SHARKBITEATTACK
10 W
Is ebikes.ca the only place to buy these now? I'm looking to buy a slow wind motor and run it at high voltage
Where to buy 9C Motors
- Thread starter SHARKBITEATTACK
- Start date
dogman dan
1 PW
In north america , yes. But the clones are all over the place.
Slow wind, you are frocked. Methods is out, Grin doesn't carry a 2810, and even in clones all I know about is a front hub from the Ebikekit trike kit.
So unless you dig up a china source, you have to go to europe. I've no idea how these guys are to do buisness with, but here's a link. They seem to have 6x10's (2810)
http://www.wheelkits.it//index.php
Hey, looks like they even have 2812's in RH. No telling if 9c or not, but I'm assuming a clone.
Slow wind, you are frocked. Methods is out, Grin doesn't carry a 2810, and even in clones all I know about is a front hub from the Ebikekit trike kit.
So unless you dig up a china source, you have to go to europe. I've no idea how these guys are to do buisness with, but here's a link. They seem to have 6x10's (2810)
http://www.wheelkits.it//index.php
Hey, looks like they even have 2812's in RH. No telling if 9c or not, but I'm assuming a clone.
John in CR
100 TW
Other than the ability to use smaller gauge wiring due to running a lower current, you gain exactly 0 by running a slow wind motor at high voltage vs a faster wind of the same motor at a proportionately lower voltage. Unfortunately the misconceptions that are causing Sharkbiteattack's desire to run such a configuration have been repeated so many times that many people treat it as fact.
John in CR
100 TW
veloman said:
Easy, different top speeds, so your voltage difference is not proportional and therefore your current difference isn't either.
edit- Actually different no load speeds would be a better guide to make sure you have the comparable rpm/voltage.
Jeremy Harris
100 MW
Comparing motors with different winds isn't as clear cut as it seems, but the observations here that the fast winds are less efficient under load is spot on.
It depends somewhat on how you choose to make the comparison, which depends very much on the bike you're going to fit the motor too, the total weight, the speed you want to ride and the typical sort of terrain you want to ride. As a general rule, it's always more efficient to run at a higher voltage, but on flat ground that difference may not be big enough to worry about. The reason is due to the way that resistive losses in the motor, controller, wiring, connectors and battery all go up in proportion to the square of current. If you reduce the current then you disproportionately reduce the losses.
Here are some worked examples (from Justin's simulator) that illustrate this. Let's take two different 9C winds (2805 and 2808) at battery voltages selected to give the same top speed for both and with the current limit set the same for both so as to allow a fair comparison.
Flat ground :
15 mph on a 2805 at 36V gives about 79% efficiency
15 mph on a 2808 at 55V gives about 81% efficiency
10% gradient :
15 mph on a 2805 at 36V gives about 63% efficiency
15 mph on a 2808 at 55V gives about 67% efficiency
The slower wind motor at the higher voltage is always more efficient. The difference on flat ground is small, but once you start climbing hills the difference gets bigger, just because the slower wind motor needs less current to deliver the required torque to get you up the hill, and less current means lower losses.
If you were to compare the really slow winds run at even higher voltages you would get an even bigger difference, I'm sure, but unfortunately the simulator only goes up to the 2808.
It depends somewhat on how you choose to make the comparison, which depends very much on the bike you're going to fit the motor too, the total weight, the speed you want to ride and the typical sort of terrain you want to ride. As a general rule, it's always more efficient to run at a higher voltage, but on flat ground that difference may not be big enough to worry about. The reason is due to the way that resistive losses in the motor, controller, wiring, connectors and battery all go up in proportion to the square of current. If you reduce the current then you disproportionately reduce the losses.
Here are some worked examples (from Justin's simulator) that illustrate this. Let's take two different 9C winds (2805 and 2808) at battery voltages selected to give the same top speed for both and with the current limit set the same for both so as to allow a fair comparison.
Flat ground :
15 mph on a 2805 at 36V gives about 79% efficiency
15 mph on a 2808 at 55V gives about 81% efficiency
10% gradient :
15 mph on a 2805 at 36V gives about 63% efficiency
15 mph on a 2808 at 55V gives about 67% efficiency
The slower wind motor at the higher voltage is always more efficient. The difference on flat ground is small, but once you start climbing hills the difference gets bigger, just because the slower wind motor needs less current to deliver the required torque to get you up the hill, and less current means lower losses.
If you were to compare the really slow winds run at even higher voltages you would get an even bigger difference, I'm sure, but unfortunately the simulator only goes up to the 2808.
dogman dan
1 PW
Which winding is best depends entirely on what kind of riding is done, at what speed at what wattage ,under what load. So many blanket statements are right for some conditions and wrong for others. I'm curious Jeremy, in your examples above, is the speed achieved with the same wattage? I would think the same speed at less efficency would require a higher wattage.
A few generalities do emerge though.
Just using enough power makes the fast winding more efficient. Don't lug the motor, and it won't be inefficient. That simple. In Jeremy's example, 15 mph might still be too slow for a really fast winding climbing 10%. You may have a high wh/mi number, but nevertheless the motor does use the power you give it efficiently with less heating of the motor if you get turning fast enough. The catch 22 is that the majority of bike hub motors are designed to work on about 1000w or less. If your riding conditions only require 1000w, you are all good. If your riding conditions require 4000w to use that particular winding, then you might need a different motor.
