Electric bike battery

[sspj9]

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

[MosherIV]

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

The current through the motor is
1000W / 48V = 20.833333333333333333333333333333

The battery can supply 48V at 11A for 1 hour,
so roughly speaking this battery can last for around 1/2 hour

Is it recommended ?
Well, are you OK with having to recharge every half hour and you will be going through the life of the battery pretty quickly
(typically they only have 500 to 1000 charge cycles to begin with).
Are you OK with that?

[sspj9]

I suppose that is fine, since I will be using it to go to university which is around 6km, so both ways will be 12km
Now, maximum speed of the bike is 45 km/h so i would be able to cover a distange of (45/2 = 23km). Therefore if I use full throttle I would have to charge every fortnight.
However, I doubt I'll use full throttle, and I sure would be using the paddle occasionally.
I suppose then 11.6Ah will do.

Question?
If the battery life is over would I be able to change the cells individually with a higher power rating?

Thanks

[MosherIV]

I suppose that is fine, since I will be using it to go to university which is around 6km, so both ways will be 12km
Now, maximum speed of the bike is 45 km/h so i would be able to cover a distange of (45/2 = 23km). Therefore if I use full throttle I would have to charge every fortnight.

I do not know how you worked out that you can charge every 2 weeks.

I said the battery will last around 30 minutes at full speed, that is with no load.
So how long is the journey in time - NOT distance.

Question?
If the battery life is over would I be able to change the cells individually with a higher power rating?

When the battery life is used up - they do not retain their charge. It does not matter how you charge, they will not keep their charge or another way of looking at it - they will not charge.
You CANNOT exceed the charging current for ANY Lithium technology battery without running the risk of starting a fire !

[sspj9]

My mistake, i meant I would charge the battery every two days 

I do mean change the individual cells not charge. So i open up the battery and change the 18650 cells which went bad individually but with a higher rating?

[MK14]

Doesn't the bike suppliers information, give you typical ranges for their bikes/batteries ?

Whatever figures they give, I'd suspect they may be over optimistic/ideal and maybe exaggerating. So would expect the real life figures to be two thirds or a half, what they say. Maybe even less than that.

There could be good independent tests/reviews which give the range.

When the battery is down to 5% to 20% of left capacity, it may be too weak to drive the bike and/or a bad idea, as the battery could be damaged (excessively run down).

Also reaching 100% full charge may be problematic as well. Maybe 90% (if done very quickly) is more realistic. (It depends on how fast the charger is, battery temperature and other factors). With enough time, 100% is possible, I guess.

The motor drives and any voltage conversion (if necessary), will waste a percentage of the energy as well.

Accelerating would probably use the most power, I would guess. Heavy battery loads, can reduce the run time, even more, because of inefficiencies in the battery. I.e. Amp/hours ratings, depend on load current over a period of time. Very quick discharges, are usually lower figures.

EDIT:
I'd be scared of getting killed/injured on it and use a safer method of transportation.

[MosherIV]

I do mean change the individual cells not charge. So i open up the battery and change the 18650 cells which went bad individually but with a higher rating?

Sorry my mistake.

It is not advisable to mix new and old batteries of any type. Older batteries would have a much lower capacity than the newer cells.
It is dangerous to over charge Lithium based batteries, again there is a risk of starting a fire.

It is not advised to mix batteries of different capacities for the same reason as above, I presume that is what you mean by "higher rating".

[sspj9]

I see, and makes a lot of sense! Well I hope it would be much more worth it than driving a car...

[sspj9]

I'd be scared of getting killed/injured on it and use a safer method of transportation.

Same goes to motor cyclists!, Well I doubt I would be reaching high speeds with a bike... At least the route from home to uni has cycle paths.

[edpalmer42]

Even though your motor is rated for 1000 watts, that doesn't mean it will always draw that much power.  When you're cruising at a constant speed, your battery drain will be determined by friction, electrical efficiency of the motor and drive system, and wind resistance.  The battery drain under these conditions will be much lower and that will give you more range or more time between charges.  I have no clue what a typical drain would be at constant speed.  The heaviest drain will be when you're accelerating from zero with full throttle.

