DaveThomasPilot

Current demand versus battery voltage

73 posts in this topic

On 7/9/2017 at 9:14 PM, Rehab1 said:

Is the rider still alive?:confused1:

Those pedals are so long that you can probably plow farm fields whith them. LOL.

my MCM4 pedal are too low to make longer. As they already are too easy to snag on slow tight turns. 

I suppose longer pedalnwill require shorter hanger so they don't scrape the road on thought slow turns 

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On 9.7.2017 at 0:09 PM, Rehab1 said:

Congrats! This a well thought out concept. So how can we test out your theory? 

Just found all the dc motor theory from an electronic bike course from a german college well summarized - but just in german... 

https://ces.karlsruhe.de/~BUB/Umwelttechnik/Elektromobilitaet_TGJ14_2012.pdf

... have to look into the details, if something has to be adopted - but seems "congruent " so far...

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Posted (edited)

On 7/9/2017 at 11:46 AM, Chriull said:

This time the values are:

U Batt average: 72,8V

U Motor Average: 18V

IMotor Max:53A Average: 41,8A Min: 30,6A

IBattery Max: 53A Average: 11,7A

PMotor: 756W

P Batt: 800W

P Mosfet: 20W

P D2: 28W (1)

(One sees here a new Voltage: V(p002) which is the voltage across Uback_emf and R2, since V(n003) the same with additionally L1 delivers an phase shifted part and not real power...)

The values seem to correlate quite good with the excel sheed - just the I Battery Max is not to be calculated easily. This also would depend on the "state" of L1

Edit: (1) ... so hopefully all wheels have active free wheeling implemented...

Don't know if you already noticed, but you can graph the power of components by holding down ALT while you click on the component in the schematic. Clicking the "title" of a graph line (like "V(n001)") with CTRL held down show you the average and integral of the currently visible graph line.

Example from a simple short-circuit -protection circuit, viewing the power dissipation graph of the load (R6) and average + integral power:

yUw62b3.png

Edited by esaj
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On 22.6.2017 at 3:52 PM, zlymex said:

 

Yesterday, I rode up a very steep hill, I monitored Id by Wheellog that even reached to 90A, and the temperature has gone up to 70 degree C.

SkiHill.thumb.gif.5e44fecaccd9fbc20c07ad7d24dd68e2.gif


In most cases, Id is larger than Ib, sometimes twice or even larger. However, the battery is not bare this PWM spikes because there is a capacitor(two for GW) paralleled with the battery input.

 

@zlymex: cold you send me the data of such a ride with motor current, battery current, speed and battery voltage?! Maybe also wirh some more different (higher) speeds ridden :ph34r:

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On 12.7.2017 at 4:30 PM, esaj said:

Don't know if you already noticed, but you can graph the power of components by holding down ALT while you click on the component in the schematic.

Great - till now i always had to enter manually someting like (v(n002)-v(p003))*id(m2) ....

On 12.7.2017 at 4:30 PM, esaj said:

Clicking the "title" of a graph line (like "V(n001)") with CTRL held down show you the average and integral of the currently visible graph line.

This one i already got by accident :ph34r:

can one also give a readable name to V(n001) like U_Batt which is shown in the graph? I just tried somthing like label network, but the graph ignored it!

 

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Posted (edited)

33 minutes ago, Chriull said:

can one also give a readable name to V(n001) like U_Batt which is shown in the graph? I just tried somthing like label network, but the graph ignored it!

Yes, but you must click the label, not the net it's attached to to see the name in the graphs, and you can't get current or power information from it (like with the "wires").

EDIT: Actually it should work just by clicking the wire the label is attached to. Weird if it doesn't work, is the label correctly attached to the network? And you haven't been using something like params or comments by accident? ;)  You can't label components, but you can change their names (like "R_load" instead of "R<some number>", same for others).

Edited by esaj
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2 hours ago, Chriull said:

@zlymex: cold you send me the data of such a ride with motor current, battery current, speed and battery voltage?! Maybe also wirh some more different (higher) speeds ridden :ph34r:

Data record sent together with the GPX file.
A higher speed data file is also sent, which is the 100km one with max speed 44km/h(according to Wheellog, but 41 according to GPS): 

 

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On 15.7.2017 at 2:40 PM, zlymex said:

Data record sent together with the GPX file.
A higher speed data file is also sent, which is the 100km one with max speed 44km/h(according to Wheellog, but 41 according to GPS): 

Thx! I combined the GL220 and the wheellog data by averaging all the values within a 1 sec intervall and ignored each values where the Gl220 showed negative current (regen braking - there the circuit works differently and is not "of interest" for this)

So i have Speed, U batt, I batt and I Motor. P batt = U batt * I batt = P motor = U motor * I Motor -> U motor = P batt / I Motor. And U Back EMF = U Batt - I motor * R coil.

