KS S20 126V Requirement Debate?

[nowjoel]

some seem to lack understanding that the voltage is not really important as it is for the amps/current... 126V and 1A is not the same as 126V and 60A, it relates the same for a battery at it's minimum. The battery capacity has not increased for this wheel, the chemistry and the battery chosen has no advantage to harness the 126V system. if you had a Lithium iron phosphate battery, it would make sense because it would add more current and voltage per cell than Lithium Ion batteries but this is not the case. I hope maybe this makes sense to you.

Edited October 30, 2021 by nowjoel

[Tawpie]

2 hours ago, nowjoel said:

126V and 1A is not the same as 126V and 60A, it relates the same for a battery at it's minimum

you lost me here... I get the first part but not the second.

Edited October 30, 2021 by Tawpie

[mike_bike_kite]

10 hours ago, nowjoel said:

I hope maybe this makes sense to you.

None  

[Seba]

On 10/13/2021 at 4:26 PM, Chriull said:

The lowered current and the increased internal resistance keep the dissipated power P=I*I*R exactly the same.

That's right.

On 10/13/2021 at 4:26 PM, Chriull said:

The real advantage of higher volts is the lower possible current - so Mosfets (as all other burdens with constant resistance) dissipate with the square of the current!

Only in theory and only if we assume that all MOSFETs are ideal devices  Unfortunately, they are not. In practice, MOSFETs that has higher voltage rating (we call it drain-source breakdown voltage, V(BR)DSS) also has higher drain-source resistance (RDS(on)). Design principles says that MOSFETs used in BLDC controllers should be rated for at least 150% of supply voltage, to withstand any transient overvoltages that are common in motor control circuits. So for 100 V battery at least 150 V transistors should be used, while for 126V we'll need to use 200 V transistors. Now if we take a look at Infineon portfolio, we can find two N-channel MOSFETs from the same, outstanding StringIRFET family that has lowest RDS(on) for a given voltage rating. For 150V it's IRF150P220 with RDS(on) at 2.7 mΩ. For 200 V it's IRF200P222 with RDS(on) at 6.6 mΩ. 

This example clearly shows that controller designed for higher system voltage will often dissipate more heat for the same power output. And this is why in higher voltage systems IGBT transistors are used instead of MOSFETs.

[enaon]

On 10/14/2021 at 10:24 PM, mike_bike_kite said:

Perhaps you have a different definition of "reliably"? I mean things like the wheel doesn't have to be put outside to charge or left inside if it's raining etc. 

This is what I found strange on the OP message. 
gw moved from 67 to 100 , no one complained, and still it was the same as ever, catching fires. no tiltback, no respect for safety whatsoever. 

The way I see it 126 is a long overdue farewell to GW and the amazing level of R&D they exhibit, like making air intake holes bigger on the commander. 

Edited November 1, 2021 by enaon

[Tawpie]

36 minutes ago, Seba said:

this is why in higher voltage systems IGBT transistors are used instead of MOSFETs.

Ah. IGBTs... flashback to a former life. Nice thing about an IGBT is that you can control the turning off and basically slam it shut—and shutting it off quicker decreases power loss in the transistor.

[mike_bike_kite]

29 minutes ago, enaon said:

gw moved from 67 to 100 , no one complained, and still it was the same as ever, catching fires. no tiltback, no respect for safety whatsoever. 

GW moved from 67 to 84 and then to 100v. At the time GW was pushing the performance envelope and the extra volts gave you more performance, if you wanted to travel at a real 30+mph then 100v was the only way to get there. I think it's impossible to provide tilt back at the real top speed of an EUC as you need more power to give that tilt back - that means you either accept a slower artificial top speed (like KS and IM) or you just turn off the tilt back (they do have tilt back up to about 30mph) and see how brave you're feeling. Weirdly, I got my Nik+ because of it's safety - I'm a fairly big guy and I wanted a wheel I could do 30mph on safely, the KS16X was known for cutting out when the battery was depleted and riders tried going close to it's advertised top speed while the Nik+ would be fairly safe.

GW do some things great but the few battery fires that have occurred are unforgivable. The original MSX was almost game changing with high top speed and a great range, the mten3 is a fun EUC that can be easily carried and even my Nik+ was pretty unique at the time in that it was manoeuvrable, fast and had great range. They really do need to correct the battery issue and it would be really helpful if they could introduce a "black box" functionality so we could see why a wheel cut out, how many times it's been crashed and what sort of impacts it's had, has the battery been balanced etc etc. I'm not sure how you could preserve the info after a fire but maybe most of the info could be updated to a phone periodically.

