Confirmation of SOC vs. Voltage Chart

[WalterM6]

I have only put the charger to my BB HSKY 48v twice so far.
When the BMS disconnects the charger, the battery voltage makes it to 54.9v.
After sitting onernite the voltage drops to 54.5v.
It does not take much runtime to see that voltage drop to 53.5v., but it takes quite a bunch of use to drop much from there. Seems that, when I turn the battery on in the morning, it is always 53.0...... I can fun it around and eventually see a resting voltage in the 52.6-52.7 range, but sit overnite and it is 53.0 the next morning.

Charger is set to 58.4v......

The BMS should never shut off the charger except in a error condition. Your battery shutting off at 54.9V indicates that one of your batteries is overcharging and exceeding the max voltage of 3.75v/cell. This isn't a cause for alarm now but keep an eye on it to make sure the shut off voltage doesn't get any lower. Your batteries need top balancing but it may settle in as the onboard balance circuit does its job.

[Pat911]

Hi Walter,

We don’t know what the cell cut off voltage has been set to in the HSKY. It may be much lower than 3.75v.

I know when I manufacture a LiFePO4 pack I set the max protection voltage to 3.65v/cell and set the charger to 3.55v/cell. You will get less than 1% SOC increase by charging above 3.55v anyhow.

Cheers
Pat.

[WalterM6]

Well I don't know what's the best setting but I always tend to follow the manufacturers recommendations. That said you still see a lot of battery recalls like the recent LG recall so maybe they don't know either. At this point we are all learning.

[Pat911]

Absolute maximums are well documented, when you see a battery recall it’s most likely due to incorrect implementation of, or faulty operation of the BMS. Cells can fail, but it’s usually the BMS, either failing itself or causing failures in the cells.

Cheers
Pat.

[Volt_Ampere]

LG recall was due to a defect in the cells themselves.

[Tom47]

A followup: I normally don't do this as I charge after any 5 or more mile run. But I decided to see just how far I could dependably push it.

I made three runs of 14.12, 15.86 and 8.31 miles in three consecutive days. This totals to 38.29 miles. The ending SOC was 13.9.

My earlier calculations of a 1.46Ah per mile were accurate the first day only. The second day it was 1.59Ah per mile. The third day it was 1.79Ah per mile.

Thus confirms my choice of charging after every longer run. I need to be ready for whatever comes my way!

And also confirms a 35 mile range to 20% SOC, exactly what E.B. told me it would be.

[Volt_Ampere]

That is great range!

[Tom47]

Originally Posted by Volt_Ampere

That is great range!

Yes, I'm very pleased with it!

With my earlier logs of 1.42 to 1.46Ah per mile, with a 27 mile run of 1.42Ah
and a 21 mile run of 1.43Ah per mile, I thought I would be easily over 40 miles range. These were done in one continuous ride.

I now see the Ah "fuel gauge" is not linear and starts to drop off after 40 SOC or so. But I feel comfortable with 35 mile range.

I just finished an 8 mile run with 260 pounds of 11 and 12 year old grandsons on the back seat. My usage was 1.97Ah per mile with the added weight! The power was there just like when it was just the two of us. But the battery drain was much greater. We would get less than 25 miles to 20% SOC at that rate.

Actually, 8 miles keeping them interested was plenty! You know, "are we there yet?".