Total pack voltage vs Average cell voltage preference

I am wondering your preference when reading voltage of your pack. Would you rather see your total pack voltage or average cell voltage.

For example, total pack for a 12s setup would be something like 47 volts.
Average individual cell voltage would be 47 /12 = 3.92 volts.

Select two options, one of the top three and one of the bottom three.

With the bottom three options this is if you need to convert your pack voltage to individual cell voltage to determine your state of charge. So if you see the value 47 volts on a 12s setup, do you need to convert it to 3.92 volts or are you comfortable with 47 volts and do not need to convert in your head to 3.92 volts.

For a quick reference I use total pack voltage, such as if I want to see how charged a battery is after it's been sitting around without use for a few days. When I want to know pack health, thats when I go to cell voltage. Mostly for me though its just easier to think in pack voltage.

if you charge a 12S pack to 47V without a BMS then you have overcharged many cells severely. unless the cells are balanced all the time there can be up to25% variation in capacity. measured pack voltage on a charged pack does not tell you anything about the state of charge. the cell can be full but resting voltage drops to 3.35V.

I sure hope you guys are talking LiPO not LiFePo.
3.95 is low for LiPo and high For LiFe.

I go by pack voltage most of the time, check cell voltage afetr a ride to see how well balanced.
Balance charge as needed, which seems to be not often.
21/2 years on my LiPo with great luck.

Dan

Cell voltage, but you already know that
As I get used to my 24s lifepo4 pack, I know that 80v+ is really good. But no idea what 70 or 65 means :-(
You should highlight 'while riding' because other ways you won't stop the charging discussion. But that's why I use cellllogs together with my BMS to monitor charging. Still more interested in the cell voltage than in the pack voltage though.

dnmun said:

measured pack voltage on a charged pack does not tell you anything about the state of charge.

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That's why I said I use pack voltage to determine a pack's state of charge, i.e. if it's charged or not.

Measuring pack voltage gives you an approximation of battery charge percent. I worked for a while in an ebike shop and sometimes I'd take one of the bikes to run an errand or drive home. Measuring the pack voltage would tell me whether or not the battery was full enough to take on a trip or if I should grab another battery. For example, a 16s LiFePO4 pack reading 52.5V means I shouldn't have a problem on the 10 mile round trip home and back. On a bike with a 49V or 50V reading, I'd be more hesitant to take such a depleted battery and instead I'd swap it out. Without checking the pack voltage, I can't approximate the state of charge of a random pack.

I use both but if I could only have one it would be lowest-to-highest individual cell voltage.

Pack voltages can be very deceiving and offer incomplete picture with regard to potential cell damage IMO.

Ykick said:

....Pack voltages can be very deceiving and offer incomplete picture with regard to potential cell damage IMO.

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The same goes for average cell voltage. The OP apparently doesn't even know the nominal voltage of his pack, and should definitely stick with a proper BMS protecting his packs. The new CA3 has a fuel gauge based on the capacity of the pack you input and the amount you have consumed. Just reset after each charge and you're golden. I program mine with 80% of actual capacity of my minimum cell group, so if the gauge gets to zero I still have good cushion. Conservative DOD's and big packs make ebike life so much easier, and batteries last far longer too.

John

How do you figure I do not know nominal voltage? Did i write anywhere that nominal voltage was not 3.7?

Also pack voltage with regard to individual cell voltages is very reliable if you stay above 3.7 volts especially if you have your packs paralled as a cell which is falling low will be charged by another.

Of course you can have an exception which is very rare but that is why you manually check your voltages after every ride.

This post also has nothing to do with average cell voltage vs actual cell voltage as it is obvious average cell is only an estimation. An estimation that is just as reliable as pack voltage as we have nothing yet to monitor individual cell voltages

I personally like to keep it simple at think of my state of charge as a per cell number as to me it is much easier and simple especially when using different pack voltages. My rc charger also uses per cell voltage.

Also amp hour to me is asking for alot of trouble because what if you did not charge your pack fully and forgot. You have to always use voltage to be safe. Hoever I Still use amp hours as a rough estimate while driving and always secondary to voltage.

But for me 4.0 volts means alot more to me then 72 volts when quickly looking at my volt guage.

For people who come from an rc background and always use per cell voltages especially when charging it is just much easier for us to use per cell voltages. It is like trying to use kph when you always used mph. It will always be easier for us to use mph and make estimations with mph.

KISS.

Nobody is saying average volt per cell is 100% acurate. But for me it is much easier to keep everything standardized using per cell value.