Motor wattage flatlines. Baffled. Any idea why???

Hi guys. I'm new to endless sphere but hear it's a must for anyone DIY'ing ebikes. And I mean just look at the pics. I am pretty deep in this project. So his name is Ghost. He started as a regular off-the-shelf RadRunner from the online store at rad power bikes. Since I got him a year ago, I've done successive modifications on him until he is now [/img] unrecognizable. Like the age old saying goes, if you replace every part of a ship over time, is it still the same ship?

In this case, kinda but not really. I've overhauled every piece of circuitry on this thing except the motor, because I wanted him to go faster. Waaaay faster. Crunched the numbers and figured out, 20? Nah I know we can go 50. Check out that 100 tooth crank gear. Came from Australia. Every piece of this infuriating puzzle has tried its hardest to keep from being put together:

-new motor didn't fit
-rear wheel not wide enough for a freewheel/cassette so no shifting
-printed and soldered a faux phase generator to disable the 20 mph speed limiter that (surprise!) didn't work
-rewired a new battery which fried the old display somehow, still not sure about that one

As well as a plethora of other problems I can't even remember. He's been operational about as long as he's been upside down scattered across the workshop.

So, that frickin speed limiter that I've been trying to rip out since the moment he first arrived?

Ordered a new controller, throttle, display and replaced all the old electronics. It took two months, the second one being more banging my head against the wall and staring at his sad corpse defeated more than anything-

BUT HES FINALLY UP AND RUNNING AGAIN!!!!!!!!

Finally today I felt like I was on top of the world again. Something to be broken that you've put so much love into is disheartening. But he's finally back. And no surprise, but he's gotten himself into trouble. AGAIN. ALREADY.

I'm about done. You know that feeling? I thought after alllll this time as soon as I had that new controller on, now he's gonna be everything I dreamed. I thought I would be keeping up with traffic, no longer looking behind me and swerving and that I would have hands down THE FASTEST means of transportation in the city. So here's what's happening. He is an untamable beast on startup. If I crank the throttle at a standstill he does a wheelie. Made me fall over a couple times. But as soon as he gets to 20 he slows to a crawl. And I have no idea why. As soon as I hit 22.5 he goes from 600 watts (he's a 500 watt with 750 peak motor) down to 400, and the more I pedal, 300, 200, 150. WHY?????? It's driving me crazy. Noticing no matter how much I pedal I can't get him above 23 for any length of time. When I thought he was finally gonna feel his potential, running at full power all the time......

My setup is a KT-LCD3 display. Yes I changed the max speed to 99 km/hr.
KT 500/750/1000/1500 watt controller
Push throttle
Idk my PAS stats but it's the standard 3 wires
Bafang brushless 5:1 geared hub motor 500 watt from rad power bikes

Is there something fundamentally flawed in my understanding of ebike wiring? Is there a perfectly good reason the motor wattage slows to a halt? Thinking maybe it's unable to spin any faster than that but questionable and if so. Seems a weird point to flatline. Something I can change in the display? Do I need to become a hacker. Aware of the P and C options stated in the manual but haven't touched them. I don't know my motor THAT well.

I know this is a long post. I'm excited. He's been a lotta fun but I find myself at a standstill. ANY thoughts are welcome. I have an old manager, disappointed grandfather, jealous brother, and ex all to prove wrong....

Good thing I scanned one last time after reading half

So fat bike Bafang with what size tires and what gauge spokes?

