More speed from BPM 36V500 26 Code 10

[MomentumUpstart]

Hi,

I have the following setup on a 26" mountain bike that was put together by a local company here in Australia. It is marketed as an offroad bike as it has large downhill style front shocks and wide 2.5" knobby tyres. The only way they can sell a bike with over 250W is to say it is offroad only.

However, I use mine for long distance commuting 20+ mile each way on very remote paths. I might see 2 other riders each day and am very respectful (although I can do the same speed on an unpowered bike just not for as long).

Currently the bike does around 20-21mph when fully charged and drops its way down to around 18mph by the end of the 20 mile ride.

The bike is quite torquey and gets up to that speed very quickly. Its noload rpm (by me lifting the rear wheel and accelerating) is around 23-24mph.

I am fairly fit and love cycling to work each day, however any more than a light pedal and the motor stops assisting.

Goal: increase top speed (path is very flat, smooth and straight) and allow the use of more pedal effort. I dont mind loosing torque as there is only a few hills and I am happy to pedal harder. Goal is to reduce travel time.

Motor:
BPM 36V500W 26 (10)
1409245426

Controller details:
Rated Voltage: 36V
Under voltage protection value: 31V
Limit Current: 22A
Nominal current: 11A
Rated Power: 500W
Wheel Diameter: 26”
Drawing Number: LK559-3-2

Ideas?

 

[Alan Quay]

I have the CST (pretty much the same, just cassette I think) and run it with a 12 FET controller (BMSB, S12P I think), up to 30 amps. You'll need to ensure your battery can deliver that current though.

Mine goes along at around 24mph on the flat.

 

[MomentumUpstart]

Thanks for the reply. Is yours code 10 and on 26" wheels?

How can I tell how much current the battery can deliver?

So to go above 24mph I would need to increase voltage which would require a new 48V battery.

 

[Alan Quay]

Thanks for the reply. Is yours code 10 and on 26" wheels?

How can I tell how much current the battery can deliver?

So to go above 24mph I would need to increase voltage which would require a new 48V battery.

There's no code on the CST, it's wound for 270 rpm.

Yes, mines in a 26" wheel.

To work out how much your battery can give you will either need to take it apart and check the BMS, ask the manufacturer or suck it and see.

Correct, to get over 24mph you will need higher voltage.

Your other option would be to add a bit of solder to the shunt in the controller. Again, you could go too far and the battery may not be able to keep up.

 

[MomentumUpstart]

Im confused if yours is 270rpm and mines supposed to be 300/310rpm and my noload speed is 24mph. Shouldnt yours have a lower noload speed? I didnt think it was possible to go over the noload rpm/speed.

Is it correct that more current will help increase speed as close as possible to the noload speed?

If the motor stops giving power underneath the noload speed does that mean that it is hitting the current limit on the controller?

I would be happy with 24mph on the flat.

 

[Nealh]

A 500w is more suited to a 48v 25/30a system then 36v so its power is not being fully utilised so over volting is a good option.
Most 36v controllers can handle 48v or 12/13s lipo and even up to 15s, most of the caps appear to be rated 63v on good controllers. A 25% increase in speed may be possible by over volting and more amps may be available as I doubt that your controller will be pulling max amps unless you are on a climb. As Alan say's the batteries bms will be the factor, 36v/48v batts with newer higher capacity 30-32 mah 18650's are using 28a bms whilst those using 26-29 mah cells tend to use a 20a bms. However some suppliers use higher amp bms on battterie's such as Eclipse on some of their 09 dolphin models.
If you are familiar with lipo then a 10c rated pack at 10ah is capable of 100amps with bursts of 200 max so pulling amps is not an issue just monitoring low voltage needs to be undertaken.

 

[MomentumUpstart]

What do you think about a KU93 controller to bump up the current to 22A?

 

[Nealh]

KU93 like yours rated 11a with max 22a output, so no diff.
amps in general = pulling power/torque.
volts = speed.
Your 500w motor code 10 300rpm @48v should get you about 32mph as at 48v it will spin at 390rpm.

 

[MomentumUpstart]

Thanks, so bms current is what the battery can apply constantly and it can apply more for short periods of time for a hill etc?

I would be happy with 24mph and am not very keen on buying another battery yet as it is a custom size to fit the inside of the bottom tube. From Alan Quays post above it seems like I could get close to 24mph with more amps.

I was also thinking about replacing the motor with a higher rpm version to give me more top end speed and I would like to pedal a bit more. However I am concerned that the rpm is not currently the limiting factor as it can't hold a consistent speed near to the nolimit speed anyway. Hmmm

 

[MomentumUpstart]

It would be awesome if I could run a constant 20A and have no increases for hills or extra load, is this possible?

 

[Alan Quay]

Im confused if yours is 270rpm and mines supposed to be 300/310rpm and my noload speed is 24mph. Shouldnt yours have a lower noload speed? I didnt think it was possible to go over the noload rpm/speed.

Is it correct that more current will help increase speed as close as possible to the noload speed?

If the motor stops giving power underneath the noload speed does that mean that it is hitting the current limit on the controller?

I would be happy with 24mph on the flat.

I think the quoted RPM must be at 36v. When I say 24mph, that will be on the flat, with a fully charged battery at 42v . Also, the tyres I'm running are so big that they are virtually the same circ. as 700c.

You are correct that the more current you give it, the closer it will go to its no load RPM. Because you have a higher winding ratio than me, and get lower RPM then I suspect it's current limiting you top speed.

