Desertprep
1 kW
If brushless motors are so much more efficient than brushed motors why are brushed motors (hub and chain drive) still being sold? Is there some other advantage?
Brushed motors?
- Thread starter Desertprep
- Start date
Drunkskunk
100 GW
Price.
There's nothing wrong with a brushed motor, but the only thing it can do better is dent your wallet less.
Brushed motors will wear out, and the brushes need to be changed out every so often. Its not as reliable as brushless.
There's nothing wrong with a brushed motor, but the only thing it can do better is dent your wallet less.
Brushed motors will wear out, and the brushes need to be changed out every so often. Its not as reliable as brushless.
Desertprep
1 kW
I see. But brushless motor mfg advertise that their motors are 20-30% more efficient than brushed motors. Is this true?
lawsonuw
1 kW
pengyou said:
That's not true as most people would read it. Decent brushed motors can get up in the the 70% plus efficiency range. (good, ones can exceed 80%) Directly adding 20-30% to that efficiency would mean that the brushless motors were getting 90% (super expensive) to greater than 100% (not really possible) efficiency. What they should say is a 20-30% reduction in losses. So assuming a 70% efficient brushed motor and a "30% better" brushless motor this would put the brushless motor at about 80% efficiency.
My 2 cents,
Marty
Drunkskunk
100 GW
Yes.
Most of my experiance with brushless motors comes from RC airplanes. with them, the brushless motors can be 40-50% more efficent.
On a brushed motor, the brushes are carbon: essentualy, resistors. They also aren't in 100% contact all the time with the stator, so you get some losses through the air gap as the brush skips along the stator pads. Then there is the frictional resistance which is low but always presant, and carbon dusting as the brushes break down, that adds some high resistance shorts between the coils, allowing some of the currant to bleed over to the coils that are suppose to be off and causing them to fight the coils that are live. it also works in reverse were they cause that coil to become a generator and feed back against the movment of the armature.
Plus its DC currant, which is the least efficent way to move electricity. Brushless motors are pulsed DC, which is essentualy AC currant, and at higher frequancy, so the losses there are much lower than brushed DC. round that all off with the fact that its a computer thats handling when to fire each coil on a brushjless motor, instead of a mechanical brush, and you get your increased efficancy in small stages.
Its all small losses of efficancy for a DC motor, but they add up.
Most of my experiance with brushless motors comes from RC airplanes. with them, the brushless motors can be 40-50% more efficent.
On a brushed motor, the brushes are carbon: essentualy, resistors. They also aren't in 100% contact all the time with the stator, so you get some losses through the air gap as the brush skips along the stator pads. Then there is the frictional resistance which is low but always presant, and carbon dusting as the brushes break down, that adds some high resistance shorts between the coils, allowing some of the currant to bleed over to the coils that are suppose to be off and causing them to fight the coils that are live. it also works in reverse were they cause that coil to become a generator and feed back against the movment of the armature.
Plus its DC currant, which is the least efficent way to move electricity. Brushless motors are pulsed DC, which is essentualy AC currant, and at higher frequancy, so the losses there are much lower than brushed DC. round that all off with the fact that its a computer thats handling when to fire each coil on a brushjless motor, instead of a mechanical brush, and you get your increased efficancy in small stages.
Its all small losses of efficancy for a DC motor, but they add up.
Desertprep
1 kW
Wow! Smart people 
To me the bottom line is the total cost of buying/operating the system over 3 years. It doesn't make sense to me if I save $140 on the controller/motor combo if I have to spend $20 a year ($60 for 3 years) to replace brushes, have to pay an extra $150 for extra batteries to make up for the inefficiency and have to factor the intangibleness of unreliability into the equation as well.
Is there some way I can come up with tangible numbers for this kind of decision?
To me the bottom line is the total cost of buying/operating the system over 3 years. It doesn't make sense to me if I save $140 on the controller/motor combo if I have to spend $20 a year ($60 for 3 years) to replace brushes, have to pay an extra $150 for extra batteries to make up for the inefficiency and have to factor the intangibleness of unreliability into the equation as well. Is there some way I can come up with tangible numbers for this kind of decision?