In this case (for simplicity) R coil includes also the on resistance of the mosfets, the wirings and connectors...

So we get kv = U Back EMF / v.

Plotting U back EMF over time (while you got up the hill) gets "level" with a Rcoil of 0,25..0,27. With Rcoil < 0,25 it rises over time, with rcoil >0,25 it decreases over time. No real idea why but imho this Rcoil of 0,26 seems to be a fine value?

With this the average kv (V/(km/h)) is 1,2 and has a max value of 1,95 and a minimum of 0,82. Could be that the measurements where not exactly synchronous? Or the inductance of the motor would have to be regarded? Or also the whole inertia of the system, which acts comparable to the motor inductance? ...

Anyhow - with this kv the maximum no load speed at a battery voltage of 67,2V would be 56 km/h, at 60V 50 km/h. (Seems a little low for this wheel with 45 km/h max speed?) The lift cut off speed should be a little bit less than these values. Are they sane for the MSuper v3? - This could be maybe the better way to get a nice kv number - compare lift-cut off speeds at different battery voltages?!

For now I put this values of your uphill ride in a Motor Current (A) over Speed (km/h) diagramm:4sXUrSA.png

Together with the motor and firmware limitations. Would be a nice addition to any app - knowing this wheel values and showing some safety value with warnings to prevent overlean?

 

 

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11 hours ago, Chriull said:

Thx! I combined the GL220 and the wheellog data by averaging all the values within a 1 sec intervall and ignored each values where the Gl220 showed negative current (regen braking - there the circuit works differently and is not "of interest" for this)

So i have Speed, U batt, I batt and I Motor. P batt = U batt * I batt = P motor = U motor * I Motor -> U motor = P batt / I Motor. And U Back EMF = U Batt - I motor * R coil.

In this case (for simplicity) R coil includes also the on resistance of the mosfets, the wirings and connectors...

So we get kv = U Back EMF / v.

Plotting U back EMF over time (while you got up the hill) gets "level" with a Rcoil of 0,25..0,27. With Rcoil < 0,25 it rises over time, with rcoil >0,25 it decreases over time. No real idea why but imho this Rcoil of 0,26 seems to be a fine value?

With this the average kv (V/(km/h)) is 1,2 and has a max value of 1,95 and a minimum of 0,82. Could be that the measurements where not exactly synchronous? Or the inductance of the motor would have to be regarded? Or also the whole inertia of the system, which acts comparable to the motor inductance? ...

Anyhow - with this kv the maximum no load speed at a battery voltage of 67,2V would be 56 km/h, at 60V 50 km/h. (Seems a little low for this wheel with 45 km/h max speed?) The lift cut off speed should be a little bit less than these values. Are they sane for the MSuper v3? - This could be maybe the better way to get a nice kv number - compare lift-cut off speeds at different battery voltages?!

I believe that the kv value(V/kph), as a parameter of the motor, can be regarded as a fixed value. The indirect measurement and calculation says otherwise, is probably because there are two much spikes(of current/torque) which in turn caused by the rough surface  of the hill path.

U batt * I batt = P motor, this equation is missing the efficiency of the main board, although may be as high as 95%, it may also be lower when hill climb where current is large. And the efficiency may be changed a lot because the current/torque spikes.

The actual current/torque spikes may be larger than I've measured because the sample intervals(0.2 second by Wheellog and 0.1 second by GL220) are not small enough. I've once seen an ad saying that the adjustment speed(from the gyro input to the motor) top up at 100 times per second.

Plus, how Gotway makes use the two current sensors and how gives away the current parameter remains a question mark.

I guess a better way to obtain the kv is the later method you mentioned: by lift test. I've measure my V3/V3s+(same motor) to be 53.5kph and 68.6 respectively when battery is full. This will give roughly 1.2V/kmp if deduct 2V(presumed) from the battery as an dead zone.

11 hours ago, Chriull said:

Together with the motor and firmware limitations. Would be a nice addition to any app - knowing this wheel values and showing some safety value with warnings to prevent overlean?