You got some setting in the KT display wrong, pas might be pooched.
You got to many accessories, all you need is
1) MOTOR
2) CONTROLLER
3) Throttle
4) Battery
5) Simple and Easy

I always recemmend, forget the KT display, ditch the controller if it needs display to operate. Otherwise go to sensorless from here
https://evfittinggreentime.aliexpress.com/store/group/15-mosfet-type/313864_259090851.html?spm=2114.12010612.0.0.31c7b0e1RPn5J0

My setup is a KT-LCD3 display. Yes I changed the max speed to 99 km/hr.
KT 500/750/1000/1500 watt controller
Push throttle
Idk my PAS stats but it's the standard 3 wires
Bafang brushless 5:1 geared hub motor 500 watt from rad power bikes

Click to expand...

itsraspberrytime said:

He is an untamable beast on startup. If I crank the throttle at a standstill he does a wheelie. Made me fall over a couple times. But as soon as he gets to 20 he slows to a crawl. And I have no idea why. As soon as I hit 22.5 he goes from 600 watts (he's a 500 watt with 750 peak motor) down to 400, and the more I pedal, 300, 200, 150. WHY?????? It's driving me crazy. Noticing no matter how much I pedal I can't get him above 23 for any length of time. When I thought he was finally gonna feel his potential, running at full power all the time......

My setup is a KT-LCD3 display. Yes I changed the max speed to 99 km/hr.
KT 500/750/1000/1500 watt controller
Push throttle
Idk my PAS stats but it's the standard 3 wires
Bafang brushless 5:1 geared hub motor 500 watt from rad power bikes

Click to expand...

A few other bits of info we need to know to be more sure of the possible problem:

What voltage is the battery?
What is the battery's continuous amp rating?
What is it's peak amp rating, and for how long?

What speed does the wheel spin with the wheel offground and full throttle?

Which exact controller/display combo kit do you have? (link to page purchased from if possible)
Which exact motor do you have? (link to page purchased from if possible)

If you list all of your exact controller settings, even the ones you haven't changed (if any), they may also provide clues. It is even possible that there are settings you can't access, either because they're locked out in that version of that controller, or if the display you have doesn't allow access to them, or both.


Some general notes:


Voltage can limit speed, if the motor winding is such that when at full throttle with no load (off ground) it only goes to X speed, then loaded speed is typically around 80% ish of that, again depending on conditions and equipment. This is the most likely problem with your setup, unless you are running a 72v battery or something like that.


You may wish to visit http://ebikes.ca/tools/simulator.html , read the entire page so you know what everything is and how it works, then setup some basic systems to see what they will do under various riding conditions. Then increase the battery voltage, or change the controller current limit, and see what behavior changes you get for the otherwise same system and conditions. It may help you understand how things interact, and what it may take to accomplish the goals you are after.


It takes around 750w to go around 28mph, depending on conditions and equipment. Once you get this setup working, then if that motor is really only capable of 500w, then going way faster than what that 500w typically gets you may overheat it. It's likely that it can handle more than 500w continously, but how much more you may have to experimentally determine.

Geared hubmotors overheat more easily than DD (non geared) hubs, because they have multiple insulation layers (airgaps) between first the stator and the rotor, then the rotor and the shell, so they can't shed the heat generated at the core nearly as easily. So "overclocking" a geared hub can take more care in monitoring and managing the heat. THe first thing that usually glitches is the hall sensors, and if they stay too hot too long they fail. The next can either be the windings burning the insulation, or the plastic gears softening up and stripping their teeth (this is less of a problem now than it used to be, but it's still there).



Current can limit speed, if the controller can't output more than a certain amount because of battery voltage drop under load. This is probably not the case since it has such great startup-from-a-stop torque.

With "smart" controllers some settings may interact with other settings in ways that might not be obvious. I don't know what your specific model controller is capable of, settings-wise.

Some PAS-capable systems will limit system capability while pedalling, but not if you are only using the throttle, if you are using the PAS cadence sensor. If the PAS sensor is disconnected or you don't pedal, such a system may go faster or have more power available for throttle-only use.




Another thing to consider, once this is working, is that that bike isn't built to handle 50mph, and you may find that if your road conditions are not "perfect" that you can be thrown off or some parts of the bike could break when you hit a pothole or a bump or bit of road debris, etc. Braking may also be an issue; I don't know which brakes you have or what those tires are designed to handle.

