Author Topic: Electric bike battery  (Read 15611 times)

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Offline Fungus

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Re: Electric bike battery
« Reply #25 on: September 22, 2016, 06:07:50 am »
you are nuts... you can use 4 of this...

How do 4 of those give you 48V and 20A?  :-//

 

Offline Fungus

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Re: Electric bike battery
« Reply #26 on: September 22, 2016, 06:09:42 am »
The thing people miss in all these calcs isn't that it's necessarily dangerous or scary at those higher speeds (a normal road bike going down a hill can easily crack 50km/h), but it's bloody uncomfortable. I typically ride at 25-30km/h and that's ruff enough.

Yep, I think the speed requirement needs to go.
 

Offline NiHaoMike

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Re: Electric bike battery
« Reply #27 on: September 22, 2016, 06:28:10 am »
I see, and makes a lot of sense! Well I hope it would be much more worth it than driving a car...
Not sure how it is at your university but at Texas A&M, a parking permit starts at over $250/semester or $2000 over 4 years. That's a good incentive to use the (free to students) shuttle buses and/or live close enough to walk/bike. And then there's the overall cost of owning a car especially if your family doesn't have a spare one for you to use. And if you're in a densely populated city, it would not be unusual for bicycling to be faster than driving, at least for short distances.

It would definitely be an interesting project if you're into power electronics. And also one with plenty to go wrong so find someone with good power electronics experience to review your design. I know someone who did a hybrid bicycle for his senior design. It's a 48V Lipo pack (forgot the Ah rating) with a C2000-based inverter. Its top speed was only 30MPH or so since he had it geared more for acceleration than top speed. Pro cyclists often hit top speeds exceeding 60MPH going downhill - definitely not something a beginner should try!

BTW, for cheap but good batteries to use, take a look at EV battery modules. You'll have to supply your own BMS but they're designed for very high currents and are built to last.
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Offline Mechatrommer

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Re: Electric bike battery
« Reply #28 on: September 22, 2016, 07:06:35 am »
you are nuts... you can use 4 of this...
How do 4 of those give you 48V and 20A?  :-//
:palm:  |O
duh do we have to go beginners section battery 101? or even down further.... 12 x 4 is what?
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Offline Fungus

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Re: Electric bike battery
« Reply #29 on: September 22, 2016, 08:18:54 am »
duh do we have to go beginners section battery 101? or even down further.... 12 x 4 is what?

48!

I was more worried about the 20A but I see I misplaced a zero - those are 20000 mAh.

(And in my defense the photo doesn't give much idea of how massive they are. They look like one of those everyday RC model batteries but they're actually 20cm long!)



Anyway, I stand corrected. One of those can provide a continuous 200A (apparently!)

Let the thread continue.  :popcorn:

(and lets hope 720cm3 of lithium never catches fire)

« Last Edit: September 22, 2016, 08:44:50 am by Fungus »
 

Offline technotronix

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Re: Electric bike battery
« Reply #30 on: September 22, 2016, 11:06:41 am »
Using a 48v 1000w motor for my electric bike,  how long will a 48v 11.Ah Lithium-ion battery last on full throttle?
Is it recommended? Thanks

To calculate the watt hours (WH) of a battery pack, multiply the voltage by the amp hours (Ah) of the pack. You will get the exact solution.
 

Offline Mechatrommer

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Re: Electric bike battery
« Reply #31 on: September 22, 2016, 11:10:48 am »
(And in my defense the photo doesn't give much idea of how massive they are. They look like one of those everyday RC model batteries but they're actually 20cm long!)
yup i didnt noticed that, but thats fair enough i guess for a 20AH system. but if you stack 13x 18650 side by side and then 3 parallel more to the top, you can get about 190 x 65 x 75 mm minimum, thats 2.6x4 = 10.4AH pack. 4x 4S 20AH lipo is about twice that. maybe OP can search 10AH lipo and i guess the dimension will be close, i was quick searching for the most expensive lipo in hobbyking. one of my point was, how are you gonna ensure balance charged of that 52x 18650? not to mention checking each single cell for damage. granted if this is personal use who do not care spending too much time maintaining, only money...

