Explain motor winding counts

[www.recumbents.com]

I have been seeing these 6x9 4x4 8x10... numbers floating around to describe the windings on motors.

I think I understand what this means, but I'd like a confirmation. A 6x9 motor is a 6 turn motor, meaning 6 turns of each wire wrapped around the stator. In this case there are 9 wires.

More wires = higher power handling. Anything else?
More windings = slower RPM

What is the advantage of using multiple smaller wires in a motor winding rather that one beefy one? Just ease in winding?

Thanks,

-Warren.

 

[Drunkskunk]

Close, but in relation to 9C motors, you have it just backwards.

a 6X10 motor has 6 strands of copper wire making 10 turns, or loops. A 9X7 would have 9 strands of copper making 7 loops.

The reason for more strands is better copper fill. A strand is round, and when it touches a bunch of other strands, there is are space because in places because the surfaces don't meet flat. thinner strands fill in those spaces better, allowing more copper to fit in the space. Better copper fill leads to a more powerfull motor.

Fewer windings, more speed, but also moves the efficency range higher.
More windings, slower speed but more efficent at lower speeds.

 

[liveforphysics]

The reason for more strands is better copper fill. A strand is round, and when it touches a bunch of other strands, there is are space because in places because the surfaces don't meet flat. thinner strands fill in those spaces better, allowing more copper to fit in the space. Better copper fill leads to a more powerfull motor.

Common fallacy.
If there were no insulation on the wires, using 1 wire that fits the slot, using 4 wires of 1/2 diameter, or using 16 wires of 1/4 diameter etc, you end up with the exact same copper fill.

However, in real life you have to have insulation around each strand, which is adding non-copper volume to the system, so going with a single large wire the just fills the slot is always the best option on paper.

In practice, it's really tough to wind big wires well without knicking the insulation and getting them to lay flat in the slot, so they go with multiple strands for ease of manufacture.

Fewer windings, more speed, but also moves the efficency range higher.
More windings, slower speed but more efficent at lower speeds.

Ehh, something like that. Kinda more like pick the windings that matches your planned voltage and end up at the speed range you want.

 

[dogman dan]

I agree, choose the winding mostly by picking a speed, and a voltage. Then pick a winding that goes that speed at your chosen voltage. Also bear in mind what the motor is doing. And include reality into the process. No fast winding is going to be good at climbing a hill with cargo, And riding fast on the flat. A winding that is very slow or very fast will not do everything.

Generalizing, slow windings do well when the motor is pulling hard at slow speeds. So cargo bikes, dirt bikes, and hill climbers like slow windings. I like my 6x10 winding commuter because it can do an uphill start without pedaling no sweat, and I can load up with cargo and climb a 10% hill.

Fast windings get better top speeds without going to very high voltages. So if a long fast ride with few stops and only moderate hills is your need, a fast winding is good. A fast winding can reach 30 mph on 48v.

Most bikes use middle of the road windings, so they aren't exessivly slow, but can still climb moderate hills like 7% grades no problem. That's the 9x7 and 8x8 windings.

One falsehood about windings is that slow windings have more torque. Not true. But the rider thinks so, because the slow winding takes off up a hill nicer. In fact, the motor is just winding out to it's top speed sooner, since it's top speed is lower. The motor is able to climb better, because it makes less heat going slow. This puts more of your power to the pavement at slow speeds, vs making heat in the motor. So there is a feeling of more power starting up.

 

[miuan]

One falsehood about windings is that slow windings have more torque. Not true. But the rider thinks so, because the slow winding takes off up a hill nicer. In fact, the motor is just winding out to it's top speed sooner, since it's top speed is lower. The motor is able to climb better, because it makes less heat going slow. This puts more of your power to the pavement at slow speeds, vs making heat in the motor. So there is a feeling of more power starting up.

Faster motors have lower resistance, thus at slow speeds, they allow more current than a slower motor at a given voltage. So their torque will be similar to the slower, more effective motors, just because they consume more current. In a real world situation, in a current limiting mode, at a given speed and full throttle, a slower motor will have better efficiency, creating higher torque = higher output power. It can actually be felt by the rider, unlike the amount of generated heat.

 

[www.recumbents.com]

Thanks guys, I added that info to the RC E-Bike Drivetrain Tutorial. http://www.recumbents.com/wisil/e-bent/rc_drive/tutorial.htm

-Warren.

 

[John in CR]

Faster motors have lower resistance, thus at slow speeds, they allow more current than a slower motor at a given voltage. So their torque will be similar to the slower, more effective motors, just because they consume more current. In a real world situation, in a current limiting mode, at a given speed and full throttle, a slower motor will have better efficiency, creating higher torque = higher output power. It can actually be felt by the rider, unlike the amount of generated heat.

