Is it possible to upgrade battery packs?

Hi,

I have a 48V 25Ah battery pack that I use with BBS02b. I don't know the make of the cells but I suspect the maximum discharge rate is no more than 20A. Since the top speed (48km/h) or average speed (40km/h) on flat is not sufficient, I am thinking of upgrading the battery pack to 52V by adding a set of 10 18650 cells in series. What do you think would most likely happen:

a) One of the pack would heat up and may catch fire
b) Increase in average speed
c) Increase in range only

If you choose (a) then please suggest the best course of action for renovating the ebike.

(a)


pull apart the battery. clean up the cells. buy as much cells as you can afford to add to the pack and make a new pack with ALL the cells evenly distributed over all the groups. so equal numbers of old and new cells in each group. do not make groups with more old cells or more news cells then other groups. they must all be equal.

Yes, build a new pack.

Doing so from used cells requires much more knowledge and testing gear than using new cells.

azad said:

I have a 48V 25Ah battery pack that I use with BBS02b. I don't know the make of the cells but I suspect the maximum discharge rate is no more than 20A. Since the top speed (48km/h) or average speed (40km/h) on flat is not sufficient, I am thinking of upgrading the battery pack to 52V by adding a set of 10 18650 cells in series. What do you think would most likely happen:

a) One of the pack would heat up and may catch fire
b) Increase in average speed
c) Increase in range only

Click to expand...

Azad,
I was in the similar situation. I bought a BBSHD 52V version but I had several 48V 20A batteries. I added 1S20P 4.2V battery in series to create 52V. I used a 36V 4.4Ah (10S2P) scooter battery to create 1S20P (44Ah). Just cut Nickel strips and solder them in parallel. You don't need to do spot welding. Because there is no BMS in 1S20P, I chose much higher capacity Ah than 48V. The min voltage of my 1S20P is 3.8V. Make sure to add a fuse to 1S20P. It works very well with BBSHD. Higher voltage gives me higher speed. I can also get longer range but I have not checked.
You need to be careful when you charge them. 1S20P is charged with a high quality power supply set to 3A CC at 4.15V. It starts with CC then goes to CV at 4.15V. It is slow because I use 3A unit. 48V battery is charged with the regular 48V 5Acharger after disconnecting 1S20P.
So far I have not had any fire. Both batteries are still cool after using 90 min with BBSHD.
I create two 1S20P to save time.

Higher voltage gives me higher speed.

Click to expand...

So far I have not had any fire

Click to expand...

would fire between your knees make you go faster?

goatman said:

Higher voltage gives me higher speed.

Click to expand...

So far I have not had any fire

Click to expand...

would fire between your knees make you go faster?

Click to expand...

Hi Goatman,
We are dealing with the safety of 1S**P 4.2V battery here. 48V battery is already protected with BMS. BBSHD uses 30A max. My 1S20P (44Ah) is used with less than 1C. So the discharging process is well within the safety range of 1S20P. It does not get warm.
I am charging 1S20P to 4.15V slowly using 0.15C charge current max (3/20).
My 1S20P is used with the max voltage of 4.15 and the min voltage of 3.8V.
When 10S2P was converted to 1S20P, the soldering was done on the old nickel strips. No soldering on 18650.
Do you see any issue here?

hey John, you want to chime in here

goatman said:

hey John, you want to chime in here

Click to expand...

i dont think any of us have enough crayons (or patience) to explain how stupid it is.

ykuga said:

azad said:

I have a 48V 25Ah battery pack that I use with BBS02b. I don't know the make of the cells but I suspect the maximum discharge rate is no more than 20A. Since the top speed (48km/h) or average speed (40km/h) on flat is not sufficient, I am thinking of upgrading the battery pack to 52V by adding a set of 10 18650 cells in series. What do you think would most likely happen:

a) One of the pack would heat up and may catch fire
b) Increase in average speed
c) Increase in range only

Click to expand...