[enaon]

1 hour ago, mike_bike_kite said:

if you wanted to travel at a real 30+mph then 100v

Not true, the s18 is a true 31mph, 84 volts, 3 parallels only. And tiltback.

I know this will not sound very nice, but I really find the talk about worrying for KS amusing, when it comes from people that are using/retailing gotways. 

I agree with the rest of your comment, gotway delivers more power for heavy riders, so one could argue it is safer. But they do it the ugly way, no safety, no precautions, backyard level at the best. 

Edited November 1, 2021 by enaon

[mike_bike_kite]

2 hours ago, enaon said:

Not true, the s18 is a true 31mph, 84 volts, 3 parallels only. And tiltback.

I know this will not sound very nice, but I really find the talk about worrying for KS amusing, when it comes from people that are using/retailing gotways. 

I agree with the rest of your comment, gotway delivers more power for heavy riders, so one could argue it is safer. But they do it the ugly way, no safety, no precautions, backyard level at the best. 

I don't think the S18 was available when the Nikola+ came out. I'm also about 210lbs (96kg) in my underwear and I suspect I'd have to be insane to travel at 31mph on an S18. I actually really like KS wheels, if the 18XL was cheaper in the UK then I'd of probably got one of those. If EUCs are ever made legal here then I might well go for an S20. Gotway has most (perhaps all?) of the safety features of KS (tilt back and warnings on current, low battery, temperature etc). The only difference is that you can turn these warnings off if you want to. I have most of my alarms left on as I mostly just cruise between 20 and 25mph.

Edited November 1, 2021 by mike_bike_kite

[enaon]

2 hours ago, mike_bike_kite said:

I don't think the S18 was available when the Nikola+ came out. I'm also about 210lbs (96kg) in my underwear and I suspect I'd have to be insane to travel at 31mph on an S18. I actually really like KS wheels, if the 18XL was cheaper in the UK then I'd of probably got one of those. If EUCs are ever made legal here then I might well go for an S20. Gotway has most (perhaps all?) of the safety features of KS (tilt back and warnings on current, low battery, temperature etc). The only difference is that you can turn these warnings off if you want to. I have most of my alarms left on as I mostly just cruise between 20 and 25mph.

I mentioned the s18 as it is actually the only ks that does true 50 cruising, the 18xl is doing 42km/h gps speed when reporting 50.  

but not all is about speed. A user shorted the charging port of the s18, nothing happened, the wheel could work with the port shorted, and after releasing the short the charging circuit was working fine. that is not the case on a mistake or a power supply fail on gotways. 

Edited November 2, 2021 by enaon

[Asphalt]

7 hours ago, Seba said:

And this is why in higher voltage systems IGBT transistors are used instead of MOSFETs.

Thanks @Seba for the very interesting information about MOSFETs!

Are you suggesting that Kingsong may be better off using IGBT for the 126V controller?

Your post lead me to brief research about MOSFET vs IGBT. It looks like IGBT is better for low frequency (<20KHz) switching, whereas MOSFET is better for high frequency (200KHz) switching. Will IGBT switch frequency be enough for the rapid switching required to keep the wheel balanced?

https://www.watelectronics.com/difference-between-insulated-gate-bipolar-transistor-igbt-and-mosfet/

Quote

1. IGBT is preferred for low frequency (Less than 20 KHz), high voltage (more than 1000V), small or narrow load or line variations; low duty cycle, high operating temperature; and, more than 5kw output power rating applications; whereas MOSFET is preferred for wide load or line variations, low voltage (Less than 250V), large duty cycles and high frequency (more than 200KHz) applications.

 

[Seba]

5 hours ago, Asphalt said:

Thanks @Seba for the very interesting information about MOSFETs!

Are you suggesting that Kingsong may be better off using IGBT for the 126V controller?

No, I don't think so. I wrote about IGBTs to show that we can't just increase voltage without facing some technological challenges. For current EUC motor controller solutions, power MOSFETs will work better than IGBTs. But we can't just increase voltage without some consequences and without facing some limitations. I already mentioned one - significant jump in transistor channel resistance, associated with higher voltage rating of the transistor. But there are also other issues like increase in required air gap to maintain proper insulation. Another possible problem is that voltages up to 120V DC are generally considered as safe voltages (EN 61140 etc.). 126V DC falls out of this category, which may cause several compliance and legal issues to US and EU distributors. For now this market segment is mostly unregulated, but it's a matter of time that EUCs as a products will get regulated (in terms of product safety).

