My first conversion project - Carrera Subway 2

[spikey]

I have an old Carrera Subway 2 bike and plan to use this as my first conversion project. I decided to get a Bafang mid drive kit for an easier installation with less wiring.

My first problem is which model to buy. I want to stick to 36V for a lighter and cheaper battery pack. I'm thinking of either BBS01 350W or BBS02 500W, would I notice any real difference between them on flat and hilly terrain.

Next I've chosen a 36V 10AH battery, would this give a range of at least 20miles and have enough current to achieve at least 20mph on flats and enough guts to get me up 10% gradients?

I shall be ordering from Elifebike as they seems to be the cheapest for the motor and battery. My shopping list is
Battery 36V 10AH http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2014-6G-1PH0.86KUF
BBS02 36V 500W http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2014-4C-S4FR.8VTVC

http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2014-4C-S4FR.8VTVC

 

[pdarnett]

Should be good with that kit, I have a subway with a Cyclocity front hub and goes great, is yours one of the subways with the geared rear hub? They were a great bike for converting.

 

[Deleted member 4366]

That setup should give you what you want. The only thing that doesn't quite add up is the battery. It seems too cheap. It's about the price of a normal 10aH 36v one, but it's maximum current is 20 to 80 amps. I think that means that it has a BMS that can be set to up to 80 amps, but what is it set to and how much current can it give? The other thing is that the charge current is quite high, which suggests that the cells are high discharge rate ones. They call it Headway battery, but Headway cells are large LiFePO4; however, they say it has LiMn2O4 18650 cells, which are small.

I think I'd ask them specifically what is the actual maximum and continuous discharge rates of that battery before ordering. A normal 36v 10aH battery with LiMn2O4 cells won't be strong enough. It's possible that their one is something special, in which case we'll all order some.

 

[spikey]

Should be good with that kit, I have a subway with a Cyclocity front hub and goes great, is yours one of the subways with the geared rear hub?

I afraid not, it has a derailleur. I got this 2nd hand so looks battle worn which hopefully be less attractive to steal especially when I've converted it.

 

[spikey]

I think I'd ask them specifically what is the actual maximum and continuous discharge rates of that battery before ordering. A normal 36v 10aH battery with LiMn2O4 cells won't be strong enough. It's possible that their one is something special, in which case we'll all order some.

Thanks for your advice. I've emailed these questions and let you know their response.

Do you think I should get a rear rack battery instead, like this http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2011-1J-91BE.18EQD. My bike have disc brakes and so sticks out, would the compatible rack fit my bike?

 

[Deleted member 4366]

That battery again is OK for a 250w motor with a 15 amp controller. If you want a more powerful motor, you have to get a more powerful battery to go with it. You can get more power from the battery by going bigger (15aH) or by getting one with a higher discharge rate.

There's a lot of different versions of the BBS01, but IIRC, the 350w 36v one is 18 amps, and the 500W one is 25 amps, so you need a battery rated at at least 12 amps for the 350w one and 18 amps for the 500W one. The problem is that you can't trust what these Chinese guys write in their listings. You can only make sense when they tell you the type of cells; however, as a general rule you can say that a 10aH battery is rated at 10 amps, 15aH at 15 amps, etc.

 

[spikey]

The ones on EM3ev 36V 15AH Samsung I guess would be perfect but was hoping for something cheaper. http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160

One thing I need to understand is what will I gain from a 350W over a 500W in reality. What are their top speeds on flats. For hills say 10% gradients, would the 500W be alot quicker or is it only 1 or 2mph difference.

 

[D8ve]

Spikey
The speed will depend on your input but the biggest difference will be the range. A higher powered motor will increase the speed and hence energy wasted in wind resistance. To get max range slow down a little and your energy costs will fall rapidly. The hill climbing bit will be quite a bit slower. But the battery will last longer.
Oh if the battery is the current limiting factor then no power difference at all between the motors as if it can only supply 300 watts then both motors will only draw 300!

 

[trex]

...
One thing I need to understand is what will I gain from a 350W over a 500W in reality. What are their top speeds on flats. For hills say 10% gradients, would the 500W be alot quicker or is it only 1 or 2mph difference.

http://www.ebikes.ca/tools/simulator.html

350W will give you 7.2mph on 10% gradient (bike + human = 100kgs), 500W 10mph. But actually, these motors can give a lot more than their nominal rating. A 350W can give as much as 550W-600W, a 500W motor 800W-1000W.
The problem with big and powerful hub motors is overheating on steep hills above 10%.

 

[Deleted member 4366]

.
The problem with big and powerful hub motors is overheating on steep hills above 10%.

Sharp intake of breath.