I think AW is correct that you're running into the RPM per volt limitations of your system. If you want the thing to turn twice as fast, you have to feed it twice as many volts.

Also to go 50 mph requires more than six times as much power as 20 mph. If you don't have at least 5kW of electrical power going into your system, you're not even in the ballpark. I doubt your motor will be very happy with that.

Yup, maybe you didn't have a speed limiter, and the manufacturer chose a winding that properly hit the top speed of the design.
You either need a faster winding or a higher voltage battery.

I'm not familiar with KT controllers at all, but some controllers have a timing advance that will increase the motor wheel RPM by up to 20%... at the expense of losing some efficiency at the controller.

Your bike is a pretty neat creation. I think that at higher speeds, you'll find the lack of suspension very uncomfortable and also unsafe, unless you live in an area with very well maintained pavement. I'd say 25-30mph is as fast as you'd want to go on it.

neptronix said:

I'm not familiar with KT controllers at all, but some controllers have a timing advance that will increase the motor wheel RPM by up to 20%... at the expense of losing some efficiency at the controller.

Click to expand...

By itself, the KT doesn't, but the OpenSource FirmWare may in some versions; I haven't looked into whether the FOC / etc was ever implemented.

amberwolf said:

itsraspberrytime said:

He is an untamable beast on startup. If I crank the throttle at a standstill he does a wheelie. Made me fall over a couple times. But as soon as he gets to 20 he slows to a crawl. And I have no idea why. As soon as I hit 22.5 he goes from 600 watts (he's a 500 watt with 750 peak motor) down to 400, and the more I pedal, 300, 200, 150. WHY?????? It's driving me crazy. Noticing no matter how much I pedal I can't get him above 23 for any length of time. When I thought he was finally gonna feel his potential, running at full power all the time......

My setup is a KT-LCD3 display. Yes I changed the max speed to 99 km/hr.
KT 500/750/1000/1500 watt controller
Push throttle
Idk my PAS stats but it's the standard 3 wires
Bafang brushless 5:1 geared hub motor 500 watt from rad power bikes

Click to expand...

A few other bits of info we need to know to be more sure of the possible problem:

What voltage is the battery?
What is the battery's continuous amp rating?
What is it's peak amp rating, and for how long?

What speed does the wheel spin with the wheel offground and full throttle?

Which exact controller/display combo kit do you have? (link to page purchased from if possible)
Which exact motor do you have? (link to page purchased from if possible)

If you list all of your exact controller settings, even the ones you haven't changed (if any), they may also provide clues. It is even possible that there are settings you can't access, either because they're locked out in that version of that controller, or if the display you have doesn't allow access to them, or both.


Some general notes:


Voltage can limit speed, if the motor winding is such that when at full throttle with no load (off ground) it only goes to X speed, then loaded speed is typically around 80% ish of that, again depending on conditions and equipment. This is the most likely problem with your setup, unless you are running a 72v battery or something like that.


You may wish to visit http://ebikes.ca/tools/simulator.html , read the entire page so you know what everything is and how it works, then setup some basic systems to see what they will do under various riding conditions. Then increase the battery voltage, or change the controller current limit, and see what behavior changes you get for the otherwise same system and conditions. It may help you understand how things interact, and what it may take to accomplish the goals you are after.


It takes around 750w to go around 28mph, depending on conditions and equipment. Once you get this setup working, then if that motor is really only capable of 500w, then going way faster than what that 500w typically gets you may overheat it. It's likely that it can handle more than 500w continously, but how much more you may have to experimentally determine.

Geared hubmotors overheat more easily than DD (non geared) hubs, because they have multiple insulation layers (airgaps) between first the stator and the rotor, then the rotor and the shell, so they can't shed the heat generated at the core nearly as easily. So "overclocking" a geared hub can take more care in monitoring and managing the heat. THe first thing that usually glitches is the hall sensors, and if they stay too hot too long they fail. The next can either be the windings burning the insulation, or the plastic gears softening up and stripping their teeth (this is less of a problem now than it used to be, but it's still there).