Using a smaller wheel helps a fast winding perk up in efficiency.
But if for whatever reason you really just prefer a 26" wheel, a slower winding can help the motor perform similarly to a faster winding in a small wheel.
If your avaliable wattage just simply means you will slow to 10 mph climbing a hill, then you must either pedal hard to speed up, or choose a winding and or wheel size that will not heat up while running at full wattage under load at 10 mph. So if you won't make the wheel smaller, or increase power, a slower winding then beomes the last option you have besides pedaling like Lance on dope.
I have ridden 1000's of miles at about 1000w (48v maximum voltage) on fast, medium, and slow windings in 26".
For long uninterrupted runs on flat ground, or hills under 5%, the fast winding really shined. Just really nice to cruise 5 mph faster on the long flat run. On just 1000w, less than 5% hills are no problemo.
For typical urban riding on routes with inturruptions only about every 2 miles, the medium winding was quite nice, and still quite fast. Climbs hills up to 8% fine. Like 10 miles of non stop rocky mountans 8% hills are no problemo with light pedaling.
For maximum wh/mi, then you obviously are slowing down. What point is there in a faster winding if you will never use full throttle? So then a slow winding gets nice. The slow winding worked best for me when hauling bigger loads but still limiting wattage to 1000. Running full throttle at 18-20 mph, I'd get great range despite a frankenbike that is heavy as hell. Climbing hills, the limit without pedaling hard would increase to about 10% rather than 5%. Routes with stops every half mile or less don't kill your range nearly as much as before with the faster motors.
Once you change the wattage though, everything is different, and you might not require as low a winding to get good performance. Just like John does it. Bottom line is, if you ARE lugging your motor on the ride you are doing, you better change something. If you won't change anything else, then changing windings is the last thing possible besides popping some EPO.
A few generalities do emerge though.
Just using enough power makes the fast winding more efficient. Don't lug the motor, and it won't be inefficient. That simple. In Jeremy's example, 15 mph might still be too slow for a really fast winding climbing 10%. You may have a high wh/mi number, but nevertheless the motor does use the power you give it efficiently with less heating of the motor if you get turning fast enough. The catch 22 is that the majority of bike hub motors are designed to work on about 1000w or less. If your riding conditions only require 1000w, you are all good. If your riding conditions require 4000w to use that particular winding, then you might need a different motor.
Using a smaller wheel helps a fast winding perk up in efficiency.
But if for whatever reason you really just prefer a 26" wheel, a slower winding can help the motor perform similarly to a faster winding in a small wheel.
If your avaliable wattage just simply means you will slow to 10 mph climbing a hill, then you must either pedal hard to speed up, or choose a winding and or wheel size that will not heat up while running at full wattage under load at 10 mph. So if you won't make the wheel smaller, or increase power, a slower winding then beomes the last option you have besides pedaling like Lance on dope.
I have ridden 1000's of miles at about 1000w (48v maximum voltage) on fast, medium, and slow windings in 26".
For long uninterrupted runs on flat ground, or hills under 5%, the fast winding really shined. Just really nice to cruise 5 mph faster on the long flat run. On just 1000w, less than 5% hills are no problemo.
For typical urban riding on routes with inturruptions only about every 2 miles, the medium winding was quite nice, and still quite fast. Climbs hills up to 8% fine. Like 10 miles of non stop rocky mountans 8% hills are no problemo with light pedaling.
For maximum wh/mi, then you obviously are slowing down. What point is there in a faster winding if you will never use full throttle? So then a slow winding gets nice. The slow winding worked best for me when hauling bigger loads but still limiting wattage to 1000. Running full throttle at 18-20 mph, I'd get great range despite a frankenbike that is heavy as hell. Climbing hills, the limit without pedaling hard would increase to about 10% rather than 5%. Routes with stops every half mile or less don't kill your range nearly as much as before with the faster motors.
Once you change the wattage though, everything is different, and you might not require as low a winding to get good performance. Just like John does it. Bottom line is, if you ARE lugging your motor on the ride you are doing, you better change something. If you won't change anything else, then changing windings is the last thing possible besides popping some EPO.
Jeremy Harris
100 MW
The reason I gave the efficiency figure is so that the difference shows more clearly. The actual power needed to maintain those speeds, under those conditions, with that weight of bike would be the same for both motors, but the power drawn from the battery would be different.
For example, if it took 600W motive power to maintain 15 mph up that hill, then with the slow wind and higher voltage the power taken from the battery would be around 895W and the power taken from the battery for the fast wind and lower voltage would be around 952W.
Not a big difference, but enough to knock around 5 or 6% off your range if you regularly ride in hills. The slower wind motor would also run very slightly cooler, I think, as the losses would be slightly lower.
As a general principle, at least for direct drive hub motors that are unlikely to run into big iron loss problems, then a higher battery voltage and lower speed wind will always, under any condition, give better efficiency, so will always use less battery power for a given output power. The difference is probably pretty small on the flat, though, and there are other issues that mean that when you get over about 80 to 90V things start to change, as controller resistive losses often start to increase once you get to the point where 4110's won't cut it safely. Some may also want to select a lower battery voltage for legal reasons, for example, here anything over 60V needs to be certified under the Low Voltage Directive to be strictly legal. This is one reason I don't go over 60V with my builds.
