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Just got an 18XL - a question on charging


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Upgrading at my current skill level does feel a bit premature. But the May news on battery (and hence wheel) shortage made me nervous - what if I can't get a new wheel once having outgrown the mcm5, which is the plan? So, what the heck..

After reading a lot on bigger wheels, including @Seba's blog post on testing the V11, I ordered eunicycles.eu's last KS-18XL, @Seba's faithful workhorse. Smooth process, swift delivery, just arrived. First impression: Quality machine. Something to grow into, while still practicing on the Gotway.

Now for the question:
Instead of the standard 1.5A charger, I bought two fast 3.5A ones. Thought I'd charge with both of those (= 7A), controlled by EucW and an HS110. Not quite the 9A @Seba uses, but close :)

So - does routinely charging in this way make sense?

 

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There is no issue with charging faster than stock, even 10A is still less than the cells normal charging specs. (Circuits can get hot hence Sebas advice to stick to 9A max)

(edit: due to new info speed for extended life might be a bit lower, see bellow)

What you do have to watch out for is that balancing gets done properly. One simple way is to monitor the voltage while charging: it should go steadily up, then flatten out slowly when getting close to 84,4V (18XL tops out around there). When the voltage given by the wheel doesn't go any higher for a while (graph is flat), and also keeps that level (save 0,1-0,2v) when disconnecting, then the balancing should have been allowed.

Not all chargers are properly set for li-ion balancing, so I would suggest trying this at least once to make sure they behave as should. (Ideally they should cut after flattening out as well, but not essential if you dont leave them connected for extended periods of time. Beside this sometimes conflict with KS handling of the charge and go in a off on loop)

Edited by div
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1 hour ago, Eeyore said:

So - does routinely charging in this way make sense?

The ks18xl has a 20s6p 18650 cells with 3500mAh. ?NCR18650GA? Most have ~1.7A a as normal charging current specified - so 1.7*6=10.2A in total. So ~7A is still nice slow(er than normal) charging, especially as divided on two connectors.

1 hour ago, Eeyore said:

controlled by EucW and an HS110.

Great combination!

I'd recommend use "disable battery balancing" and "disconnect on finish".

"Disconnect on finish" stops once charger power consumption drops to about roughly 30W.

So  that's below (efficiency!) 30W/84V~360mA charging current threshold.

Li ion manufacturer specify a charge current threshold of some 67mA per cell for cut off. So about 67mA*6~400mA!

Not using "disable battery bakancing" would let the charger be active for ?1 hour? more - imho not necessary for balancing, just stressing a little bit more the cells: 

 

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12 minutes ago, div said:

Samsung INR18650-35E according to e-wheels, though your point remains. They even have 0.6c as normal current.

The datasheet show's some interesting detail:

3.5 Charging Current Standard charge: 1,700mA 
For cycle life : 1,020mA
...
3.7 Max. Charge Current 2,000mA (not for cycle life)

First time i have seen such a note.

... But still the 7A/6 cells = 1166mA are stull about the same as this 1020mA specified for the cycle life (500 cycles with >60% capacity)

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Interesting indeed, so the "healthy" recommendation is lower than the rated "normal" speed. (?)
I might have to reconsider my 18XLs 9A charging habits.

Edited by div
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I always use 7 - 9 A charging current when I'm on tour. Still, my battery is like new despite of wheel mileage of over 20 000 km (no noticeable capacity drop, no detectable battery misbalance etc.). But for overnight charging I use current between 1 A and 2.5 A, depending on batery state of charge and available time. When I arrive late evening and I'm planning to depart early morning, I set 2.5 A as a charging current. But when I have more time, I set lower current.

Also, we can't forget that every braking is a charging condition. Actually, every ride consists of a many discharge and recharge periods. Charging currents of 10 A and more are not uncommon during a regenerative braking.

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Thanks a lot for the replies! Now I'm confused on a higher level :)

Maybe I should order a standard charger after all, and use for overnight. Also, spending some time on Battery University, plus studying datasheets, probably wouldn't hurt.

Knolwedge is Power, ya know!! :smartass:  Should alleviate the gnawing feeling of having a potential firebomb in the house.... :unsure:

 

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6 hours ago, div said:

Not all chargers are properly set for li-ion balancing

Battery cell balancing is purely a BMS feature, and all that is required from the charger is that it gives out the correct voltage. BMS will handle the rest.