I actually plotted a preliminary limit chart for this, those green-dots part is the uphill data that I sent to you(but without averaging), and purple circles is the downhill part with regenerating(which should be bounded by the lower half of the orange line).

http://forum.electricunicycle.org/topic/5915-is-there-any-other-app-i-can-use-for-my-msuper-v3-besides-the-one-on-the-app-store/?do=findComment&comment=71144

Wheellog btw is very good, I use 50A current warning(50A is the max., I hope more such as 70A because I always receive the warning when up/down hills while I know is quite safe), and 40kph speed warning. What Wheellog lack is the power warning(the so called 80% power warning is bu****it!)

Apart from this kv value(which is a very nice parameter) that describe one very important aspect of the BLDC motor(back-EMF is proportional to the speed), there should be another parameter describing 'torque is proportional to the motor current'.

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Posted (edited)

See below

Edited by DaveThomasPilot
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Posted (edited)

Quote

I was replying to a post that seems to have disappeared.  Since that post seems to have been deleted, I'm deleting the reply.

 

 

 

Edited by DaveThomasPilot
I was replying to a post that seems to have disappeared. Not sure what's going on, but I deleted what I was posting also.
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On 7/12/2017 at 9:30 AM, esaj said:

Don't know if you already noticed, but you can graph the power of components by holding down ALT while you click on the component in the schematic. Clicking the "title" of a graph line (like "V(n001)") with CTRL held down show you the average and integral of the currently visible graph line.

Example from a simple short-circuit -protection circuit, viewing the power dissipation graph of the load (R6) and average + integral power:

yUw62b3.png

What program is that. 

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7 hours ago, zlymex said:

I believe that the kv value(V/kph), as a parameter of the motor, can be regarded as a fixed value. The indirect measurement and calculation says otherwise, is probably because there are two much spikes(of current/torque) which in turn caused by the rough surface  of the hill path.

Yes - it is a fixed phase and i also think the spikes (not really all measured and not timely from wheellog and the gl220) lead to "distortions". Also the inductance of the coils and the inertia of the whole system could "influence" this value... Imho kv is only valid in a stable state of the system?

7 hours ago, zlymex said:

U batt * I batt = P motor, this equation is missing the efficiency of the main board, although may be as high as 95%, it may also be lower when hill climb where current is large. And the efficiency may be changed a lot because the current/torque spikes.

I regard the motherboard losses included in the "coil resistance" ;) It should be mainly the mosfets and they should be burdened more or less with the motor current (depends a bit if the body diodes are used for freewheeling or active freewheeling is implemented, switching losses are also somehow related to the motor current...)

7 hours ago, zlymex said:

The actual current/torque spikes may be larger than I've measured because the sample intervals(0.2 second by Wheellog and 0.1 second by GL220) are not small enough. I've once seen an ad saying that the adjustment speed(from the gyro input to the motor) top up at 100 times per second.

If also read this 100 Hz already somewhere. With the PWM frequency of ~6 kHz even 60 times more adjustments could be made...

7 hours ago, zlymex said:

Plus, how Gotway makes use the two current sensors and how gives away the current parameter remains a question mark.

:D

7 hours ago, zlymex said:

I guess a better way to obtain the kv is the later method you mentioned: by lift test. I've measure my V3/V3s+(same motor) to be 53.5kph and 68.6 respectively when battery is full. This will give roughly 1.2V/kmp if deduct 2V(presumed) from the battery as an dead zone.

Gives fortunately a 100% hit ;)

7 hours ago, zlymex said:

I actually plotted a preliminary limit chart for this, those green-dots part is the uphill data that I sent to you(but without averaging), and purple circles is the downhill part with regenerating(which should be bounded by the lower half of the orange line).

http://forum.electricunicycle.org/topic/5915-is-there-any-other-app-i-can-use-for-my-msuper-v3-besides-the-one-on-the-app-store/?do=findComment&comment=71144

Yep - now seeing it i remember!

7 hours ago, zlymex said:

Wheellog btw is very good, I use 50A current warning(50A is the max., I hope more such as 70A because I always receive the warning when up/down hills while I know is quite safe), and 40kph speed warning. What Wheellog lack is the power warning(the so called 80% power warning is bu****it!)

Wheellog is not knowing the power - as the original apps! They only have motor current and battery voltage. 

It would have to know kv and Rcoil of each wheel to calculate a real power value (U Back EMF = kv * v, U motor = Rcoil * I motor +U Back EMF-> P = U motor * I motor - Or just U back_emf * I motor which is without ohmic motor losses?)

7 hours ago, zlymex said:

Apart from this kv value(which is a very nice parameter) that describe one very important aspect of the BLDC motor(back-EMF is proportional to the speed), there should be another parameter describing 'torque is proportional to the motor current'.