For example, if it took 600W motive power to maintain 15 mph up that hill, then with the slow wind and higher voltage the power taken from the battery would be around 895W and the power taken from the battery for the fast wind and lower voltage would be around 952W.
Not a big difference, but enough to knock around 5 or 6% off your range if you regularly ride in hills. The slower wind motor would also run very slightly cooler, I think, as the losses would be slightly lower.
As a general principle, at least for direct drive hub motors that are unlikely to run into big iron loss problems, then a higher battery voltage and lower speed wind will always, under any condition, give better efficiency, so will always use less battery power for a given output power. The difference is probably pretty small on the flat, though, and there are other issues that mean that when you get over about 80 to 90V things start to change, as controller resistive losses often start to increase once you get to the point where 4110's won't cut it safely. Some may also want to select a lower battery voltage for legal reasons, for example, here anything over 60V needs to be certified under the Low Voltage Directive to be strictly legal. This is one reason I don't go over 60V with my builds.
grindz145
1 MW
I have a couple of MXUS 9C clones which are basically 9x7s. Let me know if you want one.
John in CR
100 TW
More misinformation and misconceptions.
People are using apples and oranges. Use 80V for the 8 turn and 50V for the 5 turn. Set the battery resistance very low for both, so that doesn't create a difference. Then set the current limits in the opposite ratio, and you will get much closer to identical results. The 8 turn 9C will be slightly better efficiency across the board because it has the better copper fill at 64 strands compared to 60 for 5 turn.
Statements like Knighty's "the slow wind is more efficient at slow speeds" and Dogman's incessant sales pitch for the high turn count motors are how these myths perpetuate. Once you crank up the voltage to try to get to the same power then the house of cards come tumbling down. They can be more efficient a slower speeds, but that's at lower power. At the same voltage and lower current they are better at climbing hills or in stop-n-go congested traffic.
Identical motors of different winds are identical once you consider that you simply change the current and voltage proportionately for identical performance. Manufacturers who try to call the slow wind a high torque model are just misleading you. They're a slower wind period, and once you consider that our limitation is voltage, they're a lower power wind too. It works on hills, because it takes proportionately less power to climb a hill proportionately slower. Increase voltage to try to make it a fast motor too and that advantage you had at slower and lower power goes right out the window.
Don't bother with the anecdotal evidence to attempt to claim otherwise. All I have is fast wind motors and I climb steeper hills with heavier loads than most and never pedal assist on hills, but I've never melted a motor and don't even bother with temperature sensors. The motors I used from 2008 until the middle of this year are really no different than the motors people are using now, so don't credit it to some bigger, heavier, higher power motor. They're not magic either.
People are using apples and oranges. Use 80V for the 8 turn and 50V for the 5 turn. Set the battery resistance very low for both, so that doesn't create a difference. Then set the current limits in the opposite ratio, and you will get much closer to identical results. The 8 turn 9C will be slightly better efficiency across the board because it has the better copper fill at 64 strands compared to 60 for 5 turn.
Statements like Knighty's "the slow wind is more efficient at slow speeds" and Dogman's incessant sales pitch for the high turn count motors are how these myths perpetuate. Once you crank up the voltage to try to get to the same power then the house of cards come tumbling down. They can be more efficient a slower speeds, but that's at lower power. At the same voltage and lower current they are better at climbing hills or in stop-n-go congested traffic.
Identical motors of different winds are identical once you consider that you simply change the current and voltage proportionately for identical performance. Manufacturers who try to call the slow wind a high torque model are just misleading you. They're a slower wind period, and once you consider that our limitation is voltage, they're a lower power wind too. It works on hills, because it takes proportionately less power to climb a hill proportionately slower. Increase voltage to try to make it a fast motor too and that advantage you had at slower and lower power goes right out the window.
Don't bother with the anecdotal evidence to attempt to claim otherwise. All I have is fast wind motors and I climb steeper hills with heavier loads than most and never pedal assist on hills, but I've never melted a motor and don't even bother with temperature sensors. The motors I used from 2008 until the middle of this year are really no different than the motors people are using now, so don't credit it to some bigger, heavier, higher power motor. They're not magic either.
Jeremy Harris
100 MW
John in CR said:
If it's my figures (or more correctly Justin's) figures that you're taking issue with, John, then I can assure you that I did set the same low battery internal resistance for both examples and used the same low controller resistance, and high current limit, for both examples, so the only thing affecting the results was the motor wind.
It's straightforward physics, if you increase the voltage for a given motor power, then you reduce the current. That reduced current means lower I²R losses.
Sure the difference is fairly small, just a few percent, but it is real. Whether it's important or not is down to the personal view of each of us, some might really want to get a few percent more range, some might not be bothered by it.
The bottom line is that a slower wind direct drive hub, run at a higher voltage and lower current, will always be a little more efficient than a faster wind motor run at a lower voltage. This isn't myth or anything complex, just ordinary physics at work. Motor torque is determined by the amp turn figure, so double the turns and halve the amps and you get the same torque. However, halving the current means a quarter of the I²R loss, meaning better efficiency. Of course there are other factors at work too, but reducing current for a given power is the single best thing you can do to improve overall system efficiency.
