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Defect battery again, what are the odds?


cg
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Today I used my wheel to get to the post office, that is a total distance of 1.2km...

Just before I had charged the wheel. After the trip, which was quite slow and relaxed, the wheel only showed 50% battery... and it had shaken a few times...

What are the odds of this:

20151003_005.thumb.jpg.3d09302a3862c4e75

I had planned to replace the green battery which is salvaged from a laptop when the original battery died, but now another dead battery... good I have two new batteries :)

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If the batteries are from the same manufacturing lot, I think the odds are pretty good that several may go bad if one or two have already done that. Might as well nurse it along though, as long as they don't explode or something. 

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Those seem to be some cheap chinese cells, the quality apparently isn't very high if you've already had two cells die on you. Didn't find much information them, except this:

18650 LR 1865 SI 3.6V 2200 mAh 1C / 2C 

Guess the 1C / 2C means either maximum charge / discharge -ratings, or continuous discharge / pulse discharge, a bit lowish? Considering quality cells between 2.9-3.5Ah are typically rated to around 10A continuous / 20A pulse max (about 3C / 6C), some even 30A pulse. Maybe time to get a better battery? ;)

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As I allready told on another post, I bought a Charge Doctor from a french electronicai wheeler. It indicates the load (Wh) you take along the charge, so, if you have completely emptied your battery before, it should indicate at the end the capacity the battery is sold for. (Mine is 284 Wh for 264 Wh sold, I am happy…). It also indicates the voltage along loading and the max voltage you obtain, which should be around  67,.. Volts. If you don't obtain that, your battery has someting wrong, probably a bad element like cg shows...

Edited by Maxime
difficult to understand
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Those seem to be some cheap chinese cells, the quality apparently isn't very high if you've already had two cells die on you. Didn't find much information them, except this:

18650 LR 1865 SI 3.6V 2200 mAh 1C / 2C 

Guess the 1C / 2C means either maximum charge / discharge -ratings, or continuous discharge / pulse discharge, a bit lowish? Considering quality cells between 2.9-3.5Ah are typically rated to around 10A continuous / 20A pulse max (about 3C / 6C), some even 30A pulse. Maybe time to get a better battery? ;)

yes, and the motor is 350W... so

350W/16batteries= 21.9 (W / battery)

=>25.9(W / battery) / 4V = 5.4A / battery

And I seem to remember, 1C means 'using the capacity in one hour' and

2.2Ah in the battery at 2C => 4.4A....

 

Is this how it should be calculated, if so the battery load at continous? output is 5.4A/4.4A = 125%

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yes, and the motor is 350W... so

350W/16batteries= 21.9 (W / battery)

=>25.9(W / battery) / 4V = 5.4A / battery

And I seem to remember, 1C means 'using the capacity in one hour' and

2.2Ah in the battery at 2C => 4.4A....

 

Is this how it should be calculated, if so the battery load at continous? output is 5.4A/4.4A = 125%

Forget about the motor rated wattage for a second, you'll be drawing 500-2500W during hill climbs and due to voltage sag, the voltage per cell is not going to be near 4V even at full battery. If the voltage could stay at 60V, 500-2500W would be around 8-40A, except since the voltage sags, it will be more, despite what the motor is rated for, and during braking, you'll be charging the batteries at beyond 20A momentarily. Just because the motor is rated at 350W, it doesn't mean there is anything preventing the motor driver from pushing way more wattage into it. 

Repeat a lot and continue for longer time, and apparently cells with that low ratings start to give in. The motors seem to be able to handle it, as the peaks are usually fairly short-lived (unless you climb long hills), during a longer recording, even though there were discharge spikes of 2kW and similar negative regenerative spikes, the average over the total trip was around 270-280W.

This is the graph of a steep hill climb (10-25 degrees = 17%-45% grade) with vee's MCM2s (500W/1500W motor):

Mh2LXU5.png

Power is the red graph, values are on right-hand axis (hitting 2.6kW), everything else uses left-hand axis (current hitting around 45A during a peak).  During the steepest part, my speed is around 7-9km/h. I've personally ridden that up with my 350W generic and Firewheel also. If going at even slower speed, it does use less energy,  but still probably closer to 2kW or even above at peaks. It just means the battery & motor are used beyond their rated capacities during climbs. ;)

 

 

Edited by esaj
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Are those solder-blobs, I can detect on the injured cells? If positive, the odds are very good of them going bad. Spotwelding is the way. If You live in the Copenhagen Area, like I do, I could weld a couple of strips on new cells. But this board is maybe not worth saving?

