Conversion kit for 20'' folding bike

ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
Hello all,

I live in France and i'm planning to buy a folding bike to go to work. To this day, i go to work with a vintage bike (18 km per day). I've recently got a new mission at work and it's further than before (28 km per day), but above all there is a nice hill to get there...My vintage bike is OK for small rides. I keep it in good state and care for it. But it won't be enough now.
I think about getting a folding bike (don't know if I will move and live outside city center but i think of it and i want to be able to get my bike in my car that I would left at the entrance of the city).
I haven't made up my mind yet for the folding bike. Maybe a Dahon(mariner d8) or Tern (link D8).
The idea is to convert the bike.
I've spend hours to search what would fit my needs. But i must admit that i'm still quite lost.
My weight : 63 kg.
I'm looking for an ebike solution that would let me pedal. Even if it's an ebike i want it to be a bike. The motor would be here only to help me and prevent me from arriving in a sweat at work.
So i won't probably install a throttle.

Even if I've seen all kind of conversions for this type of bikes (front hub, rear hub or middle motor), i think a hub (front or rear) would be nice and quite easy to uninstall if I want to take my bike back to its original state.

There are two things important for me :
_ being able to be assisted up to 30 km/h or so
_ I prefer a controller that would fit in the battery support (Hailong style battery). The idea is not to try to make speed records but just help me in my efforts :).

Will a 36V 250w motor (with 15A max controller) be OK regarding my needs? There are plenty of motors in this range...which one(s) would fit the best the folding bike? AKM SX85 (nice because small and light) , Q100H, Bafang, MXUS XF08/07...Or would it be better to go for 48V 250w (if it does exist, 250w motors are mostly in 36V)
Do you know a kit that provides a controller in hailong battery case? I haven't found one. But i could always buy parts separately if I have to.

thanks for any kind of help,


rgds,

Ed.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
8,346
3,338
Basildon
If you fit a rear motor in a Dahon or tern, you'll need a cassette version, which would normally have the suffix C or CST on its designation, like Q100C, AKM100CST, etc. They're a bit wider than freewheel motors, but you can normally get them in as long as the frame isn't too stiff, so avoid a bike with two thick beams running all the way to the axle.

Personally, I'd use a full size bike for a commute like that. They're still pretty easy to put in a car if you take off the front wheel and turn the handlebars 90 deg, which takes less time than it does to fold a folding bike. It's much easier to install a battery on a bike with a full size triangle frame.

With your weight, 15 amps should be enough at 36v, but 48v would be better. To get 32 km/h, you need your motor to do 260 RPM, so use a 201 rpm 36v one at 48vm or a 260 rpm 480v one. If you want to cruise at 30 to 32 km/hr, you need a 36v 260 rpm motor at 48v or a 328 rpm 48v one. bear in mind with the assistance to maintain that speed, you'd be using about 15 to 20 wh/m, which would be 350wh for the journey, so you should get a battery at least 400wh. 500wh will guarantee that you can do the journey in all conditions. That's probably a bit big for a folding bike.
 

pentiumofborg

Esteemed Pedelecer
Dec 13, 2020
1,198
330
Well, my Dahon Helios still folds neatly, even with a BBS01b:

40807


40808



...I totally understand your wish to get a folder! I get 50 real miles with the max level of pedal assist (19.2ah battery with (I think) LG cells), over hilly terrain. However, it does tend to struggle on inclines after about 43 miles, depending on the inline of the incline... and if it stops working and can't be revived easily - just put it on a bus or in a taxi quick and easy, because it folds!
 
Last edited:

ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
Hello,

thanks for the inputs.
So from what i've understood, it is possible to run a 36V motor with a 48V battery (and a 48V/15A max controller of course)? Is it safe for the motor?

thanks,
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
8,346
3,338
Basildon
Hello,

thanks for the inputs.
So from what i've understood, it is possible to run a 36V motor with a 48V battery (and a 48V/15A max controller of course)? Is it safe for the motor?

thanks,
Yes, voltage only affects the speed of the motor. It's current ot total power that would harm one. With your weight, any motor will be fine up to about 328 rpm.