I should add that this is a specific case for a direct drive hub motor that's running at an rpm below that where iron losses start to dominate, but that covers the majority of normal direct drive hub motor ebikes.
John in CR
100 TW
Jeremy,
You are helping to perpetuate the myth. You're leaving out the fact that the fewer turn count motor has shorter and thicker copper carrying the higher current, making the copper losses identical for the same power. Iron losses are also identical, because it's the same rpm. A lower speed wind is simply not more efficient across the range. I suggested the voltage change to get the difference on par with the difference in winding. Then do the comparison and the results are pretty close to identical on the simulator, with the difference resulting from the better copper fill of the 8 turn. The 8 turn would also be better than the 10 turn, due to the copper fill advantage. The 7 turn is closest, because it has 63 strands, only one less than the 8.
Maybe this will help clear the air about this once and for all. Here's the summary put out by Astro for it's small motor and the different windings available showing how the motors are identical once you adjust for voltage and current.
You are helping to perpetuate the myth. You're leaving out the fact that the fewer turn count motor has shorter and thicker copper carrying the higher current, making the copper losses identical for the same power. Iron losses are also identical, because it's the same rpm. A lower speed wind is simply not more efficient across the range. I suggested the voltage change to get the difference on par with the difference in winding. Then do the comparison and the results are pretty close to identical on the simulator, with the difference resulting from the better copper fill of the 8 turn. The 8 turn would also be better than the 10 turn, due to the copper fill advantage. The 7 turn is closest, because it has 63 strands, only one less than the 8.
Maybe this will help clear the air about this once and for all. Here's the summary put out by Astro for it's small motor and the different windings available showing how the motors are identical once you adjust for voltage and current.
Jeremy Harris
100 MW
Nope, not perpetuating any myths, just giving you hard, indisputable facts about system performance. If you halve motor the Kv in a given system, and therefore halve the current for a given power, then the overall system losses reduce (provided you're not into the region where iron losses start to play a dominant part WRT motor losses).
Note very, very carefully what I've said all along. I used the word "system". You cannot consider the motor in isolation, you have to consider the whole system, motor, battery, wiring and controller. Why do you think I was so specific about pointing out that the comparison I made earlier used the same battery total resistance and controller resistance? It was precisely to show that this is a system issue, one where there is always an advantage in running at the highest voltage you can for a given performance requirement, subject to regulatory or safety issues.
Note very, very carefully what I've said all along. I used the word "system". You cannot consider the motor in isolation, you have to consider the whole system, motor, battery, wiring and controller. Why do you think I was so specific about pointing out that the comparison I made earlier used the same battery total resistance and controller resistance? It was precisely to show that this is a system issue, one where there is always an advantage in running at the highest voltage you can for a given performance requirement, subject to regulatory or safety issues.
dogman dan
1 PW
I don't doubt your system works good John. For starters I believe you stopped using a 26" wheel long ago which makes a big difference as many agree. You don't slog up hills at 1000w, so why should you need a slower motor? Nor do you do too many 30 mile rides, so maximizing your wh/mi matters less to you. It does matter to some of us.
I'm just seeing a differing point of view more than one is right or the other wrong. You grab the sledghammer or the tack hammer depending on the nail you have to drive.
My apples of 48v 20 amps, 26" wheel was compared with apples of 48v 20 amps, 26" wheel. All used with the very same battery on the very same 15 mile commute. The only variable was the motor. There was hovever, one additional difference that may have affected my results, the "fastest" motor was aotema, while the slow or medium motors were 9c clones. Doesn't invalidate the results for the 9c clone motors though. In the end, if I want max wh/mi it's the slow motor since I'll be riding slow. If I want the max speed for the voltage of a given battery, then I want the fast motor. I just tend to drive more tacks than I do railroad spikes.
My dirt bike runs oranges, 72v 40 amps.
I guess what I am trying to say could be summarized like this. When you are frocked by the previous choice of a big wheel and a small controller, a slower motor will get up that hill. But if you have more power and a small wheel, you no longer need to ride up that hill so slow.
I'm just seeing a differing point of view more than one is right or the other wrong. You grab the sledghammer or the tack hammer depending on the nail you have to drive.
My apples of 48v 20 amps, 26" wheel was compared with apples of 48v 20 amps, 26" wheel. All used with the very same battery on the very same 15 mile commute. The only variable was the motor. There was hovever, one additional difference that may have affected my results, the "fastest" motor was aotema, while the slow or medium motors were 9c clones. Doesn't invalidate the results for the 9c clone motors though. In the end, if I want max wh/mi it's the slow motor since I'll be riding slow. If I want the max speed for the voltage of a given battery, then I want the fast motor. I just tend to drive more tacks than I do railroad spikes.
My dirt bike runs oranges, 72v 40 amps.
I guess what I am trying to say could be summarized like this. When you are frocked by the previous choice of a big wheel and a small controller, a slower motor will get up that hill. But if you have more power and a small wheel, you no longer need to ride up that hill so slow.