Azad,
I was in the similar situation. I bought a BBSHD 52V version but I had several 48V 20A batteries. I added 1S20P 4.2V battery in series to create 52V. I used a 36V 4.4Ah (10S2P) scooter battery to create 1S20P (44Ah). Just cut Nickel strips and solder them in parallel. You don't need to do spot welding. Because there is no BMS in 1S20P, I chose much higher capacity Ah than 48V. The min voltage of my 1S20P is 3.8V. Make sure to add a fuse to 1S20P. It works very well with BBSHD. Higher voltage gives me higher speed. I can also get longer range but I have not checked.
You need to be careful when you charge them. 1S20P is charged with a high quality power supply set to 3A CC at 4.15V. It starts with CC then goes to CV at 4.15V. It is slow because I use 3A unit. 48V battery is charged with the regular 48V 5Acharger after disconnecting 1S20P.
So far I have not had any fire. Both batteries are still cool after using 90 min with BBSHD.
I create two 1S20P to save time.

Click to expand...

How much speed do you get?

Mix match facts can work but are complete headache and have a lot of safety problems.
use your 48v battery as it's the one you got and later in life buy a 52 volt battery the size you need with the quality cells you need all new all known quality cells. Less chance of fire

It's a steep learning curve building a battery from scratch and from old cells.

a) and b)

More volts will make it go faster but you still can't get more than 20A out of the pack if you only add cells in series.
Also, if you use decent cells for your new 20P1S you are wasting the additional capacity that you are spending money on.

Computer crayons - note I haven't changed the initial gearing - check and change
48V to 52V with my best guess of your spec - 2KPH improvement - not a lot
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=1&batt=cust_48_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=1&batt_b=cust_52_0.2_24&tr_b=11&bopen=true

48V 20A to 48V 30A assumed improvement from rebuilding - looks like you might be close to the expected top speed anyway and as you need around 900W from a 750W motor to do 48MPH [Edit sorry I meant Kph as per the simulation], it will overheat if you put any more through it anyway.
The big problem may be cooling rather than battery or as well as battery?
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=1&batt=cust_48_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=1&batt_b=cust_48_0.2_24&tr_b=11&bopen=true&cont=cust_20_50_0.03_V&cont_b=cust_30_75_0.03_V&tf=53&tf_b=53
If it is the battery, the amount of usable torque at lower speeds is also higher with more amps. more motor amps = more overheating of course regardless of whether from volts or current

BobBob said:

It's a steep learning curve building a battery from scratch and from old cells.

a) and b)

More volts will make it go faster but you still can't get more than 20A out of the pack if you only add cells in series.
Also, if you use decent cells for your new 20P1S you are wasting the additional capacity that you are spending money on.

Computer crayons - note I haven't changed the initial gearing - check and change
48V to 52V with my best guess of your spec - 2KPH improvement - not a lot
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=1&batt=cust_48_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=1&batt_b=cust_52_0.2_24&tr_b=11&bopen=true

48V 20A to 48V 30A assumed improvement from rebuilding - looks like you might be close to the expected top speed anyway and as you need around 900W from a 750W motor to do 48MPH, it will overheat if you put any more through it anyway.
The big problem may be cooling rather than battery or as well as battery?
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=1&batt=cust_48_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=1&batt_b=cust_48_0.2_24&tr_b=11&bopen=true&cont=cust_20_50_0.03_V&cont_b=cust_30_75_0.03_V&tf=53&tf_b=53
If it is the battery, the amount of usable torque at lower speeds is also higher with more amps. more motor amps = more overheating of course regardless of whether from volts or current

Click to expand...

It is not about knowledge or experience rather cumbersomeness of tearing apart and then assembling the *whole* bike again that is of concern here.

The only reason for increase in voltage and not ampere is because of the limitation of discharge rate of 18650 cells. The cells that I already have in the pack must be 5C/6C (~18A discharge rate) because I don't get more than 900W consistent output from them. This is why I thought the only way to increase the max wattage is by increasing the voltage.

