Overcharging?

[Beekeeper]

In the Bosch system the cells are in blocks of 4
Each block will be balanced by the BMS.
Cells within each block are self-balanced as they are arranged in parallel

 

[KennyB]

I think the charger helps too. When it gets to 100%, it switches off (the light goes to green) and all the charging lights on the bike battery go out. So, it is not pushing power in all the time

I think in the Levo, the battery itself contains the BMS. This is where the firmware is.

 

[Planemo]

In the Bosch system the cells are in blocks of 4
Each block will be balanced by the BMS.
Cells within each block are self-balanced as they are arranged in parallel

So a 4P system then, cheers. Do you know if the system can balance throughout charging or only towards the end?

Each string will self-balance only as long as they are all healthy. Get a duff cell and it will take the other 3 out, but I guess the pack would need a complete strip down either way.

 

[Planemo]

I think in the Levo, the battery itself contains the BMS. This is where the firmware is.

The BMS is nearly always in the pack with the cells, but theres definately communication between the charger and the BMS with Bosch (good) unlike many systems where the charger is 'dumb' and simply carries on pumping out (albeit at a low current) when the pack is fully charged (bad).

 

[KennyB]

The BMS is nearly always in the pack with the cells, but theres definately communication between the charger and the BMS with Bosch (good) unlike many systems where the charger is 'dumb' and simply carries on pumping out (albeit at a low current) when the pack is fully charged (bad).

Butt the charging lights on the battery go out, and the light on the charger goes green, just as alan_sh described, and attributed to the charger. What I'm wondering is if the Levo battery instructs the charger to stop "pumping out".

 

[Planemo]

Yes thats exactly what happens. The BMS holds all the cards, and instructs the charger to shut down under various circumstances. The pack voltage being maxed (some multiple of about 4.25v - usually 42.5v) being just one of them. I wouldn't be surprised if there was a temp probe (or more) on the BMS/pack somewhere as well. These could also trigger a shutdown to the charger. A string of cells going out of balance would be another. This manifests itself to the user by the charger shutting off earlier than expected, or the pack not taking as long to charge as it used to.

Cheaper systems (think your common garden cheap chinese hub drives) don't have this communication with the charger and so even when the charger light is green (triggered when charger current goes below a certain threshold - usually around 150ma), the 150ma is indeed still flowing. It's not a lot, but its enough to send the cells over 4.25v if left long enough, causing irreparable damage.

I would wager that all big brand, high end emtbs use a comm system, but that doesn't mean they all balance throughout charging, which was the main point I was trying to make. If they don't, partial charging is a no-no.

 

[taxidriver50005]

Recently just upgraded controller to Kiox system from purion and noticed when controller says battery is 100% it keeps on charging for maybe another 30 minutes....this can vary but when I had purion this display just showed the battery bars flashing and I assumed it just took ages to charge to the last couple of percent, I can assume this has been balancing at the end of it's charge cycle.
Strange how manufacturers don't give any info on how much to charge too or in Bosch case any way of setting the charge limit, I can only assume they feel it's safe to fully charge or we assume it's fully charged and bms is setting safe limits for battery.

 

[Old Mike]

Yes, given that most bms' dont engage the balancing resistors until 4v at the earliest. Which is around 90%. The last 10% is where nearly all of the balancing occurs.

So by your reasoning that implies charging to 80%, that everyone thinks is good for batteries, is actually bad for batteries...

 

[apac]

So by your reasoning that implies charging to 80%, that everyone thinks is good for batteries, is actually bad for batteries...

The battery will most Probably out live your bike So don't over think it. You need to charge to 100% fairly frequently as this is where the cells get balanced. The cell balancing only takes place at the very end of the charging process when the first cells reach 4.2v If you only charge to 80% every time then eventually the cells will go out of balance. balancing can only be done on cells that have a very very small difference in voltage and once outside a certain window such as 0.050v (yes that Small a difference) the bms becomes useless at rebalancing the pack.

 

[apac]

So by your reasoning that implies charging to 80%, that everyone thinks is good for batteries, is actually bad for batteries...

The battery management system usually 'bleeds off' a min-ute amount Of excess voltage off the highest cells. This can take hours or even days. Once the difference between high and low cell voltages becomes too large then the bms can do nothing. the difference between high and low for the bms to do it’s job is actually a tiny amount. As said above it's probably only about 0.050v or maybe a little higher.... 0.1v at the most.
If balancing is not done regularly the cells begin to drift apart and the bms can do nothing about it as the cell voltage differences are too wide apart…. Even though they are still quite close to each other?

 

[apac]

Cell drift happens because cells can have different internal resistance which means they charge and discharge at different rates from each other. It just takes one rogue cell in a pack of 50 and there will be a problem.

 

[apac]

So by your reasoning that implies charging to 80%, that everyone thinks is good for batteries, is actually bad for batteries...

Its better for the longevity of the cells but not good in the long run when you have many cells strung together in series and parallel

 

[apac]

You battery pack is only as good as the weakest cell.

