Keyde 100SWXC24 with 36V?

[freerider]

Hi,

I signed in here and hope somebody already tried this configuration. I would like to use the small 24 Volt Keyde rear motor for V-Brakes but to run it with 36 Volt to reach a revolution of appr. 330 rpm.

I asked Keyde if this is possible and was told that this will shorten th lifetime of the motor. For sure they have to say this;-) Did somebody test this already? I want to use this motor in a road bike.

Thanks,

freerider

 

[Artstu]

I can't help with your question, but what speed does 330 rpm equate to in a 700c wheel?

 

[trex]

fry it more like.
330RPM with 700C is 43.5kmph. At this speed, the air resistance is above 1000W.
The keyde motor uses high reduction ratio to reach 15mph with less magnet than usual, spinning it faster will increase the chance of failure of the clutch unit.

 

[Deleted member 4366]

330rpm is 29 mph in a 700C wheel. I haven't tried it, but I don't think it'll work unless you only switch it on when you're going over 15 mph. As a general rule, you should avoid giving a hub-motor full power when it's rotating at less than half of its maximum speed. If you want to use it to help you climb hills at speeds of less than 15 mph, it'll over-heat, and with the controller in the motor, that wouldn't be good.

A guy on Endless Sphere put a 328 rpm Q100 in a road bike, but he knew how to avoid it overheating. The Q100 has a lot more metal in it, so temperature rise would be slower.

 

[freerider]

OK, understood. So it's better, to use the normal motor without integrated controller to reduce overheating.

If the motor has 260 rpm / 24 V this means 20mph or 31km/h in normal operation.
1. Climbing with 10 mph or 16 km/h:
This is half of the normal operation, so the voltage should be appr. 12 Volt (reduce throttle rotation to half power).
This can be reached using a 36 Volt battery by reducing the throttle to 1/3 also.
Do you think the motor is OK to withstand this with supporting it by myself (the hill I have to climb is 150 meters high with 6% and a short end with 10%, alltogether maybe 2 km. And I'm quite strong but tired after 40km in the morning and 40 in the evening when arriving at this hill)?
2. Max Speed on flat road:
36 Volt = 1.5 x normal operation = 336 rpm / 45 km/h or 28 mph.
Do you think I can run the small Keyde on flat roads under this conditions?

I also could take the motor with only 200 rpm / 24 Volt, so the max. speed would be 300 rpm / 40 km/h or 25 mph to reduce the risk of failure.


What do you think is the difference between the 24 V and the 36 V motor in operation? Which one is better generally?

Thank you very much!

 

[amigafan2003]

1. Climbing with 10 mph or 16 km/h:
This is half of the normal operation, so the voltage should be appr. 12 Volt (reduce throttle rotation to half power).

That's not the way it works. On a 36v system the motor is always getting 36v. It's rotational speed is controlled by PWM (Pulse Width Modulation).

 

[freerider]

That's not the way it works. On a 36v system the motor is always getting 36v. It's rotational speed is controlled by PWM (Pulse Width Modulation).

Thats new for me. I'm not a specialist, but all I have been reading so far says that the speed directly depends on the voltage (V). And the torque depends on the current (A). That also say the FAQ's I've been reading.

So I'm a bit confused now reading your answer....

Why should so many riders tune their 36V-bikes with 48 or 60 Volt?

 

[Deleted member 4366]

You're both right, but meaning different things. The maximum speed of the motor depends on the battery voltage. The power and torque depend on the energy fed into the motor. The motor is connected directly to the battery with the MOSFETs in the controller controlling the time and the direction that it gets by simply opening and closing like gates. The current is controlled by the length of the open pulses. That's it in principle, but in practice it's more complicated because of the inductive effects of the coils and the charge/discharge of the capacitors. With the voltage rapidly switching on and off for different times, you could talk about average voltage with constant current or average current with constant voltage. the end result is the same. The energy fed to the motor will be equivalent to the area under the graph.

 

[trex]

OK, understood. So it's better, to use the normal motor without integrated controller to reduce overheating.

If the motor has 260 rpm / 24 V this means 20mph or 31km/h in normal operation.
1. Climbing with 10 mph or 16 km/h:
This is half of the normal operation, so the voltage should be appr. 12 Volt (reduce throttle rotation to half power).
This can be reached using a 36 Volt battery by reducing the throttle to 1/3 also.
Do you think the motor is OK to withstand this with supporting it by myself (the hill I have to climb is 150 meters high with 6% and a short end with 10%, alltogether maybe 2 km. And I'm quite strong but tired after 40km in the morning and 40 in the evening when arriving at this hill)?
2. Max Speed on flat road:
36 Volt = 1.5 x normal operation = 336 rpm / 45 km/h or 28 mph.
Do you think I can run the small Keyde on flat roads under this conditions?