« Last Edit: September 22, 2016, 11:14:13 am by Mechatrommer »
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Offline Siwastaja

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Re: Electric bike battery
« Reply #32 on: September 22, 2016, 11:26:42 am »
one of my point was, how are you gonna ensure balance charged of that 52x 18650?

Literally exactly the same way as you do with those hobby "lipo" cells.

Quote
not to mention checking each single cell for damage.

You don't; like you don't check each square inch of those lipos for damage.

18650 cells are especially designed to be paralleled and work as larger "cells". After all, that's how they are used in their most prominent, traditional application, laptop packs.

This is beginner's li-ion 101.
 

Offline Fungus

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Re: Electric bike battery
« Reply #33 on: September 22, 2016, 11:44:48 am »
how are you gonna ensure balance charged of that 52x 18650?

As I mentioned earlier: "very carefully".

He's gonna need an awful lot of intelligent charge controller chips, temperature sensors, etc.

(I'm not saying it can't be done but it needs to be done carefully with no skimping)

He also needs to take care that batteries in the middle don't get hotter than batteries on the outside, etc.

 

Offline Siwastaja

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Re: Electric bike battery
« Reply #34 on: September 22, 2016, 11:49:20 am »
He's gonna need an awful lot of intelligent charge controller chips, temperature sensors, etc.

No, absolutely not!  :palm:

Quote
He also needs to take care that batteries in the middle don't get hotter than batteries on the outside, etc.

This is equally true with any design that has significantly poor volume-to-surface ratio.
 

Offline Fungus

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Re: Electric bike battery
« Reply #35 on: September 22, 2016, 12:01:59 pm »
one of my point was, how are you gonna ensure balance charged of that 52x 18650?

Literally exactly the same way as you do with those hobby "lipo" cells.

You mean those hobby "lipo" cells that aren't connected in series?


He also needs to take care that batteries in the middle don't get hotter than batteries on the outside, etc.
This is equally true with any design that has significantly poor volume-to-surface ratio.

You're agreeing? Disagreeing? What? :-//
« Last Edit: September 22, 2016, 12:05:48 pm by Fungus »
 

Offline Siwastaja

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Re: Electric bike battery
« Reply #36 on: September 22, 2016, 12:46:33 pm »
Every series connected block requires its own voltage measurement. This number is the same regardless of whether the blocks are made using one big 20Ah cell, or several 2.9Ah cells connected in parallel. For more info, I recommend these:
http://liionbms.com/php/wp_parallel_cells.php
http://liionbms.com/php/wp_lots_small_cells.php

Thermal design may be required if the pack volume is so large that there is this "middle" area with hindered cooling, if the discharge rates are near the maximum ratings. Slow charge helps, as the heat generated during discharge is stored in the pack, then released slowly. Temperature sensor or two in the middle of the pack is a good idea, but sensing every 18650 cell separately would be definitely overkill.
 

Offline nukie

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Re: Electric bike battery
« Reply #37 on: September 22, 2016, 12:51:51 pm »
Stick to the LG/Sammy/Panasonic 18650 designed for high cureent discharge and designed to achieve high number of cycles. Most highend power tools for eg Metabo, Festool, Panasonic and etc sports the Panasonic cells. Powertools chew through battery in no time.

RC lipo are less robust. Otherwise you see Tesla with a XT60 plug :D
 

Offline Mechatrommer

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Re: Electric bike battery
« Reply #38 on: September 22, 2016, 02:23:56 pm »
one of my point was, how are you gonna ensure balance charged of that 52x 18650?
Literally exactly the same way as you do with those hobby "lipo" cells.
that lipo has already balance charge connector and that single giant connector. all you have to do is to make custom XT60 connector to series 4 of them. disconnect later to use that hobbyking turnigy balance charger to charge one at a time if he wish to, or buy 4 for simultaneus charge if he wish to. unless the OP want to emulate the lipo XT60 and dupont connectors, he is going to solder all of them fixed in parallel and series, and he is going to need 4 "floating" similar magnitude as hobbyking intelligent charger for that, no option for 1 charger only. and if that hobbyking charger is not floating (ie share common ground) then he has to make his own floating balance charger for the 52x cells. or maybe just 1 48V lion charger i dont know.

