Yet another E-bike diy prototype - opinions?

[drebikes]

Hello, this is my first post. That said, I have read hours and ours of threads on this forum since I started documenting for this e-bike project. I'm posting to show what I plan to use for this project and hopefully get some feedback from you guys since you have much more experience than me on e-bikes.

Hard to say in a few lines, but bare with me:
*the mission profile would be to assist the rider to go up from 25 to around 30-35km/h for 80-100km (15-20mph for 60 mi)
*weight bike + rider without EV ~90kg / 180pounds
*I've used some telemetry data that shows I rarely use more than 400W leg-power, less than 3% of the time (slightly hilly course, around 20km/h average speed). Average power around 250W.
*in regards to energy , an average 1 hour 20km/h tour used some 80Wh. For the EV at 48V this would only be under 2.5Ah if I take some 80% efficiency for the motor, 90% inverter and 90% for the battery pack.
*ran a mission profile of a slow acceleration from 0 to 20km/h in 20seconds electric-only - maximum DC current 4.5A @48V

That said, it looks like I don't need much power or torque, but I want to overprovision as there's little mass or $$$ penalty if I pick beefier inverter and motor. I was thinking of:

*Kelly 24-48V 30Amp Inverter @1.7pounds link:
http://kellycontroller.com/kbs48051el30a24-48v-mini-brushless-dc-controller-p-1170.html
==> this gives a peak 1.5kW @VDC_min; probably it depends on the temperature and one won't always be able to safely pull 30A
Pluses:
-configurable DC current limit. I intend to use this setting to tweak the power / range. Will use this setting to cap max DC current pull from the batteries.
-recovery configurable between 0-20% of torque; it's going to be a RWD bike, so recovery may interesting. Will increase recovery torque until it becomes annoying
*800W 48V Kelly hub motor @they say 27lbs (has to be a mistake, right? It seems like a lot for a motor)
http://kellycontroller.com/hub-motor-48v-800wdisc-brake-p-163.html
Plus: can be equipped with thermal sensor that can be read by the controller.

Battery pack - this is a bit more complicated because I want to build it myself. Here's what I came up with:
*LiFePo4 chemistry - it just seems safer than LiPo; lower power and energy density than LiPo, but more "tame"
*16s 48VDC min pack
*either Phostech pat.C 1200mAh cell or Microvast 1100mAh cell. Both from ebay, both found some tests that show the real capacity may be more something like 1-1.05Ah; 18650 size; I plan to get a few extra just to account for possible cell-to-cell variations in capacity
==> 16 of these should give some 16-18Ah; both cells can take 5c continuous
*I only plan to charge with BMS. Discharge will be directly to the inverter with short-circuit cell protection and current-limited with the inverter
*BMS: not clear. There is the one below from ebay which should do the job, 48V and 60A max with 60V cutoff. Since I want it to be used only for charging I don't care about its weight or volume. I am searching for something better though, something where I can adjust the cutoff voltage when full.
http://www.ebay.com/itm/48V-60A-LiFePo4-Battery-BMS-LFP-PCM-SMT-System-16S-16x-3-2V-eBike-Battery-16x-3V-/321048911039?pt=LH_DefaultDomain_0&hash=item4ac0019cbf

Thanks for reading if you got so far. The basic idea was to draw a mission profile, see max speed to choose voltage, then try to "guesstimate" max current in order to pick the proper cells and the number of parallel circuits. Since I don't plan on mounting a BMS on the bike I need an intelligent inverter, and the Kelly seems to do the job. I would need some input regarding the components picked up or whatever else comes to your mind. Do you have experience with either of them?

Cheers

P.S. This is supposed to be a testing vehicle; I plan to profile temps, record mission profiles, do efficiency maps for the motor and play with cutoff voltages for the battery to improve the system. Then to do a second better bike for the missus

 

[Drunkskunk]

Welcome to the forum.

