Bike cutting out when battery on 3 bars

[Nealh]

Panny PF are meant to be 2900mah cells they are an ok low capacity cell, typically less then 2700mah is there actual rating. Again to avoid any voltage sag use at 5a or less per cell in parallel. I have a 5p PF battery and at 25a it held the sag very stably at about 3.5v climbing up from Ovingdene to Falmer, the cells were already at 3.85v or so and well into the discharge. I was happy with their performance, though there are better cells in the 2900 - 3500 10a range of 18650's.

As long as the series bus can handle 30a continuous the choice is reasonable if they are genuine.
The 5a discharge alone shows how saggy they are and have a higher internal resistance then other cells.

 

[bikemerchant]

Thanks.
An anomaly I just noticed is the advertisement of the problem battery says the cells are 2500mAh, but the cells are marked as 35E

Page Not Found - Aliexpress.com

Thanks @Nealh, the 3000mAh Panasonic NCR18650PF cells is been the only offer I've received so i guess I will go with it.
Do you think I need a new BMS also? He can provide this for an extra €35.

 

[Nealh]

They aren't 3000mah cells, the seller is either egging up there rating or doesn't know cells very well.

There are two date codes.
Old type e.g.
A6
2205
equating to in this case last week in May on the fifth day of 2016.

Or new code e.g.
B, A over V
8715

equating to 2018 July 15th.

 

[bikemerchant]

So a Panasonic NCR18650PF 3000mAh cell does not exist?
Should I ask the seller for a photo of the cells he will build the battery with?

 

[matthewslack]

I would say yes to new BMS, then the whole battery is the work of the supplier, easier if any issues later.

Do you get to keep the old cells? Chopped at 10S and add a BMS could be a usable 36V pack for light use, so they have a bit of value.

 

[Nealh]

So a Panasonic NCR18650PF 3000mAh cell does not exist?
Should I ask the seller for a photo of the cells he will build the battery with?

Correct PF are made and sold as 2900mah rating, one can nearly achieve 2900mah but only at 0.2a discharge to 2.8v which is the std industry test.
On the other hand independent testers use a more realistic discharge rate.

Mooch on ECF only rates them as 2680mah cells, his independent testing and ratings are highly regarded by many in the lion cell world and tend to be used as a bench mark for deciding on any particular cell to use for any project.
Panasonic NCR18650PF 10A 2680mAh 18650 Bench Retest Results...an ok low capacity 10A battery | E-Cigarette Forum (e-cigarette-forum.com)

 

[Nealh]

If using the the full 30a discharge of 6p cells then one can expect about 2050mah per cell (or 12.3mah for the whole battery) at 5a down to cut off at 3.2v, any lower then one is getting into deep discharge territory.

My experience is they do sag quite badly as indicated by live voltage readings but they hold up well under sag and give very good power, the voltage rebounds nicely once current demand is lessened.

 

[bikemerchant]

Thanks.
I asked the seller if he mixed up the specification and this is what he said;

my apologies, usually it's stated as 2750 or 2900, depending on source. I was able to reach 3000mAh value, of course it may slightly vary between production batch or other circumstances. But I have good experience with this particular cell and have ut in my mind as "3000" cell. here is datasheet: https://datasheetspdf.com/pdf/955257/Panasonic/NCR18650PF/1

 

[Nealh]

What range are you expecting to need ?
We know from early in the thread a 30a controller was being used, do you tend on maxing out the current all the time ?
The PF in 6p will have max 17.4ah but at the 30a max draw, the actual usable battery will be approx. 12.15ah/ 580wh worse case scenario. One will only see a out 2025 mah per cell in the p group at 30a draw & I would say one may see 20 - 25 miles max range given it is fat bike,

Your main issue will be battery sag as the battery overall voltage decreases, once one gets to 3.6 - 3.7v one is likely to see the sag drop to LVC and cutting out, if so then one will have to use PAS at a lower level to reduce voltage sag.
You can't have all the capacity and the current draw.

 

[bikemerchant]

If I charged between each return trip the longest daily trip is 15km, so should be fine.

I guess I can calculate how many A I am using by dividing the Wattage shown by 48V?
I generally don't restrict my speed, so I imagine it would be outputting 30A quite a lot?
Can I increase my range if I only started to restrict the output near the end of the battery cycle, in the times I am out for a longer ride than usual?

 

[Nealh]

You wouldn't know the true range until one tries a run out or lots of local short runs until it cuts out to exactly know. Fat tyres will have quite an effect on range via drag, but as you have said speed is the biggest killer for range as assist will be constantly on. I'm only guessing at 20 -25 miles range it may even be in the mid too high teens if maxed out all the time.

 

[bikemerchant]

Thanks, I'm waiting for the seller to get these cells through customs and then he can get the battery made up.

I just tried to hop on the bike for the first time in a few days today, from fully charged it cut out as soon as I turned on the screen without any throttle! Backlight would still light up for what it's worth.

Edit - and the backlight would stay on while the controller screen shuts itself off, unsure if this implies anything.

 

[bikemerchant]

I would say yes to new BMS, then the whole battery is the work of the supplier, easier if any issues later.

Do you get to keep the old cells? Chopped at 10S and add a BMS could be a usable 36V pack for light use, so they have a bit of value.

Yep he said I can keep them, although he suggested I leave them with him to dispose of as he says they can be dangerous.

 

[Nealh]

If one uses a 18650 torch then they will come in handy once the battery is decommissioned or how about asking him if he will cut out the bad group #11 and remove one cell from all the other groups, then use five of them to replace #11 for a 13s 5p battery it could then be a spare or back up battery.

 

[bikemerchant]

He said there is no insulation between series so he will have to strip battery down to bare cells and rebuild it.
So will take him about 3-4 hours (€120-150) - probably a better option than having the batteries lying around or disposed of?

What sort of range would I be expecting from a 13s5p battery?

 

[Nealh]

13s5p will be approx 820/830wh for me that would be 80 odd miles with my riding style and usage, but for a 1500w fat bike pulling 25/30a on throttle I could only guess at 20 miles or so.
Until one actually knows the real world wh per mile usage one gets form your set up then one can only guess.

 

[bikemerchant]

Thanks.
I remember the battery seller offered to ship the replacement cells - if I got 6 of these I could make a replacement 13s6p battery I imagine?
Probably I would have to ask for a replacement case also so I can just slide once case off and the other on?

 

[Nealh]

It isn't good practice to replace cells with new ones as the new cells will be more stressed and may fail sooner then the old ones, the 13s 5p route is the way to go as the cells are all the same age and from the same batch/year manufacture.

 

[bikemerchant]

Hopefully the work will be done in the next week.
Looking for a new rear rack battery case to keep the back up battery in, does anyone know where I could source a case exactly like this one?
291.16￡ 25% OFF|EU No Tax Electric Bicycle eBike 48V 20Ah 250w 1500w Rear Rack Battery Bafang BBS01 BBS02 + Double Layer Luggage Carrier|Electric Bicycle Battery| - AliExpress

I already asked the seller on Aliexpress but they aren't much help.

Thanks.

 

[bikemerchant]

Guy repairing the battery has some other cells in stock;

"After checking my stock, I have sufficient amount of Panasonic NCR18650PF cells, but when measure internal space of battery case, I think I can also fit "Tesla" 21700 cells. At least 4 per bank, maybe 5 or even 6, but last option that's not very likely.
Each cell is rated 4800mAh, real capacity ~4700mAh.
That would make battery with 19.2Ah nominal (4p), 24Ah (5p) or maybe 28.8Ah as highest possible capacity."

Would there be a preference of either of the above?