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Forget about the motor rated wattage for a second, you'll be drawing 500-2500W during hill climbs and due to voltage sag, the voltage per cell is not going to be near 4V even at full battery. If the voltage could stay at 60V, 500-2500W would be around 8-40A, except since the voltage sags, it will be more, despite what the motor is rated for, and during braking, you'll be charging the batteries at beyond 20A momentarily. Just because the motor is rated at 350W, it doesn't mean there is anything preventing the motor driver from pushing way more wattage into it. 

Repeat a lot and continue for longer time, and apparently cells with that low ratings start to give in. The motors seem to be able to handle it, as the peaks are usually fairly short-lived (unless you climb long hills), during a longer recording, even though there were discharge spikes of 2kW and similar negative regenerative spikes, the average over the total trip was around 270-280W.

This is the graph of a steep hill climb (10-25 degrees = 17%-45% grade) with vee's MCM2s (500W/1500W motor):

Mh2LXU5.png

Power is the red graph, values are on right-hand axis (hitting 2.6kW), everything else uses left-hand axis (current hitting around 45A during a peak).  During the steepest part, my speed is around 7-9km/h. I've personally ridden that up with my 350W generic and Firewheel also. If going at even slower speed, it does use less energy,  but still probably closer to 2kW or even above at peaks. It just means the battery & motor are used beyond their rated capacities during climbs. ;)

 

 

damn, from that graph it look like going straight uses more than 350W :/

Are those solder-blobs, I can detect on the injured cells? If positive, the odds are very good of them going bad. Spotwelding is the way. If You live in the Copenhagen Area, like I do, I could weld a couple of strips on new cells. But this board is maybe not worth saving?

That is a very nice offer @OleTC, and yes, it is soldering blobs, but on the dead battery, the soldering was not done directly on the battery, but on the old strip, so I am not sure that is the problem. The new batteries I have purchased,

20151004_003.thumb.jpg.3f06e67399feec0c9

are already with soldering strips on, but they batteries also need to be soldered to the board, so perhaps an additional strip.

another thing, I was looking a bit more on the board today, and wondering about the apparent voltage balancing there is supposed to be going on when charging, but I'm not really that can happen with this board...

My doubt is caused by the fact that all 8 battereis on each side are connected in  serial...20151003_005.thumb.jpg.3d09302a3862c4e75

but if I flip the board, only some of the terminal on the batteries seems to be connected... (the purple are connected, the green are floating)

20151004_005.thumb.jpg.329d9e479b4003bc3

How can the batteries be balanced by this? Perhaps it is double layered...

 

since I don't have a charger/discharger, I am in the process if discharging the batteries to the same level as my new batteries ˝3.65V.... when this is done I will remove the batteries and see what's on the other side of the print.

 

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damn, from that graph it look like going straight uses more than 350W :/

That is a very nice offer @OleTC, and yes, it is soldering blobs, but on the dead battery, the soldering was not done directly on the battery, but on the old strip, so I am not sure that is the problem. The new batteries I have purchased,

20151004_003.thumb.jpg.3f06e67399feec0c9

are already with soldering strips on, but they batteries also need to be soldered to the board, so perhaps an additional strip.

another thing, I was looking a bit more on the board today, and wondering about the apparent voltage balancing there is supposed to be going on when charging, but I'm not really that can happen with this board...

My doubt is caused by the fact that all 8 battereis on each side are connected in  serial...

but if I flip the board, only some of the terminal on the batteries seems to be connected... (the purple are connected, the green are floating)

20151004_005.thumb.jpg.329d9e479b4003bc3

How can the batteries be balanced by this? Perhaps it is double layered...

 

since I don't have a charger/discharger, I am in the process if discharging the batteries to the same level as my new batteries ˝3.65V.... when this is done I will remove the batteries and see what's on the other side of the print.

 

All the tabs should be soldered to the board. I just did that on my new, assembled packet.

They seem to be soldered though when I look at Your Picture. Not a really clear Picture, though.

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All the tabs should be soldered to the board. I just did that on my new, assembled packet.

They seem to be soldered though when I look at Your Picture. Not a really clear Picture, though.

yep the batteries are soldered to the board, but as noted, I still doubt the board will do any balancing since most of the batteries doesn't seem to be connected to anything...