I imagine to remember that this two parameters are the same. kv is in reality U / rotations per second so has the unit V*s with V=N*m/A*s this leads to V*s=N*m/A. Which is the unit of the factor torque/current.

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Posted (edited)

11 hours ago, zlymex said:

I actually plotted a preliminary limit chart for this, those green-dots part is the uphill data that I sent to you(but without averaging), and purple circles is the downhill part with regenerating(which should be bounded by the lower half of the orange line).

That's right - here the original wheellog data can be taken. Just the regen currents are now wrongfully shown as with positive current...

I added (quite) some lines to this dot Diagramm:

First the max current over speed lines for max Battery Voltage (67,2), nominal Battery Voltage (60V) and minimal Battery Voltage (55V). Seems that from the 55V the max speed of 45 km/h was taken... ;) 

Then the currents for continous power of 1500W and for max power of 3000W. One of these lines is with regard of Rcoil (so the power put into the motor) and the other is without Rcoil (should be about the motor output power)

As seen from the graph - the 3000W motor output power can never be reached - this line is above the max current vs. speed limit with 67,2 V Battery...

I also included one line for the currents resulting to a output power of 2,4kW as @EcoDrift has measured as max power of a 680Wh M3 on http://airwheel.ru/test-monokoles-na-dinostende/ - which seems a nicely reachable maximum!52KgArM.png

 

11 hours ago, zlymex said:

... I've measure my V3/V3s+(same motor) to be 53.5kph and 68.6 respectively when battery is full. ...

So since they have they same motor i reused the same data and increased the battery voltage. To reach @EcoDrift 's measured 4,6kw at 34 km/h i increased the current limit to 120A... I assume thats exactly the range were the cables melt...

BuIwmyj.png

Edited by Chriull
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Posted (edited)

Just since we had some times the "going up a hill faster to take some burden from the wheel" topics:

With the 1500 W Motor output graph one has 62,5A at 20 km/h for the Mv3s+. This would mean riding up a 25% incline with 100 kg at 20 km/h.

Doubling the output power to 3000 W Motor output will raise the speed for the same situation to 36 km/h. This would lead to a motor current of 69A. (At 40 km/h the current for 3000W output would be again 62,5A as with 20 km/h - unfortionately the air drag starts to play a role at this speeds...)

But with 36 km/h one is still almost double as fast going up the incline and still uses about the same motor current leading to about the same power dissipation for the mosfets, wires and connectors! -> so double range before overheating. With the increased airflow the wheel maybe never overheats then?!

Ps.: Don't try the 36 km/h uphill a 25% incline with 100 kg with low battery charge - should only be possible with fully charged batteries! ;)

Edited by Chriull
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3 hours ago, Chriull said:

I regard the motherboard losses included in the "coil resistance" ;) It should be mainly the mosfets and they should be burdened more or less with the motor current (depends a bit if the body diodes are used for freewheeling or active freewheeling is implemented, switching losses are also somehow related to the motor current...)

:P

3 hours ago, Chriull said:

If also read this 100 Hz already somewhere. With the PWM frequency of ~6 kHz even 60 times more adjustments could be made...

GL220 is able to read current at 100Hz rate(1channel), but Wheellog can't. It is very tricky as to how I motor is get, it requires a very high speed ADC because the analog output from the current sensor() is alternating very fast, and there are three phases.

3 hours ago, Chriull said:

Wheellog is not knowing the power - as the original apps! They only have motor current and battery voltage. 

It would have to know kv and Rcoil of each wheel to calculate a real power value (U Back EMF = kv * v, U motor = Rcoil * I motor +U Back EMF-> P = U motor * I motor - Or just U back_emf * I motor which is without ohmic motor losses?)

That is correct. May be it's better to allow users to enter kv value? Or just give an average kv, which is at least better than just power = U batt * I motor.

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58 minutes ago, Chriull said:

So since they have they same motor i reused the same data and increased the battery voltage. To reach @EcoDrift 's measured 4,6kw at 34 km/h i increased the current limit to 120A... I assume thats exactly the range were the cables melt...

BuIwmyj.png

This is nice.

After I saw the measured 4,6kw, I realized that speed-torque curve of my preliminary chart should be much more steep, and should even  be steeper than yours because the 4.6kW is just a sample, not the limit. If they repeat the procedure many times, it may well beyond 4.6kW.