What is the series/parallel arrangement of your battery?  48V suggests 16 cells in series, but 20A doesn't sound like it would be very good for a single string of 18650 cells.

Ed

[MK14]

I'd be scared of getting killed/injured on it and use a safer method of transportation.

Same goes to motor cyclists!, Well I doubt I would be reaching high speeds with a bike... At least the route from home to uni has cycle paths.

At least if you had an accident in a normal bicycle, hopefully the lower speeds, would tend to minimize/prevent injuries and you would be less likely to be killed. Until you go off the cycle paths, and start meeting cars ...

But if you can do up to 45 KPH, you will be much more likely to injure/kill someone else, or yourself, compared to a peddle powered bicycle, I would expect.

[sspj9]

What is the series/parallel arrangement of your battery?  48V suggests 16 cells in series, but 20A doesn't sound like it would be very good for a single string of 18650 cells.

52 x Samsung INR18650 29E (3.7V 2.9Ah) connected 13 series 4 parallel.. Doubt i could customize it at all

[Fungus]

Is it recommended?

a) 45kmh on a bike? I don't know what brakes/wheels you have but it sounds quite scary to me.

b) How long will the battery last? That depends almost 100% on aerodynamics and how level the ground is (ie. hills). Another big factor will be the weather (temperature).

This graph shows air resistance for a normal bicycle:

https://en.wikipedia.org/wiki/File:CyclingPowerComponents.svg

You want to go at 12.5m/s so you probably need all of the power from your 1kW motor.

Look at the graph though. It's very exponential. At 10m/s you only need 300W. You either need to go a bit slower or add some serious aerodynamics if you want this to be practical.

so roughly speaking this battery can last for around 1/2 hour

They won't last very long if you repeatedly discharge them in 30 minutes (in fact it might not even be possible to discharge them in 30 minutes without overheating).

[Fungus]

52 x Samsung INR18650 29E (3.7V 2.9Ah) connected 13 series 4 parallel.. Doubt i could customize it at all

Here's a datasheet: https://www.nkon.nl/sk/k/29E.pdf

Minimum discharge time is approx one hour. You'll need at least 8 parallel to achieve 1kW. Better double all your numbers. 

You're talking about $1000 of batteries that will probably last about a year (charging every two days).

You'll also need some really fancy charging electronics to avoid having to trash sets of cells because you're not charging them perfectly.

You also risk trashing batteries if cooling is uneven... and maybe a big lithium fire if you mess up.

I dunno. A moped looks cheaper/safer.

[JPortici]

Is it recommended?

a) 45kmh on a bike? I don't know what brakes/wheels you have but it sounds quite scary to me.

same. electric bikes i've used (pedal assistance) could run at most at 26 km/h and sometimes the whole thing wouldn't be stable (you had to keep the handle very tight at higher speeds or it would start oscillating)

OP, is it something you want to build for yourself? the braking system is crucial. you can kill yourself when going much slower than 45 km/h.
an electric bike will also disable the motor whenever you touch the brakes, for obvious safety reasons.

side note: our grandparents use to do this instead

i think i saw one or two when i was a little kid
this evolved into the ciao

[Fungus]

Is it recommended?

a) 45kmh on a bike? I don't know what brakes/wheels you have but it sounds quite scary to me.

same. electric bikes i've used (pedal assistance) could run at most at 26 km/h and sometimes the whole thing wouldn't be stable (you had to keep the handle very tight at higher speeds or it would start oscillating)

I once went downhill on a bike with a speedometer and IIRC I chickened out at about 30 kph. I'm not saying you can't get used to going fast on one but they really don't seem designed for those speeds. I thing you'd need a different frame geometry to keep it stable.

[helius]

For converting a bicycle to electric assist, this startup has a really cool concept. Just change the rear hub!

