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-   -   Motor rpm important? (https://www.bikeforums.net/electric-bikes/871409-motor-rpm-important.html)

ammodave 02-05-13 11:45 PM

Motor rpm important?
 
I'm considering a 36v front hub kit from BMS for my first build. I plan to use a 36v, 10.4 ah bottle battery. One motor is 36v/500w with an rpm speed of 328rpm; the other motor is 36v/350w with a speed of 201rpm. My bike is a Jamis commuter with 28"wheels; total bike and rider weight (less the electronics) is about 180lbs. Does the motor rpm really matter to me? I'm looking for 20mph and 15-20 mi unassisted. Would using a 48v/500w motor gain me anything? Sorry to be such a nimrod; I've been searching this forum for about a week but I still have questions.

DrkAngel 02-06-13 01:29 AM

(28" x 3.14) x 60 / (12" x 5280') x 201rpm = 16.7mph
(28" x 3.14) x 60 / (12" x 5280') x 328rpm = 27.3mph

CigTech 02-06-13 02:59 AM

ok as for RMP speed the 328 rpm motor will have a higher top speed. But the 201 rpm motor will have more power. So if you have flat roads go with the 328 rpm motor. But if you have hills then go with the 201 rpm motor. Most companys tell you to use the 201 rpm on 26" 700c and 28" bikes. And the 328 rpm on 24" or less bike.

Now for the 36v or 48v part of the qustion. The 36v will do just fine on flat ground but if you have hills I'd go with the 48v. The 48v will give you a little better speed. Now as far as watts go, the more watts the more power. So if you have a 36v 500 watt motor that say gets to top speed in 30 seconds then a 48v 500 watt motor will get you to top speed faster. See Volts = speed and watts = power.

Hope this helps

cerewa 02-06-13 05:59 AM


Originally Posted by CigTech (Post 15242429)
ok as for RMP speed the 328 rpm motor will have a higher top speed. But the 201 rpm motor will have more power. So if you have flat roads go with the 328 rpm motor. But if you have hills then go with the 201 rpm motor. Most companys tell you to use the 201 rpm on 26" 700c and 28" bikes. And the 328 rpm on 24" or less bike.

Now for the 36v or 48v part of the qustion. The 36v will do just fine on flat ground but if you have hills I'd go with the 48v. The 48v will give you a little better speed. Now as far as watts go, the more watts the more power. So if you have a 36v 500 watt motor that say gets to top speed in 30 seconds then a 48v 500 watt motor will get you to top speed faster. See Volts = speed and watts = power.

Hope this helps

I thought you are asking if you should buy a 48v motor even if you are set on a 36v battery. There is probably no benefit to using the 48v motor unless you match it up to a 48v battery.

In reality ebike motors are flexible in what voltage they take and the exact same motor will often be sold as 48v and 36v, just depending on what controller it's being sold with.

ammodave 02-06-13 09:54 AM

Thanks for the prompt responses. I knew that more wattage would give me more power (and less range) but I was worried that the higher rpm motor might be sluggish during acceleration. The 500w/36v motor is not available in the lower rpm; that's why I was considering the 48v motor even though I was planning on using a 36v battery. I presume these are all geared motors although the listing doesn't specify. How noisy are the geared motors? What kind of range can I expect on level ground?

FMB42 02-06-13 10:59 AM

Can you post a link to the motors and controllers that you're looking at?

My 450w geared hubmotor is a bit on the "noisy" side (especially under "heavier" loads). Not exactly loud, but probably noisy enough that the average pedestrian or non-ebiker would suspect that it's an electric bicycle (just by the sound alone). This noise is said to be fairly typical for geared hubs (direct drive hubmotors, on the other hand, tend to make more of a lower volume "hum" type of noise).

Btw, I get a range of about 20-25 or so miles from my 36v 10 ah geared hubmotor system on relatively level ground at an average speed of maybe 10 - 12mph (top unassisted speed is ~ 17mph).

Note: you should, of course, make sure that your controller is 36v compatible if you decide to run the 48v motor with a 36v battery.

DrkAngel 02-06-13 11:13 AM


Originally Posted by ammodave (Post 15243196)
Thanks for the prompt responses. I knew that more wattage would give me more power (and less range) but I was worried that the higher rpm motor might be sluggish during acceleration. The 500w/36v motor is not available in the lower rpm; that's why I was considering the 48v motor even though I was planning on using a 36v battery. I presume these are all geared motors although the listing doesn't specify. How noisy are the geared motors? What kind of range can I expect on level ground?

Check more sites!
Sounds like info, probably support, might be a bit too sparse.
AmpedBikes.com is a US based outfit with a variety of offerings, great info and USA warranty.

FMB42 02-06-13 11:31 AM


Originally Posted by DrkAngel (Post 15243586)
Check more sites!
Sounds like info, probably support, might be a bit too sparse.
AmpedBikes.com is a US based outfit with a variety of offerings, great info and USA warranty.

Excellent advice.

Also consider checking out "Ebikekit" (US East Coast) and Ebikes.ca...

Ebikekit has given me very good service (be sure to keep an eye on their "Discounted SALE Stock" section). I haven't ordered anything from Ebikes.ca yet, but they're a top-notch company according to the huge numbers of positive reviews they get. Both have very good (or better) customer support and both are widely recognized as great businesses to deal with.

CigTech 02-06-13 11:59 AM

Ok if you use a 48v motor with a 36v battery then the wattage out put of the motor will be lower then the motor is rated at.There for you will get less power out of the motor then running a 36v motor .I would not run a 48v motor on a 36v battery.

ammodave 02-06-13 03:31 PM

It's this motor http://www.bmsbattery.com/ebike-kits...-bike-kit.html. I don't know what brand the motor is but bms calls it a Q128. I'm not emotionally invested in that particular motor but I like the bms bottle battery so I thought I might save a little on shipping to buy both from bms. Anyone care to recommend a different 36v/500w+ motor for my build. I need to go front drive to keep my 8sp internal geared rear hub.

chvid 02-07-13 09:24 AM

The Q128 is reputed to be not a great motor compared to the Q100. There is discussion on this on endless-sphere. As well as tons of information on the various winds of the Q100. I have a 201rpm Q100 on 700C, and I top out in the low 20s (mph) range, running on 48 V - (the "36V 201 version"). I'm overvolting the 36V controller (hence controller LVC is inoperative, relying on BMS for LVC). If you buy the Q128, it takes a different controller than the KU63 used for the Q100. The two controllers are not interchangeable, and the right controller will come with the kit, if you don't buy the parts piecemeal. There are other small geared hub motors "out there" - the FUSIN motors unit (I've bought from there in the past), and the small Maxus gearmotor from www.emissions-free.com, which is probably the pick of the litter.

FMB42 02-07-13 12:05 PM

Amped Bikes carries a similar 36v "bottle" battery...


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