"slower, more effective motors"..."a slower motor will have better efficiency, creating higher torque = higher output power"
???????????????? I have probably the highest Kv hubmotor of anyone here, 16rpm/volt, and I'll put it up against any of the others. Slower winds are slower and lower power, period. Their place is pulling heavy loads at lower speeds. The only time they have an advantage on a typical ebike is for very steep hills where the power to go fast would be stressful for the faster system, and the slower motor can operate at good efficiency at a slower speed, which requires proportionally less power.

How you people can ride around on bikes where your normal throttle position is WOT is beyond me. That means every puff of head wind or slight uphill grade slows you down. Who would own a car whose absolute top speed was 65mph and getting from 60 to 65 took a long way, and slight incline or puff of wind slowed you down. No one would buy such a car, that's who. How can you accept the same performance from your ebike? Yet that's exactly what most of you do. Just because my bike will do 60mph doesn't mean I ride it that fast. I don't even know what the top speed of our family mini van is, but I wouldn't own it if it could overtake a truck in front of me doing 64mph.

If you want the same acceleration, just set the current limits higher, and the lower winding turn count motor can handle it. Max torque is identical regardless of turn count for an otherwise identical motor. The difference is the faster wind will keep accelerating to a higher speed, and headroom in terms of speed is a desirable thing. Then you can pass the dump truck pelting you with sand, or when you hit a headwind or slight grade you turn the throttle a little more to maintain speed. If you can't control yourself with the throttle then all I can say is that everyone is glad you're on an ebike and not on a motorcycle or in a car.

Join RASE, Riders Against Slow Ebikes. 8)

 

[dogman dan]

Sorry John, you're simply dead wrong on that one, where you say a slow winding motor slows down on every headwind or hill.

I'm sure what you meant was, low power motors, like 350 watt gearmotors with top speeds of 20 mph do that. They sure do.

But supply a 9 continent 6x10 or 5305 with 1000 watts or more of 48v, and you have a bike with a slow top speed that uses 300 watts at it's top speed. Then you throw some wind in its face and the controller simply supplies it with 1000 watts, and likely you still continue at 20 mph.

Hard to believe, but some of us do prefer a 20 mph top speed out in the public street, or in my case, I want to keep my bike path privledge. But my 6x10 windings still climb a hill or go into headwind great.

You know about my fast bike, I ride it WOT too. 8)

Another thing about winding count. Choosing the correct winding lets you have the max wattage occur at the speed you want it to be happening. I agonized a loooooong time about what 9 continent winding to run in the Death Race. I was really tempted to use a faster winding to win a race. Makes sense right?
But that particular track does not have the space to wind out to the higher top speeds. You enter corners at about 30-35 mph max, and exit some as slow as 25 mph. Turns out the winding I already have, 2807, at the volts I plan to use, reaches it's peak wattage at right about 30 mph. Right where I want it, to have maximum power exiting those corners.

On my bikes with 6x10 motors, run at 48v, they also have thier max wattage at right about where I want it, 15 mph. Out riding, you can really feel the difference. The 6x10 dirtbike just simply purrs when riding trails at 15 mph.

 

[John in CR]

Sorry Dogman, but that's simply not true. Every electric motor reaches an equilibrium based on voltage, BEMF, and load at 100% duty, ie WOT. Increasing the load in any way slows the rpm, period. Start at no load speed, keep adding load and the motor will continue to slow with every increase in load until you reach a stall. That's how motors are tested, and they measure input, torque, and rpm as they do it to come up with the nice little graphs.

If the rationale is you increase pedal effort, then why even have a throttle? Just get a pedelec. You could get around seeing the effect with some kind of artificial speed limiting deal in the controller, but that would s-u-c-k.

 

[John in CR]

Dogman,

We are in agreement on much of the other stuff, though it sounds like you need 2 ebikes not 3, because the commuter needs to be more like the race bike so max power is around your typical cruising speed. You have to control the throttle while racing, you have to control the throttle on your truck, so why ride with old lady performance on your commute when you can have fun for maybe a penny a day? Trail riding needs the slower motor, and it pays dividends up the mountain trails, which is exactly in line with what I said.

It was the erroneous and misleading statements by Miuan that I was compelled to address initially.

 

[dogman dan]

Your statement two posts above still does not match what what happens on my bike, in the real world. Ya'll know I know zero electronics, so my opinions are not based on formulas, but what my bike does out riding. Niether of my slower winding bikes slow down in the wind because they wind out at thier top speed at far lower wattage than they have avaliable. So when they get some resistance from a moderate hill or some medium headwind they simply draw up to 1000 watts and keep chugging along.

So wide open throttle gives me the speed I want, on the flat, on the hills, etc. The slow winding motors give me much much nicer starts, particularly those devilsh uphill starts. On the dirtbike, the slow winding climbs hills cooler. Very important on a trail bike. On the commuter, it simply forces me to ride at a speed that won't get me banned from the bike trails. ( bad right hand, I should cut it off) On the commuter, this motor is also ideal for any 80 mile rides I may want to take on weekends. It very efficiently mizers out the power so I don't have to think about throttle settings for 80 miles. I just crank it, and enjoy the ride.