It sounds like you have a good understanding of the math. As for the motor, that thing realy is 27lbs. its designed for a moped. 800watts nominal, its peak could be someplace over 9000. For what you specified, you need a motor with a peak closer to 800, or more. A simple 250 watt geared motor would give you the performance you needed, but a 500 watt direct drive might be better if you plan to use this as a test platform.

The Kelly controller is fine but there are better options. Its not actualy an inverter, as these motors are 3 phase DC, not AC, and they work diffrent that an AC motor would. The Infineon based controllers are programable and dirt cheap. There are many documented modifacations, and some are available with those already preformed. Telemetry can be had from several diffrent methods. I prefer the Cycle Analyst, but thats just one option. Getting a controller prewired for the CA (cycle Analyst) makes getting your telemetry easier if you go with a DIY approch.

As for batteries... Its sad tha LiFePO4 are now considered a heavy opting. Compared to the Lead Acid batteries that were normal just 5 years ago, LiFePO4 are so incredably light and compact that it seemed almost unbelievable at the time. Lipo is more like Rocket fule for Ebikes. High performance stuff sutable only when the reward outweighs the risk. But as for the LiFePO4, forget the Ebay batteries. They will be the single most important piece of the bike, and they need to be of the best quality of any other part. Making a good battery choice can make up for a poor motor choice, but make a poor battery choice and you'll be walking no matter how good any other part is.

For your stated goals, check out EM3ev.com, and look at their 500watt direct drive kit. combine that wilth a 36 volt 15amp hour battery. Moving to a 48 volt battery will gain you some extra speed if you wish, but 36v should atain 35kph without any human assistance.

 

[dogman dan]

FWIW, 20 mph on the flats with a hubmotor takes about 300-600 watts, 400w about the average. It's just not comparable to pedal wattages, due to heat losses in the controller and the motor. God, what a dream it would be for the motor to always run at 80% efficiency. But at slightly slower speeds than 20 mph, running at 200w is very possible. Even less is possible, if you pedal a lot.

EM3ev is a good starting place. 20 amps controller all you need. If you run 48v that gives you about 1200w, that much seldom actually used, but nice to have on a steep hill, where you had to stop.

I did a double take on that motor too. 27 pounds? Then I looked, and saw a solid scooter tire rim. Ahh a big chunk of steel. You want a motor made to be laced into the bike rim. That's not it.

Check out Grin cyclery while you are looking at bike stuff vendors. He's the best in the world, and you are reading this forum thanks to him.

 

[wesnewell]

Please go to the User Control Panel, select Profile, and then enter your city, state/province, and country into the Location field (country minimum) and save it. This will help people help you. Example: Wylie, TX, USA. Without knowing what country you are in it's hard to make any recommendations. Thank you.

 

[Cronus]

Hi, I just saw your post and noticed something funny in your Battery pack section and am not sure if it's a typo or misunderstanding.

You say the capacity on the LiFePo4 cells are "something like 1-1.05Ah," and "16 of those should give some 16-18Ah." That is not true if you have them in series like you suggested (16s).

Batteries in series will add in voltage with the Ah staying the same. Batteries in parallel will add in Ah while the voltage will stay the same. Does this make sense?

 

[bowlofsalad]

You are way way way over thinking all this. The trouble is, understanding a lot of how power usage goes comes from riding experience with a watt meter (such as a cycleanalyst). You could spend all day trying to calculate power consumption, range and so on in theory, but road conditions, weather, terrain, the environment will give endless variables that will make your persistent pondering a complete waste of time. Try to be far more vague in understanding the range. Check out ebikes.ca/simulator. Get some vague ideas of understanding and then buy the components you want. After riding a few hundred miles, you'll likely start to really grasp how things work.

The best thing you can do when concerned with range is to consider aerodynamics and rolling resistance, but mostly aerodynamics. The sooner you get the ebike stuff going, the better, it's a lot of fun and very much worth it.

