Custom BLDC Controller Closed Loop

Hello Guys,

I am going to make an e bike for my collage project. I am studying electrical/electronics engineering. My main goal is to produce an e-bike at around 1-3 kW power and also have an electronically controlled CVT gearbox to give a higher speed/ torque band making the bike more versatile. I will make my own speed controller using a micro controller.

Now I am new to this forum and e-bikes in general. This project is still in the planning/ research stage so any feedback would be appreciated.

So here are my plans so far:

MOTOR:

I am looking at two motors so far

1. http://e-bike-diffusion.com/index.php?module=produit&prd_id=509&url_retour=http%253A%252F%252Fe-bike-diffusion.com%253A80%252Findex.php%253Fmodule%253Dcategorie%2526code_cat%253D26%2526page_start_num%253D3

This motor is rated at 1kW but it seems that people have driven it to 3000W+ and they havent had any problems.

2. http://www.goldenmotor.com/frame-bldcmotor.htm

I am also looking at this motor which is rated at 3000W

Obviously if I can get the 1kW motor to 3kW it would be great since it is much cheaper.

Battery Pack:

I have found a battery pack 48v 15ah with a 50A constant discharge which would not be enough for 3kw but its decent. However it will cost 500usd to get to my door.

I have also found a 6s 16ah pack from hobbyking at 85 euros and I was planning to connect 2 of them in series. That will give me more than enough constant discharge however it would be 44.4v.

Another option would be to buy single cells and make my own pack. I have found 10ah cells from headway at 20$ a pop IIRC.

Any recommendations?

CVT

I also have a good background in mechanical things as well. I am also planning to do a gear box similar to this but obviously smaller


And I would control the belt via a linear actuator or a stepper motor

If you guys could recommend alternative parts or give me some advice that would be great

Best Regards Glenn

No one???? Did I post this thread in the wrong section or something?

glenn0010 said:

No one???? Did I post this thread in the wrong section or something?

Click to expand...

right place. it's just that...
the EV you're proposing has been built by several members of this forum so there isn't much to comment on. Member Rassy built a mid-drive version using a NuVinci CVT and with their "autoshifter" - Basically a computer-controlled motor-driven shifter.
I believe his current project uses a Bafang 750W mid-drive unit (crank drive) and the same transmission scheme.
IOW you should be able to just buy the stuff.
-But do make an attempt to make a better CVT please.
search: Fairbrook NuVinci for more information.

What are you attempting to actually make?
-race bike, dirt bike or a locally legal cruiser?

Everything you can imagine e-bike-wise has likely already been built... since before the turn of the 20th century actually.
What most of us are interested in is refining the beast.

Hello ddk thanks a lot for responding

My main aim is to build something resembling a dirt bike. I think 3kW should give me ample torque

Regarding the cvt I will research the part you told me about in detail when I get home. However it should not be a problem as I already have three different designs in my head of which I will soon post pictures.

My main aim with this thread is to gather some information before I start buying parts since I am an e bike newbie, this will be my first project.

So the info I really want is what do you thin about overwatting the 1kW motor to 3kW. I have read that some people have already done it. Or should I go with the 3kW rated motor which is a lot more expensive.

Also please give me some recommendations on the battery pack what should I use? If you see the first post there are some details about what I have found so far.

Thanks a lot I really appreciate your response and help.
Once I get the go ahead from my collage I will start ordering parts and start making my speed controler and start uploading pictures.

Best Regards Glenn

glenn0010 said:

Hello ddk thanks a lot for responding

My main aim is to build something resembling a dirt bike. I think 3kW should give me ample torque

Regarding the cvt I will research the part you told me about in detail when I get home. However it should not be a problem as I already have three different designs in my head of which I will soon post pictures.

My main aim with this thread is to gather some information before I start buying parts since I am an e bike newbie, this will be my first project.

So the info I really want is what do you thin about overwatting the 1kW motor to 3kW. I have read that some people have already done it. Or should I go with the 3kW rated motor which is a lot more expensive.

Also please give me some recommendations on the battery pack what should I use? If you see the first post there are some details about what I have found so far.

Thanks a lot I really appreciate your response and help.
Once I get the go ahead from my collage I will start ordering parts and start making my speed controler and start uploading pictures.

Best Regards Glenn

Click to expand...

