XTreme XB-700Li controller mod suggestion?

[ProDigit]

Hi all,

I own an XTreme XB-700Li e-bike/scooter/motorbike whatever you will want to call it!
It has a 700W brushless motor,and a 48V/20Ah liPo battery.
I'm pretty content about the device, except for it's speed.

I live in Florida, where these bikes still are allowed to go 30MPH max (Unlike the rest of the country where they can only go 20MPH).

So I did some tests, and came to the conclusion that the bike can go faster.
There is a limiter within the bike, literally limiting it to a ~10MPH speed, and with limiter unplugged, it can go 20MPH.
The internal meter displays 27MPH, but an external speedometer tells me I'm going only 20MPH.

I find this speed quite unsafe to drive in the city, being constantly surpassed by other cars.
what I would like is to have a 10MPH boost, or increase in speed.
Worst case, I'd be really happy if my bike would go just 5MPH faster! That 5MPH makes a big difference to me!

I'm very sure that the bike is limited to the controller's speed, as with semi flat tires, going on a light hill, with wind against, the bike drives just as fast as going downhill wind in the back and fully inflated tires.

I already wrote the company, and they said that's the fastest the bike can go.
Yes, the limiting factor is definitely the controller.

So my choice is either to change the controller, or modify it.
Heck, if someone could help me getting even 2MPH more out of it, you'd be a champion!

I believe adding a second battery in parallel with the primary battery will not solve the issue, as the battery pack has more than power enough to push the bike beyond 35MPh if you ask me! I'm pretty shy of adding another battery in series with the pack i have now. If it would help, I would put a 3-6V battery max in series. I don't want to burn the controller, nor the internal electronics.
Only problem would be finding a 3-6V 20Ah battery (40Ah peak) with BMS and charger (and a way to charge them, presuming if having the battery connected in series with the other battery charging like this would not work).

Any suggestions?

If not, what would be a very good replacement controller? I don't need to go 50MPH, 25 to 30MPH is more than enough!

[amberwolf]

What is the unloaded wheel speed (off ground) at full throttle without any limiting in place? Take something like 80% of that speed, and that is likely to be the max road speed you will get out of that motor at your particular battery voltage.

It is possible that without increasing voltage the wheel won't spin any faster even with a different controller; it might simply be the fastest it will go at your current battery voltage.

If the controller is actually limiting speed even with the limiter disconnected, then if you have an oscilloscope available you can see this by connecting the scope across two phases of the motor. If the scope can't handle that voltage input, then you could hook it from ground to the gate input of any phase, inside the controller. Either one will show you the commutation waveform, and if that is sliced up by PWM even off-ground no-load full-throttle, then you could increase speed by changing to a controller that does not do that under the same conditions, as the average voltage will be higher.

If you don't have a scope I'm not sure of an easy way to know if a different controller will change anything or not, without also increasing battery voltage.

[ProDigit]

I'm pretty sure it's the controller that's limited. Unfortunately off ground I won't be able to measure speed very well, but I'll do this test regardless.

The battery has 20A continuous power, and a 700W motor (@48V = 14,5A).
I've also seen results of people gaining similar speeds on direct drive motors, with lower battery capacities, and lower motor power handling.
I'm quite sure the motor could go upto 35, if not 45MPH.

The controller probably does not rotate pulses fast enough through the various phase wires of the motor.

Unfortunately I do not have an oscilloscope available for further testing.

[amberwolf]

Depending on how it's made, you could move the wheel speed sensor from the non-motor wheel to the motor wheel, assuming that's the problem with measuring motor speed. Or use an old bicycle speedo, or similar.

Regarding motor wattage/etc. vs speed: Unfortunatley just because a motor is capable of a certain wattage doesn't mean it's wound in a way that allows it to spin as fast as a similar wattage motor. For instance, the 9C 28xx comes wound in several varieties (2807, 2808, 2810, 2812, etc), all of which are rated for 500W but can be run at 2KW, at least. However, each of the windings has a different top speed, if they are all at the same voltage on the same controller.

That's why I recommend verifying its speed off ground at a particular voltage, so you have a better idea what is limiting it.


FYI--if the off-ground motor speed is still only 20MPH, then the controller is definitely limiting it, because it ought to spin around 20% faster than that if the 20MPH loaded speed on the road was limited because of the voltage of the motor, or the wattage of the controller.

[ProDigit]

There are certain types of motors that are limited in their speed, and others when ran without load they'd spin out of control.

This motor is of the first type, it has a higher torque than the secondary motor type, but it's speed is limited, even under no load. Yet when driving the motor past it's maximum rated speed, the motor will start to throttle. And I have not seen any of this happening (yet).
I firmly believe that this motor has more to offer; and it's limitation is the controller; I'm more than 90% sure of that!

[nicobie]

The head admin. of this forum has a saying that you need to follow more often.

"One test is worth 1000 opinions"

"80% sure" doesn't cut it.