Battery switches off at full throttle

[Sparfuchs]

Hello EV friends,
i built a e bike with a mxus 3k turbo, a sabvoton 72150 and a 20s6p pack with a 50A BMS. The seller claims that peak is 150A, but i got told it's unrealistic. My problem is that if i go full throttle it does wheelies but suddenly everything is "dead" and can't be switched on again (full charged battery). As soon as i connect the charger for a second and then disconnect it, everething works great again and the lcd shows about 83v. My guess is that it pulls so much power at full throttle that the voltage gets below 60v (Discharge Cut-off Voltage) for a second and tells the BMS to power of. Is that possible ? I'm also sure i could use better setting on my controller because i had max. Amps. Does someone know what i've to do or what settings i could try to avoid that ?

Thanks for your help
Best regards
Sparfuchs


Here the specs of my battery according to the seller:


Battery Model:72V 21Ah
Nominal Capacity (AH) :21ah
Nominal Voltage (V): 72V
Cell Source Resistance (mΩ) :within 38mΩ
Cell Specification :Use Samsung 3500MAH Cells
Cell Combination :6-parallel 20-series

Lifecycle:more than 800 cycles
Battery Size :300*200*80*260*50*70MM
Battery Weight : About 6kgs

Charge:

Way of charge:CC/CV

Standard charge Current:5A

Max Continuous Charge Current:5A

Charge Cut-off Voltage: 84V

Cell Overcharge protection Voltage:4.2V

Charge Temperature Range :0 - 45°C

Discharge:

Max Continuous Discharge Current:50A

Peak Discharge Current:150A

Discharge Cut-off Voltage:60+/-1 V

Cell Overdisharge protection Voltage:2.75V

Discharge Temperature Range: -20 - 60°C

 

[john61ct]

The seller claims that peak is 150A, but i got told it's unrealistic. My problem is that if i go full throttle it does wheelies but suddenly everything is "dead" and can't be switched on again (full charged battery). As soon as i connect the charger for a second and then disconnect it, everething works great again and the lcd shows about 83v. My guess is that it pulls so much power at full throttle that the voltage gets below 60v (Discharge Cut-off Voltage) for a second and tells the BMS to power of. Is that possible ?

Not just possible but very common and likely here.



> specs of my battery according to the seller

LOL 98% outright lie like crazy, link please?


> Samsung 3500MAH Cells

Exactly which model? New, Grade A and genuine?


> Max Continuous Discharge Current:50A
> Peak Discharge Current:150A

Have you tested what the reality is?

 

[Dak77]

Sounds like 35E cells . They seem to be the go-to cell to push those capacity claims for prefabbed packs. That's a lot of amps for a 6P configuration with those . Sag into LVC sounds very likely.

 

[flippy]

That setup will not do 150A. Even 50A is pushing it with those cells if you want any reasonable amount of cycles out of them. The bms triggers on LVC at that load. Pulling that current from this pack is basically just making a dead short.

The specs of this pack are utterly made up. It will not last more then a few months at best with daily use before you see considerable performance drops.

Anything above 12A is killing that pack.

These cells are for laptops, not vehciles.

 

[Sparfuchs]

Not just possible but very common and likely here.


> specs of my battery according to the seller

LOL 98% outright lie like crazy, link please?


> Samsung 3500MAH Cells

Exactly which model? New, Grade A and genuine?


> Max Continuous Discharge Current:50A
> Peak Discharge Current:150A

Have you tested what the reality is?

Thanks for your reply john61ct,

It's a aliexpress battery pack, so i'm not surprised the description is wrong But i didn't know better when i bought it. Here's the link: https://de.aliexpress.com/item/32954363991.html?spm=a2g0s.9042311.0.0.27424c4dIY4Jos

All i know is, the text on the cells says:

INR18650 - 35E
SAMSUNG SDI
2G25

Hopefully its at least a original cell.

