My 14-C has died.....what went wrong!?

[HermanTheGerman]

8 hours ago, Marty Backe said:

I'd barely be able to ride my wheels if I limited myself to 50% battery range 

Maybe I'm playing a game of Russian Roulette, but I regularly ride my wheels down to 25%, and periodically to 10% - 15%. No problems so far - knock on wood.

I suppose you could avoid dropping to 10%, but I think 50% is being unnecessarily conservative. Probably 20% is a good middle ground for those concerned.

I'm probably an outlier in this regards, but my view is to enjoy the wheels. Use them. Don't let the pursuit of extended lifetimes limit the enjoyment of the wheel.

I can't agree more.

In the 15 months I ride my KS16 now I often rode it down to 10%, sometimes even to 3%.  I assume that this is between 15% to 25% of the REAL battery capacity. I never had any problems with the batteries until now.

[Marty Backe]

1 hour ago, Keith said:

Marty is absolutely right and as @Chriull has said above 10% isn't usually 10%, most wheels will have a quite conservative low voltage alarm so 10% is often more like 30% in reality. Some like the IPS wheels monitor individual cell voltages and alarm on the lowest cell - it is a great pity more do not do that.

However there is a huge difference in driving down to 10% because you are on a long ride and deliberately running the wheel down because you have heard a dumb rumour that it will improve the battery. Do not also forget that it is a low voltage alarm, if the wheel is ridden very slowly or left on to flatten itself you will pull the battery down way way lower than if it is ridden normally down to 10%.

However I do know that later KS-14C's had their low voltage cut off lowered right down to (I think it might have been 48V?) On mine it is 55 volts so my range is terrible, and I know I can safely flatten it to 0% as that is still 55V on the pack.

Very interesting. I didn't understand the relationship between the wheel battery notifications and the actual battery condition. Good to know that even at 10% I'm not really stressing the batteries. But 90%+ of the time I'm done riding by ~25%.

Another reason I love the large battery capacities of Gotway wheels. You rarely drain the batteries, even on long rides.

[Chriull]

10 minutes ago, Marty Backe said:

Very interesting. I didn't understand the relationship between the wheel battery notifications and the actual battery condition. Good to know that even at 10% I'm not really stressing the batteries. But 90%+ of the time I'm done riding by ~25%.

Another reason I love the large battery capacities of Gotway wheels. You rarely drain the batteries, even on long rides.

For 67,2V Gotways @JumpMaster had 52,9V for 0% and 65,8V for 100% decoded in Wheellog - seems to be what GW ?uses/used?

This 0% shown at 52,9V are 3,3V per cell.

"Most mobile phones, laptops and other portable devices turn off when the lithium-ion battery reaches 3.00V/cell on discharge. At this point the battery has about 5 percent capacity left. Manufacturers choose this voltage threshold to preserve some energy for housekeeping, as well as to reduce battery stress and allow for some self-discharge if the battery is not immediately recharged. This grace period in empty state can last several months until self-discharge lowers the voltage of Li-ion to about 2.50V/cell, at which point the protection circuit opens and most packs become unserviceable with a regular charger. ( See BU-808a: How to awaken Sleeping Li-ion )

Power tools and medical devices drawing high current tend to push the battery voltage to an early cut-off prematurely. This is especially apparent at cold temperatures and in cells with high internal resistance. These batteries may still have ample capacity left after the cutoff; discharging them with a battery analyzer at a moderate load will often give a residual capacity of 30 percent.
...
To prevent triggering premature cutoff at a high load or cold temperature, some device manufacturers may lower the end-of-discharge voltage. Li-ion in a power tool may discharge the battery to 2.70V/cell instead of 3.00C/cell;"
(from http://batteryuniversity.com/learn/article/premature_voltage_cut_off )
and
"To get accurate readings, the battery needs to rest in the open circuit state for at least four hours;"

[Keith]

On 29/08/2017 at 9:43 AM, Chriull said:

Most mobile phones, laptops and other portable devices turn off when the lithium-ion battery reaches 3.00V/cell on discharge. At this point the battery has about 5 percent capacity left. Manufacturers choose this voltage threshold to preserve some energy for housekeeping, as well as to reduce battery stress and allow for some self-discharge if the battery is not immediately recharged. This grace period in empty state can last several months until self-discharge lowers the voltage of Li-ion to about 2.50V/cell, at which point the protection circuit opens and most packs become unserviceable with a regular charger. ( See BU-808a: How to awaken Sleeping Li-ion )

"To get accurate readings, the battery needs to rest in the open circuit state for at least four hours;"

This is why this is nothing like an exact science. When above you say:"3.00V/cell on discharge. At this point the battery has about 5 percent capacity left" you are talking about under an average power loading from that phone. If you measure the Open Circuit Voltage (OCV) then there is virtually nothing left at 3 volts and it takes very little current draw to drag that down to the 1.5V point that will do permanent harm see the Texas Instruments graph below of OCV versus capacity (SOC=State of Charge)

Batteries have significant internal resistance so under load a significant part of the voltage drop is due to that resistance, so how low your wheel says your battery capacity is rather depends upon how much current you are pulling out of it.

Since parallel packs reduce the net internal resistance then a bigger battery pack will read a higher voltage under load for a given state of charge than a smaller pack. And by the way, phones and other consumer electronics, including 18650 cells used for torches and Vaping come with a protection circuit built into the battery or individual cells which will shut the cell off to prevent under voltage. Those cells would be dangerous in an EUC. 

Since we are in the habit of disabling BMS output protection (where it does exist) as being potentially a faceplant waiting to happen and since, with the exception of those few wheels with additional signalling wires from the battery to the main board, on most of the others the main board can only monitor the battery's output voltage so will not see a single cell being low, it is safe to say we do not have any such protection on most of our batteries. Ironically we do have BMS charge protection circuitry, so it is possible that the BMS might prevent charging if a cell or cells has/have got too low despite being unable to prevent them getting that low in the first place.