I also could take the motor with only 200 rpm / 24 Volt, so the max. speed would be 300 rpm / 40 km/h or 25 mph to reduce the risk of failure.


What do you think is the difference between the 24 V and the 36 V motor in operation? Which one is better generally?

Thank you very much!

I would be very wary of running a motor at higher voltage than the manufacturers' specification.
You have several parameters to take into account: maximum power output, maximum torque, maximum RPM, maximum efficiency.
These parameters are useless on their own because they don't happen at predictable places (you can't calculate them), you need to get a motor report from the manufacturer to be sure.
Assuming you have an adequately powerful battery and controller, you need to concentrate on the motor's performance. First, its 'sweet spot' where the motor efficiency is at its best. Keyde claims 85% - I'd take it with a pinch of salt. Most motors have peak efficiency around 75%-80%. Their motors have no clutch, that means there will be a small amount of 'cogging' when you ride unassisted. Either side of this sweet spot, efficiency drops rapidly down to below 20% at its lowest speed and highest speed. ebike.ca has a motor simulator for you to play with. Mainly, you need to give yourself a speed target on flat roads without headwind. At legal speed (25kph), you need 160W assistance (in addition to 80W of your pedalling power) to overcome air resistance which will increase rapidly at power 3 (cubic) of the speed. At 35kph (22mph), you need 520W of assistance to overcome air resistance. The wheel's RPM is directly proportional to the speed, 22mph = 280 RPM on 26" wheels. You need the motor sweet spot to be 'spot on' this zone to avoid stressing your motor and battery. The motor chart usually gives the torque value for the RPM - you need to check that the torque value is sufficient to overcome the wind resistance, at 22mph, you'll need at least 17.6NM at 280 RPM. Then check the power input for that speed. The difference between power input and power output is converted into heat.
At 75% efficiency, your motor needs to shed about 173W in heat. Much more outside the sweet zone.
This is an ideal scenario. Not many motors happen to have the sweet zone at 280 RPM.
That's why you need to see that all the numbers you want are printed black on white on the motor test chart.
It is an easy job for a large motor like an 8-Fun BPM to reach 22mph but not for the diminutive keyde.

 

[jackhandy]

[quote="trex, post: 210169, . Mainly, you need to give yourself a speed target on flat roads without headwind. At legal speed (25kph), you need 160W assistance (in addition to 80W of your pedalling power) to overcome air resistance which will increase rapidly at power 3 (cubic) of the speed. At 35kph (22mph), you need 520W of assistance to overcome air resistance. [/quote]

Trex, that's interesting - (please excuse me hijacking your thread, Freerider) - Where can I find a wind & road-resistance type calculator?
It's always good to have facts & figures to back-up an opinion.
There was a bloke on here recently who cast doubt on my statement that assistance up to 25mph would play hob with range : He went on to say that the increased wind resistance was counteracted by covering the ground quicker.
Now, I'm all for something for nothing, but that didn't seem kosher, even to a numbnuts like me
What would be the energy required to maintain 25mph?

 

[Alan Quay]

[quote="trex, post: 210169, . Mainly, you need to give yourself a speed target on flat roads without headwind. At legal speed (25kph), you need 160W assistance (in addition to 80W of your pedalling power) to overcome air resistance which will increase rapidly at power 3 (cubic) of the speed. At 35kph (22mph), you need 520W of assistance to overcome air resistance.

Trex, that's interesting - (please excuse me hijacking your thread, Freerider) - Where can I find a wind & road-resistance type calculator?
It's always good to have facts & figures to back-up an opinion.
There was a bloke on here recently who cast doubt on my statement that assistance up to 25mph would play hob with range : He went on to say that the increased wind resistance was counteracted by covering the ground quicker.
Now, I'm all for something for nothing, but that didn't seem kosher, even to a numbnuts like me
What would be the energy required to maintain 25mph?[/quote]


Maths will prove the point Jack:

From trex numbers above, and assuming a 35k journey:

At 35k/h, journey takes 1 hour, at 600w. You would need 600wh.

At 25k/h, journey takes 1.4 hours, at 240w. 336wh consumed.

As always in physics, you don't get summit for nuffink.

 

[trex]

What would be the energy required to maintain 25mph?

My model predicts 937W on flat roads without headwind for 25mph (40.1 kph), minimum torque 28NM @ 322 RPM on 26" wheel. Can someone with a CA confirm this?