power problem with Wisper 806SE

[vfr400]

Is that a characteristic of the particular motor used on the Wisper 806SE?


So badass type dongles aren't effective on the 806SE?

It's a typical characteristic of many electric bikes.

Why would you want a Badass dongle on a Wisper when you can derestrict it for nothing? Dongles of any type have no effect on current or power. They only interfere with the speed signal to fool the controller into releasing the speed limit.

 

[Deleted member 25121]

It's a typical characteristic of many electric bikes.

Why would you want a Badass dongle on a Wisper when you can derestrict it for nothing? Dongles of any type have no effect on current or power. They only interfere with the speed signal to fool the controller into releasing the speed limit.

Let me put that another way - since Badass dongles work with Bosch, Brose, Continental, Fazua, Giant, Kalkhoff(Impulse), Panasonic, Pendix, Shimano, Specialized and Yamaha motors am I right in thinking that these motors don't exhibit your typical characteristics?

Do you know for sure that Wisper 806SE motors exhibit your typical characteristics?

I'm just surprised that the back EMF has such a big effect at such low cycle speeds.

 

[vfr400]

Let me put that another way - since Badass dongles work with Bosch, Brose, Continental, Fazua, Giant, Kalkhoff(Impulse), Panasonic, Pendix, Shimano, Specialized and Yamaha motors am I right in thinking that these motors don't exhibit your typical characteristics?

Do you know for sure that Wisper 806SE motors exhibit your typical characteristics?

I'm just surprised that the back EMF has such a big effect at such low cycle speeds.

I'm not sure what your point is or what your question is. Ask it again from first principles.

I think you've got completely mixed up. Back emf has no effect at zero speed, small effect at low speed and big effect at high speed. It's the thing that limits every electric motor to a maximum speed.

The amount of back emf depends on the motor's KV, which is how many rpm it takes to generate 1 volt.

When you choose a hub-motor for an electric bike the KV is a very important characteristic. If it's too low, the bike won't reach 15 mph. If it's too high, the motor will be inefficient and overheat. The ideal for a legal bike is somewhere around 7.2 for a 36v battery, which will mean that the motor will generate 36v at 260 rpm and give maximum power (not torque) at around 15 mph. That's why I say 260 rpm is typical for OEM bikes. It's basic good design.

The same characteristics affect crank motors, but instead of bike speed, it's crank speed they have to get right. If they choose a KV too low, the motor will max out and produce no power at a normal cadence. Too high will make the motor run inefficiently. The problem here is that people have different cadences. Some prefer a low cadence of 60 or less and some prefer closer to a 100. Unfortunately, there's no solution to that other than make sure you knowthe characteristics of the motor in the bike you're buying

 

[Deleted member 25121]

I'm not sure what your point is or what your question is. Ask it again from first principles.

Let me try for the 3rd time:

You said "At around 260 rpm,the back emf is 42v so your motor has no net voltage, no current can flow and you have zero power. " and "At 14 mph, it's almost certain that you will be in the zone where the back emf is controlling the current below 15 amps, so you won't get maximum current."

What is the maximum speed you could get out of your typical bike, even with a dongle or speed restriction otherwise disabled, before the back EMF results in zero current flowing (ie zero assistance being available), 14mph seems very low?

 

[Deleted member 25121]

When you choose a hub-motor for an electric bike the KV is a very important characteristic. If it's too low, the bike won't reach 15 mph. If it's too high, the motor will be inefficient and overheat. The ideal for a legal bike is somewhere around 7.2 for a 36v battery, which will mean that the motor will generate 36v at 260 rpm and give maximum power (not torque) at around 15 mph. That's why I say 260 rpm is typical for OEM bikes. It's basic good design.

A motor's "KV" rating it is the number of revolutions per minute that the it will turn when one volt is applied under no load conditions.
So with 36V applied to it, a motor with a KV of 7.2 will produce 259.2 rpm under no load conditions.

The paragraph I've quoted makes no sense whatsoever to me.

 

[vfr400]

A motor's "KV" rating it is the number of revolutions per minute that it will turn when one volt is applied under no load conditions.
So with 36V applied to it, a motor with a KV of 7.2 will produce 259.2 rpm under no load conditions.

The paragraph I've quoted makes no sense whatsoever to me.

A motor is a two-way transducer. If you apply a voltage to it, it will turn. If it turns, it'll produce a voltage. The KV is the ratio between the voltage and turning speed whichever way round you want to work it or define it.

Look at it like this. You have a motor with a KV of 7. You apply 1v to it and it will accelerate to 7 rpm and not go any faster. The reason is that at 7 rpm, it generates 1V in the opposite direction, so net voltage is zero. Without a net voltage, no current can flow and the motor stops accelerating.

Use Ohm's law: current =volts/resistance

The resistance doesn't change, so as the motor speeds up, the net voltage goes down and the current goes down with it.

The net voltage at any RPM = battery voltage - back emf
= 36 - RPM/KV

Current = (36 - RPM/7.2)/resistance

At 259.2 rpm, Current = (36- 259.2/7.2)/R = (36-36)/R = 0

No current means no power and no acceleration.

 

[Deleted member 25121]

A motor is a two-way transducer. If you apply a voltage to it, it will turn. If it turns, it'll produce a voltage. The KV is the ratio between the voltage and turning speed whichever way round you want to work it or define it.