Those speeds are for 26" wheels. For 20", you need proportionally faster. For sustained speeds of 32 km/h, you need a 328 rpm 36v one running at 48v. That will limit your choice of motor a lot because most are around 250 rpm.
 
Last edited:

Nealh

Esteemed Pedelecer
Aug 7, 2014
12,896
5,033
57
West Sx RH
In France one may need to be careful of being caught with a throttle ebike.
 

ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
Hello,

i keep on trying to understand what would fit what i need.
How ebikes work is nicely explained here :

https://ebikes.ca/getting-started/ebikes-parts-explained.html

the first chart gives relations between max speed and motor winding.
From what i've read, for a 20'' wheel:

328 rpm would give 30/32 km/h.

they also say to choose a motor winding and battery voltage that is at least 15-20% faster than the running RPM gave by the chart in order to achieve the target speed.

so either a 328 rpm motor at 36V or the same motor (but at 260 rpm and 48V) should give the same speed (or so).
So what would be the best setup?

Nevertheless, i still don't understand how speed relates (if it does) to current sets by the controller. If someone could explain, that'd be great. I know a motor can handle a max current ; beyond it would melt. So my question is : how could i know if values in the table are OK with a standard controller for exemple ( 36V 328 rpm with 15A max would give 30km/h?)?

thanks,
Ed.
 
Last edited:

vfr400

Esteemed Pedelecer
Jun 12, 2011
8,346
3,338
Basildon
The voltage determines the maximum speed the motor can spin to, but you need more power to go faster. You need 250w to do 15mph on the flat without pedalling and 1000w to do 30 mph.

It's quite complicated, though simple once you understand it. Lets say you have a 36v system with a 328 rpm motor and 15A controller. from experience, the motor will max out at about 21mph downhill. On the flat, you get about 18mph.
There are three things that control how much power you get:
1. The controller limits the current to 15A, so the most you can take from the battery is 540w
2. The motor has a diffent efficiency at different speed. At 5 mph, it will be around 50%, so you get 270w at the wheel. At 15mph efficiency would be about 70%, so 378w at the back wheel.
3. The back emf from the motor. As soon as the motor starts turning, it becomes a generator, and it generates a voltage opposite to the battery's. At 328 rpm, it generates 36v, which cancels out the battery, and is why the motor won't spin any faster. At 15 mph, it'll be generating about 27v, which leaves 9v (36v-27v) to power the bike. That's probably not enough to get 15amps through the motor, so the controller's 15A limit is no longer relevant, and the motor speed is the thing that's ccurrent is ramping down until it becomes zero at about 21 mph, and power = volts x current, so it goes down too.. That's why you can only reach 18 mph on the flat.

Now, if you change the battery to 48v, at 15 mph, you have 48v-27v = 21v to drive current through the motor, which is more than twice as much before. Basically, everything happens at 30% (7mph) further up the speed range. The motors max speed become 28 mph and you'll get good power to 20 mph before it starts ramping down. You should be able to cruise comfortably at around 22 mph, taking into consideration that the wind resistance accelerates upwards with your speed and starts to become increasingly more significant once you get past 15 mph.

The next thing to consider is battery usage. If you're running at full power at 20 mph, you'd probably be at around 12A, which would drain a 12Ah battery in an hour. That would be a range of 20 miles.

To answer your question, the most current you can get with a 15A controller, regardless of voltage is 15 amps. At something like 70% of maximum rpm (which is dependent on voltage), the current ramps down. This is the reason why it never does any harm to derestrict a hub-motor system - because you'll actually be running the motor with less current. Increasing the voltage only allows you to use the same current more of the time.
 