 

1 hour ago, Eeyore said:

Now I'm confused on a higher level :)

Like I recently wrote in another thread, battery care is something one can nerd over to no end. I like facts and practical experience:

I have seen dozens of reports on malfunctioning batteries that have turned out to be unusable and unsafe, only due to not letting the pack balance properly.

OTOH, I haven’t seen a single rider reporting an issue that is caused purely by premature cell wear or aging.

 Therefore I see no reason to recommend steps that intend to extend battery life.

 Even without optimal care, the EUC battery packs will take the 18XL to 30000km before capacity is expected to have reached 70%. With optimal care this can extend to 60000-90000km.

Which has more value to you: To have 10% more range after 30000km, or not having to jump through hoops every time you charge the wheel?

 

1 hour ago, Eeyore said:

Also, spending some time on Battery University, plus studying datasheets, probably wouldn't hurt.

Great site. Just remember that recommendations for charging a single cell can’t always be directly transfered to a huge battery pack with 20 cells in series. EUC is an exceptional use case for li-ion cells. Be aware of the exceptions.

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51 minutes ago, mrelwood said:

Battery cell balancing is purely a BMS feature, and all that is required from the charger is that it gives out the correct voltage. BMS will handle the rest.

Yes, that’s why my previous sentence mentioned that the balancing should have been allowed, implying that the charger didn’t do the balancing but permitted the BMS to do it: by providing the correct voltage, but also by tapering out the amperage (CV phase). Not all chargers are properly set up to allow li-ion balancing, the fairly common JR-T450 have illustrated that.

I don’t see the point of picking a sentence and use the wording to find a way of talking down to me. Had you read my content you could have understood that I do have an idea of how charging and balancing work.

OP is seeking fairly generic info, I’m not going to write a book of details or formulate my sentences so they are bomb proof against snark.

Edited by div
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58 minutes ago, mrelwood said:

Which has more value to you: To have 10% more range after 30000km, or not having to jump through hoops every time you charge the wheel?

 

The latter, definitely. Thanks for this.

In the "another thread", you said -

Quote

Charging the 18XL at 10A, the highest current the charging connector allows, still charges at under 0.5C per cell. This is already much less than the recommended 0.8C “to extend battery life”. Charging the wheel at lower than 5A offers no benefits at all. [My bolding]

Guess I'll take that as to skip the 1.5A standard charger and go with 7A from the two "fast" ones, via EucW/HS110 (?)

 

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14 hours ago, div said:

Yes, that’s why my previous sentence mentioned that the balancing should have been allowed, implying that the charger didn’t do the balancing but permitted the BMS to do it: by providing the correct voltage, but also by tapering out the amperage (CV phase). Not all chargers are properly set up to allow li-ion balancing, the fairly common JR-T450 have illustrated that.

I don’t see the point of picking a sentence and use the wording to find a way of talking down to me. Had you read my content you could have understood that I do have an idea of how charging and balancing work.

OP is seeking fairly generic info, I’m not going to write a book of details or formulate my sentences so they are bomb proof against snark.

That was sensitive. I’m sorry you took my post that way. It was definitely not intended. I wasn’t able to read your post the way you now described that it ought to have implied.

 If someone corrects any details that are wrong or misleading in a forum post, the intention is not to talk down to the original poster, but to correct any misunderstandings both for the poster as well as for everyone who will ever read the thread. To me it’s one of the great benefits of a public forum, that faulty information and bad tips get corrected. It’s not a contest or a fight about who knows better. 

 That was my intention, to help people understand how the “mysterious” balancing works. I’m sorry I read your wording wrong.

 

 Regarding the JR-T450 charger you mentioned, the charge log I found kept the voltage steadily at 67.43V (assuming a commonly exaggerating KS measurement) for 1 hour and 25 minutes before slowly starting to drop (due to the charger cutting off the charging). To me it sounds like it would allow most of the balancing to happen during the CV stage, just like any other charger that is capable to charge the battery to its full capacity. But I do need to read more about the charger in question.

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Sorry if I was overly sensitive, thank you for the comment.

The JR-T450 had early versions where it would go in a loop of stoping and starting at the end, probably due to surface tension and a cutoff set too early (longer threads about it on endless sphere under the name Luna).
I have also seen various charger behavior with KS wheels, mostly due to many chargers having a cyclic amperage for some reason, and when this gets close to zero, the 18XL will turn off and on, making CV phase stressful. Anyhow.. that’s why I mentioned to OP to check if that part went well. Will probably so considering he probably bought the eunucycle chargers set for KS.

Edited by div
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