Look at it like this. You have a motor with a KV of 7. You apply 1v to it and it will accelerate to 7 rpm and not go any faster. The reason is that at 7 rpm, it generates 1V in the opposite direction, so net voltage is zero. Without a net voltage, no current can flow and the motor stops accelerating.

Use Ohm's law: current =volts/resistance

The resistance doesn't change, so as the motor speeds up, the net voltage goes down and the current goes down with it.

The net voltage at any RPM = battery voltage - back emf
= 36 - RPM/KV

Current = (36 - RPM/7.2)/resistance

At 259.2 rpm, Current = (36- 259.2/7.2)/R = (36-36)/R = 0

No current means no power and no acceleration.

I see what you were trying to say now.

So back to your typical ebike motor running at 260rpm, what road speed would that equate to in top gear?

 

[vfr400]

I see what you were trying to say now.

So back to your typical ebike motor running at 260rpm, what road speed would that equate to in top gear?

On the flat, pedalling steadily with a fully-charged battery, about 20 mph.

 

[Deleted member 25121]

On the flat, pedalling steadily with a fully-charged battery, about 20 mph.

So this wouldn't explain the problem the OP posted where he is losing assistance over 13mph.

And Badass type dongles would only provide another 5mph with one of your typical ebike motors, as would removing the 15mph limit on the controller (if that was possible).

These are the points I was trying to make yesterday starting at 2.28pm. We got there in the end, thanks

 

[vfr400]

So this wouldn't explain the problem the OP posted where he is losing assistance over 13mph.

And Badass type dongles would only provide another 5mph with one of your typical ebike motors, as would removing the 15mph limit on the controller (if that was possible).

These are the points I was trying to make yesterday starting at 2.28pm. We got there in the end, thanks

You can't fit a Badass dongle to an OEM hub-motored bike, like a Wisper because the speed sensor is inside the motor. Also, I'm pretty sure that the speed sensor is only used to show the speed on the LCD. Instead, the controller picks up the speed for the speed limit directly from the motor halls.

 

[Deleted member 25121]

You can't fit a Badass dongle to an OEM hub-motored bike, like a Wisper because the speed sensor is inside the motor. Also, I'm pretty sure that the speed sensor is only used to show the speed on the LCD. Instead, the controller picks up the speed for the speed limit directly from the motor halls.

Hub motors?
I didn't mention hub motored ebikes, I was talking about your typical motored ebike (hub or crank) that apparently can't go any faster than 20mph irrespective of how the 15mph limiter is sensed.

 

[vfr400]

Hub motors?
I didn't mention hub motored ebikes, I was talking about your typical motored ebike (hub or crank) that apparently can't go any faster than 20mph irrespective of how the 15mph limiter is sensed.

Your post #20. You were asking specifically about a Wisper 806SE that has a hub motor. I already explained how the power characteristics of crank motors are different. If you still don't understand, read back through the thread again.

 

[Deleted member 25121]

Your post #20. You were asking specifically about a Wisper 806SE that has a hub motor. I already explained how the power characteristics of crank motors are different. If you still don't understand, read back through the thread again.

Yes, this thread started with the OP was asking about the Wisper 806SE and I was asking whether your comments about back EMF on typical ebike motors applied to the Wisper 806SE.

In which of your posts did you explain how the power characteristics of crank motors are different???

Anyway, the bottom line is that your comments from #19 onwards didn't actually explain the problem the OP posted where he is losing assistance over 13mph. QED.

 

[mpbarrett]

....

Anyway, the bottom line is that your comments from #19 onwards didn't actually explain the problem the OP posted where he is losing assistance over 13mph. QED.

I started this, and I am still listening, but am almost afraid to post any more comments or to have an opinion on this thread... ;(

mike

 

[vfr400]

OK, I'll shut up now and let the argumentative tw@ts explain how to sort you out.

 

[Woosh]

It's not likely to be the battery, but maybe it is because I can't understand what you mean by the current going up. Please explain.

You get more information here:

http://www.e-bicycles.eu/video/tc480_manual.pdf

The TC488 LCD has 5 blobs represnting power output.
He says that if he keeps pushing, power seems to cut out when the power reaches 5 blobs.
his theory is plausible though. Either the controller trips or it's programmed to trip.

 

[Deleted member 25121]

I started this, and I am still listening, but am almost afraid to post any more comments or to have an opinion on this thread... ;(

mike

I don't blame you.
Why don't you contact Wisper Bikes customer support about the problem, they seem to have a good reputation on here so should be able to help:
support@wisperbikes.com

 

[MikelBikel]

You get more information here:

http://www.e-bicycles.eu/video/tc480_manual.pdf

The TC488 LCD has 5 blobs represnting power output.
He says that if he keeps pushing, power seems to cut out when the power reaches 5 blobs.
his theory is plausible though. Either the controller trips or it's programmed to trip.

Thanks, that's v.useful, shows how to change some things, like trip & odo.
Changing the wheel diameter to a smaller value might raise the max wheel rpm, while speed display would also presumably then be incorrect (too low).
The current while pedalling on level5, 14.4-15.5mph is presently shown going max, then suddenly min, then suddenly max, etc.., instead of holding a steady cruise current. Hence the uncomfortable surging of the torque that's felt. I can't see a setting for gently ramping the current down at the max though, so maybe it can't be altered.
Cheers, Mikel