@ simosmcmuffin this is a long video about the vesc6, what does it say will be the efficiency of running at something like 12s and 15mph vs 6s and 15mph (same setup otherwise)? so the test being running at half duty cycle vs 100%.
Point was to show how much losses the VESC can experience with high motor currents at 50% and 100% duty as Vedder shows in a few minutes of the timestamp I shared the video with. And I think the blanket statement that running the VESC with higher voltages is more efficient by default is not necessarily true.
Granted, the total average power at 15 mph are not that big, with my tests having about 260 Watts continuous, now even with 6S, it would be just a bit over 11 battery amps. But my point still stands that the VESC is much less efficient at 50% duty as Vedder also states and calculates.
And as for the OPâs range needs, just like you @Hummie have said and I quote: âwhenever I see an opportunity to push the finger to the metal I do itâ, so he might end up traveling a lot faster on the 12S and ending up with less range therefore.
Thanks. Its just the esc that losses efficiency at lower duty cycle and not the motor right? I guess I could watch the movie and probably will but can u explain how the duty cycle and frequency are related on the current control program and foc? I read the frequency changes. What frequency range is it?
Iâm mainly wondering about the frequency as I believe at higher frequencies a ferromagnetic material will become magnetized and be reversing polarity quickly and a hysterisis occurs and âŚpoof an induction heater.
The frequency produced by the esc and the current put out by it will be smoothed by the inductance of the motor as it takes time for the magnetic field to build so i think the motor is only exposed to this slower âcommutationâ frequency regardless of esc frequency and no torque ripple or hysterisis.
Canât say about the variable frequencyâs effect on efficiency as my current controller is a static frequency at 24 kHz if I remember correctly and the upcoming InstaSPIN controller will also be static frequency.
In my understanding variable frequency drive is more for induction motors and Iâm not exactly sure what benefits it brings to the BLDC motorsâŚ
The following code snippet is from the VESCâs bldc-master repo, from mcpwm.h file
#define MCPWM_SWITCH_FREQUENCY_MIN 3000 // The lowest switching frequency in Hz
#define MCPWM_SWITCH_FREQUENCY_MAX 40000 // The highest switching frequency in Hz
#define MCPWM_SWITCH_FREQUENCY_DC_MOTOR 25000 // The DC motor switching frequencyYouâre completley right @Maxid, Iâm not sure how I overlooked that. 12s 8000mAh (series) will get me just as far as 6s 16000mAh (parallel). For anyone thatâs not sure how: Letâs say that a 12s 8000mAh setup drains in an hour with a constant top speed of 20 mph; which means that my range is 20 miles per charge. A 6s 16000 mAh setup drains in 2 hours (twice the capacity) with a constant top speed of 10 mph (half the voltage); which means my range will still be 20 miles. Running with higher voltage means less current draw, so the entire system runs cooler and more effeciently. Seems like series is the way to go for me!
Thanks
but if youâre going slow itâs more inefficient at 12s and might as well stay at 6
@SimosMCmuffin
Where were you 6 months ago when I was starting my build? I let myself get convinced into the high voltage argument even though I never plan my gf to go above 18mph⌠(limited in bldc⌠
)
So? That going faster drains your battery quicker was always known. High voltage is still the way to go. We have no data on how the duty cycle efficiency changes range (if at all)
Speed is constant.
Not necessarily. You also have no data on how higher current affects range. Yes we have an equation to correlate resistance to heat produced but I for one have not gone through my whole system and added up resistance, have you? Efficiency of BLDC at 50% is pretty terrible as far as I remember⌠I havenât done the math in a few years
Why would you? assuming the same resistance in either scenarios the high voltage one will produce less heat - as to how much we donât know, just like we donât how the actual effect of the duty cycle efficiency. Why would you then say
when we have no idea and nobody is going to measure? @SimosMCmuffin even said he is using his own motor controller - as to how his data correlates to the VESC we also donât know. For me this would be too many variables and Iâd stick to the proven solution that is: higher voltage is better than higher current.
Iâm an engineer that is always striving for the best performance. Thatâs why.
@PXSS Ive heard foc mode is more efficient.
Do u think motorâs effiency would affect range such drastically even if speed is higher?
I think it would âlevel outâ
Letâs say - with inefficient motor efficiency and low speed you consume 10wh/km, for example.
Then with higher efficiancy of motor, even when speed is higher (and wind / rolling resistance too), u might still consume very close to 10wh/kmâŚ
At least this.is how.i see it but we need.some hard data for.thisâŚ
This was solely based on measuring the resistance. Even as an engineer striving for the best it is unnecessary to measure the individual resistances of your setup. The higher current scenario will always generate more heat than the high voltage scenario since a resistance of 0 is impossible.
What you can do (and I agree if you want the best) is find out how much the duty cycle efficiency matters. But in order to do this you also donât need to measure the resistances. You would have to make actual riding tests and compare the ranges with each other (just like what @SimosMCmuffin did at different speeds you would have to do at different voltages and the same constant speed on a dyno if possible)
Correct. Specially at partial loads. I havenât read much into it since school though and donât really remember how it works.
If you are running at 50% duty cycle then definitely. Even my high end RC ESCs ($400 - Kontronik Jive Pro) hate being at 50% duty cycle without lots of airflow.
What Iâm looking into isnât really related to speed though. I know my gf never rides above 18mph, usually more like 12-15mph. Her setup is made to top out around 40mphâŚ
@Maxid Yes, you are correct that the higher voltage would be more efficient as resistance is not zero. But losses in bldc are significant. I want to say significant enough to offset the high voltage gains.
I was extremely exhausted last night. Iâve only gotten 6 hours of sleep over the past 3 days⌠I realized that I geared her setup wrong⌠Right now, its 16:36, so top speed ~40mph since shes 110 lbs⌠If I gear it to 14:44 then top speed will be ~22mph.
That takes advantage of both high duty cycle and high voltage
Thank you! That was going to be my next point: Gearing can make all the difference and was the reason why I could go 35km/h on my first 6S build with a 149kv motor by choosing an âuncommonâ ratio of 20/28 for my kegels.
I would love to know how big the losses due to the duty cycle actually are. If someone is ever going to measure or calculate let me know. For the average joe I guess the easiest is still to just go as high of a voltage as possible and then adjust the speed via the gearing.
If VESC can run on 5S then I can probably still test it as both her and my setup split into 2 5S packs to charge
Itâs rated 3S to 12S. âŚexcept enertion 4.13 boards, cause he doubt its clever to save money on caps and so that one is only 10S
Please do test with the different voltages and same speed. On vedderâs site I was told the losses at half duty would be pretty small in comparison to full And please do a temp test on the motor for both. My batteries are all hard wired.
I think u can limit the vesc duty cycle to make it a better test
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