Fast Charging the S18

[FinRider]

I got myself a 84V5A fast charger and just tried it out.

The wheel charged to 83.5V at 4.95 A, then it slowly dropped off the amperage to 3,5A at 84V and then finally settled at 0.5-1.0A at 84.5V. 

It got to 84.2V really quick and then it took probably an hour more to get to the 84.5. It never stopped though, so I disconnected it at 84.5V, not sure if it is safe to go past that.

I never bothered to look how the wheel behaves on the stock charger, will do so after my ride tonight. It was weird though that it didn't stop charging?

 

[Chriull]

43 minutes ago, FinRider said:

not sure if it is safe to go past that

It is safe.

https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

The data sheet says standard charge is downto 50 mA. So end of charge should be about 0.15A for the 3p pack.

Batteryuniversity recommends ~3%C which would make about 0.45A charge current threshold.

51 minutes ago, FinRider said:

84.5V

Vootage measurement is not too accurate in this range. With "normal" voltmeters +/-0.5V or more are to be expected.

[FinRider]

2 hours ago, Chriull said:

It is safe.

https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

The data sheet says standard charge is downto 50 mA. So end of charge should be about 0.15A for the 3p pack.

Batteryuniversity recommends ~3%C which would make about 0.45A charge current threshold.

Vootage measurement is not too accurate in this range. With "normal" voltmeters +/-0.5V or more are to be expected.

Thanks for your input Chirull.

A small update. For full disclosure, I update the firmware to 2.06 before attaching the fast charger.

 I took the wheel out for a quick 20km spin, battery drained to 69% so range seems to hold fine although it was 3 degrees "warm" outside. I attached my stock charger to the wheel and let it "slow" charge to full. It has been charging for 2 hours now and the voltage is back up to 84.5V and the charge light just went off. It had been sitting at 0.5A charge rate for the last 30 minutes with the voltage at 84.5. Now that the charge light is green, the current rate is still showing as 0.3-0.4A --> is this the "trickle charge" that the wheel is accepting when balancing the cells? I will monitor it over the next few hours and report back my findings.

[Chriull]

3 hours ago, FinRider said:

Now that the charge light is green, the current rate is still showing as 0.3-0.4A --> is this the "trickle charge" that the wheel is accepting when balancing the cells?

Balancing starts about once constant current stops and constant voltage starts until end of charge...

[Planemo]

Agreed, balancing doesn't really stop until you see the amp draw stay steady. The steady state amp draw will vary between chargers, but the flatline is all you need to look for on all of them.

[FinRider]

ok, so here is what is happening now.

I left the charger on the wheel overnight. It has now been attached for a total of 13 hours. The voltage shows 83.8V and the current draw is 0.3A. This is probably the bluetooth connection that the wheel is keeping alive during the charge cycle. It is even active when switched off. 

Is there a way to force disconnect the BT when the wheel is on its off state?

[Chriull]

@FinRider - all this numbers are reported from the S18? Or has your charger some voltage/current display?

1 hour ago, FinRider said:

for a total of 13 hours. The voltage shows 83.8V and the current draw is 0.3A.

This sounds like BMS cut off inbetween (some cell overvoltage threshold reached)?

And after this charge stop the wheel seems not to shut off and drains battery.

1 hour ago, FinRider said:

Is there a way to force disconnect the BT when the wheel is on its off state?

Maybe https://forum.electricunicycle.org/topic/20300-end-of-charge-battery-drain-workarounds/  could be about this problem?

 

[resolin]

Hi

I´m think to prove to use a 15 A charger in my S18 only sometimes, it can be dangerous? it can damage the battery if I use it only sometimes?

Thanks

[Chriull]

5 hours ago, resolin said:

Hi

I´m think to prove to use a 15 A charger in my S18 only sometimes, it can be dangerous? it can damage the battery if I use it only sometimes?

Thanks

Yes.

3p manufacturer specified max charge current should be somewhere around 4.5A.

[Eucner]

10 hours ago, Chriull said:

3p manufacturer specified max charge current should be somewhere around 4.5A.

KS-S18 first batch had LG M50T cells which were prone to thermal runaway. Limited charge current will reduce the risk. Later models Samsung 50G cells should be fine with 14.55 A fast charging. The KS-S18 v2 is available with Molicel P42A cells. They are good up to 25.2 A fast charging. Would there be other limiting factors than cells?

[Chriull]

On 9/15/2023 at 11:53 AM, Eucner said:

Would there be other limiting factors than cells?

The plug, connectors, wiring, charge side protection and current measurement circuitry could impose current limits below this ~15 or 25A.