John in CR
100 TW
The OP is wanting a slow wind motor and then go to high voltage based on the myth that both of you are perpetuating. He either wants good hill climbing and high speed, or he's thinking the slow wind gives him better torque and the high voltage makes up for the speed loss of the slow winding. Neither of those thought processes are accurate, and the myth upon which it is based is widespread with portions of it repeated on this forum on a daily basis. Narrowly defining your statements to make them technically accurate but misleading overall does no one any favors.
Jeremy for your "same system" comparison, how about same everything, bike, battery, controller, even motor, but the motor has each phase split in half for series/parallel switching of the windings....Guess what? The parallel setting (low turn count motor) is more efficient and has higher power. Where the series connection (high turn count motor) is a benefit only in being more efficient going slow up hills and in the early stage of acceleration from zero or very low speed like when stuck in congested traffic.
Dogman, The 20% smaller wheel I run is more than offset by the much greater load my ebikes push, so it's not the reason I don't melt motors, though for any given speed the higher rpm of the smaller wheel creates better heat dissipation. Don't presume that just because most of my rides are short errand rides that I don't go on long rides too. I have a 60 mile battery on one of my bikes right now. You don't think I carry the extra weight around for nothing do you? I ride at generally higher speeds than you do, which includes steeper hills. No I don't slog up them. I zoom up them, and my riding requires more power, power which a slow wind motor simply isn't capable, and those who try all have heat problems. That's because the slower wind motors are less efficient at these powers, and that's because they are pushing their stators into saturation, something you actually encourage by talking about pushing 3kw into your high turn count motors.
If you guys want to make useful true statements about slow wind motors without being misleading, then you're restricted to they're better at lower power and slower speeds. Otherwise I'll counter with the following factual generalization. Given our general limitation on voltage whether it's the practical 100V limit of controllers or arbitrary legal cutoff of 60V, then the higher Kv, faster turn count hubbie is capable of higher power. That means it is ultimately capable of higher speed and better hill climbing. Another true statement is that they are capable of the same torque.
John
Jeremy for your "same system" comparison, how about same everything, bike, battery, controller, even motor, but the motor has each phase split in half for series/parallel switching of the windings....Guess what? The parallel setting (low turn count motor) is more efficient and has higher power. Where the series connection (high turn count motor) is a benefit only in being more efficient going slow up hills and in the early stage of acceleration from zero or very low speed like when stuck in congested traffic.
Dogman, The 20% smaller wheel I run is more than offset by the much greater load my ebikes push, so it's not the reason I don't melt motors, though for any given speed the higher rpm of the smaller wheel creates better heat dissipation. Don't presume that just because most of my rides are short errand rides that I don't go on long rides too. I have a 60 mile battery on one of my bikes right now. You don't think I carry the extra weight around for nothing do you? I ride at generally higher speeds than you do, which includes steeper hills. No I don't slog up them. I zoom up them, and my riding requires more power, power which a slow wind motor simply isn't capable, and those who try all have heat problems. That's because the slower wind motors are less efficient at these powers, and that's because they are pushing their stators into saturation, something you actually encourage by talking about pushing 3kw into your high turn count motors.
If you guys want to make useful true statements about slow wind motors without being misleading, then you're restricted to they're better at lower power and slower speeds. Otherwise I'll counter with the following factual generalization. Given our general limitation on voltage whether it's the practical 100V limit of controllers or arbitrary legal cutoff of 60V, then the higher Kv, faster turn count hubbie is capable of higher power. That means it is ultimately capable of higher speed and better hill climbing. Another true statement is that they are capable of the same torque.
John
Jeremy Harris
100 MW
I keep saying, John, this is no myth, but hard science. You cannot ever just consider the motor in glorious isolation, as it is the performance of the whole system on the ebike that matters, and much of the stuff that impacts efficiency is outside the motor and constrained by other factors, like practicality, weight and size.
This is the point I keep trying to make, but which, for some reason seems to go straight over your head. Maybe I can help make things clearer by ignoring what's going on in the motor for a moment and just looking at the rest of the system.
Let's take two cases where the same total electrical input power is needed, 2000W. I'll use some fairly optimistic resistance figures, ones that are lower than I suspect most ebikes of this power will have in reality, just to minimise the efficiency losses for this comparison (this is what I did with those earlier simulation runs, BTW).
1) Let's assume we can use a controller with decent FETs and that it has a total in circuit resistance of 0.05 ohms.
2) Let's also assume that we use fairly heavy 10g wire and good connectors for both ebikes and have a total wiring and connector resistance on the bike of 0.02 ohms.
3) Let's assume that the battery chemistry is the same for both voltages and that we use identical cells to make up the battery packs, that have an internal resistance of 0.002 per volt of total battery voltage.
4) Let's look at two direct drive hub motors, with different winds but exactly the same iron and frictional losses. One has a wind that gives a Kv of half of the other. Let's assume that the losses in both motors are the same under all conditions and that we can therefore ignore them for this comparison.
5) Let's assume that for our 2000W the fast wind motor requires 50V at 40A and the slow wind motor requires 100V at 20A.
Now let's look at the system losses, excluding the motors:
Battery losses:
The 50V battery will have an internal resistance of 50 x 0.002 = 0.1 ohm. At 40A the losses will be 40² x 0.1 = 160W, which is 8% efficiency loss.
