Supplier of 8fun bafang bpm hillclimber kit

[jayuk]

I have now found out which code (wind) of bpm motor i will be getting!

It's a code 10 originally intended for an 18" wheel (275 rpm)

i will also be using a 48v battery on the 36v version of the motor too, so this should up the torque a little & general acceleration.

I will post pics when all fitted & up & running, I am still waiting for the kit to be put together as Cell Man is very very busy at the moment!

The bike will mainly be used to go to & from work & as it happens this will now nearly all be done on a cycle track!

 

[mechaniker]

i will also be using a 48v battery on the 36v version of the motor too, so this should up the torque a little & general acceleration.

If you want more torque as an 250Watt motor, it is more easy and cheaper to use the BPM 350Watt-version or the 500Watt-version as to upgrade the battery
to 48Volt

also you can order the bpm with higher rpm as 275 if you want more speed

forget the code, nobody on bafang know how to use the code ;-) you must tell them how much rpm you want. Or better the company who order for you must tell them the rpm what you want

regards
frank

 

[jayuk]

Hi frank

Cell man did indeed explain that you can get almost identical performance from 36v & 48v by using different rpm speeds of the motor. He gave me 3 speed options, i choose the 275rpm wind. As far as im aware there is a 2 to 3 mph increase in speed with the rpm figures you have listed above?.
I have been told this setup should reach approx 27mph which is more than enough & will be used sensibly!

 

[NRG]

A 275RPM motor in a 700c wheel will give you 22.6MPH unloaded, any smaller wheel will be slower...only if you overvolt the motor will it go faster.

 

[mechaniker]

I have been told this setup should reach approx 27mph which is more than enough

you always can get the same performance from 36v as from 48v, it only depend on the motor-power/cooper-winding´s

there is a rule, higher rpm reduce the torque! the lower torque you can compensate with higher Ampere-cut on controller.
With 250watt you cant get 27mph it is to low power, the wind what works against you need a lot of power from your motor

you need 400watt motor for this and around 320rpm for this. So i suggest to buy a 500watt/320rpm motor or a 250watt/275rpm runs by 48v motor(this overvolting give you around 400Watt and also 340rpm.

This speed and power need a big battery if you want drive this speed often and you only can give low support by your leg´s , i suggest min. 12amp otherwise your range is very low.

To build up a bike like this is no problem but i think a bike wich is able to for 20mph is enough and dont need such big battery and it is enough for a bike

In the beginning i also want this power but later i said "better buy a motorbike for this speed" it is more save on this speed as an normal bicycle
No Car-driver can imagine such speed on a bicycle so it is most time only a question of time to have dangerous situation or a crash with a car and belief me to crash with a car on riding a bicycle is not a good experience, i know it ;-) and after crash no insurance pay for your maybe brocken leg´s because you had ride an illegal bicycle, think about this also

regards
frank

 

[jayuk]

I think there's been a misunderstanding, i'm not trying to get a 250w motor to 27mph as you say thats not possible.
i have actually ordered the bafang bpm 350w 36v hub motor to use with a 48v a123 battery ive also ordered.

As for the speed like i say it wont be used recklessly, as i'm only using for my journeys to & from work approx 5 miles each way so the battery capacity should be fine. i would probably be at around 17mph to 20mph most of the time & 95% will be on cycle track. to be honest i think i would rather stick to a mountain bike than a moped as the traffic in rush hour round here has become shocking.

I do appreciate your helpful replys though!

thanks
jay

 

[mechaniker]

I think there's been a misunderstanding, i'm not trying to get a 250w motor to 27mph as you say thats not possible.
i have actually ordered the bafang bpm 350w 36v hub motor to use with a 48v a123 battery ive also ordered.

hi jay,

ok now i got it ;-)
this combination will work and fullfill your wishe´s because the 350Watt on 48V have around 500watt and the rpm will be also enough for to receive 27mph

i wish some fun on riding
frank

 

[jbond]

175rpm is for 28",195rpm is for 26", 220rpm is for 24",255rpm is for 20", 275rpm is for 18" and around 320 is for 16"

Are these no-load rpm for the specified voltage (24v, 36v) or rpm for just far enough below no-load that it will drive the average bicycle to the legal limit of 25kmph?

Take a typical 26"/47-559 tyre with a circumference of 2050mm.
195*2050*60/1,000,000 = 23.985 KMPH

So I guess these are not no-load rpm but a designed maximum speed with no-load actually around 27kmph. Working backwards, this gives a no load rpm for a 26" wheel of ~210rpm

So let's say you want to go 25mph(40kmph) before power cuts off. For the same 26" tyre, you need 325rpm. Which means a 320-16" motor if running at the design voltage. With a typical 700c-35 tyre this would give 42kmph instead of 40.

Now of course, none of this says whether there's enough power to actually do the speeds. But it gives an indication of where, with a bit of tail wind, slope and some pedalling, the power assist will drop off. So here's some rough, a 275rpm motor in a 26" wheel will do about 20mph with an over-run up to 22mph before power drops to zero. In a 700c wheel, the figures are more like 22 and 24mph.

Now a 275rpm 36v motor should do 366 at 48v if the no-load rpm is a constant rpm/v. That gives us 45 kmph= 28mph. At that speed, wind resistance is a big factor so actual top speed is more likely to be 25mph because the motor probably doesn't have enough power to pull 28. So a 275rpm-36V BPM run at 48v, generating 500w constant should pull 25mph. Which is a sanity check with mechaniker's comments above.

The downside to all this is efficiency and torque. If you actually ride below 15mph, go up relatively steep hills or use the speed all the time, range will suffer because the motor will be working below it's peak efficiency and may not have enough torque to just power up the hills.

So in a nutshell, If we don't care too much about legality, a 275rpm-18" motor in a 26" or 700c wheel looks about right. With a boost from 36v to 48v if we want to go for real speed.

What I'm not sure about yet is the merits of running a 24v motor at 36v or even 48v. Burnt wires and magic smoke?

 

[overthehill]

24 V hub

but Jay is running a 36 V hub surely that is ok

 

[jbond]

but Jay is running a 36 V hub surely that is ok

He's planning a 36v hub at 48v I believe. I'm curious about running a 24v at 36v or even 48v.

 

[mechaniker]

He's planning a 36v hub at 48v I believe. I'm curious about running a 24v at 36v or even 48v.

You can let run the 24v motor on 48v but you must reduce the Ampere (you must check that the motor never go higher as 600Watt consumption.
It give you highspeed support but the torque on low speed go more and more worse.

regards
frank

 

[jayuk]

It looks like i should have my BPM kit through within the next week.
All thanks to Cell_Man over on the endless sphere forums

Indeed it was'nt as cheap as what Bmsbattery would have been but all the components will be better quality.

Once i have it all fitted i will add some photo's

jay