It's hard to predict. Brush wear is only one factor. I've put many, many miles on a brushed motor and the brushes are still fine. Whenever it craps out, it is inexpensive to replace.
Brushless motors will never need new brushes, but controller reliability tends to be an issue. It's a trade-off.
Brushed or brushless, the higher quality units will last longer.
The difference in motor efficiency will affect battery cost, but again, other factors such as charger design and depth of discharge will play a greater role in battery life.
By overdesigning, you can generally increase service life. Use a motor that's a bit larger than needed. Use a battery that's way larger than needed so the depth of discharge is limited.
Pay attention to other failure modes. Many e-vehicle problems are caused by bad connections in the wiring and corrosion. Water getting into the controller is another common cause of failure. Most commercially available systems use undersized wire to save money. Upgrade to heavier wire.
Brushless motors will never need new brushes, but controller reliability tends to be an issue. It's a trade-off.
Brushed or brushless, the higher quality units will last longer.
The difference in motor efficiency will affect battery cost, but again, other factors such as charger design and depth of discharge will play a greater role in battery life.
By overdesigning, you can generally increase service life. Use a motor that's a bit larger than needed. Use a battery that's way larger than needed so the depth of discharge is limited.
Pay attention to other failure modes. Many e-vehicle problems are caused by bad connections in the wiring and corrosion. Water getting into the controller is another common cause of failure. Most commercially available systems use undersized wire to save money. Upgrade to heavier wire.
Drunkskunk
100 GW
you can, but there is a lot of information you would need to go through first, all specific to your needs.
If I remember right, what you need is a bike that can go 100 miles through the countryside in rural China. Not an easy task.
it might be easier to start by coming up with a plan for a bike that can acomplish this goal, and come up with a list by type and price of all the parts you would need to do it safely and reliably, THEN start analyzing it for cost VS reliability.
When you already have a plan for a bike that will meet your most important goal, its easier to start making comparisons and putting together tangible numbers to compare various parts for it.
If I remember right, what you need is a bike that can go 100 miles through the countryside in rural China. Not an easy task.
it might be easier to start by coming up with a plan for a bike that can acomplish this goal, and come up with a list by type and price of all the parts you would need to do it safely and reliably, THEN start analyzing it for cost VS reliability.
When you already have a plan for a bike that will meet your most important goal, its easier to start making comparisons and putting together tangible numbers to compare various parts for it.
Eric G
1 kW
First I totally agree with the what's been said above...
I've been running brushed motors in an ebike for a few years now.This was my choice of motor because of the cost factor. I have yet to replace a set of brushes and ride daily and have put 1100 kilometers on a new Clyte brushed motor since May of this year.The reason for the getting a new motor was for extra power I bumped up from 250watt to 600watt the old motor still runs fine. I plan on keeping this setup for at least another few years.Yes there will be some maintenence cleaning out and brush replacement down the road but I don't really see that as an issue. I remember reading that the brushes should last to about 6000 miles.
The only issue with my setup I see arrising is my batteries which are 36v7.2ah sla.They're still holding out but distance is limited,with light pedaling I can go ~ 10 kilometers before the batts get to ~ 30% to 40% depth of discharge but that all depends which way the wind blows and how strong. These batteries should last me a year.When they die I'll be switching to another chemistry.
As DS says plan it all out first to find out what will meet your needs and then go from there...
Good Luck
Eric
I've been running brushed motors in an ebike for a few years now.This was my choice of motor because of the cost factor. I have yet to replace a set of brushes and ride daily and have put 1100 kilometers on a new Clyte brushed motor since May of this year.The reason for the getting a new motor was for extra power I bumped up from 250watt to 600watt the old motor still runs fine. I plan on keeping this setup for at least another few years.Yes there will be some maintenence cleaning out and brush replacement down the road but I don't really see that as an issue. I remember reading that the brushes should last to about 6000 miles.
