Considering converting my wife's folding bike

[John_S]

My wife is strongly considering an e-bike for herself after seeing how useful my Woosh Big Bear has been for me. She doesn't drive, and an e-bike would really help her to get about.

She has an ordinary folding bike with 20 inch wheels, which I'm thinking of converting for her. This is the model: http://www.halfords.com/cycling/bikes/folding-bikes/mizani-city-unisex-folding-bike

She needs a setup that has a lot of torque as we have a fair few hills round here and she weighs about 17 stone. I think that something such as a 48v Q128h motor paired with a 20a controller would meet her requirements. I'm thinking of the following setup from BMSBattery:

The 48v 201rpm Q128h rear motor in a 20 inch wheel: https://bmsbattery.com/ebike-kit/776-q128h-48v800w-rear-driving-e-bike-motor-wheel-ebike-kit.html

The 48v sinewave controller with included PAS, throttle, LCD etc.: https://bmsbattery.com/controller/698-sine-wave-controller-for-09-case-controller.html

The 48v 12.5ah case-08 bottle battery: https://bmsbattery.com/ebike-battery/817-48v116ah-case-08-bottle-panasonic-battery-pack-battery.html

Plus a pair of torque arms.

If any of you knowledgeable forum members could give me your opinions on this setup that I've chosen and if you could tell me if this setup would work okay, it would be much appreciated. Thank you.

 

[Deleted member 4366]

I think that's overkill for a 20" wheel. At 48v, 15 amps is enough for a 17st rider on 26" wheels, so 20amps would make it very jerky. You can turn down the power in the LCD, so it's not a big problem.

You need the 328 rpm motor for small wheels unless you want it to go dead slow. 201 rpm would be 11.5 mph max and more like 9 mph before power starts dropping off.

The controller you've chosen is for the Dolphin batteries, which you can buy from BMSB with the controller pre-installed, or you can buy your chosen shark battery with an 18A controller pre-installed.

Lastly, wouldn't one of these batteries be better.

https://bmsbattery.com/ebike-battery/779-48v116ah-case-02-panasonic-battery-pack-battery.html

The one you've chosen is very relatively heavy with 65 cells in it, while as the rack one has only 52 and it has a compartment for any small aluminium box-type controller, so you can use this one, which is 14A. It's the one I use with a Q128C in a 26" wheel, so you'd get 30% more torque in a 20" wheel:

https://www.aliexpress.com/item/36V-250W-48V-350W-Controller-LCD-LCD6-Display-Meter-PAS-Set-E-bike-Conversion-kit-Dual/32834523159.html?spm=2114.10010108.1000023.9.52fa4216csrOQG

 

[John_S]

Thanks for your reply d8veh. I realize that the 201rpm option on a 20" wheel will max out at around 12mph, but of course that comes with the advantage of having very high torque. I think we'd prefer that option than going for the 328rpm one which has higher speed but lower torque. My wife doesn't mind having a low top speed as long as her bike can tackle the hills.

I think that if we can fit large, thick tyres to the wheels it will improve upon the top speed slightly, while also helping with suspension and traction.

I think I'd like to stick with the 12.5ah shark battery I've chosen. The 11.6ah rear rack battery is more expensive and has a lower range. Would the shark battery I've chosen be easy enough to connect to the controller that I chose that is designed for a dolphin battery? If not, I'll follow your suggestion of buying the battery with the 18a controller pre-installed.

 

[Deleted member 4366]

Two wires to connect the battery to the controller is all you need.

 

[harrys]

D8veh, I have found that racks for 26" bikes are too tall for a folder. I installed two racks (these had no battery trays) last year, and had to cut the struts shorter. My dilemma with these little bikes was finding a battery that didn't ruin the looks of the bikes.

I'm using 260 rpm Q100H rear hub motors from BMS battery. Spoked them myself. Had to do the first one twice. (In/out didn't work.) We are 10.5 and 14 on your stone scales. 17A torque simulation controllers from PSWpower. 36V batteries, although I've used 52V on occasion. No hills where we live. With a 48T/11T gear combo, 18 mph is about as fast as I care to spin the pedals.

My choice is to use smaller batteries and carry a spare (or two) for longer rides. I can fit a 36V 10S-3P inside the seat bag. Good for 14 miles. The above was a freewheel so I used a Q100H. My wife's folder had a cassette, but I also used a Q100H because it's a little more power.

The Q100H is very mild mannered, but if going up a steep hill, there's enough weight over the rear wheel that it can lift the front wheel. Something you will need to watch for on a Q128. Still, more motor is always good.

 

[John_S]

That's a nice looking bike! Very neat and cool looking.

Anyway, I've gone ahead and bought the kit, but I decided that the 201rpm Q128h in a 20" wheel was in fact too slow. So I went ahead and ordered the same but in a 24" wheel. I then bought a refurbished adults mountain bike with 24" wheels on Ebay (looked to be a high quality bike and a real bargain at £74), which I intend to fit the kit to.

Am I correct in saying that the 201rpm in a 24" wheel would have a top speed of about 14.5mph?

 

[Deleted member 4366]

Top speed depends on the voltage. You can calculate the speed at 48v, but it will be about 10% faster when the battery is fully charged and 17% less when the battery is empty.

 

[John_S]

I think the top speed would be about 14.5mph according to a thread I found on Endless-sphere. The thread includes a very useful chart of the different top speeds of different sized wheels at different rpm.

I noticed that the kit I bought has no speed sensor. Do you know if it is possible to use a speed sensor with this setup? Its not a problem for me that there's not one included, although I'd still prefer that there was one.

 

[harrys]

If you bought the Q128H from BMSbattery and also their controller that has the round motor cable that matches the motor cable, that should be wired already for a speed sensor inside the motor. I believe you need the P1 parameter to be 1 to have it work right.

I have a Q128H sitting here, and it works as above with a KT-controller. I forgot what rpm or voltage I bought. It must be a 36V 201 rpm. I have it in a 26" rim.

 

[Deleted member 4366]

You can use an external, internal or no speed sensor. Without a speed sensor, the controller gets the speed signal from the motor halls, but it'll go to zero when freewheeling.

 

[John_S]

Thanks for your replies guys.

Just one more thing I'm curious to know, which would you say will be the better hill climber, the kit that I've chosen for my wife (48v 201rpm Q128h in 24" wheel, 48v 20a controller/battery) or my current Woosh Big Bear (36v 230rpm BPM in 26" wheel, 36v 20a controller/battery)?

Thanks.

 

[Deleted member 4366]

The Q128 will give about 44% more torque. It'll be no contest.