not to mention checking each single cell for damage.
You don't; like you don't check each square inch of those lipos for damage.
2 options... 1) if you have thick pocket, yes you dont have to check each cells in lipo, just buy new, throw out of spec lipo away. 2) but if we have thin pocket, we will check each cells and take out the damaged cells like i did to 2 of my 4s lipo a year ago, now they are 3S only, i sensed the other one cells are deteriorating fast too so i'm going to mod them to become 2x 2s lipo, but i think i'll combine them to become 1x 4s lipo again. but if i have thick pocket next month i'll just throw them away knowing they will fail soon enough. mostly due to my ignorance of how lipo batteries should be stored, i stored them at full charged capacity :palm:, lipo are meant for continous heavy usage.

not to mention checking each single cell for damage.
18650 cells are especially designed to be paralleled and work as larger "cells". After all, that's how they are used in their most prominent, traditional application, laptop packs.
This is beginner's li-ion 101.
yes but they are batteries too, like the other batteries, sooner or later they will die too. batteries in general 101 ;) furthermore he is going to buy misc 18650 from unknown seller. i will say 1 year lifetime tops, half a year under heavy usage, to all the 52 cells. my condolences to all my vaping 18650s, both cheap and branded.
« Last Edit: September 22, 2016, 02:26:01 pm by Mechatrommer »
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Offline NiHaoMike

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Re: Electric bike battery
« Reply #39 on: September 22, 2016, 02:57:05 pm »
Take a look at EV battery modules out of Leafs and Volts. They are about the same price (sometimes even a little cheaper) per Wh but will definitely outlast those hobby packs.
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Offline Harvs

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Re: Electric bike battery
« Reply #40 on: September 22, 2016, 11:19:24 pm »
Back to talking about this specific use case.

My experience with daily use, over almost identical distance (5km each way, each day) albeit over very hilly terrain which I don't know about the OP, you use far less power than the OP is assuming.

I use something like 100Wh per round trip, and I let the motor do pretty much all the work on the hills.  So I get around a working week out of the batteries before they need charging.

If you do the sums on that, even using HK lipos that are only good for around 200 charges, that's going to be 4 yrs before they're going to need replacing.  I'd say that's probably going to be close to the life of the whole setup.
« Last Edit: September 22, 2016, 11:22:38 pm by Harvs »
 

Offline helius

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Re: Electric bike battery
« Reply #41 on: September 23, 2016, 12:00:45 am »
Here's a question:
Is there any advantage to multiple gears in an E-assist bike? They make it possible to pedal efficiently over different grades and speeds, since people can only apply so much torque while pedaling. But electric motors can apply huge levels of torque, helping the rider to go up hills without shifting to a low gear. At higher speeds, using a high gear helps the rider maintain a comfortable cadence. So do E-bikes only need high gears?
 

Offline Harvs

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Re: Electric bike battery
« Reply #42 on: September 23, 2016, 12:50:45 am »
Here's a question:
Is there any advantage to multiple gears in an E-assist bike? They make it possible to pedal efficiently over different grades and speeds, since people can only apply so much torque while pedaling. But electric motors can apply huge levels of torque, helping the rider to go up hills without shifting to a low gear. At higher speeds, using a high gear helps the rider maintain a comfortable cadence. So do E-bikes only need high gears?

Gears are a massive help on hills, it lowers the strain on everything and gives you the ability to climb things you would probably be pushing a normal bike up.  The market is being taken over by mid-drives for this reason, once you ride a mid-drive which still has the 5 or 6 rear gears you never want to go back. 
 