 

[taxidriver50005]

You battery pack is only as good as the weakest cell.

Totally get what you saying BUT the likes of Toyota hybrid batteries only charge to 80% and are guaranteed for I think now 15years

 

[The EMF]

??? so much info……can’t take it all in……..I’m of to ride my Great Whyte ???

 

[Old Mike]

Its better for the longevity of the cells but not good in the long run when you have many cells strung together in series and parallel

Longevity IS the long run. Thats literally what it means.

 

[apac]

Car manufacturers use completely different systems to bikes. You cannot compare the two.

 

[apac]

Longevity IS the long run. Thats literally what it means.
[/QUOTE

Longevity IS the long run. Thats literally what it means.

Carry on charging your pack to 80%. You may get lucky and it will never get out of balance. I’ve built a number of large battery packs over the last10 years and have monitored bms’s with analytical devices and cells go out of balance eventually if not kept in balance. It usually when charging. They can sometimes re equalise when discharging But in the end they drift.

 

[Planemo]

So by your reasoning that implies charging to 80%, that everyone thinks is good for batteries, is actually bad for batteries...

Yes.

Not unless you are confident that your charging system is sophisticated enough to balance throughout charging, as I mentioned previously.

Most non-car (or cheaper, smaller) systems only balance at the END of the main charge process. As apac says, it's mainly cars which run sophisticated systems. Primarily because partial charging is highly likely to occur (and necessary) on a regular basis, but also due to the sheer cost of replacing a pack if it goes out of balance.

Alternatively, charge to whatever you want if you only have one cell (a mobile phone for example). But theres no ebike that I know of with just one cell

 

[Planemo]

Recently just upgraded controller to Kiox system from purion and noticed when controller says battery is 100% it keeps on charging for maybe another 30 minutes....

This is exactly what I would expect to see. Green lights on chargers usually trigger when the output current has dropped to a pre-determined level (say 150mA). This is set within the charger. It's basic to say the least. This doesn't mean the battery is balanced, it just means that the cells are getting pretty full. It then takes further time for the cells to balance and 'top off'. This can take between 30mins and 2 hours depending on how unbalanced the cells are. If they are particularly unbalanced you're stuffed, because as soon as one cell hits the over voltage limit (usually 4.25v) the BMS will shut down all current input, leaving any unbalanced cells...well...unbalanced. The charger will still show a green light though.

On my Bosch system, I don't have a choice of extending charge time after a green light, firstly because there isn't a light on my charger (or I haven't seen it) but also because the system shuts itself down anyway. So I don't have the option to 'extend charge time to balance'. I suspect (hope) that the system won't shut down until this occurs anyway though so I'm not too fussed.

 

[Ducman71]

@apac @Planemo Great comments on cell balancing above, thank you. Hypothetical real world situation... You come back from a ride with 35% SOC remaining, and you won't ride again for perhaps 1-2 weeks. Do you:
a) Leave it at 35% and just fully charge the night before the next ride.
b) Charge it fully when you get back and let it sit at 100% until the next ride.
c) Partially charge to 70%-80% when you get back, then charge to 100% the night before the next ride.
d) None of the above; something different entirely.

 

[Coolcmsc]

@apac @Planemo Great comments on cell balancing above, thank you. Hypothetical real world situation... You come back from a ride with 35% SOC remaining, and you won't ride again for perhaps 1-2 weeks. Do you:
a) Leave it at 35% and just fully charge the night before the next ride.
b) Charge it fully when you get back and let it sit at 100% until the next ride.
c) Partially charge to 70%-80% when you get back, then charge to 100% the night before the next ride.
d) None of the above; something different entirely.

a)

 

[Coolcmsc]

Just found this excellent thread ?
The message seems clear to me and it fits with reality too.
I do get out regularly and never less than once a week. And, more importantly, I never know how long my ride will be so thankfully, charging to 100% is real world and, overall, the best techy approach too.
Ride more and ponder less I say ?

 

[alan_sh]

I probably do it all wrong, but I ride, get back, put it on charge, leave it. Next ride, take it off charge and off O go.

Alan

 

[Planemo]

@apac @Planemo Great comments on cell balancing above, thank you. Hypothetical real world situation... You come back from a ride with 35% SOC remaining, and you won't ride again for perhaps 1-2 weeks. Do you:
a) Leave it at 35% and just fully charge the night before the next ride.
b) Charge it fully when you get back and let it sit at 100% until the next ride.
c) Partially charge to 70%-80% when you get back, then charge to 100% the night before the next ride.
d) None of the above; something different entirely.

a) would be fine. In an ideal world though, you would do c) albeit to 50~60% rather than 80% which is a bit high for a storage charge.

I would do a) though. Unless the bike wasn't going to be used for months (I am not a winter rider lol) where I would partial to 50~60%.

 

[Ducman71]

Ride more and ponder less I say

Totally agree. I've got a variety of bikes waiting for me every opportunity I do have to ride though, so the eMTB can't get all of the attention Having a simple, no-nonsense protocol for charging it makes it easy to ponder less about when and where I should choose to ride it.