It was 48km/h and not mph that I mentioned and this is what I can achieve on fresh charge. But I wanted to increase to 60km/h. Actually, if I run the throttle while on the stand, it can go to 60km/h but not when I am riding it. This leads me to believe that it is the power that is the bottleneck and not the rpm.

azad said:

It was 48km/h and not mph that I mentioned and this is what I can achieve on fresh charge. But I wanted to increase to 60km/h. Actually, if I run the throttle while on the stand, it can go to 60km/h but not when I am riding it. This leads me to believe that it is the power that is the bottleneck and not the rpm.

Click to expand...

you always lose about 15% in rpm on a good motor (more on a bad one) between freewheeling and loaded. its how motors make actual power.
they need to "lag behind" the power curve in order to actually pull the magnets along with enough force. (extremely simplified)

azad said:

It was 48km/h and not mph that I mentioned and this is what I can achieve on fresh charge. But I wanted to increase to 60km/h.

Click to expand...

An increase from 48v to 52v won't come anywhere close to 60km/h on the road with your current setup.

azad said:

Actually, if I run the throttle while on the stand, it can go to 60km/h but not when I am riding it.

Click to expand...

That is nowhere close to a fair comparison and running it like that for any prolonged time is not good. If you need to go 60km/h you ideally need a 72v upgrade in power system as well as a significant battery upgrade.

OK, so a 72v upgrade is overkill and 52v can still give you the need for your speed with the right setup ... https://electrek.co/2018/10/19/diy-fast-electric-bike/
https://www.youtube.com/watch?v=mLoQg27Y24E&t=2s

eMark said:

OK, so a 72v upgrade is overkill and 52v can still give you the need for your speed with the right setup ...

Click to expand...

why would 72V be too much?

azad said:

It is not about knowledge or experience rather cumbersomeness of tearing apart and then assembling the *whole* bike again that is of concern here.

Click to expand...

Sorry, i wasn't meaning to be patronising, it's a consideration when advising people what to do to know how happy they are with a spot welder or a spanner

azad said:

The only reason for increase in voltage and not ampere is because of the limitation of discharge rate of 18650 cells. The cells that I already have in the pack must be 5C/6C (~18A discharge rate) because I don't get more than 900W consistent output from them. This is why I thought the only way to increase the max wattage is by increasing the voltage.

Click to expand...

If you have limited discharge rate (and I'm not sure you do) then this will also limit the new cells you add
If you add them in parallel (say one to each parallel pack so effectively be 12 in series then you bring the current capacity of the whole pack up. The right way to do that is by rebuilding the pack
For a complete crazy redneck appreoach you could add your extra cells in parallel instead of series or in addion. 10A from a single cell is not completely daft
I simulated being able to improve the voltage and then ran a second simulation which showed the improvement from increased current.
I understand that you don't want to break down and rebuild the battery pack and hope the simulation illustrates the pros and cons - I'm not really here to give advice
You will notice that whatever you do, more power through the motor will mean it overheats so yoiu need a bigger motor if you want to go much faster

azad said:

It was 48km/h and not mph that I mentioned and this is what I can achieve on fresh charge. But I wanted to increase to 60km/h. Actually, if I run the throttle while on the stand, it can go to 60km/h but not when I am riding it. This leads me to believe that it is the power that is the bottleneck and not the rpm.

Click to expand...

yeah, I meant Kmh not Mph, I used Kmh in the simulation I put up there for you - did you see it?

Sorry to say this but it looks as though you may be already going the max speed according to the simulation which means that you may get no benefit from rebuilding the battery for more current and only a 2 kph from going to 52V

My vote - if you want more power get a bigger motor but that bafang is not cheap so...
Add a hub motor?

flippy said:

you always lose about 15% in rpm on a good motor (more on a bad one) between freewheeling and loaded. its how motors make actual power.
they need to "lag behind" the power curve in order to actually pull the magnets along with enough force. (extremely simplified)

Click to expand...