The only issue with my setup I see arrising is my batteries which are 36v7.2ah sla.They're still holding out but distance is limited,with light pedaling I can go ~ 10 kilometers before the batts get to ~ 30% to 40% depth of discharge but that all depends which way the wind blows and how strong. These batteries should last me a year.When they die I'll be switching to another chemistry.
As DS says plan it all out first to find out what will meet your needs and then go from there...
Good Luck
Eric
safe
1 GW
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I've put about 2,500 of my bikes total 3,150 miles on the same cheap brushed motor from Unite. I don't baby it either and run flat out as hard as possible all the time. As long as your motor is appropriate for what you are doing and you aren't making some sort of heating mistake (a whole other topic) I'd guess that the cheap $80 motor will do well enough.
Batteries wear out faster than motors do so if you are going to focus your money on something for maximum return I'd focus on the battery side.
The Unite motors are cheap and get about 80% peak efficiency. The brushless motors typically peak at about 88% or slightly higher, but then they cost about twice as much. The controllers are also more expensive too. Cheap brushed controllers can be had for $50.
There's also the initial investment question... just how much to you want to spend initially? You get better stuff if you pay more, but how long do you plan on sticking with the same bike? My experience has been that you tend to use a bike a lot for a year or two and then upgrade to something new after that. For someone wanting to get into electric bikes the idea of spending $1000 just to get in is a little bit frightening.
After a while you become an "addict" and want more and more... so then you spend more without realizing it... 
Batteries wear out faster than motors do so if you are going to focus your money on something for maximum return I'd focus on the battery side.
The Unite motors are cheap and get about 80% peak efficiency. The brushless motors typically peak at about 88% or slightly higher, but then they cost about twice as much. The controllers are also more expensive too. Cheap brushed controllers can be had for $50.
There's also the initial investment question... just how much to you want to spend initially? You get better stuff if you pay more, but how long do you plan on sticking with the same bike? My experience has been that you tend to use a bike a lot for a year or two and then upgrade to something new after that. For someone wanting to get into electric bikes the idea of spending $1000 just to get in is a little bit frightening.
After a while you become an "addict" and want more and more... so then you spend more without realizing it...
Desertprep
1 kW
Arrow "After a while you become an "addict" and want more and more... so then you spend more without realizing it... "Shocked
..... a while?
................a while?
..........................A WHILE?
hehehehehehe time is a very relevant thing I think it is too late for me and I have only had my ebike for 6 weeks.
..... a while?
................a while?
..........................A WHILE?
hehehehehehe time is a very relevant thing
I think it is too late for me and I have only had my ebike for 6 weeks.
ChopperMan
10 W
This is the cost / performace setup between my brushed / brushless setups;
Brushed - Powerbyke geared hub motor and 36V 40Amp scooter controller, £105 and 15mph. 7mph up an 8% hill.
Brushless - Puma geared hub motor and C'lyte 35Amp controller, £440 and 20mph. 14mph up an 8% hill.
This was on the same MTB and 36V 18Ah SLA battery pack. If you live in a hilly area and are of generous a disposition, the high power brushless setup is worth every penny.
From the point of view of reliability, neither have failed on me, yet. Brushed setup 1,000+ miles this summer, 50% off road. Puma only 50 testing miles. So time will obviously tell.
Cheers,
Ian
Brushed - Powerbyke geared hub motor and 36V 40Amp scooter controller, £105 and 15mph. 7mph up an 8% hill.
Brushless - Puma geared hub motor and C'lyte 35Amp controller, £440 and 20mph. 14mph up an 8% hill.
This was on the same MTB and 36V 18Ah SLA battery pack. If you live in a hilly area and are of generous a disposition, the high power brushless setup is worth every penny.
From the point of view of reliability, neither have failed on me, yet. Brushed setup 1,000+ miles this summer, 50% off road. Puma only 50 testing miles. So time will obviously tell.
Cheers,
Ian
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