[Siwastaja]

With 1000W constant power on an Ebike, you'd be going so fast that you'd be scared.

You won't probably draw 1000W except for short peaks, like accelerating, going uphill (which will be saved back during the next downhill by zero consumption), etc.

More realistic average power for you daily commute would most likely be in the 200-500W range depending on how fast you go. 1000W capable motor, inverter and battery pack makes a nice ebike because sometimes you want the extra power to overcome some non-average situations (like uphills).

I welded a pack made of Samsung 29E cells for a friend. It was ca. 50 cells. He's been very happy so far. These cells are nice because they are "old tech" and very cheap in quantities, but still high tech compared to many "hobbyist" solutions like LFP cells. You can see his videos here: . I only did the welding, having built the robot welder that can directly weld copper sheet to the cells. Part3 of the video series shows the welding, while part5 shows the bike up&running.

When using Samsung 29E's, thing of them being capable of 2C peak, 1C continuous power. You want to actually limit the discharge current to about 2C, maybe 2.5C max, by some active design (limit in the inverter) so that you don't blow the protection PTCs open in the cells.

[Mechatrommer]

52 x Samsung INR18650 29E (3.7V 2.9Ah) connected 13 series 4 parallel.. Doubt i could customize it at all

you are nuts... you can use 4 of this... http://www.hobbyking.com/hobbyking/store/__80906__Multistar_High_Capacity_4S_20000mAh_Multi_Rotor_Lipo_Pack_AU_Warehouse_.html
or 4 LA batteries in series. easier to maintain...

[langwadt]

And in EU the limits for an e-bike is 250W and only assist when pedaling and doing less than 25kmh, beyind that it becomes  a motorbike or moped and requires insurance, type approval etc.

[Harvs]

I ride a 750W ebike converted using a BBS02 motor kit and hobbyking packs http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=19499 and their 2S packs, to a total of 14s @ 10Ah.

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.

Where you do need the power though (at least in my case) is climbing hills.  The higher powered motor means I can still be doing 20km/h up a hill where I'd normally be down in the lowest couple of gears.  Makes for a great commuting bike.

[ez24]

For converting a bicycle to electric assist, this startup has a really cool concept. Just change the rear hub!

Looks interesting

[zlymex]

I have a electrical uni-cycle with 1000W motor too, battery is 850Wh(5-parallel 16-series of Panasonic NCR18650PF), the typical range is 80km when cruising at 20km/h even road for rider of 65kg. The unicycle is less efficient than a bicycle because it use extra power to balance.

[Fungus]

For converting a bicycle to electric assist, this startup has a really cool concept. Just change the rear hub!

...except they've been on "pre-order" status for as long as I can remember.

[Siwastaja]

52 x Samsung INR18650 29E (3.7V 2.9Ah) connected 13 series 4 parallel.. Doubt i could customize it at all

you are nuts... you can use 4 of this... http://www.hobbyking.com/hobbyking/store/__80906__Multistar_High_Capacity_4S_20000mAh_Multi_Rotor_Lipo_Pack_AU_Warehouse_.html
or 4 LA batteries in series. easier to maintain...

  

[Fungus]

you are nuts... you can use 4 of this...

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

[Fungus]

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.

[NiHaoMike]

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.

[Mechatrommer]

you are nuts... you can use 4 of this...

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

 

duh do we have to go beginners section battery 101? or even down further.... 12 x 4 is what?

[Fungus]

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. 

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

[technotronix]

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.

[Mechatrommer]

(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...

[Siwastaja]

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.

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.

[Fungus]

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.

[Siwastaja]

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

No, absolutely not! 

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.

[Fungus]

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?

[Siwastaja]

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.

[nukie]

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

[Mechatrommer]

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 , 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.

[NiHaoMike]

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.

[Harvs]

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.

[helius]

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?

[Harvs]

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. 

[NiHaoMike]

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.

[Harvs]

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.

[mtdoc]

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:

[mtdoc]

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.