Current can limit speed, if the controller can't output more than a certain amount because of battery voltage drop under load. This is probably not the case since it has such great startup-from-a-stop torque.

With "smart" controllers some settings may interact with other settings in ways that might not be obvious. I don't know what your specific model controller is capable of, settings-wise.

Some PAS-capable systems will limit system capability while pedalling, but not if you are only using the throttle, if you are using the PAS cadence sensor. If the PAS sensor is disconnected or you don't pedal, such a system may go faster or have more power available for throttle-only use.




Another thing to consider, once this is working, is that that bike isn't built to handle 50mph, and you may find that if your road conditions are not "perfect" that you can be thrown off or some parts of the bike could break when you hit a pothole or a bump or bit of road debris, etc. Braking may also be an issue; I don't know which brakes you have or what those tires are designed to handle.

Click to expand...

This is all great information. Really good perspective here. I've thought a lot about all that. My tire diameter is 20 inches. I've been riding him around all week, and I've done a lot of research also on this type of motor. Turns out some people with a geared motor can go about 28, but because I have a smaller wheel diameter the motor tops out at 23, which is actually pretty well rounded relative to the tire size, both are about a third larger. So that makes a lotta sense to me. There's a couple times that I have indeed gotten him up to 40. For whatever reason my display cannot read above 26. Thought that was interesting. I guess when the motor is no longer the source of power (gravity and pedaling), it doesn't know how to pulse the correct speed anymore, or something. It kinda feels like one of those things that makes sense even though you're not exactly able to pinpoint it? But I I have a GPS speedometer on my phone, yes I'm wary of using that as my go to system of speed measurement, but considering it's shown a good fifteen miles an hour faster than the bike, I'm gonna go with it instead.

So, I COULD dig up the URLs to all the parts I bought, but it really doesn't matter. The display and controller are both pretty standard. I swapped everything out and did my own wiring because the stuff it came with of course has that stupid American restriction of not going any faster than 20

The battery is 100 amp peak. And it's wired in parallel with the battery that came with the bike, which was perfectly capable of running the motor by itself. Keep in mind I haven't changed the motor out. It's the one that came with the original RadRunner factory model. In fact I tried to swap it out, but it's such a that a completely normal standard size motor didn't fit. Still running a 48 volt system

Soooo now that I have a spare motor, controller, display sitting in a box all sad and unloved, I might as well build another ebike, right? You mentioned increasing to a 72 volt system, and I've been thinking a lot about that. But I have bets in and I'm going all in believing that it really is the motor slowing me down, nothing more. That spare motor is 1500 Watt DIRECT DRIVE. They work most efficiently at high RPMs, which is exactly the opposite of a geared motor. I'm hoping my dream bike is all plug and play at this point. Seems like the worst is over, and that's all based on getting over my inexperience. Is there anything that feels better?

Oh also they don't overheat as easily!

Ohhh yes. Experimentally the only place I feel completely safe going above 40 is on the highway, paradoxically. I know it's dangerous and I COULD die, but it's where I have the best control. Sorta almost died last night ngl. That's where super sexy steampunk semi truck horn backpack comes in. And the flashlight that's 40 times brighter than car headlights. But I haven't got them installed just yet umm for my brakes? They're disc brakes. Haven't tuned them up in a hot minute and honestly gravel is ALWAYS my limiting factor, not my brake power. I could easily flip the bike with the front, and could easily slip out with the back. I almost do both, pretty much daily. Sooooo yeah

FAT TIRE there is no way I'm running any below four inch treads with speeds that high. Can you imagine a 700 tryna go that fast? I can. It would be going more sideways than forwards. Nope. And I'm running no more than 12 psi too. That seems to be my sweet spot.

