2200 Watt motor 170kv or 90kv - e-bike

I know this forum is mainly for esk8 but i think they are pretty similar, i’m building my first e-bike and i need to choose the motor, i want to reach about 20mph so 2200W should be enogh, my question is should i got for a 90kv or 170kv, in both case i need to gear down the motor and given the same Watt with the right gear i should reach same speed/torque ration. is there any advantage in a motor spinning faster? i red somewhere that brushless motor works better at rpm is it true?

i did not say it runs BETTER at high rpm, I said it ran more EFFICIENT at higher rpm

I know very little but I’d assume the 170kv. also, depends on what hills you want to climb?

i was not talking about you :smiley: that’s something i red around, i appreciate your help, i just want more opinion, i would prefer running low rpm to be more quite

The motor you choose is dependent on what batteries you’re going to use. If you’re going with a standard vesc to control the motor, you’re limited to a maximum of 12s. If you have a different controller in mind, then you may be able to go higher.

For a given wattage, running at a higher voltage will require less current, which means less heat.

The power of a motor is rpm*torque. Torque is determined by current.

Running higher voltage, means you run higher rpm. Higher rpm means you need less torque for the same power.

Less torque means less current.

They’re all connected!

To get the most out of your motor, it’s best to run it as high speed as possible. This means high KV.

If you’re only going to go for 8s, you definitely want to go with the higher KV.

i think something is not right, if the motor have the same Watt the maximum output power is the same so if i use a 1.8 time gear at the 90kv motor i should obtain the 170kv. is there anything special about brushless motor that make them more efficien at high speed as @grecoman say?

It takes more amps to get up to speed (way more) than to stay at speed. Once you hit max efficiency (about 95% duty cycle) the board will draw waaaaaaay less amps than if you were constantly stopping and starting.

i will adapt the gear to the motor, let’s say i use a 3.7:1 gear for the 170kv and a 2:1 for the 90kv motor, the final wheel kv will be about 45 kv for both configuration and 2200W, is there any advantage in one of the 2 configuration or the are equivalent?

Definitely 90kv. Problem with ebikes is that since the wheels are so big, they require a massive reduction. Our standard 83mm longboard wheels are significantly smaller than the, what is it, 24 inch bike wheel? E bikes are a lot more torque low rpm than that of our outrunner motors which are more low torque high rpm by comparison.

You are going to find you will need a crazy low gear ratio.

3 Likes

Maybe this could help?

Welcome to the esk8 forum.

See below a quote from one of the major esk8 companies on the forum. He explains why running a motor close to 60k erpm provides the best efficiency by balancing low rpm copper losses with high Rpm iron losses.

Considering the above, I would suggest calculating your ideal KV as follows.

60,000erm/(Voltage x motor pole pairs) = Ideal KV

Example: 48V battery with a 14pole motor(7 pole pairs)

60,000/(48x7) = 178KV

1 Like

Your gearing is usually limited, so 1:2.5 is realistic. You can easily calculate the motor rpm for the desired top speed and you know your voltage, which should be as high as possible (12s). This in combination will tell you the ideal KV.

The vesc-project has a nice calculator: www.vesc-project.com/calculators

120-170kv is the range you should look at. Lower KV motors draw less amps and are better for the esc and battery.

Frank

1 Like

I think of e bike as assisted bike. we all have very efficient drive at low speed (aka legs). so my theory is e bike should focus on top speed and assisting for hills.

Just did the maths for you

12S battery , 14/37 transmissinon ( e.g. HTD 5M belt drive), 90mm wheel 40 km/h top speed (very fast) desired.

motor KV =145

Frank

1 Like

Thanks! that was exactly what i was looking for,. Now i just need to choose a good sensored motor, i was looking at ollin but the 170kv is out of stock, alien power system has some good motor, any suggestoin on the brand? same for the vesc, i need som suggestion, i think i will stay between 120kv and 180kv with a 8/10s battery to leave some sapce for improvement in the future

I just had 4 motors custom built by Alien power and I cant say anything but good things about the customer service I received. Excellent communication, very experienced and knowledgeable staff, and fair prices.

what vesc did you use? that seems to be the part more likely to fail

Ive had excellent experiences with the Enertion FOC box. Ive also been using the VESC 6’s from Trampa since they were released in Beta without any problems. Both companies have provided great customer support as well.

http://www.trampaboards.com/136-kv-2400w-dc-brushless-motor-6364-61-p-12967.html

Frank

that looks really good but the price is way higher than the competition, i think i will go for a alien power system 3300W 130kv for around 80/90 pound, i don’t see why this motor is twice the price