 

[Eucner]

1 hour ago, Seba said:

Another possible problem is that voltages up to 120V DC are generally considered as safe voltages (EN 61140 etc.). 126V DC falls out of this category, which may cause several compliance and legal issues to US and EU distributors. For now this market segment is mostly unregulated, but it's a matter of time that EUCs as a products will get regulated (in terms of product safety).

It is already regulated in the EU. Maximum voltage is 100 VDC. So far regulation is enforced weakly.

[Seba]

1 hour ago, Eucner said:

It is already regulated in the EU. Maximum voltage is 100 VDC. So far regulation is enforced weakly.

Fortunately for now it's still only a new standard, not regulation. But it's very likely that this standard will be included in upcoming regulations, whatever it will be - a new PLEV-related directive or existing EU Regulation 168/2013 or/and Machinery Directive 2006/42/EC. So it's a matter of time and I don't think we'll have to wait too long...

[yoos]

9 hours ago, Asphalt said:

Will IGBT switch frequency be enough for the rapid switching required to keep the wheel balanced?

To address only that specific question: yes, absolutely enough. A d=19" wheel going v=100kmh makes about 10 full rotations per second (f=v/πd). That is 10Hz in terms of frequency. Thus, 20KHz (= 20 000Hz) should be more than enough to smoothly drive the wheel and balance it without jerking. In other words, the reaction time of, say, a 10KHz rated device is 0.0001 seconds which is extremely quick -- you would never notice this kind of delay (for some comparison -- in professional gaming, 0.010 second is considered fantastic ping and that is 100 times slower than IGBT reaction time)

[Eucner]

1 hour ago, Seba said:

Fortunately for now it's still only a new standard, not regulation.

EU standards are a way to show compliance with applicable directives, and so part of the regulation. EN 17128 is not a harmonized standard. It just doesn't cover all requirements of directives. Not following a standard is much longer way for the manufacturer's to show compliance. It rarely happens.

[duanew]

3 hours ago, yoos said:

To address only that specific question: yes, absolutely enough. A d=19" wheel going v=100kmh makes about 10 full rotations per second (f=v/πd). That is 10Hz in terms of frequency. Thus, 20KHz (= 20 000Hz) should be more than enough to smoothly drive the wheel and balance it without jerking. In other words, the reaction time of, say, a 10KHz rated device is 0.0001 seconds which is extremely quick -- you would never notice this kind of delay (for some comparison -- in professional gaming, 0.010 second is considered fantastic ping and that is 100 times slower than IGBT reaction time)

You are missing how many coils and magnet regions there are per rotation.  I am sure this varies per the wheel model.

[Chriull]

2 hours ago, duanew said:

You are missing how many coils and magnet regions there are per rotation.  I am sure this varies per the wheel model.

The number of coils just determine the possible states the wheel can be positioned. With 3 coils (one per phase) that's 120°, with the ~53 used in EUCs it should be about 6°... this seems to be a needed number for nice slow speed movement. Although one can feel sometimes some "rumbles" at slower speed.

So with ten rotations per second there are about 10*53 "states" where the controller can interfere. Most probably some "some inbetween control" should be possible. So some 1-2 kHz should be about the maximum sensefull "control loop frequency".

The choosen control loop frequency is usefully the lower limit for the used PWM frequency.

For better smoothing of torque ripple (modelling sinusodial/specially adopted phase currents by pwm) and to get out of the nasty audible frequencies the EUC manufacturers choose higher frequencies now.

In the beginning most wheels had very nerving ~6-8kHz whining sounds...

Afair ninebot one e+ had in it's advertisments about 100 measurements a second ...

So with about 3(+) times the reachable speed today still some 300 samples a second could be enough...

...maybe at some high speed pothole encounter higher control loop frequencies could make (seldomly) some difference?

However no frequency range to stress any modern power electronics components. 

[yoos]

4 hours ago, duanew said:

You are missing how many coils and magnet regions there are per rotation.  I am sure this varies per the wheel model.

Indeed, I omitted that for simplicity and perhaps I shouldn't have. Anyway, ~50 positions as estimated by @Chriull still keeps the required frequency low enough.

 

1 hour ago, Chriull said:

...maybe at some high speed pothole encounter higher control loop frequencies could make (seldomly) some difference?

I don't think so: the wheel is not powerful enough to rebalance quickly enough to make advantage of an even higher frequency. Suppose you hit a bump which tilts your wheel almost instantly. Even if the controller reacts instantly to this tilt and applies the max torque to balance the wheel, it will take considerable time (compared to 1/f which would be 0.1ms or less) for this torque to get the body and pedals back to level.