You know what? it

https://www.ebay.com/itm/Risunmotor-24-48V-KT-LCD3-Display-Meter-Control-Panel-for-eBike-Electric-Bicycle/333895171836?pageci=12145308-8de2-4ad7-821a-0b116ae8c1a5

https://www.ebay.com/itm/48V-30A-KT-Controller-For-750W-1000W-Brushless-Motor-Ebike-Electric-Bicycle/174123230222?pageci=d1bcfc79-6f11-4d53-ad4c-c5f1da3d3089

itsraspberrytime said:

FAT TIRE there is no way I'm running any below four inch treads with speeds that high. Can you imagine a 700 tryna go that fast? I can. It would be going more sideways than forwards. Nope. And I'm running no more than 12 psi too. That seems to be my sweet spot.

Click to expand...

Don't tell pro cycle racers who routinely reach 60 mph and more on mountain stages. On 700x25 tires.

[youtube]IMVVhB-3lVg[/youtube]

Fat bicycle tires aren't rated for that kind of speed; heat buildup and accelerated wear will be an issue. It's high pressure bicycle tires that are capable of going fast without problems. Check out what gravity bike racers use. Mostly high pressure 20" freestyle tires.

[youtube]CAn9aGthdI0[/youtube]

itsraspberrytime said:

For whatever reason my display cannot read above 26. Thought that was interesting. I guess when the motor is no longer the source of power (gravity and pedaling), it doesn't know how to pulse the correct speed anymore, or something.

Click to expand...

If the casing (wheel hub) is spinning faster than the motor, and the speed sensor is one of the motor halls, then the speed will only be whatever the motor is spinning at. If the speed sensor is a separate one just inside the motor casing (common with geared hubmotors, but not universal) then it directly detects wheel speed.

Yours appears to be of the former type. If so, there are two potential fixes for this, depending on the controller / display design.

IF the controller/display have the option to use an external speed sensor rather than just the motor halls (some can't use anything else), then:

You can use a sensor like this, mounted on the frame or fork near the wheel:
https://ebikes.ca/shop/electric-bicycle-parts/ca-accessories/ca-speedo.html
with a magnet on a wheel spoke, with one wire to ground, and the other to the external speed sensor input.

If you check the motor wiring, you may find a white wire (could be any color, but white is common) that is not presently connected to your controller, that may have a speed signal on it (six pulses per wheel rotation, usually), and that could be connected to the external speed sensor input.

It may require changing a setting in the controller/display, or physical wiring changes, to do this as well.

I'll look at the links you gave to controller and display to see if this is possible, if you want to do this.

So, I COULD dig up the URLs to all the parts I bought, but it really doesn't matter. The display and controller are both pretty standard.

Click to expand...

There aren't "standard" controllers or displays. There are at least several different "brands" with different communication protocols frequently preventing using one display with a different controller, for example. There *are* a number of common designs, but there are variations on them that do different things. (even with the KT controllers and compatible displays, there is significant variation, not only in hardware, but in software.)

Also different sellers of the "same" thing may actually be selling very different versions of them. Some of them even call the item they are selling by a brand name that implies it is one thing, when in fact it is not that "brand" and is not actually the same thing. So it can greatly help troubleshooting in many cases to know exactly which one was used, and have a link to the actual sale page so the troubleshooter can directly go read the specs and info.

I swapped everything out and did my own wiring because the stuff it came with of course has that stupid American restriction of not going any faster than 20

Click to expand...

There isn't any "American restriction". (there is a federal definition of an ebike, in the CPSC regulations, but it isn't applicable to everything). Each state has it's own laws, and some have no limit, and some have the three-class system with different limits on each, and some have other limits (IIRC some still make ebikes illegal).

But there are some sellers that do restrict their bikes to 20mph (or other speeds) for whatever reason they each have.

Radpower, presumably to make things easier for them to troubleshoot problems with their customers, doesn't have any customizability in the settings on their bikes (you have to change the hardware to change the way the bike works). I've done that for someone before (swapped the controller and wiring and display out) so they could get the PAS to work the way they needed it to, which seemed silly, when a simple setting change would have done this if Rad had left access to those available (but even Rad cannot change any of the settings).

