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I wanted to ask if a brushless controller Current actually affects electric bicycle speed.
At the moment I have a 48V 250W brushless controller, rated current of 5A and maximum current of 10A. protection voltage is 42V.

Here is a more detailed picture about my controller plugs, etc:

enter image description here

So my main question is: if I switch to a same brushless controller but just this time with lets say a maximum Current of 17A, will it make any difference in any way?

I also tried talking with the manufacturer and I didn't get a flat answer; they said it won't affect on the speed but I read in a few places that it might.

My Battery: 48V 13Ah
My Motor: 48V 250W ( model: bafang swx02 )

Also another question, is there any way to make my ebike drive faster than 25 km/h without switching the motor?

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To a first approximation (a flat, level road), increasing the current capability (not the current) will have no effect on your speed.

A BLDC motor is effectively driven at a certain AC frequency, and the motor turns at one revolution per cycle of the drive. As long as the motor gets enough current to produce the force necessary to overcome friction and drag, increasing the current available won't change anything. And you should note that, from a power perspective, it's clear that your battery and motor are well-matched. The motor is rated for 5 amps @ 48 volts (peak 10 amps), for a total of 240 watts (480 peak). The motor is rated for 250 watts, so the motor is the limiting factor.

So the first thing you would need to do is replace the motor. However, you would also probably need to replace the controller as well. I suspect there is a speed limiter somewhere in there.

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  • \$\begingroup\$ Nice to meet you WhatRoughBeast, I really appreciate your helpful comment it got me to see it in a different way, and I've got a similar question to you. I was wondering this whole about my controller because when I used to put my 48V battery on my friend's bike it used to drive about 35 km/h when on my bike it's only 25 km/h. And the weird part is that he has a 250W motor as well, the whole point of a 48V battery that it can reach 35 km/h+ but the speed I get to, is the same when I also use a 36V battery. \$\endgroup\$ – user146333 Apr 14 '17 at 18:24
  • \$\begingroup\$ "the whole point of a 48V battery that it can reach 35 km/h+ but the speed I get to, is the same when I also use a 36V battery." - could be his motor has higher Kv or is geared higher, or your controller is limiting speed (though the instructions say it shouldn't) or the battery voltage is collapsing. In any case going from 36V to 48V (33% higher) will not increase speed from 25K to 35k+. You need at least 40% higher voltage (and ~2x more power) get that speed increase. \$\endgroup\$ – Bruce Abbott Apr 14 '17 at 18:40
  • \$\begingroup\$ But this is the weird part, that on my friend's bike even when I change from his 36V battery (that gets 30 km/h full charged) to a 48V battery it gets to about 35+ km/h, but on my bike it functions like a 36V battery. I doubt the battery voltage is collapsing but at first I thought the problem was in the controller, limiting me. I asked a seller he told me this specific ebike model was made to save battery, so I was sure it's only the controller and not my motor because my friend has a similar motor, any tips on what changes could be make to the controller to drive faster? \$\endgroup\$ – user146333 Apr 14 '17 at 18:52
  • \$\begingroup\$ @LiquidElectricity - Without seeing the controller circuitry, there is simply no way to tell. In the worst case, the controller is built around a micro-controller chip, and the speed limit is built into the software. And yes, limiting top speed is a good way to extend battery life - aerodynamic drag increases as the square of velocity, so doubling speed (assuming drag is the big energy loss) will cut range by about 50%. \$\endgroup\$ – WhatRoughBeast Apr 14 '17 at 23:04
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The motor will draw whatever current it wants to unless the speed controller limits current for torque control or to protect itself. If your motor would normally draw less than 5A at top speed then using a higher rated controller won't make a significant difference (it might be very slightly faster due to lower voltage drop across the FETs in the controller).

Motor speed is proportional to voltage. If you want more speed (and can't gear it up) then use a higher voltage battery. Just realize that it will draw more power, which may damage the motor or controller if their ratings are exceeded. You will need a higher voltage controller as well as extra batteries, so you might consider replacing the entire drive chain.

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  • \$\begingroup\$ Thanks for the helpful comment! I up-voted as a thank you :) \$\endgroup\$ – user146333 Apr 14 '17 at 18:19
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Voltage correlates to raw (unloaded) speed, current correlates to torque and overall power (loaded speed). The current handling of your motor is going to limit your speed. There won't really be a way to go faster without changing out your motor.

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  • \$\begingroup\$ Thanks for the helpful comment! I up-voted as a thank you :) \$\endgroup\$ – user146333 Apr 14 '17 at 18:19
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open the controller, find the shunt and add a bit of solder it will increase amps output allowing more torque, as well as speed if the current was limited down low enough (which 5A sounds a little low to me) this would cost a bit off of the battery range.

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  • \$\begingroup\$ "add a bit of solder" as in short circuiting the shunt resistor? Doesn't sound like a safe procedure to me. \$\endgroup\$ – Huisman Jan 6 at 22:15

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