July 27, 20196 yr 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. Edited July 27, 20196 yr by vfr400
July 27, 20196 yr 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?
July 27, 20196 yr 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.
July 27, 20196 yr 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 ;)
July 27, 20196 yr 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.
July 27, 20196 yr 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.
July 28, 20196 yr 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.
July 28, 20196 yr 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.
July 28, 20196 yr Author .... 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
July 28, 20196 yr 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.
July 28, 20196 yr 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
July 30, 20196 yr 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
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