1.9kg Bafang motor

[Andrew harvey]

No.
The maximum power is not produced at maximum efficiency, typically this would occur towards the top of the speed range for the motor, whilst the maximum power is produced further down the speed range.

If the controller was able to supply more current than motor could draw then maximum power would be produced around half the no low speed.
At the no load speed the back emf of the motor is just below the supply voltage, within a couple of volts, the motor drawing only sufficient power to over come it's clogging torque. so at half this speed the back EMF would be half the supply voltage.
With the motor and controller sets we use the current is limited by the controller so we do not get maximum power at half speed.
For an SB motor with a 60A controller I've measured 44A at 36V supply at 12mph, the no load speed of the motor was 24mph. this gives a power output of (44 X 18)w, 792w.
With a 20 controller I was getting 44A on hill starts droping to 20/25A after the first inrush, the current fell to 20A as the bike accelerated until about 15mph, when the current started to fall of more linearly.
Given that the Back EMF is a linear function, a reasonable approximation for the output would be
15/24 x 36 x 20 = 450w
The 15/24 function is the reduction factor for the back emf compared to the supply voltage at 15 mph.
Please remember that these are backyard experiments so they can only be considered as approximations.

Back to efficiency, have you ever felt that you can get more out of your battery on days when your feeling energetic and going for it than on a normal day when your plodding to work, (my opinion ), you are not just adding more power but also running the motor in it's more efficient zone and hence getting more out .

 

[NRG]

The amount of power put into a PM motor is equal to the battery voltage times the current. The amount that is converted into mechanical power is equal to the back-emf voltage times the current. The conversion efficiency from electrical to mechanical energy is therefor simply the ratio of the back-emf voltage to the applied voltage.


Information about Hub Motors

Ah! Thanks Dan, that's cleared it up.

 

[jbond]

The 622 and 700c are the same thing, both 28"

Doh! my bad. Of course I meant 26" and 700c.

 

[NRG]

I've been trawling the endless threads on Endless Sphere(!) and whilst I've not sorted this out in my head yet it appears there's more to this than meets the eye....certainly with regard to the intelligent controllers like the Infineon based ones.

The current use Andrew observed on his bike could be accounted for by a setting for these controllers that multiplies the phase current at the expense of voltage so at half speed the motor could well be drawing more than the supply current. There's also a Blanking factor that can be set for x number of seconds to allow for high current draw during startup...effectively increasing torque for a brief period to aid acceleration from standstill. I need to go over threads again, there's a lot of noise and no single place where all this stuff is written.

I also found a couple of posts about calculating power output at the motor and if I've read them correctly the 1Kw electrical input I see on my Peugeot translates into 855W output at the motor.

On another tack I looked at the effect of voltage on wheel speed given the 3 speed settings I have on the bike. These seem to be programmed to 100%, 75% and 50%

I checked with three different battery voltages and the ratios remained the same so I was able to work out the motor Kv as 25.95 or 6.035 after the 4.3:1 gear reduction. Just over 2v for every 1mph @ 100% so on low speed setting (50%) a voltage increase raised the speed at half the 2v = 1mph ratio or 2v = 0.5mph

I use the low speed setting a lot and get around 7.5Wh from it compared 11~12Wh when on medium. Of course my average speed is lower at around 12~13mph vs 16~17mph but its curious to see that over the same route the peak input amps to the controller is very similar at 20 or so...more reading needed I think to understand what's going on.....

 

[jbond]

This is all on the Peugeot? Is the motor sensored or sensorless?

On a sensorless motor, I can't work out what frequency the controller is feeding the three wires. Is it timed to match the current motor RPM, presumably using the other two phases to work out where the magnets are?

My perception is that the BPM motor and SB controller produce just as much torque at low revs in all three modes. On a steep enough hill so that speed is below 11mph, the hill climbing ability seems to be the same. As if the motor is receiving 36v at max amps. And I kind of think that acceleration up to the max speed in each is the same. So 0-11, all three modes are the same, and 11-16 is the same between medium and high. So the modes are really just a max speed limit. But that doesn't match up with your voltage results.

 

[daniel.weck]

On a sensorless motor, I can't work out what frequency the controller is feeding the three wires. Is it timed to match the current motor RPM, presumably using the other two phases to work out where the magnets are?

I believe that the back-EMF of the hub motor is used by the controller to compute phase angles and to feed the 3 phase wires with suitable current bursts, removing the need for hall-sensors (and the 5 extra wires).

My perception is that the BPM motor and SB controller produce just as much torque at low revs in all three modes. On a steep enough hill so that speed is below 11mph, the hill climbing ability seems to be the same. As if the motor is receiving 36v at max amps. And I kind of think that acceleration up to the max speed in each is the same. So 0-11, all three modes are the same, and 11-16 is the same between medium and high. So the modes are really just a max speed limit. But that doesn't match up with your voltage results.

As far as I know, the 3 (configurable) levels correspond to current (A) limitations. In practice, this indeed results in various achievable top speeds, but the torque with an electric motor is pretty much always there from the lowest speeds.

Just from the top of my mind after a tiring day...so I could be wrong
Cheers, Dan

 

[jbond]

As far as I know, the 3 (configurable) levels correspond to current (A) limitations. In practice, this indeed results in various achievable top speeds, but the torque with an electric motor is pretty much always there from the lowest speeds.