I already ordered a CA V3 but haven't got it yet, so haven't tested the battery yet.

 

[Sparfuchs]

Sounds like 35E cells . They seem to be the go-to cell to push those capacity claims for prefabbed packs. That's a lot of amps for a 6P configuration with those . Sag into LVC sounds very likely.

Thanks for your reply Dak77,
you're right. 6p of 35E cells will never ever do 150 amps

 

[Sparfuchs]

That setup will not do 150A. Even 50A is pushing it with those cells if you want any reasonable amount of cycles out of them. The bms triggers on LVC at that load. Pulling that current from this pack is basically just making a dead short.

The specs of this pack are utterly made up. It will not last more then a few months at best with daily use before you see considerable performance drops.

Anything above 12A is killing that pack.

These cells are for laptops, not vehciles.

Thanks for your reply flippy post,

you're right, 150 amps is way to much and not possible for this battery.. But 50 amps should be a quite reasonable number for this battery, isn't it ?
Because the datasheet says "Max. Discharge Current: 8,000mA (for continuous discharge) 13,000mA (not for continuous discharge).
So a 6p pack should be 6p x 8A = 48 Amps continuous discharge and 78 Amps peak. Please correct me if i'm wrong.
So i think if i use it at 48 amps or 78amps peak that's exactly what the battery is made for ?
Why do you think "anything above 12A is killing that pack" ?

 

[Sparfuchs]

As i can't return my battery pack and don't won't do harm it, i'll just set the settings to 48 amps continuous and 78 Amps peak and hope this will avoid the problem with the battery
Or does anyone have another solution ?

Thanks for your help

 

[flippy]

Why do you think "anything above 12A is killing that pack" ?

because i have tested these cells and have already repaired some from other people that were less then a year old but completly shot.

these are laptop cells, not high drain cells. the hit on lifecycles is simply too high to run these at anything above 0.5/C

use these at the datasheet limits and you will get 300 cycles out of them if you are lucky.

 

[Sparfuchs]

Why do you think "anything above 12A is killing that pack" ?

because i have tested these cells and have already repaired some from other people that were less then a year old but completly shot.

these are laptop cells, not high drain cells. the hit on lifecycles is simply too high to run these at anything above 0.5/C

use these at the datasheet limits and you will get 300 cycles out of them if you are lucky.

Hmm.. this are bad news.
Because if i use them "your" way it won't be fun driving i guess and if i use them the datasheet way or worse - the sellers way, it won't work for long. That sucks but good to know, so thanks

 

[flippy]

if you use them as it is right now every day you wont last beyond the summer with this pack.

cells like the samsung 29E is the highest you want to go on a capacity standpoint. anything above that is not suitable for ebike or scooters. unless you are tesla and shove 8500 cells in a pack. for packs like yours i would take the 25R or something like that. at least that one can push some decent amps.

 

[Dak77]

Why do you think "anything above 12A is killing that pack" ?

because i have tested these cells and have already repaired some from other people that were less then a year old but completly shot.

these are laptop cells, not high drain cells. the hit on lifecycles is simply too high to run these at anything above 0.5/C

use these at the datasheet limits and you will get 300 cycles out of them if you are lucky.

Hmm.. this are bad news.
Because if i use them "your" way it won't be fun driving i guess and if i use them the datasheet way or worse - the sellers way, it won't work for long. That sucks but good to know, so thanks

My wife has a Radrunner with a similar battery except it's only 13s5p and she has a lead foot...err lead thumb to be more exact . The controller on that contraption peaks at like 18amps I believe and after a year, the capacity has shown a noticeable drop. It still has probably 80% of its new capacity, but it's clearly not the best cell choice for even that very light load in ebike terms. Read through the below thread when you have time and you will learn a lot about the real life capabilities of various "balanced parameter " cells and " high energy (high capacity) cells. There are other threads that have valuable info as well , but I can't remember what and where they were. If you're adventurous, there's a few people here that run pouch cell packs for higher current demands and they have some good points . It probably sounds like you're only getting the negative points of view , but the reality vs mass marketing solutions are very different. People here don't sell batteries , they just use their real world knowledge and pass it on so new riders don't get duped . A couple years ago I would have definitely fallen into the same trap.


https://endless-sphere.com/forums/viewtopic.php?f=14&t=103092

 

[fatty]

As i can't return my battery pack and don't won't do harm it, i'll just set the settings to 48 amps continuous and 78 Amps peak and hope this will avoid the problem with the battery
Or does anyone have another solution ?