I played around with the simulation for that bafang (which is probably wrong) and managed a peak speed on the flat of 48 kph from a 48V battery by tweaking gearing
I then changed the slope of the hill till the motor was unloaded and he was doing 82 Kph
Peak efficiency would be at 85% of unloaded RPM or around 68Kph but peak power output if we're stuck with that motor seems to be around 60% of max revs?
Could be wrong, values are probably wrong and it probably doesn't matter for this OP but here's the graph and the sim.
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=0.93&batt=cust_48_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=0.93&batt_b=cust_48_0.2_24&tr_b=11&bopen=true&cont=cust_20_50_0.03_V&cont_b=cust_30_75_0.03_V&tf=53&tf_b=53&grade_b=-20&grade=-20

azad said:

OK, so a 72v upgrade is overkill and 52v can still give you the need for your speed with the right setup ... https://electrek.co/2018/10/19/diy-fast-electric-bike/
https://www.youtube.com/watch?v=mLoQg27Y24E&t=2s

Click to expand...

I am not sure how this is achieving 40mph (60km/h) when this battery (48V 15Ah) is smaller than what I have (48V 25Ah). Even if motor is 1500W the battery is only 750W so it can't provide high speed/torque at low wattage unless this battery has ridiculously high discharge rate. This is a rear wheel drive as well while I have a mid drive which is more efficient.

BobBob said:

If you have limited discharge rate (and I'm not sure you do) then this will also limit the new cells you add


Sorry to say this but it looks as though you may be already going the max speed according to the simulation which means that you may get no benefit from rebuilding the battery for more current and only a 2 kph from going to 52V

My vote - if you want more power get a bigger motor but that bafang is not cheap so...
Add a hub motor?

Click to expand...

Why do you think discharge rate is not a problem? (Aren't 18650 cells commonly rated as 20A continuous discharge rate?)

I am interested in mid-drive because I live in hilly area, also I don't like the drag of hub motor.

Any suggestions for mid-drive better motor would be great.

Ah is about range more than power.

Even a tiny pack can get up to high speed,

in fact lower weight, less load to push

you just don't get many miles.


The quality of the cells used is the key to power capacity, and longevity.

john61ct said:

Ah is about range more than power.

Even a tiny pack can get up to high speed,

in fact lower weight, less load to push

you just don't get many miles.


The quality of the cells used is the key to power capacity, and longevity.

Click to expand...

Yes! agreed, edited the answer already.

But how do you think such *good* quality cells are available. All I can see is that the best ones are rated at max 20A/30A or 5C/6C discharge rate.

That is asking too much.

You aren't trying for cheap are you?

Top notch brand new grade A cells, all from the same production run.

And also bring the C-rate down by going to bigger Ah capacity.

azad said:

BobBob said:

If you have limited discharge rate (and I'm not sure you do) then this will also limit the new cells you add

Sorry to say this but it looks as though you may be already going the max speed according to the simulation which means that you may get no benefit from rebuilding the battery for more current and only a 2 kph from going to 52V

My vote - if you want more power get a bigger motor but that bafang is not cheap so...
Add a hub motor?

Click to expand...

Why do you think discharge rate is not a problem? (Aren't 18650 cells commonly rated as 20A continuous discharge rate?)

I am interested in mid-drive because I live in hilly area, also I don't like the drag of hub motor.

Any suggestions for mid-drive better motor would be great.

Click to expand...

Have a look at the simulations I did for you and try changing some of the settings. Let me know if it is unclear, happy to help.

According to the simulation, 47Kmh is your top speed from that motor so if you are achieving it then there is nothing wrong with your battery, also putting more power through will overheat it in a few minutes - again have a look at how fast it overheats if you want to go 60 Kph

Yes 18650 cells might discharge at 20 amps each when new, 35A if they are really good, so they would have to be pretty knackered or low spec if only putting out 20A between 10 of them.