The 100V battery will have an internal resistance of 100 x 0.002 = 0.2 ohm. at 20A the losses will be 20² x 0.2 = 80W, which is 4% efficiency loss.
Controller losses:
At 50V and 40A the controller loss will be 40² x 0.05 = 80W, which is a 4% efficiency loss
At 100V and 20A the controller loss will be 20² x 0.05 = 20W, which is a 1% efficiency loss
Wiring and connector losses:
At 50V and 40A the wiring and connector loss will be 40² x 0.02 = 32W, which is 1.6%
At 100V and 20A the wiring and connector loss will be 20² x 0.02 = 8W, which is 0.4%
The total efficiency losses, excluding the motor, for each case are:
For the fast wind motor, system losses = 8% + 4% + 1.6% = 13.6%, or a system efficiency, less motor, of 86.4%
For the slow wind motor, system losses = 4% + 1% + 0.4% = 5.4%, or a system efficiency, less motor, of 94.6%
Hopefully you can see where I was coming from earlier, when I stated that for a given system, at a given power requirement, a higher voltage will always give better efficiency. The difference is enough to pretty much swamp the minor motor efficiency variations, although it is worth noting that the fixed resistive losses in direct drive hub motors (things like the limited size of axle wires) will mean that running at a lower current/higher voltage for a given power does give a small advantage to the slower wind motors even then.
This is the point I keep trying to make, but which, for some reason seems to go straight over your head. Maybe I can help make things clearer by ignoring what's going on in the motor for a moment and just looking at the rest of the system.
Let's take two cases where the same total electrical input power is needed, 2000W. I'll use some fairly optimistic resistance figures, ones that are lower than I suspect most ebikes of this power will have in reality, just to minimise the efficiency losses for this comparison (this is what I did with those earlier simulation runs, BTW).
1) Let's assume we can use a controller with decent FETs and that it has a total in circuit resistance of 0.05 ohms.
2) Let's also assume that we use fairly heavy 10g wire and good connectors for both ebikes and have a total wiring and connector resistance on the bike of 0.02 ohms.
3) Let's assume that the battery chemistry is the same for both voltages and that we use identical cells to make up the battery packs, that have an internal resistance of 0.002 per volt of total battery voltage.
4) Let's look at two direct drive hub motors, with different winds but exactly the same iron and frictional losses. One has a wind that gives a Kv of half of the other. Let's assume that the losses in both motors are the same under all conditions and that we can therefore ignore them for this comparison.
5) Let's assume that for our 2000W the fast wind motor requires 50V at 40A and the slow wind motor requires 100V at 20A.
Now let's look at the system losses, excluding the motors:
Battery losses:
The 50V battery will have an internal resistance of 50 x 0.002 = 0.1 ohm. At 40A the losses will be 40² x 0.1 = 160W, which is 8% efficiency loss.
The 100V battery will have an internal resistance of 100 x 0.002 = 0.2 ohm. at 20A the losses will be 20² x 0.2 = 80W, which is 4% efficiency loss.
Controller losses:
At 50V and 40A the controller loss will be 40² x 0.05 = 80W, which is a 4% efficiency loss
At 100V and 20A the controller loss will be 20² x 0.05 = 20W, which is a 1% efficiency loss
Wiring and connector losses:
At 50V and 40A the wiring and connector loss will be 40² x 0.02 = 32W, which is 1.6%
At 100V and 20A the wiring and connector loss will be 20² x 0.02 = 8W, which is 0.4%
The total efficiency losses, excluding the motor, for each case are:
For the fast wind motor, system losses = 8% + 4% + 1.6% = 13.6%, or a system efficiency, less motor, of 86.4%
For the slow wind motor, system losses = 4% + 1% + 0.4% = 5.4%, or a system efficiency, less motor, of 94.6%
Hopefully you can see where I was coming from earlier, when I stated that for a given system, at a given power requirement, a higher voltage will always give better efficiency. The difference is enough to pretty much swamp the minor motor efficiency variations, although it is worth noting that the fixed resistive losses in direct drive hub motors (things like the limited size of axle wires) will mean that running at a lower current/higher voltage for a given power does give a small advantage to the slower wind motors even then.
Lebowski
10 MW
OK, Jeremy, your equations etc are correct but don't describe what really goes on (I'm in Johns camp by
the way, and not only because he lives in a tropical country
so cold here now).
The 50V versus 100V battery, of course you want the same range from the system so your 100V is, for instance, 1P
while the 50V is a 2P battery. Then the losses in the battery are the same for both cases.
Same goes for the controller. At 50V you'll use 4110's while at 100V 4115's (as an example). Point is, the 50V
controller will have lower on-resistance FETs than the 100V controller such that the losses are the same again.
It all comes down to personal preference...
the way, and not only because he lives in a tropical country
so cold here now).The 50V versus 100V battery, of course you want the same range from the system so your 100V is, for instance, 1P
while the 50V is a 2P battery. Then the losses in the battery are the same for both cases.
Same goes for the controller. At 50V you'll use 4110's while at 100V 4115's (as an example). Point is, the 50V
controller will have lower on-resistance FETs than the 100V controller such that the losses are the same again.
It all comes down to personal preference...
