What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

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What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Nov 12 2020 2:53pm

QS 205 motor V3...

I've just watched this presentation by Grin Tech, at 2:16:00, Justin from Grin Tech explains that the torque for different kv motors will be the same, and efficiency is also the same, but a higher kv motor will allow for higher speeds when climbing the same hill (provided we input higher phase amps).
https://www.youtube.com/watch?v=c96n0Ma ... chnologies

Can I conclude from this that having it if I have high enough battery and phase amps, I can go with a higher kv motor (QS 205 3T), as this will give me the best of both worlds (high torque for hills and high top speeds).

Why is everyone pushing for higher turn motors (4T and 5T), when we can achieve the same amount of torque by pushing through higher amps through a 3T motor.

Am I correct?

My planned setup:
QS205 V3 4T motor (but would like to go to 3T for higher speeds)
Sabvoton 200A controller (battery amps)
79.2V 22s15p battery (able to push out 300 battery amps in short bursts)

I would like to achieve high speeds of 90 - 100 kph but would also like to have massive low end torque.

Thanks!

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by markz » Nov 12 2020 3:49pm

You can play around with different KV motors here: https://ebikes.ca/tools/simulator.html
MXUS 45H has various turn count motors, you must go to the bottom of the list to 'Show All'
Open System B to compare two different motors.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by ZeroEm » Nov 12 2020 3:59pm

pushing for higher turn motors
No body is pushing, get the motor that fits your setup. if you running a 36V 20A controller then a 3T might not be the best, just saying.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by john61ct » Nov 12 2020 10:00pm

Yes, if you know you want high voltage for top speed anyway apparently it doesn't matter.

But if your existing gear or poverty/frugality dictates a low pack voltage, then you need to pick the winding that will get you to the top speed you need at that voltage.

A couple of **very** strongly opinionated members will probably come along shortly to state that the above is all wrong, without explaining why 8-(

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by Balmorhea » Nov 13 2020 12:00am

mbgjt1 wrote:
Nov 12 2020 2:53pm
Justin from Grin Tech explains that the torque for different kv motors will be the same, and efficiency is also the same,
Torque per amp is not at all the same from different motor windings. It's only the maximum possible torque that's the same, and that implies very different controllers and batteries to get the same performance out of different windings.

Higher speed requires greater power, which you have to supply. It consumes more energy per distance, which you have to supply.

There's no free lunch here. The most efficient lunch is to go as slowly as you are willing to go, using the most cost-effective battery and controller. You pick an appropriate motor and/or winding to match the other constraints you've chosen.

You most definitely can decide up front, "I'm going to use X motor", or, "I want to go Y miles per hour", but in that case you will sacrifice cost-effectiveness and in many cases efficiency and all-round performance too.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by goatman » Nov 13 2020 12:33am

what about wye/delta switch with 5t motor?

heres a video of a wye/delta bike

https://www.youtube.com/watch?v=_aLrTRaEMOE

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by MadRhino » Nov 13 2020 2:21am

Hub motor Kv is meant to match wheel size. There are no other reasons, but it does seem hard to understand for many.

Wheel size does command a hub motor Kv that will let you build a system that is powered with reasonable voltage for the speed that you plan to achieve. If your choice of Kv is too far from the wheel size match, up or low, it will force you to feed either very low, or very high voltage. This will create complications and/or efficiency problems.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by dogman dan » Nov 13 2020 6:07am

The real reason to pick a slower wind motor, is not efficiency per se. Its to go slow.

Two examples,

Delta trikes (adult trikes) need to stay below 15 mph in general, because steering them gets tricky when ridden faster, and the rider may be 80. Pick a slow motor, so that at 36v the trike is truly slow, without being underpowered on a hill. As a bonus, efficiency improves not inside the motor, but simply because at 7 mph there is little wind resistance.

Or, say you want a 100v 5000w bike with lots of power, but don't want to actually ride 50 mph ever. Again, you can push the same 5000w into a suitably sized, but slow motor, and not ride quite so fast at top speed.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Nov 14 2020 7:49pm

john61ct wrote:
Nov 12 2020 10:00pm
Yes, if you know you want high voltage for top speed anyway apparently it doesn't matter.

