Question Understanding battery pack math

[tbone1004]

@stuartv since you posted all of the BMS configs, and kudos to @Jon Nellis to leaving all of that unlocked on the BMS since the users may have different cells than what shipped from him! Also interesting that it has a cycling capacity so the SoC is based on leaving a bit of buffer on the end, great choice to have so when you hit 0 you still have a floor below it and don't risk serious damage to the cells when you hit 0.

Since you have a programmable charger. Depending on what you're trying to prioritize, since the balancing starts at 4v/cell and it's marked at 4v=80% then I would do my mid trip charges to 4*18=72v for maximum cycles and only use the 74v for a pre-trip charge or if you see the cells are out of balance, so say 0.1v of a gap from the highest to the lowest cell which will trigger the top balancing. I would personally never charge more than 74v since balancing starts at 72v.

 

[stuartv]

@stuartv since you posted all of the BMS configs, and kudos to @Jon Nellis to leaving all of that unlocked on the BMS since the users may have different cells than what shipped from him! Also interesting that it has a cycling capacity so the SoC is based on leaving a bit of buffer on the end, great choice to have so when you hit 0 you still have a floor below it and don't risk serious damage to the cells when you hit 0.

Since you have a programmable charger. Depending on what you're trying to prioritize, since the balancing starts at 4v/cell and it's marked at 4v=80% then I would do my mid trip charges to 4*18=72v for maximum cycles and only use the 74v for a pre-trip charge or if you see the cells are out of balance, so say 0.1v of a gap from the highest to the lowest cell which will trigger the top balancing. I would personally never charge more than 74v since balancing starts at 72v.

The Genesis manual says to give it a partial charge to bring it into the range of 62V to 67V.

So, I have programmed my charger to charge it to 67V by default. I had the impression that 67V is the 80% value.

What you are saying and charging it to 72V (and that 72V is 80%) certainly makes sense. So now I am unclear on what I should be doing.

Do I need 3 charging profiles?

Charge to 67V for storage?
Charge to 72V for normal use where I know I won't need full capacity?
Charge to 74.8V when I want/need a full charge?

 

[Jon Nellis]

Don't try out-thinking the battery, especially with limited understanding.

1. Charge it FULLY before diving, you never know what you might need. (Do you only fill your breathing gas to 80% if you don't plan on using it all?)

2. If it is much below 62V at the end of diving AND you are not going to use it for a couple weeks, give it a partial charge to ANYWHERE between 62V an 67V.

3. Do something better with your time than worrying about a couple volts here or there, that really don't matter. For example, you could spend you time researching how batteries work and the factors that affect them, to build your understanding and knowledge base, so you don't have to ask random people on the internet what they think you should do, after the manual already told you the only two things you really needed to know. ...or you could go get a nice slice of cake.

 

[tbone1004]

Don't try out-thinking the battery, especially with limited understanding.

1. Charge it FULLY before diving, you never know what you might need. (Do you only fill your breathing gas to 80% if you don't plan on using it all?)

2. If it is much below 62V at the end of diving AND you are not going to use it for a couple weeks, give it a partial charge to ANYWHERE between 62V an 67V.

3. Do something better with your time than worrying about a couple volts here or there, that really don't matter. For example, you could spend you time researching how batteries work and the factors that affect them, to build your understanding and knowledge base, so you don't have to ask random people on the internet what they think you should do, after the manual already told you the only two things you really needed to know. ...or you could go get a nice slice of cake.

and 4. be grateful that you have a manufacturer that actually understands batteries and is willing to use the manual to teach you best practices instead of some of the others that give you very useless information