About overwattin the motor, it all depends if you are adding volts of amps, both will be dangerous in different ways: amps will produce much heat and might melt and lead to a short circuit and kill the motor. Voltage will also be dangerous since much voltage can short circuit something that was not designed to receive such amount of voltage, also it can make phase amps go high too. As you already did, checking for someone that has done it before is a good option.

About battery it is all up to budget and goals. If you not really in a budget, go for high quality LiFePO4 packs made from realiable manufacturers (a123 systems, Headways, cant remember others right now) because they offer a average good C rate (maybe 10C on higher quality cells) with good capacity and its frocking safe. 18650 li-ion cells are a good choice, they are kinda light, reliable, safe, not so expensive and the packs can be built to fit any shape, since the cells are really small. RC lipo packs are a good choice if you need ridiculous amounts of power in a small/light pack, they can offer up to 70C, but they are really unsafe and don't last much cycles too. Maybe lifepo cells can handle 2500+ cycles, li-ion (18650) about 1600+ and lipo about 800+, but it all depends on the usage they get.

As my request for battery is not high power, i use a 48v 20Ah LiFePO4 pack bought from chinese supplies sun-thing28, its good for about 1.5C.
As you need 3kw of power, any of the chemistries i quoted above can deliver such power, but lifepo4 to handle this power will require good quality cells, not cheap chinese-ebay packs.

I'm really interested about your custom build cvt engine! Good luck.

out-a-my-territory are dirtbikes\

Not to worry!
the major forum-players which includes dirtbike builders/riders will eventually take notice of this thread and offer far mo betta advice than I could.

....ahhh
too late LOL

Do yourself a favor and forget the CVT. Why get hammered with a 10% hit to efficiency that isn't necessary? Instead, invest the CVT weight in more motor, and you'll come out ahead. A properly sized properly geared single speed wins every time. Tesla couldn't shake the idea of a tranny until they all failed before finally going single speed. Trains have single speed electric motors. Brammo had a gearbox on their consumer version emoto, but that was for familiarity, not need, since their race bikes are single speeds. The list goes on and on.

An under-powered rig might justify the use of multiple gears, but only because the tranny is so light in the form of a derailleur or a Retro-Direct 2 speed.

Virtually all of us dreamed of multi-speeds and CVTs until we came to really understand electric motors. Gassers have trannies because they need them. Electrics don't need them except in very specific dual uses where one requires very low speed with very high loads, but a simple 2 speed that is rarely shifted is the way to go there.

ddk said:

out-a-my-territory are dirtbikes\

Not to worry!
the major forum-players which includes dirtbike builders/riders will eventually take notice of this thread and offer far mo betta advice than I could.

....ahhh
too late LOL

Click to expand...

I'm not in the dirt bikes territory also, but batteries are kinda of a interest of myself hahaha

John in CR said:

...
An under-powered rig might justify the use of multiple gears, but only because the tranny is so light in the form of a derailleur or a Retro-Direct 2 speed.

... Electrics don't need them except in very specific dual uses where one requires very low speed with very high loads, but a simple 2 speed that is rarely shifted is the way to go there.

Click to expand...

John in CR has it right. Except trains don't climb grades over 3% unless they use specialized engines or multiple engine setups.

Anecdote time!
(because personal experience is so personal)
who I Is
I build locally-legal (under-powered) bikes/trikes for my personal use and consult with other local builders, sometimes lending a wrench.
I live in a (very) hilly area and carry (very) heavy loads.
Getting On with the anecdote
I built a bike using a Fallbrook* 1st gen CVT.
After a bit of experimentation I realized a couple of things :
things 1- I really only used two settings, for a 275% gear change (i.e. a two-speed only)
things 2- The transmission is considerably larger and heavier than the small geared-hub motor that drives it's input

Previous to building this CVT-equipped bike (trike, actually) I installed two motors per trike for AWD with about a 3/1 difference in gearing and no transmission.
After my CVT experience I'm once again using two motors with 2/1 and 3/1 difference in gearing and no transmission.
(3 different trikes doing it differently)
If a motor manufacturer made a 1000W two-speed motor that suited my particular needs (and is reliable) I'd use that in loo of two motors.