Jeremy Harris
100 MW
Lebowski said:OK, Jeremy, your equations etc are correct but don't describe what really goes on (I'm in Johns camp by
the way, and not only because he lives in a tropical country
The 50V versus 100V battery, of course you want the same range from the system so your 100V is, for instance, 1P
while the 50V is a 2P battery. Then the losses in the battery are the same for both cases.
Same goes for the controller. At 50V you'll use 4110's while at 100V 4115's (as an example). Point is, the 50V
controller will have lower on-resistance FETs than the 100V controller such that the losses are the same again.
It all comes down to personal preference...
Yes, if you change the comparison so that you use a different battery, controller etc, then of course you will get a different result, but that's the apples and oranges thing again. The controller and wiring losses are reasonably valid, though. Also, it makes sense to use the lowest resistance controller you can no matter what the system voltage. Certainly the battery internal resistance would be lower for the lower voltage case, if you changed the ground rules to make the cells dissimilar for each case.
For example, let's go back to the comparison I made originally, where the requirement was for the same top speed and the same ability to climb a 10% gradient hill, a fairly typical sort of requirement. The system voltages worked out at 36V for the 2805 motor and 55V for the 2808 motor for the required performance. You could easily use the same 12off 4110 FET controller for both of these (which is exactly what I did in that comparison) as that would give the same cost, size and weight for each. You could also adjust the battery capacity to give the same range for both cases (which is also exactly what I did originally) and that does change the internal resistance for each. You still get a few percent efficiency advantage from running the slower wind motor at a higher voltage though, just because of the fact that the resistive losses are proportional to the cube of current.
The point I've been trying (and failing, it seems) to make here is that it is always more efficient to use a higher voltage and lower current in any system in order to get a given power. I don't see how this can be disputed, TBH.
Jeremy Harris
100 MW
OK, as this seems to be hard for some to understand, here is another worked example, using the 2805 and 2808 motors referred to earlier, but doing what I did earlier and assuming that the range and performance requirement is the same for both.
Let's say we have two identical bikes, ridden by riders with exactly the same weight.
One bike has a 2805 motor, one has a 2808 motor.
We want the same top speed from each and we want the same range for each, plus each has to be the same weight.
To get the same top speed, range and battery weight, one bike has a 36V battery with a capacity of 23Ah, the other has a 55V battery with a capacity of 15Ah (i.e. both bikes have ~825 Wh available).
The 36V battery has an internal resistance of 0.036 ohms, the 55V battery has an internal resistance of 0.055 ohms (internal resistance has been scaled to reflect capacity and voltage)
We use the same controllers on both bikes, with a total resistance of 0.01 ohms
The wiring and connectors are identical on both bikes, and have a total resistance of 0.02 ohms
We need 1000W to get the performance we need.
Which bike has the lowest losses and is the more efficient?
Here are some numbers:
The bike with the 2805 (fast wind) motor has battery, controller and wiring losses of about 51W (5.1%)
The bike with the 2808 (slow wind) motor has battery, controller and wiring losses of about 28W (2.8%)
Clearly the bike with the slow wind motor is more efficient than the bike with the fast wind motor. This isn't rocket science and shouldn't be the subject of a lengthy debate here at all. Anyone doing as I did originally, who runs a few comparisons through Justin's ebike simulator will get similar results, results that match well to real performance.
Let's say we have two identical bikes, ridden by riders with exactly the same weight.
One bike has a 2805 motor, one has a 2808 motor.
We want the same top speed from each and we want the same range for each, plus each has to be the same weight.
To get the same top speed, range and battery weight, one bike has a 36V battery with a capacity of 23Ah, the other has a 55V battery with a capacity of 15Ah (i.e. both bikes have ~825 Wh available).
The 36V battery has an internal resistance of 0.036 ohms, the 55V battery has an internal resistance of 0.055 ohms (internal resistance has been scaled to reflect capacity and voltage)
We use the same controllers on both bikes, with a total resistance of 0.01 ohms
The wiring and connectors are identical on both bikes, and have a total resistance of 0.02 ohms
We need 1000W to get the performance we need.
Which bike has the lowest losses and is the more efficient?
Here are some numbers:
The bike with the 2805 (fast wind) motor has battery, controller and wiring losses of about 51W (5.1%)
The bike with the 2808 (slow wind) motor has battery, controller and wiring losses of about 28W (2.8%)
Clearly the bike with the slow wind motor is more efficient than the bike with the fast wind motor. This isn't rocket science and shouldn't be the subject of a lengthy debate here at all. Anyone doing as I did originally, who runs a few comparisons through Justin's ebike simulator will get similar results, results that match well to real performance.
dogman dan
1 PW
John, that IS what I keep saying. Slow winding climbs a hill or leaves a stop sign better when used with low power and low speeds. It's true though, that a few years back I thought they would do more. But even then I don't recall calling it more torque, only that it felt that way to the rider.
When I up the power on the slow motor on my dirtbike, and roar around on really steep hills or other high load situations I melt motors. Not as quickly as I melted faster windings when I screw myself with a 26" wheel, but I still melt a motor a year at least. Feed a cheap little 9c motor too much power under load, you'll melt em.