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Personally I would check it up completely, so every battery is connected.  Or discard the whole thing. Maybe the BMS board could be reused...

hmm but what should i connect the batteries to? my question concerns the circuit layout. where it seems the circuit layout is such that the batteries are not connected... anyway, I still haven't desoldered the batteries since they aren't discharged, so I guess we will know when I turn desolder and turn the print ;)

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  • 2 years later...
On 10/3/2015 at 10:33 AM, cg said:

Today I used my wheel to get to the post office, that is a total distance of 1.2km...

Just before I had charged the wheel. After the trip, which was quite slow and relaxed, the wheel only showed 50% battery... and it had shaken a few times...

What are the odds of this:

20151003_005.thumb.jpg.3d09302a3862c4e75

I had planned to replace the green battery which is salvaged from a laptop when the original battery died, but now another dead battery... good I have two new batteries :)

CG... what amount of  amperes are you draining form those cells??
Lishen LR... are very good cells ..
and if you are removing them from a notebook battery... they are not copies... they are real lithium cells... 

from one (1) Lishen LR you can drain 1.8Amps constant current... they will warm a bit..when get below 3.5V ...
so you drain 1.5amp.. o r 1.6amp for do not ruin the chemistry of the lithium cell in hot summer days ...

if you put two (2) cells on parallel (sharing the load).... then you can put something that drain's 3 amps or 3.5 amp from that battery of two parallel cells without problem...

now in peaks you can take from one (1) of them ... 3 or 4 ampers .... maybe 5.... depending of how long and how often are those peaks..
and with two (2) cells on parallel.... you can take .. 7  o 8 ampers .... maybe 10 o 12 amps.... depending of how long and how often are those peaks

I use this cells for refurbish old cadmium (Ni-Cd) tools.... screwdrivers / drills /angular grinders .. and they really work very well...

You can use those in a range of 3V to 4.25V...
chargin over 4.25 it will last 0.01v on each recharging cicle... same if you discharge below 2.90V...

So.. keep in mind that if you are at 3.2V in 1.6amp... and apply a peak of 3 ampers or 4 ampers ... you will go below 2.5V during that peak...
damaging the cell while that peak is on... so you should cut the job to 3.4V or 3.5V in that cases...

Meaby you are demanding from them more ampers than they can give you...
and the internal welding in the positive peton is breaking down... (it works as a last fail safe... a kind of rudimentary fuse)
So... put more cells on parallel...
Or use high drain cells.. like this ones...
Samsung INR 30q .. 15Amps constant current.. » https://www.ebay.com/itm/262938237966 
Samsung INR 25R .. 25Amps constant current.. » https://www.ebay.com/itm/262964124594 
LG DBHG2 .. 30Amps constant current » https://www.ebay.com/itm/263021514938

Or meby the cells that are failing...
do not hold the same amount of charge that their partners...
and they are discharging to "zero" while the others not...

In this case .. recharge them independently to the same level... 4.25V if you can...
apply something that drain 1.6amp... (a car cigarette lighter resistor for example)
and check how much it sinking the voltage..
a cells in good conditions with 1.6Amp .. should go down from 4.25V to 4.15V...
4.18v ..4.17v is really good.. brand new.. (coming in from 4.25v)
4.10v .. 4.11v still good.. (coming in from 4.25v)
4.05v .. 4.04v is OK.. a bit Depleted.. but ok... 
if it goes below 4V .. you can not use it...

keep in mind that if you put in serie (adding the voltage) a cell that give you 4.18V under 1.6amp of drainng... with one that give you 4.05V...
when the one with 4.18v ..  reaching 3.2V and still works OK .... the 4.05v will already be really below 2.4v or 2.2v... and after one or two charging cycles... shee is death...

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I think that your issue of unbalanced cells which drop to 0V is the result of either a problem with the BMS or the charger. And it happened a few times around me that Chargers were not at 67-67,2V , as a result the battery was never properly balanced and when they get very unbalanced (more than 0,03V from my experience) it is very diffult to balance them because the BMS will stop the charge to protect overcharged cells).

I happened to balance again an Msuper 3 battery without unwrapping the batteries with a lot of patience. You need to leave the charger for several days, the bms will cut the charge each time cells reach the maximum and will try to dissipate some energy (long process). When the voltage drops sufficiently, the charge will restart.

However you will need to change the died cell before trying to balance the one already replaced. 

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