Aboot batteries:
I suggest you look at Li-ion batteries with internal BMS since this is your college project. If you have the time and skills building a battery is doable and less expensive but requires serious expertise and yup, time.
LiFe batteries for the most part would have to have bigger-er capacity to get a C rate-of-discharge you gonna require.
Otherwise I'd suggest learning about R/C LiCo batteries, because they offer the greatest power density ...but require a fair amount of attention to safely use.
Did I say "fair"? I meant lots.
I use R/C LiCo, but I got time to spare where you don't because I'm retired and you're not.
(and an engineering background i haz)

Hope some of this rambling is useful...

* i usually mistake the name... mostly as failbrook.

While it sounds like an interesting bike, CVT are less efficient than standard gears and can't handle as much torque.
Gas motors have a narrow efficiency range and a narrow torque band, so a CVT can help by keeping the motor only running in it's peek performance RPM range.
An electric motor has a very wide torque band starting from Zero RPM, and is efficient all across it's RPM range. A CVT's main benefit would be wasted, while it's 2 main drawbacks would become liabilities.

A 2 speed transmission might be of some use, but only of you can come up with a seamless and high efficiency design.


If you really just want a CVT for the cool factor, you might want to rethink the motors. Since CVT don't handle torque well, you could use a low torque, High RPM motor with the CVT tied directly to it's output, before a large gear reduction to the wheel. That way the CVT is handling the power, but not the torque. it would still be inefficient, but at least it could be smaller, lighter, and more likely to survive the torque loads.

Thanks for the great response guys

So I have spoken to my lecturer and unofficially they have accepted my project proposal without the CVT since they want me to focus on the electronic/programming side of the project so it seems like most of you guys are correct. Experience trumps ambition

Regarding Batteries:

@ddk: I have searched for Li-on battery pack at around 15aH and have struggled to find the needed C discharge rating since for 3kW I need around 70A continuous discharge current. If you know of any suitable packs or manufacturers please let me know.

Obviously the 48v 15ah with a 50A constant discharge pack is not enough for 3kW but its close. And it is very convenient since all I need to do is hook it up. But it is 500$ to get to my door is that a reasonable price? It is a LiFe battery, do they have protection for agains over discharge and stuff like that (that is the BMS's job right? I am a newbie in batteries)

Right now it seems that the most feasible pack are two of there connected in series

http://www.hobbyking.com/hobbyking/store/__66310__Multistar_High_Capacity_6S_16000mAh_Multi_Rotor_Lipo_Pack_EU_Warehouse_.html

I know that LiPos can be dangerous if you over discharge them so I was going to connect one of these to them so when they are getting too low I am alerted.

http://www.ebay.com/itm/1-8S-Checker-Tester-LED-Lipo-Battery-Voltage-Indicator-Buzzer-Alarm-Low-Voltage-/221324965283?pt=LH_DefaultDomain_3&hash=item3387fef5a3

What do you guys think. Right now therefore finding a suitable battery pack is the main challenge I want to approch the 3kW value as much as possible

Thanks for your great response I am loving ES

P.S. I want the bike to be a 'Dirt Bike' so torque is the main goal. However I thought that the CVT would make it more versatile since I could have a higher top speed since you are limited by the Kv rating of the motor regarding rpm (RPM/V)

glenn0010 said:

...

@ddk: I have searched for Li-on battery pack at around 15aH and have struggled to find the needed C discharge rating since for 3kW I need around 70A continuous discharge current. If you know of any suitable packs or manufacturers please let me know.

Obviously the 48v 15ah with a 50A constant discharge pack is not enough for 3kW but its close. And it is very convenient since all I need to do is hook it up. But it is 500$ to get to my door is that a reasonable price? It is a LiFe battery, do they have protection for agains over discharge and stuff like that (that is the BMS's job right? I am a newbie in batteries)

Right now it seems that the most feasible pack are two of there connected in series

http://www.hobbyking.com/hobbyking/store/__66310__Multistar_High_Capacity_6S_16000mAh_Multi_Rotor_Lipo_Pack_EU_Warehouse_.html

I know that LiPos can be dangerous if you over discharge them so I was going to connect one of these to them so when they are getting too low I am alerted.

http://www.ebay.com/itm/1-8S-Checker-Tester-LED-Lipo-Battery-Voltage-Indicator-Buzzer-Alarm-Low-Voltage-/221324965283?pt=LH_DefaultDomain_3&hash=item3387fef5a3

Click to expand...