As for which components and such to use with your bike, that is your beautiful curse. There are many options and they all have their pros and cons.

 

[dogman dan]

What you want is pretty easy, and can be done with any bike hubmotor that goes 20 mph, so 400w at least at max power.

I'd go with 36v and 20 amps controller. Then ride at sub 20 mph for max range. At 20-25 mph, 1 ah per mile for 36v bikes is a good way to size a battery, for a daily commute where you want to use less than 100% of the battery each day.

Definitely, it takes many cells to make a 36v 15 ah pack out of cells that are not 15 ah cells. Paralell cells till you have 15 ah, then series connect 16 of those cell groups.

But going slower, you can go much further. 10 ah of 36v should be quite capable of 15 miles going slow, using 100% of it.

 

[Tommy L]

A plug and play system is an option as well.

Bionx makes a plug and play package with torque sensing. Turn it on and pedal. Very low watt hour consumption.

Although I'm a hot-rod type of ebiker, I also have 2 Bionx systems (1 for me, 1 for wife) on our catikes.
Turn on, pedal and auto power assist.

Tommy L sends......

 

[drebikes]

Hallo, thanks for all the replies. I've been sent to a Li-Ion battery course by my employer last week, awesome for this side-project too. I'll run thru the replies when @home

I've filled up some of the details in my profile. Unfortunately here in France choices are few in regards to parts for diy or full-systems. One motivation behind this project is the unavailability of something interesting to buy and besides I'm a diy-er since forever on all kind of things.

Associated with my living in France comes the problem that few ship here from outside (US, CAN, etc). Ebay is a good option since they do ship from Asia. For example I've tried a bit to find a A123 distributor in Fr that sells under 1000 cells, no luck. Unfortunately I'll have to go with cheapo batteries for the first pack since this is all ebay has; I'm not going Ultrafire, I'm hoping for something decent. I will validate each and every cell composing the pack and buy a few extra for good measure and take safety coefficients like only using 1/3 of the max C-rating advertised. It's not ideal, it is what it is, if you have experience with capacity dispersion between cells I'm very interested.

BTW about the pack capacity calculation, I mixed up my Wh and Ah somewhere. It would be nice to serialize cells and multiply both voltage and amperage

What do you think of these 3 cell types? Any one of them at least slightly above ultrafire-level?
http://endless-sphere.com/forums/viewtopic.php?f=14&t=51638

Thanks a lot, great forum

 

[drebikes]

@Drunkskunk Thanks for the welcome, it was great before when I was just lurking, now it's even better
I would like some alternatives on the inverter. Do you have a link for one of those programmable Infineon controllers? As I see it the inverter will be the highest end part on my bike because of what I was rambling on the previous post: I'm limited to ebay cells, so it's important to have a good control on the DC current and voltage to protect the pack.
It is funny how LiFePos have gotten to be considered heavy, we just got spoiled with Lipo. In a few years we'll probably see LiFePos with Titanium cathode and then the energy density will be even lower, but also will have hundreds of C-s.
I have a reason to go for 48V and that is lower the current draw at the same power level. Lower current is lower losses and a bit more range, and less stress on the cheapo cells I'm saddled with.

@dogman I was using the ebikes.ca for their simulator. Up until today I haven't realised the "purchasing" pages work only on IE. My Chrome shows blank pages. I'll look to see what they have. Yeap, that motor is pretty heavy and unnecessarily powerful for what I need. Add insult to injury shipping for it adds another 100$. The controller is ok, I'll stick with that until I find something better.

@wesnewell done

@Cronus It does make sense, I mixed up my units

@bowlofsalad I tried to estimate the power loss due to rolling resistance starting from telemetry data shared by SRAM last year in the Tour de France to have an order of magnitude. Agreed with you, at some point I just have to make it work and see from there

@Tommy L : I'll take a look at it and if anybody sells it in France, cheers