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ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
Hello Vfr400,

thanks very much for your post.
When we talk about those speeds, it relates to only throttle (only motor)? What happens if we pedal? Does it affect the way the motor reacts? After all, the motor does its work but we're also involved by pedaling.

one thing i don't understand in your post :
At 15 mph, it'll be generating about 27v, which leaves 9v (36v-27v) to power the bike. That's probably not enough to get 15amps through the motor, so the controller's 15A limit is no longer relevant, and the motor speed is the thing that's ccurrent is ramping down until it becomes zero at about 21 mph, and power = volts x current, so it goes down too.. That's why you can only reach 18 mph on the flat.
sorry i'm lost reading this. :)

to resume : if I take 2 systems :
a marked-328 rpm 36v- motor running at 36V
a marked-260 rpm 36v- motor running at 48V (ie 333 rpm)

there is no difference here? I mean the second system won't do any harm to the motor?

about one of your previous post, you said (in order to cruise at 32 km/h) :
328 rpm 36v one running at 48v
is there any motor that will handle this? Because 328 rpm is already fast. Running it at 48v will make it run even faster ((328/36)*48 = 437 rpm. Are these 250w motors able to handle this?

thanks,

rgds,

Ed
 
Last edited:

Surf_Wonder

Pedelecer
Jul 15, 2020
34
8
Folding bike on inclines? I had one, it was a 20inch - I sold it and don't miss it and my current wheel is 500w which handles inclines and weights with ease. I'm not a speed demon so there isn't anybody looking at me sideways on the road.

So if your wheels are smaller and your inclines aren't minor... good luck :)
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
8,346
3,338
Basildon
Hello Vfr400,

thanks very much for your post.
When we talk about those speeds, it relates to only throttle (only motor)? What happens if we pedal? Does it affect the way the motor reacts? After all, the motor does its work but we're also involved by pedaling.

one thing i don't understand in your post :


sorry i'm lost reading this. :)

to resume : if I take 2 systems :
a marked-328 rpm 36v- motor running at 36V
a marked-260 rpm 36v- motor running at 48V (ie 333 rpm)

there is no difference here? I mean the second system won't do any harm to the motor?

about one of your previous post, you said (in order to cruise at 32 km/h) :


is there any motor that will handle this? Because 328 rpm is already fast. Running it at 48v will make it run even faster ((328/36)*48 = 437 rpm. Are these 250w motors able to handle this?

thanks,

rgds,

Ed
The speeds I mention are based on much personal experience and are for a person of moderate weight and moderate pedal effort. When we talk about the max RPM of the motor, that's no load, i.e. with the wheel in the air. The max rpm is at the nominal voltage. When the battery is fully charged, it'll be 10% more, and when empty, it'll be 10% less.

The back emf is counter-intuitive. It's just the way motors work - a fact of life, like gravity and magnetism. Regardless of how you power it, a 36v 260 rpm motor will generate -36v at 260 rpm, so at 260 rpm, there is 36v from the battery trying to push current through the motor and -36v being generated by the motor pushing it back with the same force, so it can't flow, which is why it's the max speed at that voltage. The back emf is proportional to speed, so the motor generates -9v at 65 rpm, -18v at 130 rpm and -27v at 195 rpm.

If you have a small wheel it has to run fast. 20mph with a 20" wheel is 348 rpm.

As a general rule, you should choose a motor and voltage such that the max rpm is 1.3 times the rpm at your modal speed. Therefore, if you want to travel everywhere at 20mph with 20" wheels, you need 1.3 x 348 rpm= 452 rpm. If you like to pedal hard all the time, you could go down to about 1.2 or 417 rpm.

When comparing voltages remember that the ratios are 7:10:13, not 24:36:48 because that's how many 3.6v cell-groups are in each battery. The 24v, 36v and 48v are only nominal.

A 36v 260 rpm motor is identical to a 48v 328 rpm one in all respects apart from the label. It has the same bearings, clutch, gears, hall sensors, speed sensor, wire, magnets and casing.
 

ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
Hello,

thanks vfr400.

OK so i've made simulations thanks to motor simulator from ebike.ca.
I'v also made lots of research to find motors that would be ok.
For a 36V setup 15A max, I ended up with these two :

Bafang G310.250 at 8T (10.5 rpm/V so 378 rpm)
AKM 100sx (q100H) at 328 rpm.

here are the simulations:

40933

G310 would be really fine i think. Unfortunately, Grin is out of stock. I've found another place (motowoks) but they have the 10T version (280 rpm) although they told me it's 280 rpm loaded so 328 rmp unloaded or so. But i doubt about it since these rpm are done when unloaded. Plus, Grin advise the 8T version for 20'' wheel.