I don't know the intricacies of modern algorithms but I suspect they filter out small fluctuations and also have some dampening and retardation built in. This should conserve energy, reduce stress on the system, make for a smoother ride and, perhaps most importantly, it should protect from self-induced oscillations (I have seen some videos of older wheels going into a wild rodeo mode, violently oscillating back and forth at >1Hz or more). Roughly speaking, such dangerous behavior is more likely if the algorithm tries to balance as quickly as possible and energy gets pumped into rodeo behavior.

[mrelwood]

6 hours ago, yoos said:

(I have seen some videos of older wheels going into a wild rodeo mode, violently oscillating back and forth at >1Hz or more).

Oh yes, the wonderful MSX rider from a few years ago! It was a bug in a new firmware (maybe on the first 100V MSX?), on a non user upgradable wheel…  It was quite a setback I’m sure. Some people debated what the actual reason could’ve been, but I don’t know if they came to a solid conclusion.

6 hours ago, yoos said:

the wheel is not powerful enough to rebalance quickly enough to make advantage of an even higher frequency.

I have to dig up the MSX “Crash test” videos that GW themselves published.

 They let the wheel slam onto a curb without a rider. The wheel launched directly upwards to about 1.5m high, staying PERFECTLY straight and balanced the whole time it was in the air. It left me hugely impressed of the tech we ride on. 

[Unventor]

It is some time back. But if I recall right one way to remove the electricity static noise or wine was to increase the frequency use in the motor (or how you would explain it).

As I recall it moved from 10k to 12 or 14K on the KS18L. It had the benefit to remove the motor noise and some of the vibrations when trolleying the wheel. But you can feel it still if you are close to standstill and just push the wheel so slightly until it is on edge to move. 

Now the S20 might look good on paper in many ways, but...

I am not sure 126V is problem free. That mixed with its top speed and its weight, it do hold some risk in the event of a crash, that being a hardware fault or rider error or surrounding traffic to blame. Such a wheel doing a cutout ballet down the road pose a risk. 

That is why I don't really see the need to push this far for an EUC.I know others disagree. But if you think a crash on a can at 70kmh, that can be fatal. And here you have ,any safety system often, on an EUC not so much.

A suprise crash at 70kmh...not a risk I would take. It might be a great wheel, the S20, but I am reserved or sceptical at least for now. 

[yoos]

7 hours ago, mrelwood said:

They let the wheel slam onto a curb without a rider. The wheel launched directly upwards to about 1.5m high, staying PERFECTLY straight and balanced the whole time it was in the air.

It takes much less energy to balance the wheel without a rider (the shell+batteries weighs 10-20kg and is close to the wheel vs 100kg with rider with a center of mass roughly 1m away from the axle, since you care not only about mass but also about leverage). If you slam onto a curb with rider the wheel will not stay balanced (assuming there are power pads to firmly connect the rider to the wheel). Here's a video where Ian manages to tilt the MSX (or whatever wheel is in the video) while trying to get over a log. So while wheels are very powerful they can still be overpowered -- tilted with such force that they do not manage to regain balance, or they do get back to level, but it takes time (e.g. half a second). Anyway, I think that improving the feedback loop frequency is not on the list of urgent improvements for EUCs. Proper BMS, Reliability, QC seem much more important (and also straight-forward to implement!)

 

[yoos]

7 hours ago, Unventor said:

As I recall it moved from 10k to 12 or 14K

While modern wheels seem rather silent (fans notwithstanding) to humans, 10-20KHz is still in the middle of a dogs hearing range. I wish EV manufacturers would at some point make an effort to reduce noise well into 100KHz so that animals would be less disturbed, if only to help prevent dog attacks. 

Edited November 3, 2021 by yoos

[mrelwood]

3 minutes ago, yoos said:

It takes much less energy to balance the wheel without a rider

Of course. My point was mainly about the feedback loop frequency you mentioned. Since for it to be able to compensate the tire hitting the curb, and tire flex and rebound while the wheel is launched upwards, the frequency is already definitely enough for riding in any situation.

 

3 minutes ago, yoos said:

Ian manages to tilt the MSX

Me too, it was a common occurrence for me to overpower the 84V MSX at near zero speed while doing really gnarly off-roading.

 

3 minutes ago, yoos said:

Anyway, I think that improving the feedback loop frequency is not on the list of urgent improvements for EUCs. Proper BMS, Reliability, QC seem much more important (and also straight-forward to implement!)

I agree fullheartedly!

[FunTech4Real]

On 10/13/2021 at 9:15 AM, Jason McNeil said:

There is quite a lot of buzz surronding the 126V battery pack on the S20, but I haven't been able to find much in the way of dissenting voices of whether this ambitious specification is necessary, desired & what trade-offs would be the consequence of this 30s4p pack configuration.  