I know I'm addressing someone who should know most this stuff, but the additional information is for the curious.
Most other Li-ion chemistries have poorer C ratings than LiCo formulations (which can be had with outrageous C-ratings that I wouldn't particularly trust in lol) This results in having to use a much higher Ah capacity battery for cycle-life protection over a considerably smaller LiCo pack.
The Multistar 16Ah x 10C rating should allow 160Ah continuous so yep, they should work fine for your project.

'legal' e-bikes use 5-30A depending on the motor controller settings, hence they can be suitable for most secondary battery chemistries.

But then there's the ES crowd...
For higher discharge duties LiCo batteries currently offer the most cost-effective choice.

The Multistar cells are relatively new (to me at least). I'll be making a large purchase soon; they're considerably smaller than the 5Ah cells I currently (sic) use at similar Ah setups (20-25 Ah) so I'll be able to stuff MORE Watts in the same battery space.
All my packs are fashioned from HK Turnigy 20C 5A cells. I package the cells in a 4P-5P configuration, safely able to discharge over 200A.

The real issue with LiCo cells is keeping series-connected cells voltage-balanced. Not really an issue if you use a BMS to keep the cells balanced....b-b-but I found through experimentation that using multiple cells in parallel reduces this balance issue to the point where I haven't needed to balance cells for a couple of years. I do check balance before and after charging.
Exception to this is 3 so-called HK-sourced nanotech cells that never stay in balance. I use them anyway.

Important safety noteWhile over-discharging any secondary cell is bad, overcharging is mucho times worse and can result in cells going into spontaneous deconstruction (heheheh) While esp. bad for LiCo, this is true for all secondary battery chemistries.
If you are limited to using LiCo cells because of budget, space or weight you need to:
Check individual cell voltage for balance before and after charging. A suitable BMS that will do that for you. (somewhat)
Note-I don''t use a BMS so I offer no comments about where to acquire a suitable unit. OR since you're a student of hard/soft electrical stuff, design your own.
Side note-I've yet to find a manufactures' BMS whose specs suit my over-protective self
-my self-preservation is HIGH and is always foremost on my personal agenda
(did I mention redundancy lol.)

Me... I own both expensive and inexpensive balance chargers I mainly use as battery testsuites.
I also own a somewhat useless LiPo Celllog (meh, it was cheap enough... you can get from about any hobby store/source that deals with R/C toys and stuff)
But most importantly, I use a verified-for-accuracy multimeter - used to verify the accuracy of the other stuff and also measure individual/cell packs if something feels amiss.


PS, that battery you mentioned for $500 is a reasonable price

Hello again Guys,

DDK you are a gold mine :lol:
Thanks for responding.

So after some more research regarding battery packs it seems that I'm gonna go with the 48V 15Ah chinese pack at 500$. It is reasonably priced and it comes with everything such as a charger and I assume a BMS as well. It is convenient form and cheap it seems. I have tried to source some other packs or try to create my own from lipos or single cells but this seems to be the most continent. The only drawback is that I won't be able to reach 3kW with it cause of the 50A max discharge.

Having said that, how much current do you guys think I should draw from the batteries not to ruin it. I was thinking about 40-45A max.

Regards Glenn

glenn0010 said:

Hello again Guys,

DDK you are a gold mine :lol:
Thanks for responding.

So after some more research regarding battery packs it seems that I'm gonna go with the 48V 15Ah chinese pack at 500$. It is reasonably priced and it comes with everything such as a charger and I assume a BMS as well. It is convenient form and cheap it seems. I have tried to source some other packs or try to create my own from lipos or single cells but this seems to be the most continent. The only drawback is that I won't be able to reach 3kW with it cause of the 50A max discharge.

Having said that, how much current do you guys think I should draw from the batteries not to ruin it. I was thinking about 40-45A max.

Regards Glenn

Click to expand...

Tell us what chemestry, and if possible the links to the battery you have in mind. Also, consider that cheap LiFePO4 are long lasting but they are not made to deliver much power, so consider buying a 20Ah pack, so you can use it below its limits.

That is alot of money for a 15ah pack. You should be able to setup a pack of that capacity for $300. Also, stay away from Chinese anything........

