper fill”, so the stator teeth can be wound with either many turns of small diameter wire, or fewer turns of fatter wire. A low turn count is a “fast” motor, and…many turns would make the motor spin slower when they both have the same volts applied. If you buy a MAC geared hub, they are listed by turn-count. A 6T is the fastest, and they also stock a 7T, 8T, 10T, and a 12T motor.

A fast 6T hub motor might get you up to 25-MPH in a 26-inch wheel when using an inexpensive 36V battery, but…it will bog down badly on a medium steepness hill. Lots of heat. If you wanted to reduce the hill-climbing heat, there are several things you could do.

Raising the voltage would add more horsepower (745-Watts = one-HP) so the motor would bog down less, but going from 36V to 48V would also raise the top-speed about 25%. At the higher voltage, a 6T going 31-MPH might be too fast for you, and you end up using “half-throttle”. Swapping to a higher turn-count motor (a slower wind) means you can use full-throttle, a higher voltage (for more power), and still maintain your desired top-speed.

The most common controllers support both a 36V battery and a 48V battery, the next bump up in controller power tops out at a 72V battery, and there are even controllers available that will support up to 100V.

 

[flangefrog]

Is the volts and/or amps split between the 3 phases?
Or are we into the wave making process. I did not realize the output of the controller was ac, or sinusoidal waveform, perhaps multiple or sin and cos and tan maybe.

Yeah sorry I made a mistake. The power will be concentrated into one phase (or possible two for a short time) at a time. On a sine controller all phases will be powered most of the time with different amounts to each phase based on the waveform.

 

[d8veh]

I still think it's better not to consider the controller and motor as a buck converter because that makes it difficult to understand the effect of he back emf. If you separate the two and look at the controller as a current controller, you can see how the current changes with speed. The above recent explanations don't take that into consideration.

 

[Hummina Shadeeba]

Is the volts and/or amps split between the 3 phases?
Or are we into the wave making process. I did not realize the output of the controller was ac, or sinusoidal waveform, perhaps multiple or sin and cos and tan maybe.

Split? I think when it's going to the phases it's been converted similarly to how a transformer transforms ac, except this is transforming dc. So converting the volts to amps. So someone tells me. Haven't read the buck converter thing and the rest in that great link yet but will. Thank you
you could say it splits the volts and amps between the 3 phases in that they are all receiving the same equal amount and ratio
some esc produce sine and some trapezoidal waves and there's some esc that produce shapes between the two. ( Ideally I think the wave shape fed would match what the motor will produce if it were used as a generator. )
The esc output isn't really ac In the typical sense although people argue about it.


But I still feel no one has answered the earlier question I asked as to what would happen with a 100 volts and 1 amp going DIRECTLY to the motor and what power would be produced immediately. 100 watts is an easy answer and maybe right but what do voltage do for induction if anything. At this point I'm still believing in such a scenario time to spin up the motor to the 100 x kv rpm speed is necessary to get that 100 watts. Maybe it's not a realistic scenario.

 

[Asterix]

But I still feel no one has answered the earlier question I asked as to what would happen with a 100 volts and 1 amp going DIRECTLY to the motor and what power would be produced immediately. 100 watts is an easy answer and maybe right but what do voltage do for induction if anything. At this point I'm still believing in such a scenario time to spin up the motor to the 100 x kv rpm speed is necessary to get that 100 watts. Maybe it's not a realistic scenario.

It's not a realistic scenario.
You try to equate a BLDC motor to a resistor, which it is not. It's more like a water wheel.
If you hold the terminals of a 100V battery directly to any two legs of your BLDC motor, the current will be so high that your motor will die.
In a normal situation, the controller (for a 120 degree motor) will only connect very briefly (the battery terminals) to two of the three legs, 1ms or less, then cut off the power, waiting for the motor to move a notch before connecting power to the next two legs. The current flowing through the coil causes the motor to turn a bit and also store up some of the energy inside the coil while the battery is connected. When the battery is disconnected, the back emf in the coil will replace the battery's voltage and continues to push the motor along until the enegy that the coil collected is used up and back emf drops to zero. The cycle will continue with the second two legs then the third and last two legs.
Let's assume that you have no load on the motor, the motor will spin up rapidly, the current intensity (Amps) will be much higher than 1A at first, then gradually drops as the motor gains speed, down to about 0.1A. If the motor is under load, then the current will drop to 1A and stays at 1A. If the motor is stalled, then the controller will detect this condition and cuts the current. You can only maintain a steady state of 100V and 1A at a particular RPM and particular load, chaing the load or changing the RPM will increase or decrease the current.