So, because I have a massive battery (little or no sag), and up to 30a available, mine will go closer to the no load RPM.

The ku9x controller is a 9 FET unit. I have a 12 FET one.

 

[MomentumUpstart]

Thanks, that makes perfect sense now. Im finally learning something!

What tyres are you running?

If I did raise the current by adding some solder to the shunt or purchasing a 12 mosfet controller how can I read the amps? And are there any basic ways to see if the battery is not coping? I was thinking run it for a short time and measure the volts to see if it has dropped excessively

 

[Alan Quay]

Thanks, that makes perfect sense now. Im finally learning something!

What tyres are you running?

If I did raise the current by adding some solder to the shunt or purchasing a 12 mosfet controller how can I read the amps? And are there any basic ways to see if the battery is not coping? I was thinking run it for a short time and measure the volts to see if it has dropped excessively

I'm running DMR motors on that bike, 2.4" as I recall. They are extremely 'tall'.

As for measuring stuff, you need a watt meter between the battery and controller. They store data like max current, lowest volts, etc.

http://pages.ebay.com/link/?nav=item.view&id=390932345418&alt=web

 

[MomentumUpstart]

Thanks, in your scenario with plenty of amps then extra gearing helps get more speed. But i think in my case I am limited by amps so lower gearing wont help me. I changed from 26x2.5 tyres to 26x1.1 tyres and Im still review stats to see if it was any faster. All I know for sure is that my arse was killing from the loss of shock absorption with the thinner tyres!

I just bought a watt meter so will be interesting to see what amps it is running.

This is a complete bike still with 1 year warranty so im thinking about starting another bike build if I want more speed, instead of stuffing up this one. Geeze it seems its all about the battery! Controllers and motors are pretty cheap in comparison. And without the right battery it doesnt matter what fancy motor and controller you have.

 

[trex]

...
so im thinking about starting another bike build if I want more speed, instead of stuffing up this one...

If you want torque, get a BPM, if you want speed, get a crank drive motor.
Hub geared motors are limited by their no load speed by design. 350W BPM code 10 gives 201 RPM at 36V as practical upper limit and still with reasonable torque. To get it spin faster, you have to increase the voltage. With a crank drive, you can modify the gearing gain to get a little more speed. Typically, a 250W crank drive is equivalent in pulling power to a 350W BPM code 10 at 200 RPM but you can eek a bit more speed out of it by using 11T on the rear cog, reaching about 22mph-23mph. A BBS02 25A 500W that will work with your present battery will give you a top speed of 28mph. That's what most s-pedelecs are.

 

[anotherkiwi]

Typically, a 250W crank drive is equivalent in pulling power to a 350W BPM code 10 at 200 RPM but you can eek a bit more speed out of it by using 11T on the rear cog, reaching about 22mph-23mph.

50-12 or 50-13 would be my choice, it would be gentler on the rear sprocket and chain. Can a 50 tooth chain wheel be mounted to the GSM kit trex?

 

[trex]

I reckon a 13T is a very sensible choice for low wearing. The GSM comes with 46T chainring. Maybe 50T is a better choice. You can fit any other chainring made for BBS01/BBS02.

 

[MomentumUpstart]

If you want torque, get a BPM, if you want speed, get a crank drive motor.
Hub geared motors are limited by their no load speed by design. 350W BPM code 10 gives 201 RPM at 36V as practical upper limit and still with reasonable torque. To get it spin faster, you have to increase the voltage. With a crank drive, you can modify the gearing gain to get a little more speed. Typically, a 250W crank drive is equivalent in pulling power to a 350W BPM code 10 at 200 RPM but you can eek a bit more speed out of it by using 11T on the rear cog, reaching about 22mph-23mph. A BBS02 25A 500W that will work with your present battery will give you a top speed of 28mph. That's what most s-pedelecs are.

Thanks for the post. I am still to learn about the crank drive motor. The price of them here was what made me choose the rear hub motor. I was just looking for best value to commute 20 miles to work. The simplicity of the rear hub motor attracts me also.

I also do mountain biking and I completely acknowledge that crank drive would be much be much better weight balance, not to mention braking the rear wheel with hub motor does bugger all due to its extra weight.

The one thing I dont like about crank drive is the power going through the chain and gears. I struggle to keep a normal road bike changing gears properly (very lazy on maintenance). I ride a single speed for short distances under 12 miles. I currently leave the ebike in the hardest gear possible and was thinking about shortening the chain and skipping the derailleur to stop the chain bouncing around and add some efficency.

It sounds like the crank drive is much better for someone that wants to pedal hard with the added power. Is there anyway to get that same experience in a rear hub? Would the highest possible noload rpm on a 500W rear hub motor do the trick? I can change the gears to harder ones too to allow me to keep assisting at higher speeds.

 

[MomentumUpstart]

Why isnt changing the rear hub motor to a higher rpm version (or increasing the volts) the same as changing the gearing on a bicycle with a crank drive motor?

Currently as soon I start to pedal with some effort the power assistance reduces greatly and it feels like I put in heaps of effort but i gain no speed.

 

[trex]

Why increasing the volts the same as changing the gearing on a bicycle with a crank drive motor?

Hub geared motors are characterised by their constants Km (motor size constant) and Kv (motor velocity constant or back EMF constant).
When your motor spins, it creates back EMF, when the back emf is as strong as the battery voltage, the current going through your motor is nil, you have reached maximum no load RPM.

https://en.wikipedia.org/wiki/Motor_constants

Your RPM = Kv * battery voltage. As simple as that.