In other places, as you are, the problems are different. I've found a great solution to my problems with the 10 wind motor. You have different problems where you ride, and solved them your way very nicely. Luckily you have some beefy motors to do it with. Your throw the watts at it method may not work so well with a 9 continent motor, unless your ride is very short.

Hopefully the Death Race is short enough for me to throw 3500 watts at my bike for 12 laps without melting. I know for sure, I'll be about to melt on the last lap. It's either brakes on full or throttle on full in that race, for 10 miles. No room for any cruising. Just on off, on off.

Edit. Of course, half the reason I overreact, is that I misunderstand all that motor theory. But the idea of pick a speed, then decide on a voltage, then pick a motor that matches the speed range you want at that voltage works well.

 

[John in CR]

So when they get some resistance from a moderate hill or some medium headwind they simply draw up to 1000 watts and keep chugging along.

Sure, but chugging at a lower speed. It has to be at a lower speed for the motor to draw the higher current, since it's the rpm driven BEMF that limits current throughout the full duty range. That is everything above the max power point. Like I said, that's without some kind of speed limiting going on in the controller that artificially doesn't permit full duty max speed. It may be that the bike in question is geared so low through the high turn count winding that the speed change is small enough that you don't really notice it. Claiming that your WOT speed doesn't decrease up slight grades or into head winds, is no different than saying WOT isn't faster going with the wind or down a slight grade or changing to a more aerodynamic tuck. More likely, you've just become accustomed to it and vary your pedal output subconsciously to compensate and maintain the same cadence. Just try it with no pedaling and see for yourself.

I've stated a number of times that I believe the appropriate set up is so your typical cruising speed is just above the motor's max power point at WOT. With the same cruising speed the overall effect on efficiency is miniscule, but it enables you to maintain that speed over a range of load conditions, and you have the ability to more safely pass. Here it's nearly impossible to find a totally flat road and it's typically windy. Riding an ebike at WOT as the usual throttle position would be miserable.

At first the new found speed may get used, but that novelty wears off and you end up riding at whatever speed you are comfortable. I've actually found myself generally riding slower now than a year ago, and my bike is faster and much more powerful than it used to be. I actually have to let off the throttle for curves going up a 7% hill that I used to chug up at WOT.

 

[dogman dan]

Ok, now I'm beginning to understand what you are getting at. I suppose the motor does slow down some for it to draw more current. I just don't notice it, I'm happy in my the speed zone I want. The slower windings don't slow that much. I suppose the winding count must affect the back emf, so a smaller decrease in speed has similar effects as a larger decrease in speed on a high count motor? You notice it more on the high count motor, because you have to slow more to increase the back emf?

I slow down about 2 mph at most for a stiff headwind or 4% hill. So I tend not to even notice it. A fast winding, underpowered bogs a lot more, and is very noticeable. On the dirt bike, climbing very steep hills, it will slow to 10 mph or so. But mostly it chugs along at just about 15 mph, which is about as fast as I can ride and stay on the trail and out of the cactus. So again, I don't think so much about it being slowed, because it's going just the right speed for that particular trail system.

My own problem is often the bad right hand. When I put 72v on my dirtike, and had 2500 watts, the bad right hand melted er down in about 45 min. Shoulda had the thermometer on it.

It was fun! But not as nice as the whole previous summer's riding limited to 20 mph, without melting. So for me, the 6x10 and 1000 watts seems to work better, or at least longer. :lol:

 

[John in CR]

It would be very difficult for me to tell the diff between 15mph and 13mph too, because both are simply too slow. :lol: I'd notice 30 slowing to 26 though.

 

[LegendLength]

When I put 72v on my dirtike, and had 2500 watts, the bad right hand melted er down in about 45 min. Shoulda had the thermometer on it.

the 6x10 and 1000 watts seems to work better, or at least longer.

Small offtopic question dogman: I have a new build with the same stats (6x10 motor at 72v, 50A max) so I wonder if you could give me any advice to avoid the same fate. I know you sometimes ride in very hot weather but should it be ok as long as the motor is not uncomfortable to touch?

I'd like to install a temperature guage and will look into getting it done locally. From memory anything under 200 degrees F (i.e. water boiling point) is ok right?

 

[dogman dan]

That seems to be about it 200F for any real length of time. Others have gone higher, but I believe the durations were not as long.

Keep it below 180F, and you can ride basicly infinite duration. And gee guess what, on a 90F day, that's around 800 watts that does that. So you see where watt ratings on motors come from. We can still run 3000 watts for a short time though, especially if we ventilate the hub.

The other thing to know about that melted motor of mine. I was flogging it like a dog that shit in my shoes. Went out and was climbing slopes I can barely walk up for 45 min of hard core riding. Taking trails I never take, because at 1000 watts, you cant. Then poof. So you will have better results if you don't ride like I do. 15% slopes will be no problem. Just give the motor a breather after climbing them.