Thanks for your help

You are exactly correct: the BMS should have been selected or programmed to respect these current limits you have calculated, but as you can see, this is never the case for Aliexpress.

In the end, batteries are consumables. If you respect the current limits in the datasheets, you should get adequate performance and longevity from the pack.

 

[flippy]

It still has probably 80% of its new capacity

80% is the industry standard level that qualifies a cell/battery as failed/consumed/worn out and is in most countries also the level where warranty applies.

You are exactly correct: the BMS should have been selected or programmed to respect these current limits you have calculated

its not the BMS that fails here, its the user/consumer device (aka: the controller) for using more power then the battery can actually deliver. its a fail on the battery maker to have used/programmed the bms wrong as it should never allow such currents to flow.

people tend to forget that the bms is only a protection device, not a control device. this is also why your TV is running on the same breaker as your toaster despite there being a massive difference in power consumption. the fuse does not give a shit, as long as you remain under its limit. the bms is exactly the same thing, just with more fancy lights.

 

[Sparfuchs]

Another question i need help with... Does someone know what controller settings have to be chosen in my case ? I hope i got the first four set correct already ? But what about the other ones ? I'd think that i could set them as high as i want because it could never get too much with my week battery and the low dc amps set ? But i'm not sure about that and my controller is unlocked so i might mess it up if i do wrong.

 

[Dak77]

It still has probably 80% of its new capacity

80% is the industry standard level that qualifies a cell/battery as failed/consumed/worn out and is in most countries also the level where warranty applies.

You are exactly correct: the BMS should have been selected or programmed to respect these current limits you have calculated

its not the BMS that fails here, its the user/consumer device (aka: the controller) for using more power then the battery can actually deliver. its a fail on the battery maker to have used/programmed the bms wrong as it should never allow such currents to flow.

people tend to forget that the bms is only a protection device, not a control device. this is also why your TV is running on the same breaker as your toaster despite there being a massive difference in power consumption. the fuse does not give a shit, as long as you remain under its limit. the bms is exactly the same thing, just with more fancy lights.

80% is stupidly inaccurate. It's very noticeable though.

 

[fatty]

its not the BMS that fails here, its the user/consumer device (aka: the controller) for using more power then the battery can actually deliver. its a fail on the battery maker to have used/programmed the bms wrong as it should never allow such currents to flow.

people tend to forget that the bms is only a protection device, not a control device. this is also why your TV is running on the same breaker as your toaster despite there being a massive difference in power consumption. the fuse does not give a shit, as long as you remain under its limit. the bms is exactly the same thing, just with more fancy lights.

Of course it's the BMS. The controller doesn't know what cells are in the pack, and even if sold as a kit, the battery or controller could be changed. As I've written before, the BMS should protect against peak overcurrent; the controller should be configured to manage continuous discharge.

 

[flippy]

80% is stupidly inaccurate. It's very noticeable though.

care to share why this industry standard is "stupidly inaccurate"?

 

[Dak77]

80% is stupidly inaccurate. It's very noticeable though.

care to share why this industry standard is "stupidly inaccurate"?

No I meant my guestimate was stupidly inaccurate. I was brainfarting off the hip when I said it probably had 80% left. It likely is closer to 90% , but the drop in capacity after the first year , 100ish cycles , was very noticeable. I haven't discharged it completely to test the capacity accurately. Just ignore my babble.