 

[zombiess]

what would happen with a 100 volts and 1 amp going DIRECTLY to the motor and what power would be produced immediately.

100V and 1A imply that you have a 100 ohm phase to phase resistance which is most likely not what you are after. I'm going to make the assumption you are trying to use DC equivalent being output by the 3 phase inverter.

You may only apply 100V, or 1A, if the phase resistance is < 100 ohms, not both. It's either voltage sourced or current sourced. The phase resistance would then determine the missing variable.

power = application of work over time. Not enough info here.

If the motor resistance (I'm ignoring effects of inductance for simplicity here) is 0.200 ohms and you apply 100V, the motor will draw 500A = 100V/0.2ohms. If you apply 1A to the 0.200 ohms then the voltage has to be 0.2V = 1A * 0.2ohms

As soon as a current limit is imposed, the voltage has to change. If you had 0.2ohms phase resistance and 100V of supply with a current limit at 20A, then the voltage applied to the motor would be 4V = 0.2ohms * 20A.

 

[cwah]

What's the best motor for 40-45mph top speed and mega acceleration?

 

[spinningmagnets]

Cwah, rear hub, or non hub with a left side chain (like the deathbike)?

 

[cwah]

hub would be better maintenance wise

 

[John in CR]

Define "best".

 

[cwah]

Best in term of efficiency, thrust and weight combined.

 

[amberwolf]

Cwah, I think this discussion needs to go in one of your project threads, and not in this discussion thread, which is not about which motor is best, but about how they work.

Perhaps Spinningmagnets can move it into whichever of your existing question threads you would prefer it in?

 

[Hummina Shadeeba]

I'm probably asking a question I've asked before and not getting the answer I want :? But, aren't amps the only force of inductance and therfore amps are what creates torque and not the voltage? I get that you need a high enough voltage to produce the amps over the resistance but at the heart of s motor is inductance coils and they run on amps? Are electrons with more energy, such as with higher voltage, more effective at producing a stronger magnetic field in a motor or is an amp an amp?
I'd like to believe simply that the value of voltage in a motor is its ability to push amps and possibly increase speed, and that's simple enough. As long as you're running the motor at roughly half of the kv x volts ...and the voltage is high enough to push the amperage you need...is there another function of higher voltage in a motor?

 

[ferret]

I'm probably asking a question I've asked before and not getting the answer I want :? But, aren't amps the only force of inductance and therfore amps are what creates torque and not the voltage?

Yes, (phase) amps create torque and the volts create the amps.


I get that you need a high enough voltage to produce the amps over the resistance but at the heart of s motor is inductance coils and they run on amps? Are electrons with more energy, such as with higher voltage, more effective at producing a stronger magnetic field in a motor or is an amp an amp?

An amp is an amp. It will generate the same torque in the motor. However since power (Watts) is the multiplication of amps by volts you will generate more power from the same amps at higher voltage.

I'd like to believe simply that the value of voltage in a motor is its ability to push amps and possibly increase speed, and that's simple enough. As long as you're running the motor at roughly half of the kv x volts ...and the voltage is high enough to push the amperage you need...is there another function of higher voltage in a motor?

To reach higher RPM. Max unloaded RPM=KVxV. If you're running the motor at roughly half of the kv x volts and end up moving at a walking pace you will want to increase voltage (or KV) to reach a speed that is useful.
Also with higher voltage you can make the same power at lower currents (Amps) which can be an advantage when selecting controller, battery, wireing etc.