It's others that put thier interperetations on it based on thier fantasy of getting a magical motor. We all know the guy who writes and writes about his fantasy bike, and tries to get one of us to say it will be a dream come true. Then we keep replying, yeah, BUT. Insert "it will cost more than $1000" or "you will need a 30 pound battery" here.
It's true, the originator of this thread may be dissapointed when he gets a 2810 9c. He'll find it only moderately fast at 72v, and it damn sure isn't going to be more powerfull than a 2807 9c. But if he rides though lots of stop signs, he'll use a little less of his battery starting up again over and over. if he feeds it 3000w, he'll still be able to melt it. The slower top speed will mean that he can't feed it 3000w at full speed on the flat, so that makes it take a wicked hill or headwind to melt a motor. Wicked hill defined as about 15 to 20 degrees, degrees not %. STEEP. But he won't melt down climbing 10% for miles and miles of it, and will be able to climb steeper hills without melting down if he can keep it going 12 mph. Going slower on the flat, he just won't be drawing much more than 1200w because that is usually all it takes to go 30 mph. So in the end, the cooler motor is partly just a result of riding no faster than 30 mph or so.
No special winding will make a 9c perform like a larger motor with big magnets and pounds more copper. It will just perform cooler more efficient, at the slow end of the rpm spectrum is all.
That's why I took the 9c off my heavy cargo bike recently, and put a faster winding more powerfull 5304 on it. Once I had a better motor, I put it on the heavy cargo bike immediately. But if I had the opportunity to replace the 5304 with a 5305, I'd do it. The faster longtail is fun, but it does us up a battery mighty fast.
When I up the power on the slow motor on my dirtbike, and roar around on really steep hills or other high load situations I melt motors. Not as quickly as I melted faster windings when I screw myself with a 26" wheel, but I still melt a motor a year at least. Feed a cheap little 9c motor too much power under load, you'll melt em.
It's others that put thier interperetations on it based on thier fantasy of getting a magical motor. We all know the guy who writes and writes about his fantasy bike, and tries to get one of us to say it will be a dream come true. Then we keep replying, yeah, BUT. Insert "it will cost more than $1000" or "you will need a 30 pound battery" here.
It's true, the originator of this thread may be dissapointed when he gets a 2810 9c. He'll find it only moderately fast at 72v, and it damn sure isn't going to be more powerfull than a 2807 9c. But if he rides though lots of stop signs, he'll use a little less of his battery starting up again over and over. if he feeds it 3000w, he'll still be able to melt it. The slower top speed will mean that he can't feed it 3000w at full speed on the flat, so that makes it take a wicked hill or headwind to melt a motor. Wicked hill defined as about 15 to 20 degrees, degrees not %. STEEP. But he won't melt down climbing 10% for miles and miles of it, and will be able to climb steeper hills without melting down if he can keep it going 12 mph. Going slower on the flat, he just won't be drawing much more than 1200w because that is usually all it takes to go 30 mph. So in the end, the cooler motor is partly just a result of riding no faster than 30 mph or so.
No special winding will make a 9c perform like a larger motor with big magnets and pounds more copper. It will just perform cooler more efficient, at the slow end of the rpm spectrum is all.
That's why I took the 9c off my heavy cargo bike recently, and put a faster winding more powerfull 5304 on it. Once I had a better motor, I put it on the heavy cargo bike immediately. But if I had the opportunity to replace the 5304 with a 5305, I'd do it. The faster longtail is fun, but it does us up a battery mighty fast.
Lebowski
10 MW
This is however not the correct scaling. Lets go to the (numerically easier) 100V and 50V example. Lets say the 100 V has 0.1 Ohm internal resistance. For 50V we split the 100V battery in 2 of 50V (each having 0.05 Ohm). As we want the same capacity we place the two 50V batteries in parallel and end up with 0.025 Ohm internal resistance. Factor 2 in voltage -> factor 2 in current but factor 4 in internal resistance.Jeremy Harris said:
So, if 55V has 0.055 Ohm 36V will have 0.0236 Ohm... 1000W taken will have 18.2W losses for both.
Jeremy Harris
100 MW
Lebowski said:
Yes, my arithmetic error, not that it changes the overall outcome. The slower wind system is still more efficient than the faster wind system. I cannot for the life of me see why this point is so contentious, it seem to be blindingly obvious to me that reducing the system current for a given power will improve overall efficiency. After all, this is the reason power distribution companies step up the voltage on transmission lines, it's not really something that difficult to grasp, is it?
FWIW, the figures in my last post, when corrected for the arithmetic error I made when doing the sums, change by about 1% to:
The bike with the 2805 (fast wind) motor has battery, controller and wiring losses of about 41.3W (4.1%)
The bike with the 2808 (slow wind) motor has battery, controller and wiring losses of about 28.1W (2.8%)
The slow wind motor system is still more efficient overall than the fast wind motor system.
John in CR
100 TW
Electric companies have to carry the power the same distance. The motor does not, because the not only are each turn of the windings thicker wire, but they are also shorter. Identical copper fill in an otherwise identical motor will have identical efficiency with voltage and current changed proportionately for the same rpm and power.
shock
1 kW
All this jargon belongs in technical!!
Need more 9c sources in USA!!
Need more 9c sources in USA!!
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