Keep in mind I haven't changed the motor out. It's the one that came with the original RadRunner factory model.

Click to expand...

Your original post said that "the new motor didnt' fit". Since there is so much other DIY involved, I'd assumed that you had fixed that problem and were just commenting on that.

You can do the test suggested to find out the unloaded motor speed, and then expect around 80% of that when loaded.

Most likely it's simply that that specific motor simply can't go faster than that at the voltage it's being run at.

In fact I tried to swap it out, but it's such a that a completely normal standard size motor didn't fit.

Click to expand...

FWIW, there isn't really a "standard size motor".

Regarding dropout width (OLD), as well as dropout/axle type and size, there are a bunch of different bicycle frame standards, and there are some motors that fit some of the bike frame standards...but there are some frame standards that don't have any motors that fit them (unless they are custom-made to fit that specific frame standard). There are also some bike frames custom built to no standard that are either designed around a specific motor or have a motor also custom built for them. Some frames wont' even accept a hubmotor without a torque plate and potentially cutting the frame because they use thru-axles. (there is only one thru-axle hubmotor I've seen so far, by Grin Tech).

The most common rear hubmotors tend to use about 135mm for their axle shoulders, but not all of them do that directly--some are a little narrower and require spacers, and some a little wider and require bending the frame to make them fit.

The other problem is axle diameters. Most of them use 10mm axle flats, but the axle diameter (the rounded sides) may be 12-15mm or more, and some dropouts simply aren't that deep, and either require filing them to fit the axle in fully, or making a torque plate that bolts or clamps to the frame & dropout, that then *is* deep enough for the axle. (if using disc brakes, the caliper mounts may also be put on this plate, offset from the original mounts, because the axle is now not in quite the right place to center the rotor where it will fully enter the caliper if that is mounted in the original mounts).

Soooo now that I have a spare motor, controller, display sitting in a box all sad and unloved, I might as well build another ebike, right? You mentioned increasing to a 72 volt system, and I've been thinking a lot about that. But I have bets in and I'm going all in believing that it really is the motor slowing me down, nothing more. That spare motor is 1500 Watt DIRECT DRIVE. They work most efficiently at high RPMs, which is exactly the opposite of a geared motor.

Click to expand...

That depends on the specific motor. The faster you spin a DD motor (well, any BLDC motor), the more eddy currents are generated in the laminations and the more drag it has, and the less efficient it can become. The geared motor itself is actually already spinning faster than the DD motor, and is using the planetary gearset inside to slow that output down for the wheel, to give greater torque (at the cost of speed).

I recommend going to the Grin Tech motor simulator and exploring it to learn about this and other behaviors you may need to know about before going further with that new bike.

itsraspberrytime said:

FAT TIRE there is no way I'm running any below four inch treads with speeds that high. Can you imagine a 700 tryna go that fast? I can. It would be going more sideways than forwards. Nope. And I'm running no more than 12 psi too. That seems to be my sweet spot.

Click to expand...

FWIW, it is generally better to run tires designed for the speeds you're after (which those tires are unlikely to be, if they are original with the bike like the motor). Many fat tires are little more than treaded balloons (some with knobs) (the 26" x 4" Kenda I have here is like that), unfortunately.

If they are 20" bicycle rims, then you can usually use 16" moped and motorcycle tires on them as a direct fit, and those tires *are* designed for that, as well as being made for lower pressure then the bicycle tires usually are. They're also thicker and more puncture resistant, and generally last longer.

I use the Shinko SR741 2.25" on the rear 20" wheels of SB Cruiser. They last me MUCH longer than any of the bicycle tires I've tried on those wheels, and ride better and grip better. There are much wider versions of these and other such tires available that will likely fit your rims.

You'll probably want to get some long (12"+) MC tire levers to get them on and off, though, and I'd also recommend swapping out for MC/moped tubes while you're at it.