We all know that the current generation of these motors have KV values can easily achieve the limited 70KPH max speed (KS are not likely going to increase this) well within the 84V-100V operating envelope, with margin to spare.

While there might be a slight improvement in acceleration, this will come at the expense of fewer parallels, increased series internal resistance—leading to higher pack operating temperatures—uncharted (for KS) territory in PCB/electronics designs, step-up chargers, etc.      

The historical track record of S18 battery packs has not been great, experiencing a >15% defect rate (unable to charge...); though KS says that they've addressed this on the most recent batches. My concern is that the S20 is already a high-stakes Wheel, adding an unnecessary complex requirement of 126V, while 100V would serve just as well, or better, could very well result in production delays, cost overruns & other unknowns. 

Of course I've raised these topics with KS, but as of right now, they're commited to 126V. Regardless of what the outcome is, we're going to try to get the final board & pack design externally validated.   

  

I disagree that current wheels can provide both the necessary torque and speed for all riders in all circumstances while using a 100v peak system. I'm 6'4'', 210lbs, and I live in an area with extreme hills all around me. I'm pretty much one of the worst case scenarios the EUC companies try to prepare for, as I use far more power than an average rider. On the contrary, my 6 year old daughter weighs 55 lbs and she rides up insanely steep hills on a mten3 at 20 MPH and I have no concerns about her overpowering the wheel because she's so light. Also, my girlfriend weighs 120 lbs and she can push the S18 extremely hard on any hill and it never beeps at her (where as it beeps endlessly when I ride it because I'm always on the verge of overpowering it). Now onto me.... I ride a RS19 HT and I'm scared to go over about 25 MPH while going up monster hills because I can feel that I'm starting to overpower it (I've tested overpowering it at low speeds on very steep off road hills many times in order to find the limits of the wheel). The RS19 HT has been sort of the gold standard for a high torque wheel and I can still overpower it somewhat easily at low speeds on extreme off-road trails. Also the RS19 HT top speed is too low for me to ride it at fast as I want. I like to be able to go about 35 MPH, which is fine on the RS19 if the batteries are close to full charge and I don't make any rapid forward or back movements, but I have to be extra careful about not overpowering the wheel at this speed and if the batteries are below 50% then I won't even think about going this fast. I also cannot go 35 MPH up a hill that is only somewhat steep without having to worry about overpowering. 

I also owned an EX.N (original high speed model) and that wheel is basically a RS19 HS with more batteries and the controller is likely pushing a little more power. The EX.N was not noticeably easier to overpower at low speed (5 MPH insane hill test) than the RS19 HT, BUT the EX.N would overheat almost immediately when doing an extreme hill climb. I literally overheated the wheel in less than 60 seconds one time on an insane hill (80*F ambient temp; wheel started at 85*F and hit 175*F in less than 60 seconds). The RS19 HT runs massively cooler than its high speed counterpart (or the high speed EX.N) when riding at lower speeds or doing a lot of hills (things that need the torque) because the motor is tuned for it. 

I'm ranting too much here... the point is:
- The current high torque wheels don't even have enough torque for me, and they certainly don't have enough speed
- The current high speed wheels have enough speed, but not enough torque, and they are far too easy to overpower

Sure a wheel could be built that runs at 50 volts and has a 6,000 watt hour battery pack and a matching 6,000 watt continuous motor and it would have enough torque and speed for my needs. To get both more torque and speed out of an electric motor, you either need to feed it more power (which is constrained by the batteries), or you can increase the range of the voltage that is fed to the motor (by adding more batteries in series). There is no way a wheel with a 2,200 watt hour battery pack of LG M50T cells can provide me with enough torque and speed when running at 100v peak. If the same amount of cells are instead configured to run at 126v peak, then there might be enough torque and speed to satisfy my needs. I think that the 126v design of the S20 is the single most important feature of the wheel. There will be no way to know for sure until we actually get to test it. KingSong could have used cells with a much higher discharge (and charge) rate to get more power out of a 2,200 watt hour pack, but that would have likely cost a lot more money. Using a 126v system is likely a cheaper way to get more power out of the same amount of cells without buying more expensive cells. 


Increasing the number of cells in series from 24 (100v) to 30 (126v) increases the range of voltage provided to the motor from 28.8 volts to 36 volts. By range, I mean the maximum voltage provided to the motor minus the minimum voltage provided to the motor.  A higher voltage range enables the motor to increase its speed without reducing torque. 




 

Edited November 7, 2021 by sevin7
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