See the range of commonly available cells and note that capacity in mAh is not related to discharge rate in Amps
https://eu.nkon.nl/rechargeable/li-ion/18650-size/sort-by/ontlading2/sort-direction/asc.html

Total storage of your battery might be 25 Ah x 48V = 1.2 Kwh that's 1.2 Kilowatts for an hour or 120W for 10 hours etc

As you have 10 18650 cells in parallel then your discharge rate is proportional to the number of cells in parallel
If one 18650 can discharge at 20A then 10 can discharge at 200A x 48V or 9.6 Kw and discharge in 12 minutes

I'm not the right person to advise on mid drives, I understand the motor and battery bit but don't know much about the differnt brands of motor or about mid drives
******************

Regarding Ah vs A:
lets say he has a 6P battery with some 30A cells, that's 180A x 48V 8.6Kw. With a fast wind (low turn count) to use the high current he could go a lot faster than 40 MPH, he could also get a bigger hub motor say 3 Kw or two of them

Problem is that with that motor you will overheat in 14 minutes at 47 Kph or 1.3 minutes at 60 Kph
https://ebikes.ca/tools/simulator.html?mid=true&motor=MBBS02&gear=1&batt=cust_72_0.2_24&tr=11&motor_b=MBBS02&mid_b=true&gear_b=1&batt_b=cust_48_0.2_24&tr_b=11&bopen=true&cont=cust_40_100_0.03_V&cont_b=cust_30_75_0.03_V&tf=53&tf_b=53

BobBob said:

azad said:

BobBob said:

If you have limited discharge rate (and I'm not sure you do) then this will also limit the new cells you add

Sorry to say this but it looks as though you may be already going the max speed according to the simulation which means that you may get no benefit from rebuilding the battery for more current and only a 2 kph from going to 52V

My vote - if you want more power get a bigger motor but that bafang is not cheap so...
Add a hub motor?

Click to expand...

Why do you think discharge rate is not a problem? (Aren't 18650 cells commonly rated as 20A continuous discharge rate?)

I am interested in mid-drive because I live in hilly area, also I don't like the drag of hub motor.

Any suggestions for mid-drive better motor would be great.

Click to expand...

Have a look at the simulations I did for you and try changing some of the settings - you might learn how changing the controller, motor or battery might help you

According to the simulation, 47Kmh is your top speed from that motor so if you are achieving it then there is nothing wrong with your battery, otherwise you would not achieve that top speed

Yes 18650 cells might discharge at 20 amps each when new, even more if they are really good ones, so they would have to be at 10% of that to be only putting out 20A between 10 of them. That may mean the battery is totally knackered. I guess someone may have built it out of 2A cells
See the range of commonly available cells and note that capacity in mAh is not related to discharge rate in Amps
https://eu.nkon.nl/rechargeable/li-ion/18650-size/sort-by/ontlading2/sort-direction/asc.html

Total storage of your battery might be 25 Ah x 48V = 1.2 Kwh that's 1.2 Kilowatts for an hour or 120W for 10 hours etc it tells you nothing about discharge rate except that youcan guess that a 25Ah pack must have lots of cells in parallel

As you have 10 18650 cells in parallel then your discharge rate is proportional to the number of cells in parallel
If one 18650 can discharge at 20A then 10 can discharge at 200A x 48V or 9.6 Kw so you might discharge in 12 minutes

Click to expand...

I see that according to simulation I can achieve 48km/h top speed which I actually can get with fresh charge on flat. But I can also see that current draw from the motor briefly spikes above 1000W until 1300W but never stays at that level. This leads me to believe that battery can not supply that much discharge quickly. I am not sure what cells have been used but what I know is that BBS02b can be pushed to 1400W and some crazy enthusiasts have already done that.

See here someone has achieved 82km/h from BBS02b.

https://www.youtube.com/watch?v=OctRu79TcQ8

azad said:

But I can also see that current draw from the motor briefly spikes above 1000W until 1300W but never stays at that level. This leads me to believe that battery can not supply that much discharge quickly. I am not sure what cells have been used but what I know is that BBS02b can be pushed to 1400W and some crazy enthusiasts have already done that.

Click to expand...

the spikes you see are that extreme because the controller pules really "loud" and your ampmeter is too slow to catch that properly. use a analog meter if you want some natural and more accurate measurement.

or buy a really expensive ampmeter....