Best controller for QS138 V3 70

[harrisonpatm]

If 150 battery amps were a limit for the motor .. why not 1500 amps at 10% duty cycle?

For an oversimplification, you're not entirely wrong. This is why motors (and batteries) often have continuous power ratings as well as peak power ratings; my 8000w rated hub motor can output 14,000-16000w for a few seconds. I don't have the electrical engineering background to explain why and how, so I don't want to post something entirely wrong, but one of the reasons you don't want to run batteries or motors in that fashion is that it can be terribly inefficient.

 

[ah004m]

For an oversimplification, you're not entirely wrong. This is why motors (and batteries) often have continuous power ratings as well as peak power ratings; my 8000w rated hub motor can output 14,000-16000w for a few seconds. I don't have the electrical engineering background to explain why and how, so I don't want to post something entirely wrong, but one of the reasons you don't want to run batteries or motors in that fashion is that it can be terribly inefficient.

Your components will generate heat proportional to the current (amps) and their resistance. Quite important, heat is generated as the square of the current (it’s not linear). Therefore, your duty cycle logic cannot be linear. In addition, there are matters of heat resistance and dissipation. If you have a 10 minutes duty cycle, then you will operate at max power for one minute before cooling for 9 minutes. If you have a 10 sec duty cycle, then you’ll operate at max for one second before 9 seconds cooling. Heat needs time to flow away from its source / dissipate and therefore the 10 second duty cycle will see far lower localized temperatures than the 10 minute cycle. Failures happen locally in your components, not systemically. In other words, you aren’t concerned about the average temperature of your motor, controller, etc. It’s the temperature on the specific wire, mosfet, resistor, etc that determines failure. As an example, your average motor temperature might reach 120C but the temp of the failed winding reached 160C thus causing its insulation to fail. Again, this is why the 10 sec duty cycle is safer. It allows the local temperatures to remain closer to the average/system temperatures.

If you were to 10x your rated current, you may also start risking mechanical failures... but more likely something would melt within the first 0.5 seconds.

Hope that helps.

 

[Hummina Shadeeba]

What’s the max amps the qs138 can take before saturating. I want to program my controller’s motor n battery amps.

Is the motor a good candidate for Vesc MTPA?

 

[DogDipstick]

What’s the max amps the qs138 can take before saturating. I want to program my controller’s motor n battery amps.

Is the motor a good candidate for Vesc MTPA?

( MOTORCAD )

I have not seen any real enumerated current maximums. This is a good question. I was conversing with someone who was putting 42kW into a 138 the other day.

Dont know how much was waste. Heres a screenshot of that.

 

[j bjork]

Here is a little from someone who actually dynoed a qs138 90h (so the 70h will saturate earlier)
It seems the 90h starts saturating at 800A, but still gives pretty good extra torque at 900A, and higher voltage should help with extra rpm :

QS 138 90h V3 - verification of parameters and limits

I have prepared some facts regarding this motor, based on laboratory measurements on the motor dynamometer and several years of experience working with it. The most important information to consider when designing your motorcycle:

• The maximum power at the motor shaft that I achieved is 40HP.

The supply voltage under load at this maximum power is 87.6V - a highly efficient li-ion source 24s, measured at the controller terminals.
It is IMPOSSIBLE to achieve greater power at the motor output based on a pack with a nominal voltage of 72V (20s), regardless of the controller used.
I achieved this power with a maximum efficiency of 86%, resulting in a source power of 34kW.

• The maximum phase current during tests is 460ARMS (800A), allowing for a maximum torque of 80Nm.

This is the recommended current limit; higher current significantly changes the value of the torque constant Kt [Nm/A], and additional current has little effect on torque increase (600Arms generates 100Nm).

• The rotational speed for this maximum power is 5010rpm, much higher than the rated speed of the motor.

Increasing losses start to have a greater impact on total losses, particularly losses related to the frequency of stator magnetization (eddy current losses and hysteresis losses). Powering the motor above 24s (100.8V) is economically unjustifiable; the power losses alone amount to several hundred watts converted into heat.

• The continuous power of this motor is 8kW at an ambient temperature of 20°C.

This value is much lower than the peak value of maximum power lasting a few seconds, due to the effectiveness of heat exchange with the surroundings. Depending on the application and the average load value, controller settings should be adjusted accordingly.

Best regards

 

[Hummina Shadeeba]

Here is a little from someone who actually dynoed a qs138 90h (so the 70h will saturate earlier)
It seems the 90h starts saturating at 800A, but still gives pretty good extra torque at 900A, and higher voltage should help with extra rpm :

QS 138 90h V3 - verification of parameters and limits

I have prepared some facts regarding this motor, based on laboratory measurements on the motor dynamometer and several years of experience working with it. The most important information to consider when designing your motorcycle:

• The maximum power at the motor shaft that I achieved is 40HP.

The supply voltage under load at this maximum power is 87.6V - a highly efficient li-ion source 24s, measured at the controller terminals.
It is IMPOSSIBLE to achieve greater power at the motor output based on a pack with a nominal voltage of 72V (20s), regardless of the controller used.
I achieved this power with a maximum efficiency of 86%, resulting in a source power of 34kW.

• The maximum phase current during tests is 460ARMS (800A), allowing for a maximum torque of 80Nm.

This is the recommended current limit; higher current significantly changes the value of the torque constant Kt [Nm/A], and additional current has little effect on torque increase (600Arms generates 100Nm).

• The rotational speed for this maximum power is 5010rpm, much higher than the rated speed of the motor.

Increasing losses start to have a greater impact on total losses, particularly losses related to the frequency of stator magnetization (eddy current losses and hysteresis losses). Powering the motor above 24s (100.8V) is economically unjustifiable; the power losses alone amount to several hundred watts converted into heat.

I think the qs138 70 is the same Kv but just over 3/4 the length so could assume 3/4 the current possible, so 600 amps peak before saturating

I wonder about him writing it’s not economical to run it over 100v and would like to see a graph. I’m doing 118v full charge and will post one. Even if running so fast starts getting inefficient it’s still possible and seen it up to 7000rpm posted by manufacturer

can I assume 600 amps x 100 volts(maybe with voltage sag) equals 60,000 peak watts possible for the qs138? Or with 83% efficiency 49,800 watts?
Or even more voltage would be possible and another bike I made with it is doing 126v full charge.

 

[j bjork]

I dont know, but if it is possible I guess it will take a lot more than 100v to overcome the back emf to be able to feed 600A when the motor reach 100v.

 

[Hummina Shadeeba]

Why does he decide 72v is the maximum?
I assume the gearbox has a speed limit but what specifically is the obstacle? Why do gears and speed not go together?
worth using thinner oil if doing 126v?

The newest qs138 v3 has bigger bearings.

 

[j bjork]

Why does he decide 72v is the maximum?
I assume the gearbox has a speed limit but what specifically is the obstacle? Why do gears and speed not go together?
worth using thinner oil if doing 126v?

The newest qs138 v3 has bigger bearings.

I cant see anything about 72v being maximum, the only thing he is saying about 72v is that it is impossible to get more than the 40hp he gets with his 24s pack if you run 72v.

That is because his pack dosent have much sag, so you will have lower voltage if you run 20s, even with an even lower ir battery. And he is already feeding the motor what it can take in pA at that voltage and rpm.

That is my interpretation of what he is saying at least. About higher voltage not being economical, as I understand it losses go up too much. So running for longer times at higher rpm will probably overheat rather quickly.