But if your existing gear or poverty/frugality dictates a low pack voltage, then you need to pick the winding that will get you to the top speed you need at that voltage.

A couple of **very** strongly opinionated members will probably come along shortly to state that the above is all wrong, without explaining why 8-(
That's exactly what I thought thank you.. but also, would a lower turn motor be able to handle more current (battery and phase) before overheating?

In that case I may just go with a 3T motor since I am pairing it with a 79.2 V pack

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Nov 14 2020 7:51pm

Balmorhea wrote:
Nov 13 2020 12:00am
mbgjt1 wrote:
Nov 12 2020 2:53pm
Justin from Grin Tech explains that the torque for different kv motors will be the same, and efficiency is also the same,
Torque per amp is not at all the same from different motor windings. It's only the maximum possible torque that's the same, and that implies very different controllers and batteries to get the same performance out of different windings.

Higher speed requires greater power, which you have to supply. It consumes more energy per distance, which you have to supply.

There's no free lunch here. The most efficient lunch is to go as slowly as you are willing to go, using the most cost-effective battery and controller. You pick an appropriate motor and/or winding to match the other constraints you've chosen.

You most definitely can decide up front, "I'm going to use X motor", or, "I want to go Y miles per hour", but in that case you will sacrifice cost-effectiveness and in many cases efficiency and all-round performance too.
I am also worried about acceleration, so for a higher kv motor to have the same acceleration as a lower kv motor, you would need to feed it more amps, which may cause the motor to overheat at lower speeds... am I correct?

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Nov 14 2020 7:53pm

MadRhino wrote:
Nov 13 2020 2:21am
Hub motor Kv is meant to match wheel size. There are no other reasons, but it does seem hard to understand for many.

Wheel size does command a hub motor Kv that will let you build a system that is powered with reasonable voltage for the speed that you plan to achieve. If your choice of Kv is too far from the wheel size match, up or low, it will force you to feed either very low, or very high voltage. This will create complications and/or efficiency problems.
In your opinion, would you pair a 3T or a 4T motor with a 17" moto wheel? I want to choose the 3T winding because it allows for more speed and then push higher volts / amps through it (22s pack, 250 - 300 amps). Top speed of 90 to 100 kph, but really good torque up to that speed.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Nov 14 2020 7:55pm

dogman dan wrote:
Nov 13 2020 6:07am
The real reason to pick a slower wind motor, is not efficiency per se. Its to go slow.

Two examples,

Delta trikes (adult trikes) need to stay below 15 mph in general, because steering them gets tricky when ridden faster, and the rider may be 80. Pick a slow motor, so that at 36v the trike is truly slow, without being underpowered on a hill. As a bonus, efficiency improves not inside the motor, but simply because at 7 mph there is little wind resistance.

Or, say you want a 100v 5000w bike with lots of power, but don't want to actually ride 50 mph ever. Again, you can push the same 5000w into a suitably sized, but slow motor, and not ride quite so fast at top speed.
Ok so you're limiting your top speed, and therefore it requires less amps / voltage to reach the desired speed by using a lower kv motor. I think I understand now.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by john61ct » Nov 14 2020 8:07pm


mbgjt1 wrote: would a lower turn motor be able to handle more current (battery and phase) before overheating?
No, the amount of copper and iron and the motor thermal shedding design dictate that.

But having already decided on a high voltage, I think the wheel size and desired top speed pretty much tells you the winding to choose?


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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by Balmorhea » Nov 14 2020 8:33pm

MadRhino wrote:
Nov 13 2020 2:21am
Hub motor Kv is meant to match wheel size. There are no other reasons, but it does seem hard to understand for many.
It's also for limiting top speed to less than the available power would otherwise achieve. This can be key for staying legal/under the radar/courteous, depending on where you ride.

It's also for mitigating heat problems before they occur.