AKM100sx is easier to find. It's a classic.

Do you know suppliers who stock the G310.250 Bafang hub?

thanks,

Ed
 
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vfr400

Esteemed Pedelecer
Jun 12, 2011
8,346
3,338
Basildon
Q100H is
Hello,

thanks vfr400.

OK so i've made simulations thanks to motor simulator from ebike.ca.
I'v also made lots of research to find motors that would be ok.
For a 36V setup 15A max, I ended up with these two :

Bafang G310.250 at 8T (10.5 rpm/V so 378 rpm)
AKM 100sx (q100H) at 328 rpm.

here are the simulations:

View attachment 40933

G310 would be really fine i think. Unfortunately, Grin is out of stock. I've found another place (motowoks) but they have the 10T version (280 rpm) although they told me it's 280 rpm loaded so 328 rmp unloaded or so. But i doubt about it since these rpm are done when unloaded. Plus, Grin advise the 8T version for 20'' wheel.

AKM100sx is easier to find. It's a classic.

Do you know suppliers who stock the G310.250 Bafang hub?

thanks,

Ed
Bafang has changed the designation of it's motors. a lot of resellers don't use that number. Also, there are loads of clones, which are probably just as good. Have a look what's on Aliexpress
 

ed22

Finding my (electric) wheels
Feb 15, 2021
6
1
OK. but how do we know the new designations? If you have any informations about it, please tell me. Had a look on aliexpress and none of the motors i've seen seemed copies of the 310. Maybe you know one...
thx
 

Driiven

Just Joined
Mar 1, 2021
2
0
Hello all,

I live in France and i'm planning to buy a folding bike to go to work. To this day, i go to work with a vintage bike (18 km per day). I've recently got a new mission at work and it's further than before (28 km per day), but above all there is a nice hill to get there...My vintage bike is OK for small rides. I keep it in good state and care for it. But it won't be enough now.
I think about getting a folding bike (don't know if I will move and live outside city center but i think of it and i want to be able to get my bike in my car that I would left at the entrance of the city).
I haven't made up my mind yet for the folding bike. Maybe a Dahon(mariner d8) or Tern (link D8).
The idea is to convert the bike.
I've spend hours to search what would fit my needs. But i must admit that i'm still quite lost.
My weight : 63 kg.
I'm looking for an ebike solution that would let me pedal. Even if it's an ebike i want it to be a bike. The motor would be here only to help me and prevent me from arriving in a sweat at work.
So i won't probably install a throttle.

Even if I've seen all kind of conversions for this type of bikes (front hub, rear hub or middle motor), i think a hub (front or rear) would be nice and quite easy to uninstall if I want to take my bike back to its original state.

There are two things important for me :
_ being able to be assisted up to 30 km/h or so
_ I prefer a controller that would fit in the battery support (Hailong style battery). The idea is not to try to make speed records but just help me in my efforts :).

Will a 36V 250w motor (with 15A max controller) be OK regarding my needs? There are plenty of motors in this range...which one(s) would fit the best the folding bike? AKM SX85 (nice because small and light) , Q100H, Bafang, MXUS XF08/07...Or would it be better to go for 48V 250w (if it does exist, 250w motors are mostly in 36V)
Do you know a kit that provides a controller in hailong battery case? I haven't found one. But i could always buy parts separately if I have to.

thanks for any kind of help,


rgds,

Ed.
Hello Ed - you could try www.humancycle.cc for their excellent ebikes or the electric conversion kits all regenerative using the KERS self charging technology. As far as we know very best on the market. Cheers
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
12,896
5,033
57
West Sx RH
Hello Ed - you could try www.humancycle.cc for their excellent ebikes or the electric conversion kits all regenerative using the KERS self charging technology. As far as we know very best on the market. Cheers
Sounds like a plug from an insider.