Matt

Hello,

Here is the link how ever I have gone back and forth via e mail to discuss the details. 20ah is just to expensive for me. Also the contact told me that the discharge rating of the 10ah-20ah packs are the same at 50A continuous:

http://drowsen.en.alibaba.com/product/60256331562-0/2015_hot_selling_japan_engineer_team_oem_factory_24v_36v_48v_bottle_tube_bottle_lithium_ebike_battery_pack.html

Best Regards Glenn

What they are telling you and what they have published are two different things. I would call that highly dubious and avoid it completely.

They claim the 30000mha (30 amp hours) battery is capable of 1C, 45 amps. That math doesn't add up as 30 x 1 = 30, not 45.

If you aren't already aware, the "C" rating is the output of a battery expressed as the number of times it's capacity. 1C means 1 times it's capacity, so a 10Amp hour battery at 1C would have a maximum 10 amp continuous output. A 10 amp hour battery with a 2C rating would have a 20 amp output. So a 30Ah battery at 1C can't have an output of 45 amps. And it would be unlikely that a battery made from the same cells but lower capacity would have a higher output.

Buying Ebay batteries is a high stakes gamble. Some people win. Many people lose their money and receive unserviceable junk.

One of those “experience” things - whenever “sales engineers” say max 50A, I automatically assume 25-30A best case.

Be very careful with battery packs direct from China. Basically, no reasonable return mechanism = Caveat Emptor!

Your design is begging for high C rate battery pack. Hard to do properly and cheaply. That’s why many of us make a deal with Devil and learn about RC Lipo.

Thanks for the response guys!

SO what is the best way to proceed here? Can you guys recommend any packs, links, manufacturers anything?

Maybe something similar to this? 2 of these in series * 3 in parallel giving me 44.4V and 15ah?

I am really a noob at this could you guys 'make' me some packs?

Thanks

I have found these http://www.headway-headquarters.com/40152s-15ah-headway-cell/#reviews

But they are only 3C = 45A cont discharge :/

Headways are a good choice, especially for a prototype project like yours. Those aren't the cells that I would use, but they would work. Here's another for consideration. http://www.greenbikekit.com/phosphate-38120-headway-cell.html

Keep in mind that V * A = W works both ways. you can increase you wattage by increasing your amps, but you can increase the watts by increasing the voltage. So if the battery you picked has a max output of 45 amps, you could instead increase the voltage from 48 to 72 to get your wattage up.

Helllo,

TBH I am more scared to increase my voltage than the current. Do you think the motor I linked in the top can handle 72V?

glenn0010 said:

Thanks for the response guys!

SO what is the best way to proceed here? Can you guys recommend any packs, links, manufacturers anything?

Maybe something similar to this? 2 of these in series * 3 in parallel giving me 44.4V and 15ah?

I am really a noob at this could you guys 'make' me some packs?

Thanks

Click to expand...

A very trusted source em3ev you can have packs made with high power cells or high energy cells, check the 20r cells for your needs.

Ykick said:

One of those “experience” things ------- That’s why many of us make a deal with Devil and learn about RC Lipo.

Click to expand...

RC Lipo is like a hot but unfaithful wife....... Exciting and radically wild, but you gotta keep and eye on her. :wink:

Matt

glenn0010 said:

Helllo,

TBH I am more scared to increase my voltage than the current. Do you think the motor I linked in the top can handle 72V?

Click to expand...

Don't be scared of DC voltage. Amperage is what kills. Voltage just F@#$@# hurts!

Any voltage and any amperage is dangerous. A watch battery has enough of both to drop you stone cold dead if you hold it in your hand, and are very unlucky. It's probably never actually happened or ever will, but it is technically possible. A Taser stun gun pumps out 120,000 volts. while it's moderately uncomfortable ( ) it's rarely deadly.
I work for a phone company, and we're around voltage all the time. Ringing voltage on a phone line is 88 volts, while normal talk voltage is 48. If you grab a line when it's ringing, you feel it, although we take no extra precautions against contact with it. It's considered safe, though uncomfortable to get hit with it. It's also a lot of fun to hit someone else with, and so Hijinx ensue. Add some amperage behind it, and you may get burned. Many of us have, but it's rarely something more serious than a dab of ointment and a bandaid will cure.

To sum up, you can't be afraid of voltage and hope to work on anything electrical. Fear is probably as dangerous as apathy when working on anything that can kill you.


edit (I'm Shocked! I made it through a whole post about electricity without making one single pun!)
(Oh, wait...)