Hub-motors don't overheat on steep hills if you have a low winding speed. My Xiongda got me up the mighty Lincoln hill at Ironbridge. It was hardly warm at the top. Saneagle was riding alongside me on his BPM, which could steam up it. It could get up there so quick that it wouldn't have had a chance to get hot. Unfortunately, he decided to ride with me. His motor didn't get hot, but he melted the phase wires on his controller.

I had every type of geared hub motor, and I've been up every type of hill, and I've never had a motor overheat with one exception. I think you'd only get problems if you lived in the mountains. I used to give my old QSWXK5 some abuse too, and that never overheated either in 2000 miles. The only motor I've overheated was a 328 rpm Q100 on a long hill because it didn't have enough power for its speed.

The Ebikes.ca stimulator does tell a different story, but all those graphs are for no pedalling. Have you ever overheated a motor?

 

[trex]

no, never. slightly warm to touch but never hot.
I think overheating on the ebike.ca is taken to mean that the motor may suffer dammage.

from their notes:

• Overheat In[g]: This is a prediction on how long it would take the motor to overheat (reach 150oC) based on a simple first order thermal model that assumes the motor is not spinning and in still air. The actual time to overheat on a vehicle moving outdoors and associated air cooling would be substantially longer. It none the less provides a good relative indicator of how much the motor is being stressed until we develop a more complete model.

 

[Deleted member 4366]

That probably explains it then. With the motor spinning and moving through the air, there'll be a big difference. I think there's only a danger of melt-down if you have a high-speed motor. or low-powered one.

 

[trex]

...
There's a lot of different versions of the BBS01, but IIRC, the 350w 36v one is 18 amps, and the 500W one is 25 amps, so you need a battery rated at at least 12 amps for the 350w one and 18 amps for the 500W one. The problem is that you can't trust what these Chinese guys write in their listings. You can only make sense when they tell you the type of cells; however, as a general rule you can say that a 10aH battery is rated at 10 amps, 15aH at 15 amps, etc.

woosh said they have the BBS01 36V 18A on their way, arriving middle of July. I suppose it's around the right power to weight ratio. I find my BBS01 a little weedy at times.

 

[spikey]

Thanks Trex for the info on what I can expect between a 350W and 500W motor. I think I might as well go for a 500W.

I've found a thread on Endless-Sphere titled 'New Bafang Crank-drives' over 100 page long which is killing my eyes. Still haven't reach the end yet.

I'm looking at high discharge batteries on Aliexpress and they seem to use ICR18650-26F http://www.scribd.com/doc/82409398/Samsung-2600mAh-ICR18650-26F . Is this a good cell to use as a 36V 13AH battery?

 

[trex]

you get 50 x 2600mAH = 13AH. The battery will weigh about 3.4kgs
The cells can do 2C, so maximum continuous current will be 26A. That should be enough for 350W BBS01 but a bit weedy for 500W - most people would go for 15AH or 20AH batteries with 500W BBS02.
The alternative is woosh 15AH battery kit (battery, charger, fitting), a bit pricey at £349 but it's built with 2900mAH ICR18650-29E, same weight, more power.

 

[spikey]

The Woosh battery looks good but obviously have to pay a premium for this. I like the look of this new bottle battery shape but it looks like it is fixed to the bike's bottle cage screw holes if I'm not mistaken. Is this fixing strong enough for holding this amount of weight, I mostly be riding on roads.

 

[Aushiker]

http://www.ebikes.ca/tools/simulator.html

350W will give you 7.2mph on 10% gradient (bike + human = 100kgs).

I can get better than that with my 36V 350w .... I am getting around 15 to 16 km/h throttle only up a 6% gradient from a near stop start. Weight of bike and human closer to 120 kg.

Andrew

 

[Deleted member 4366]

You need 291w of output power to take 120kg up a 6% gradient at 15km'h, not taking into consideration wind resistance. To overcome the wind resistance, you need about 80w, so 370w total. At that speed, your motor will be about 65% efficient, so that's 569w into the motor. The controller's about 90% efficient, so 632w from the battery, which is 15.8A. Therefore, your estimate seems to be about right according to the calculation.

If you turn it round the other way, a 15 amp controller will get a 120kg bike and rider up a 6% gradient at 14.2 km/h in neutral wind.

 

[Aushiker]

That is good to know d8veh.

Andrew

 

[spikey]

You need 291w of output power to take 120kg up a 6% gradient at 15km'h, not taking into consideration wind resistance. To overcome the wind resistance, you need about 80w, so 370w total. At that speed, your motor will be about 65% efficient, so that's 569w into the motor. The controller's about 90% efficient, so 632w from the battery, which is 15.8A. Therefore, your estimate seems to be about right according to the calculation..

That's a great and detailed answer D8veh... did you get a new computer for your birthday?

I'm on the light side, 70kg, so I assume the motor will take me up the hill faster.