It's also for matching desired performance to low cost/high availability electrical components.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by Balmorhea » Nov 14 2020 8:35pm

john61ct wrote:
Nov 14 2020 8:07pm
mbgjt1 wrote: would a lower turn motor be able to handle more current (battery and phase) before overheating?
No, the amount of copper and iron and the motor thermal shedding design dictate that.
Low turn counts have lower resistance, thus less heat at any given current. But they also make less torque at any given current, and these values trade off against each other.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by Maciek » Nov 14 2020 9:12pm

Hello Everyone,
Can someone tell me what 3T, 4T, 5T in QS Motor 205 50H V3 exactly means? Number of turns of copper? Has to be more than that, I think. 30, 40 or 50 turns per coil? Also what would be max rpm of this motor, 4T version, with 72V battery? Manufacturer says 650rpm, AliExpress says 850 rpm. Wonder which one is trying to misled me! Thanks, Mike from NY
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by MadRhino » Nov 15 2020 8:09am

Maciek wrote:
Nov 14 2020 9:12pm
Hello Everyone,
Can someone tell me what 3T, 4T, 5T in QS Motor 205 50H V3 exactly means? Number of turns of copper? Has to be more than that, I think. 30, 40 or 50 turns per coil? Also what would be max rpm of this motor, 4T version, with 72V battery? Manufacturer says 650rpm, AliExpress says 850 rpm. Wonder which one is trying to misled me! Thanks, Mike from NY
This motor is available in 3 different 4t windings: 28X4 = 765 rpm@72v, 30X4 = 820 rpm@72v, 33X4 = 956rpm@72v

4T is winding turns per slot. 33X4 is 33 strands 4 turns.

Choose the winding to match the wheel size in order to achieve the top speed that you want.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Dec 20 2020 10:46pm

MadRhino wrote:
Nov 15 2020 8:09am
Maciek wrote:
Nov 14 2020 9:12pm
Hello Everyone,
Can someone tell me what 3T, 4T, 5T in QS Motor 205 50H V3 exactly means? Number of turns of copper? Has to be more than that, I think. 30, 40 or 50 turns per coil? Also what would be max rpm of this motor, 4T version, with 72V battery? Manufacturer says 650rpm, AliExpress says 850 rpm. Wonder which one is trying to misled me! Thanks, Mike from NY
This motor is available in 3 different 4t windings: 28X4 = 765 rpm@72v, 30X4 = 820 rpm@72v, 33X4 = 956rpm@72v

4T is winding turns per slot. 33X4 is 33 strands 4 turns.

Choose the winding to match the wheel size in order to achieve the top speed that you want.
So the 956rpm@72V 4T winding is 13.28 kV, which is the same as the 3.5T?

I think I will go with the 3T winding (15.6 kV) coupled to a 20" rim. All simulations show that this winding has the best acceleration between (30 and 50 mps) compared to the 3.5 and 4T motors.

What are your thoughts?

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by MadRhino » Dec 21 2020 3:05am

The reason I prefer 3t or 4t to 3.5t, is related to even resistance of each phase. Winding fractions of turns does increase the error in the exact length of copper wire used for each phase. If winding 3 turns, it is easy to stop each completed turn exactly. But, if winding 3 turns and a half, one might go a little further than half, or a little less, as compared to the phase that’s been done before. Now think that winding electric motors in China is commonly a sub contracted job, done by women and children at home. :wink:
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by mbgjt1 » Dec 21 2020 4:12am

MadRhino wrote:
Dec 21 2020 3:05am
The reason I prefer 3t or 4t to 3.5t, is related to even resistance of each phase. Winding fractions of turns does increase the error in the exact length of copper wire used for each phase. If winding 3 turns, it is easy to stop each completed turn exactly. But, if winding 3 turns and a half, one might go a little further than half, or a little less, as compared to the phase that’s been done before. Now think that winding electric motors in China is commonly a sub contracted job, done by women and children at home. :wink:
I really hope they've got a decent training program for the women and children winding the motors :|