That may be right, but I'm sure the 3 levels also limit speed/rpm. So in low mode, regardless of medium gradients up, down or flat, the bike does the same speed and the motor torque cuts at the same point. Going up a properly steep track in low, it will give me the full power of the motor and it wouldn't do that if it was current limited (compared with top)

I'd love to know exactly what the SB controller with it's 3 modes and throttle is actually doing. It feels like the 3 modes are 3 max speeds, with the throttle being able to cut this back. On top of this, I think there's a max current limit. Max speed in top seems to be roughly match the current limit with not much over-run so the slightest gradient drops the speed back a touch.

What I'm not sure about is if the throttle also makes the torque and acceleration variable.

 

[daniel.weck]

That may be right, but I'm sure the 3 levels also limit speed/rpm. So in low mode, regardless of medium gradients up, down or flat, the bike does the same speed and the motor torque cuts at the same point. Going up a properly steep track in low, it will give me the full power of the motor and it wouldn't do that if it was current limited (compared with top)

I'd love to know exactly what the SB controller with it's 3 modes and throttle is actually doing. It feels like the 3 modes are 3 max speeds, with the throttle being able to cut this back. On top of this, I think there's a max current limit. Max speed in top seems to be roughly match the current limit with not much over-run so the slightest gradient drops the speed back a touch.

What I'm not sure about is if the throttle also makes the torque and acceleration variable.

Yes, it looks like the ParamaterDesigner.exe firmware configuration tool uses threshold values in terms of a percentage of the max nominal speed (thus why position "high" of the 3-way switch can be 120%):

Endless-sphere.com • View topic - Infineon Controller Technical

Endless-sphere.com • View topic - NEW Crystalyte/Infineon controller LIMITED TO MED SPEED ????

There are still discussions about whether the 120% setting actually means 100% duty cycle + increased motor timing advance. Quote:

"
For a 2 pole motor, about 35-40deg advance results in peak mechanical power output possible for a given voltage.
For our motors with a zillion poles, just a few degrees results in a large effect.
"

 

[jbond]

The Alien Aurora apparently uses a motor-controller-handlebar switch set that all comes from SB. Is it possible that this is actually an Infineon (clone) board inside the controller?

 

[NRG]

This is all on the Peugeot? Is the motor sensored or sensorless?

Yes, my Alien GSII is single speed. The Bafang motor on the Peugeot uses sensors

On a sensorless motor, I can't work out what frequency the controller is feeding the three wires. Is it timed to match the current motor RPM, presumably using the other two phases to work out where the magnets are?

Can't provide an answer but I do know that the sensorless motor/controllers (the controller chip spec sheet I read) pulls one phase high, a second low and the third is used to sense the back EMF zero crossing point for position.

My perception is that the BPM motor and SB controller produce just as much torque at low revs in all three modes. On a steep enough hill so that speed is below 11mph, the hill climbing ability seems to be the same. As if the motor is receiving 36v at max amps. And I kind of think that acceleration up to the max speed in each is the same. So 0-11, all three modes are the same, and 11-16 is the same between medium and high. So the modes are really just a max speed limit. But that doesn't match up with your voltage results.

Yes, agreed although (I'll test today) I think on my bike Low may give more torque...anyhow it could be that in low mode the voltage is actually half and the current doubled...pure assumption on my part after looking at the ES threads....

 

[NRG]

It appears that on my setup medium not only gives a higher speed than low but also more power when climbing hills despite the current draw being broadly similar from the battery. Climbing a hill at 8mph in low and then switching to medium causes the bike to accelerate...

 

[jbond]

Curious. In response to the above I did a test today. There's a steep footpath nearby. I started on pedelec in low and it was doing about 9mph. Switch to med and then high and it made absolutely no difference. I think the SB controller on the Aurora is a slightly later version than the GSI/II Perhaps they changed the controller strategy.

 

[NRG]

The Gs II is single speed, this is on my home built Peugeot. It would appear the controller and setup is different to the Aurora.

 

[Andrew harvey]

The current use Andrew observed on his bike could be accounted for by a setting for these controllers that multiplies the phase current at the expense of voltage so at half speed the motor could well be drawing more than the supply current[

This is true, the motor current can at low speeds exceed te supply current, how?
The controller incorperates capacitors which charge up when the motor isn't drawing current and discharge when the motor is drawing current, so when the output mosfets are turned on you get the battery current plus the capacitor current through the motor. However if you try to calculate the motor power using this motor current you need in to include a factor for the width of the power pulse, on domestic Ac supply this would be your RMS, (root mean square ). As the tota power out put can never exceed the power imput the total amount of current drawn, ( amps x time ) can not exceed the total supply current. Reading the supply current you are in effect reading the average current at that speed / throttle setting, good enough for aproximating power out put.

I'd love to know exactly what the SB controller with it's 3 modes and throttle is actually doing. It feels like the 3 modes are 3 max speeds, with the throttle being able to cut this back. On top of this, I think there's a max current limit

How does the controller limit current?
The controller out puts are basically on/off switchs, they are on or off. The controlling factor is the time for which they are on or off, the controller limits current by shortening the pulse width, ( hence the name Pulse Width Modulating Controller ), you get the same peak current but for a shorter time. With the three speed setting you could aso have a limit on the frquency of the pulses, which would give full power at a particular speed but then above the the maximum speed set by the pulse frequency nothing.
In this instance you would get maximum power up to a set speed.

I think on my bike Low may give more torque...anyhow it could be that in low mode the voltage is actually half and the current doubled

What is the motor voltage?
The motor voltage driving the current is the forward voltage minus the back EMF, so at;
0mph back EMF=0V , motor voltage = battery voltage ;
At no load speed back EMF = battery voltage , motor voltage = 0V :
You then apply this across the speed range.

I hope this makes some sense, it's an awful long time since I studdied up on the subject.