The limit chart of an EUC in some way resembles the SOA of a MOSFET, where there are many time dependent curves. The max power on the DC curve is similar to the rated power where the motor is allowed to run continuously without over heat. The peak power on the other hand is dependent on how short the period may be, and if the duration is short enough, the peak power may well reached to the max point on the speed-torque curve, which(in the case of V3s+ with full battery) is(roughly) 82V * 240A / 4 = 4.92kW, and this figure is very much dependent on the voltage.
SOA.gif.9e2c4044a2c12aef54aed85189022832.gif

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Posted (edited)

14 hours ago, zlymex said:

This is nice.

After I saw the measured 4,6kw, I realized that speed-torque curve of my preliminary chart should be much more steep, and should even  be steeper than yours because the 4.6kW is just a sample, not the limit. If they repeat the procedure many times, it may well beyond 4.6kW.

The 4.6 kw are (at least with my numbers) quite the absolute maximum. Also the red max current over speed line for ubatt =82v (ups a typo... should be 84V. Imho the numbers are right - have to check) is the absolute maximum - one can never ever reach a point beyond this line without increasing the battery voltage or changing the motor characteristics .

also ecodrift tried with his measurements to get the maximum and should get quite close with his dynamometer.

ps.: as 3000w is the max with 68v battery voltage.

how do you get 82v * 240 A / 4 as max power?

pps.: got it ;) as written the 82V were a type - it should be 84. And the max current of the red limit line is 220A -> 84*220/4=4605W

Edited by Chriull
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Posted (edited)

Added some lines to the "limit" graph:

current for motor output power of 750, 1500, 3000 and 4600 Watt

current for an incline of 0°,5°, 10° and 20°

But as these incline graphs are "static" they are only valid for driving a certain constant speed! If one "drives" along this line from 0-40 km/h it means one accelerates and by this uses again more current!

So i included one last graph "current for incline 0° and acceleration of 1 m/s²" - this should be a comfortable acceleration (0-36 km/h in 10 seconds). This needs a bit more current than a 5° incline...

FOQTwjR.jpg

 

Ps.: The GW does not have a fixed speed limit - just a recommendation? So the orange line (max speed) makes no real sense?

Edit: Changed the graph to show non possible "states" in grey (depending on battery voltage)

Edit2: Removed "Speed Limit", Added axis and graph title

Edited by Chriull
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Could not resist to try the same for my KS16C. kv was estimated with 1,44 V/km/h from the lift-cut-off tests. The internal resistance of the motor (and mosfets+wiring) was estimated by taking @EcoDrift's max output power measurement (2,2kW) - which were also quite precise for the MSuper V3 and MSuper V3+.

These leads to the following limiting graph:

JCG6b00.jpg

PS.: I did not drive up to 42 km/h on the KS 16 C - this points came either from lifting it over a tree trunk or the one time it drove into the bushes without me...:ph34r:

 

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17 hours ago, Chriull said:

Added some lines to the "limit" graph:

current for motor output power of 750, 1500, 3000 and 4600 Watt

current for an incline of 0°,5°, 10° and 20°

But as these incline graphs are "static" they are only valid for driving a certain constant speed! If one "drives" along this line from 0-40 km/h it means one accelerates and by this uses again more current!

So i included one last graph "current for incline 0° and acceleration of 1 m/s²" - this should be a comfortable acceleration (0-36 km/h in 10 seconds). This needs a bit more current than a 5° incline...

RUX6CEF.jpg

Ps.: The GW does not have a fixed speed limit - just a recommendation? So the orange line (max speed) makes no real sense?

Edit: Changed the graph to show non possible "states" in grey (depending on battery voltage)

It's a very nice chart again especially some dynamic factors are introduced such as inclination and acceleration.

I think the orange line(max speed) should be eliminated because the definition by GW is in a broad sense. I rather use something like 'rider's limit' to narrow the actual/physical limit incase riders make small 'mistake' just like the cordon on a cliff platform.

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On 18.7.2017 at 4:21 AM, zlymex said:

Apart from this kv value(which is a very nice parameter) that describe one very important aspect of the BLDC motor(back-EMF is proportional to the speed), there should be another parameter describing 'torque is proportional to the motor current'.

 

On 18.7.2017 at 0:44 PM, Chriull said:

I imagine to remember that this two parameters are the same. kv is in reality U / rotations per second so has the unit V*s with V=N*m/A*s this leads to V*s=N*m/A. Which is the unit of the factor torque/current.

We have P motor output = I motor * U Back EMF = I * kv * v  and P mechanic = M * r * v so I * kv * v = M * r *v and I = M * r  / kv.

or how it is imho normaly defined: P motor = I * kv * omega = P mechanic = M * omega -> I = M / kv ( with omega as rotations per second)

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