Offline NiHaoMike

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Re: Electric bike battery
« Reply #43 on: September 23, 2016, 01:21:19 am »
Here's a question:
Is there any advantage to multiple gears in an E-assist bike? They make it possible to pedal efficiently over different grades and speeds, since people can only apply so much torque while pedaling. But electric motors can apply huge levels of torque, helping the rider to go up hills without shifting to a low gear. At higher speeds, using a high gear helps the rider maintain a comfortable cadence. So do E-bikes only need high gears?
The main problem is that standard (not fixed) bicycle gears do not handle reverse torque very well. One solution is to add a solenoid to lock the gear shifter during regen. But according to the one who did the hybrid bicycle project, for a top speed of around 30MPH, changing gears doesn't give that much advantage. Better to just use a motor with a higher current rating and higher current MOSFETs, then let the inverter do the "impedance matching".

Even electric cars generally just have one gear.

BTW, for a real project, add a planetary gearset along with a second motor and inverter, then program it to operate as a CVT just like how Toyota does it with their Hybrid Synergy Drive. Then you can do some neat tricks like pedaling while stopped to charge the battery (probably better on a tricycle since then you wouldn't have the issue of keeping it balanced) and getting full regen to a complete stop by pedaling backwards. But that's probably too complex for a beginner so just start with a single motor. Putting the motor on the rear wheel gives better traction when accelerating from a stop while putting it on the front wheel gives better regen performance. With the motor on the rear wheel, you can also use the bicycle as an emergency/mobile power generator by putting it on a stand (that lifts the rear wheel) and pedaling with the regen on.
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Offline Harvs

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Re: Electric bike battery
« Reply #44 on: September 23, 2016, 01:43:38 am »
Regen is practically useless on a bicycle, you simply don't brake that much from any significant speed and going down hills you usually just coast.

The reality is, the mid-drives like this:
http://em3ev.com/store/index.php?route=product/product&product_id=166
Are close to being an ideal solution for $500 + battery and can be installed on most bikes by the average punter.

Or if you've got cash to burn, the Bosch versions are less powerful (i.e. they're road legal) but have much nicer control systems.  The Chinese version has a bit of a rough control system due to the lack of pedal torque sensing, but has loads of power.
 

Offline mtdoc

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Re: Electric bike battery
« Reply #45 on: September 23, 2016, 02:21:38 am »
For converting a bicycle to electric assist, this startup has a really cool concept. Just change the rear hub!
Looks interesting


They got the idea for the name and look from:

 

Offline mtdoc

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Re: Electric bike battery
« Reply #46 on: September 23, 2016, 02:38:19 am »
Here's a question:
Is there any advantage to multiple gears in an E-assist bike? They make it possible to pedal efficiently over different grades and speeds, since people can only apply so much torque while pedaling. But electric motors can apply huge levels of torque, helping the rider to go up hills without shifting to a low gear. At higher speeds, using a high gear helps the rider maintain a comfortable cadence. So do E-bikes only need high gears?
The main problem is that standard (not fixed) bicycle gears do not handle reverse torque very well.

I think he means gears on the bike - not the hub motor.

Yes, if you deal with hills, bike gears help immensly.

I have a 1000W hub motor ebike using a 48V nominal (16s) 20 Ah LiFePO4 battery pack.  The bike is a 18 speed mountain bike. My commute is 6 miles downhill 1500ft elevation loss.  If I ride home on my ebike, I can put it in the top gear and pedal to help the motor to maintain a speed of 25-30 mph. The motor still draws about 15 amps while I'm pedaling.  To maintain that speed without any pedaling up the steep parts of the grade means 20+ Amps.  With my ebike I can be home in 20 minutes. Without my regular bike, it takes me an hour  ::)

Lots of reinventing the wheel (so to speak!) in this thread.

LiFePO4 battery packs work well for ebikes. They can take a fair bit of abuse. The power density is not quite as good as LiPo's but still good enough. The hardcore eBike DIY'ers mostly use Lipo packs built up from HobbyKing packs.

One good source for for ebike motors, controllers, LiFePO4 packs etc is Conhis Motors.  Lots of LiFePO4 ebike packs on ebay as well.

In the US there are several small shops that build eBike controllers and LiPo battery packs.  Many just put together there own LiPo battery pack using HobbyKing packs.

An excellent Ebike centric forum is Endless Sphere  Lots of smart people (some EEs) with extensive eBike building experience.

 


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