But to conclude the 3T would be able to handle the most current because it is packed with the thickest copper wires (less turns so thicker wires). Therefore, coupling that to a 20" wheel should ideally give the best results in terms of torque and acceleration around the entire power band of the motor.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by dogman dan » Dec 21 2020 6:29am

Just pick the turn count that reaches the top speed you want in the size wheel you choose. For street use home made motorcycles, its hard to beat the advantages of a 20" bike rim, or similarly size diameter at the rubber, scooter rim. This is what John in CR taught us. You get great torque in the smaller wheel, and at 72v +, plenty of speed. If you want to look like a bike, build a bike, for 30 mph max or so. No bike going 50 mph passes for a bike.

Again, pick a "normal" or fast motor unless its really slow that you want. Stop worrying about efficiency differences you can barely measure. The main thing that will make you unhappy with a home made motorcycle is not enough copper in it. Go big and you will be happy, whatever turn count you choose. Make fine speed adjustments to your pick simply by changing the voltage. Still too slow at 72v, go to 100. Want to pass for a bicycle, simple, run 48v or 36v. Dial it in to your liking, because that motor is going to last forever if its big enough. Its not going to get overheated, likely not even get hot. Too small a motor, that will cook off nice and quick.

The turn count is not the critical decision for a "motorcycle with pedals". What is critical, is just picking the large motor, which you have.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by Chalo » Dec 21 2020 12:33pm

mbgjt1 wrote:
Dec 21 2020 4:12am
But to conclude the 3T would be able to handle the most current because it is packed with the thickest copper wires (less turns so thicker wires). Therefore, coupling that to a 20" wheel should ideally give the best results in terms of torque and acceleration around the entire power band of the motor.
No. It yields a wider power band than higher turn counts. But starting torque is likely to be lower than with higher turn counts, because torque per amp is lower. In order to get equal torque from zero RPM, you'd have to drive the stator to full saturation, which is risky.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by ZeroEm » Dec 21 2020 6:41pm

An acceleration spread sheet was posted in the last week in another thread, downloaded it, played with my trikes settings. Plugged in different windings and wheel sizes. Was quite surprised in the findings. Lower turn count and smaller wheel does not always equal more acceleration, top speed yes. Going to swap out my 7T leafmotor for a 5T edge motor, now after running the numbers have mixed feelings in doing so.
It will slow my trikes acceleration down, even with a smaller wheel. The trike will have a higher top speed and will get to my speed limit of 28mph slower. Now I can put a smaller wheel and get an ASI 2000 to get my acceleration back.
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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by dogman dan » Dec 22 2020 7:02am

Acceleration is going to be fine, for any bike provided you have a big motor, and big amps.

I used to kill harleys off the line with an old clyte 5304 26 inch wheel, and only 40 amps of 48v. The harleys would catch me quickly, but lost about a second shifting to second usually. Nor was there a race on, just saying if you have any copper in that motor, it will accelerate fast enough to not hold up a car behind you till you reach whatever your top speed is.

The OP is after more of course. Sounds like he wants a dragstrip bike. Any wind he picks is going to boogie.

As for you, ZeroEm, change to a higher speed motor ONLY if you want that faster top speed.

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Re: What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

Post by MadRhino » Dec 22 2020 8:00am

dogman dan wrote:
Dec 22 2020 7:02am
Acceleration is going to be fine...

The OP is after more of course. Sounds like he wants a dragstrip bike. Any wind he picks is going to boogie.
Yep, electric acceleration is very good off the line and high power is not required to be ahead when the light turns green.

I don’t believe the OP needs a drag bike. He is just tempering with theory from the simulator, but doesn’t realize yet the practical side of the story. 20+ kw direct power without a clutch, is enough to scare any motorcycle rider at first try. Enough to do a full backflip on a start if the bike is not designed for this. Even with proper geometry, it is enough to drift off the street out of a turn with a throttle twist a tad too nervous. A sub 100 lbs ebike with that kind of power is a monster of aggressivity that requires a well tempered rider.
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