Something that i saw on youtube-controller question.

[mountainsport]

Hi All,

Is it possible for 48volt 20amp battery using a 20amp controller push up to speeds of 30mph? At times I do get confused, I understand that they all work together in unison-48v equals the (strength) 20amp equals the (distance) and 20amp controller equal to in other words the (regulator). Please do not quote me on this but this is the way that I am thinking, whether right or wrong.

Therefore, in hindsight a higher amp controller should really bump up the speed of the bike. I've even seen again on youtube 1000watts/500watts motors-48volts batteries doing way over 30-40mph. Are these people for real or in a dream world by themselves ?
Can someone explain so that I could understand this once and for all.
I know that this is a simple question for you all

Mountainsport.

 

[oigoi]

A 48v battery with a 20a controller on a suitable motor you are talking about roughly 1000W so 30mph would seem a realistic speed to me. I have a 24v motor rated at 500W (not sure how many A it is drawing) and comfortably cruise in the 20s.

 

[amigafan2003]

Yes, easily. My bike does 25mph @ only 63v / 11 amps.

You just need a high turn (or wind) motor to do high speed - something like a 14t Bafang BPM would do 30mph @ 48v.

Basically, on a motor, voltage determines the speed at which the motor spins. Amps on the controller determines how strong the motor is - or how quickly it gets to top speed and amp/hours on the battery determines how long those amps on the controller can be suplpied for - think of it like a fuel tank on a car.

They are all interrelated though - if you have high voltage you have high speed on the motor, but it also needs the amps to be able to turn at that speed- i.e. 48v might give you the potential for 30mph but if you only have 5 amps from the controller you'll be lucky to get to 15mph (power draw increase logrithmically as sped/wind resistance increases - i.e. you need twice the amount of energy to do 15mph as opposed to 10mph and twice as much again to do 20mph, twice as much again to do 25mph etc). Also, you might have a motor that can do 30mph @ 48v and the controller set to 40 amps but if your battery only has 5amp/hours capacity you'll run out of energy in 7 minutes, so what's the point?

A good ebike is one that balances all these three factors so no one individual component is stressed too highly.

 

[103Alex1]

Getting extra speed on the flat is pretty straightforward. You just have to trade off that the high wind motors which easily give you greater speed on the flat usually don't climb so well.

 

[Deleted member 4366]

48v and 20A would be enough to reach 30mph in favourable conditions, but, depending on the size of the rider, 25mph would be a more realistic speed, and it depends a lot on the winding of the motor. You'd need one woound for about 40mph to be able to sustain 30mph, and then your acceleration and climbing would be poor.

 

[mountainsport]

Getting extra speed on the flat is pretty straightforward. You just have to trade off that the high wind motors which easily give you greater speed on the flat usually don't climb so well.

Alex,

That is a very good and valuable hidden point too, that one really touched me.

Mountainsport.

 

[mountainsport]

Yes, easily. My bike does 25mph @ only 63v / 11 amps.

You just need a high turn (or wind) motor to do high speed - something like a 14t Bafang BPM would do 30mph @ 48v.

Basically, on a motor, voltage determines the speed at which the motor spins. Amps on the controller determines how strong the motor is - or how quickly it gets to top speed and amp/hours on the battery determines how long those amps on the controller can be suplpied for - think of it like a fuel tank on a car.

They are all interrelated though - if you have high voltage you have high speed on the motor, but it also needs the amps to be able to turn at that speed- i.e. 48v might give you the potential for 30mph but if you only have 5 amps from the controller you'll be lucky to get to 15mph (power draw increase logrithmically as sped/wind resistance increases - i.e. you need twice the amount of energy to do 15mph as opposed to 10mph and twice as much again to do 20mph, twice as much again to do 25mph etc). Also, you might have a motor that can do 30mph @ 48v and the controller set to 40 amps but if your battery only has 5amp/hours capacity you'll run out of energy in 7 minutes, so what's the point?

A good ebike is one that balances all these three factors so no one individual component is stressed too highly.

Nicely explained buddy.

Mountainsport.

 

[mountainsport]

48v and 20A would be enough to reach 30mph in favourable conditions, but, depending on the size of the rider, 25mph would be a more realistic speed, and it depends a lot on the winding of the motor. You'd need one woound for about 40mph to be able to sustain 30mph, and then your acceleration and climbing would be poor.

d8veh,

In other words you are saying that a fast winding motor with a 40amp controller should increase more torque/acceleration and hill climbing ability?

Mountainsport

 

[Marctwo]

According to the formula used here, to move a cycle/rider @30mph through still air on the flat takes a bit less than 800W. Given an optimum efficiency of 80%, you'd need to supply ~1KW or more.

I don't know as much as the other guys about motors but my understanding is:
When the motor runs at full speed without resistance, it draws very little power. When you add resistance like the friction of a bike/rider cutting through the air, the motor slows down and draws more power to try to reach it's full speed. The greater the resistance, the slower the motor and the more power is drawn. So it's a question of how much speed the motor loses before reaching the required (1KW) power draw. Assuming the motor is 80% efficient at 30mph... which is quite an assumption. If not, you'd need to get the lycra out.

A high speed motor will lose more speed than a high torque motor to get to the same power.

 

[Deleted member 4366]

d8veh,

In other words you are saying that a fast winding motor with a 40amp controller should increase more torque/acceleration and hill climbing ability?

Mountainsport

That's right. To put it in perspective, a 30mph restricted petrol scooter's motor produces about 2.5 kw upwards.

 

[Scimitar]

As a quick comparison - my 750W 36V hubmotor will hit 26mph on the flat, when the battery is not long off charge, so about 38V under load and it's drawing approx 22A at that point. The slightest hill and it shoots up to 30A, though.
Throttle control is a finesse - it's possible to cruise along on a whisper and draw a miserable 6A to sustain 15mph, so I could really eke it out if I wanted, but I can't be bothered with that.

 

[mountainsport]

As a quick comparison - my 750W 36V hubmotor will hit 26mph on the flat, when the battery is not long off charge, so about 38V under load and it's drawing approx 22A at that point. The slightest hill and it shoots up to 30A, though.
Throttle control is a finesse - it's possible to cruise along on a whisper and draw a miserable 6A to sustain 15mph, so I could really eke it out if I wanted, but I can't be bothered with that.

Hi Dave,

You say your hitting 26mph on your bike, but with what size controller are you using? I know that it is down to the individual, either requiring more speed/torque/acceleration and distance,how is the controller size determined or rated?

Mountainsport