Config options: small-motor / front / 20" / existing battery

[footloose]

Would appreciate advice of others with expertise in small motor builds.

I’m considering a build using either a Q100 or Bafang SWXU.
Would be front wheel drive, in an old Raleigh 20 folder (extensively modified, it rides very well, a favorite bike).
Don’t need brute strength or rocket speed in this build.
Value lower-weight over higher-performance.
Ride profile: 12 mile round trip, 80% flat, but with one significant (~8%, ~1mile) hill.
Not ideal, but can recharge at office if necessary.
15-18MPH top end fine.
Lots of stops and starts. Longest straight, flat run w/o stops <1 mile.
Don’t mind pedaling.
Plus need to carry the bike up a couple of steps into train.

I’d like to use an existing battery system I already have, currently powers Commuter Booster setup.
It is a homemade 6S3P A123 LiFePO pack.
Built of 3 discrete 6S1P modules, could be rewired into 18S1P using all three, or 12S1P by using only 2 of the packs.
In perfect world, I'd keep existing battery config so I could swap it between bikes.
For purposes of consideration, here are the basic parameters of each possible battery config:

6S3P (current config):
VMAX: 22.8V
VNominal: 19.8V
VMin: 15V (my choice… could safely go down to 9.6V in theory... but below 15V it drops quickly)
Ah: 6.9

12S1P:
VMAX: 45.6V
VNominal: 39.6V
VMin: 30V
Ah: 2.3

18S1P:
VMAX: 68.4V
VNominal: 59.4V
VMin: 45V
Ah: 2.3

So here is my quandary: What is the ideal motor / controller / battery config?

For example:
Q100 24V 328 RPM motor, under-volted using 6S3P battery, but slightly over-amped using a 24V controller with “partially soldered shunt”?
Q100 36V 201 RPM motor, slightly over-volted using 12S1P battery, with a standard 36V 9FET controller?
SWXU 36V 201 RPM Motor, way over-volted using 18S1P battery, with a 48V 9FET controller?
Give up on re-purposing existing battery pack?
Other?

Lots of possibilities. Advice appreciated!

 

[-dg]

18S1P:
VMAX: 68.4V
VNominal: 59.4V
VMin: 45V
Ah: 2.3

I'd choose the high voltage with a slow wind motor, too much current needed for the hill otherwise and you need all the battery you have and a little. But, with 68.4 volts make sure the controller can handle it (75V caps, power resistor etc).

The sticky point is that this is almost but not quite enough battery: 60V * 2.3Ah = 138 watt hours. At even 10 watt hours per mile which is very very low you will need (12*10) 120 watt hours. There is no reserve for your hill or wind or battery age or anything. You could probably do it if you only used the motor on the return trip, but what's the fun of that? Can you get one more of these 6s1p modules? Because that would help a lot.

I'm planning on 14s 5.0 Ah lipo for a similar build which will give 260 watt hours. I'm hoping to get 15 miles range and budgeting 14 watt hours per mile plus about 20% in reserve. (15*14 = 210)

 

[d8veh]

You're making things hard with your batteries. Q100 Nirvana is the 36v 328 rpm in a 20" wheel with 12S lipos at 48v and 17 amps. Alternatively you can use the 24v 201 rpm one with the same voltage and current. Your 2.3 AH isn't really enough.Why not get some hobbyking lipos?

 

[footloose]

Thx for thoughts, guys.
A year ago, when I started looking into E.S. stuff,
I formed an initial impression that I might want to stay away from LiPo...
awkward issue of "short thermal ramp".
I'm a bit less concerned now. They still have "str", but it's clear
that a lot of builders use them without problem.
May need to re-think my original aversion to LiPo.

 

[-dg]

Q100 36V 201 RPM motor, slightly over-volted using 12S1P battery, with a standard 36V 9FET controller?
SWXU 36V 201 RPM Motor, way over-volted using 18S1P battery, with a 48V 9FET controller?

The 6 FET controller is more than enough for either the Q100 or the SWXU. Neither will be happy with much over 15 amps.

 

[dnmun]

you should make your battery configuration compatable with the BMS you use and the charging voltage. most people would go to 16S if they could but you are limited by numbers of the 18650 lifepo3 cells you have?

 

[chisixer6]

I loved small wheel ebikes, currently have 4 small wheel ebikes running, using q100 or bafang motor. for 12 miles, should be no problem, when it comes to the hill, pedal assist really helps. I run 3 of the 4 on 48v 2p, the other is 75v 2p. The thing with a front driver, is slipage on takeoff, if you don't do it gently. I have my batteries in the front triangle, I use Turniqy 6s 5a batteries.

 

[-dg]

I loved small wheel ebikes, currently have 4 small wheel ebikes running, using q100 or bafang motor.

Which bafang front motor are you using and how does it compare with the Q100? Thanks!

 

[chvidgov.bc.ca]

You will need a front fork replacement on the Raleigh 20 (been there done that)...the dropout width is too narrow on a stock R20. You would have to use a Q85 on a stock R20, not a Q100. I've run a Crystalyte 404 on an R20 with the replaced front fork. I've also had a new bottom bracket put in, with a local expert on R20s - which gives you better gearing options.

http://endless-sphere.com/forums/viewtopic.php?f=6&t=5975

 

[footloose]

...front fork replacement on the Raleigh 20...

Thanks for calling that out. Fortunately, not an issue at this point. Few years ago I started rebuilding this bike along lines suggested by Sheldon B. At this point, there are only 2 original or unmodified parts remaining: the two little chrome levers for tightening frame and stem. All else is replaced / modified / upgraded / stretched / shortened / lengthened / tweaked somehow. Learned a lot in the process, and what a bargain -- I've probably spent only 50% more than a brand new Bike Friday folder would have cost me :wink:

 

[chisixer6]

-dg;

I have 2 bafang front motor, I believe they are swxk model, got 1 two years ago on my 1st ebike kit from Clean Republic, the other I got from Bike Wagon on ebay, motor only. the clean republic is a 26" wheel on a MTB, the other is 16" wheel, mounted on my clwb recumbent. Both are 24v 250watt rated, but I overvolt them to 48v. I can cruise with other bikes with no problem, top speed is probably in the low 20's.
The cutie 100, on my twin 16" wheel ebike and is rear driven. Probably my favorite, handles great, good speed and lightweight, easy to carry down some stairs. This is 36v over volted to 48v, can hit low 20's, quick acceleration.
My 4th FWD is powered by an Ebikekit front motor,twin 20" wheels, not sure who makes it for them, but I over volted this one to 75v with a Lyen controller, is really quick acceleration, has tendency to spin the wheels on fast starts, because of small wheels, I don't think it will go much over 25mph.
I use turniqy 6s 5a Lipos, running on 12s2p on ride 10 to 15 miles, 12s4p on longer rides.

Jerry

 

[footloose]

Jerry -- What is make / model of your twin 16 inch bike? I have a B.F. tikit, great bike, have ridden on a couple 200+ mile tours (not electric). Always wondering how it might do with some boost...

 

[chisixer6]

footloose;

something I welded together using cro mo tubing and parts of frames.

I also built a twin 20"(451) with a much longer rear triangle to house my 9c hub. I will install the 9c a little later. Hoping the longer rear triangle will help keep the front wheels down.

 

[footloose]

Very nice bike! Longer rear triangle looks natural, proportion is just right.