BMS and mppt victron not showing same voltage

[Tomthumb62]

Also, a question I've never seen replied to is, since both 14v and 14.4v mean 100% charge, will this 100% state stay longer if the battery is at 14.4v instead of 14v, when it's under load?

Not really. I forget the details, but at 14.0v, the battery is something like 98% full. It can take a long time to get that last 2% in, which isn’t really a great use of your solar production. If you had even a slightly bigger battery, you’d get more storage out of that solar production than the last 2%.

Also, once it hits whatever high point you’ve set it at, say 14.4v, and you remove the charging source, it’ll drop back down to about 13.4v fairly quickly. It’s STILL 100% full at 13.4v, it’s just now at its resting voltage. This assumes no or little loads.

 

[marcello]

Not really. I forget the details, but at 14.0v, the battery is something like 98% full. It can take a long time to get that last 2% in, which isn’t really a great use of your solar production. If you had even a slightly bigger battery, you’d get more storage out of that solar production than the last 2%.

Also, once it hits whatever high point you’ve set it at, say 14.4v, and you remove the charging source, it’ll drop back down to about 13.4v fairly quickly. It’s STILL 100% full at 13.4v, it’s just now at its resting voltage. This assumes no or little loads.

Thanks, I thought 14v was already 100%. In fact even 13.8 is 100% (I thought)
What voltage should I charge it to, to get 100%?

 

[740GLE]

I don’t care about getting every whr out of my battery, so I value low stress on the cells vs max storage.

I have it set for 14v and absobtion time of 2hr, this allows the cells to balance. My smart shunt says it gets to 100% because that’s who I programmed it to recognize a full battery. If I’m leaving a few AH on the table I won’t lose any sleep.

 

[marcello]

I have it set for 14v and absobtion time of 2hr, this allows the cells to balance.

Does it mean you have to not use the battery during 2 hours to let it balance ?

 

[Tomthumb62]

Thanks, I thought 14v was already 100%. In fact even 13.8 is 100% (I thought)
What voltage should I charge it to, to get 100%?

I know, it’s confusing.

Resting voltage is different than charging voltage.

A lifepo4 battery, resting for at least a few hours at 13.1V, with no loads or charging, is at approximately 40% SOC. In order for the battery to reach 100.000% complete charge, it needs to reach 14.6v and remain there for a certain amount of time. Once it goes into float charge or charging is removed, and all loads are off, it will settle out at approximately 13.3-13.4v. IT’S STILL FULLY CHARGED AT THIS POINT.

And yes, 13.8v is basically considered fully charged, but I think it’s something like 98-99%. If you look at two glasses of water and one is 98% full and the other is 100%, can you tell the difference without quality scientific measuring tools? I mean, can you tell by just looking at them? No. And in the real world, it just doesn’t matter. If a few watt hours are going to be life or death for you, then just make bigger battery bank. Add on another 100Ah and call it a day.

Also, the absorption time needed after the battery has reached its set full point (bulk or boost set to 13.8-14.6v) can sometimes be difficult to achieve on solar. To my limited knowledge, absorption needs to be about 15-90 minutes and the voltage is held at the set point as the amperage slowly and consistently reduces. If you have any passing clouds or what not affecting solar production, that will upset your absorption phase. How much this matters I don’t know.

What I do know is while lifepo4 C 12v CAN be charged to 14.6v, many on this forum don’t bother for a number of reasons. One being is the theory that charging to the top most voltage is stressful to the cells. Think about it. You have a suitcase that can hold 14.6 liters of clothing. You pack 14.0 liters and dang the thing is pretty full, it’s getting hard to pack any more in there. You then spend another hour packing in the last 0.6 liter and then when you try to zip up the suitcase (this is now the absorption phase), the thing is bulging and you might be a bit concerned about the stress being put on to the zipper.

I have my solar charge controller set for bulk (also known as boost on some devices) to 14.0v. I don’t need the extra few bits of juice and it’s theoretically a bit less stressful on the cells.

My shore charger I only use a couple times a week or less and I set it a bit stronger to 14.25v. An occasionally fuller charge is less stressful than daily. In theory.

 

[GSXR1000]

Thanks, I thought 14v was already 100%. In fact even 13.8 is 100% (I thought)
What voltage should I charge it to, to get 100%?

14v can be just takes longer in absorption phase

 

[marcello]

I know, it’s confusing.

Resting voltage is different than charging voltage.

A lifepo4 battery, resting for at least a few hours at 13.1V, with no loads or charging, is at approximately 40% SOC. In order for the battery to reach 100.000% complete charge, it needs to reach 14.6v and remain there for a certain amount of time. Once it goes into float charge or charging is removed, and all loads are off, it will settle out at approximately 13.3-13.4v. IT’S STILL FULLY CHARGED AT THIS POINT.

And yes, 13.8v is basically considered fully charged, but I think it’s something like 98-99%. If you look at two glasses of water and one is 98% full and the other is 100%, can you tell the difference without quality scientific measuring tools? I mean, can you tell by just looking at them? No. And in the real world, it just doesn’t matter. If a few watt hours are going to be life or death for you, then just make bigger battery bank. Add on another 100Ah and call it a day.

Also, the absorption time needed after the battery has reached its set full point (bulk or boost set to 13.8-14.6v) can sometimes be difficult to achieve on solar. To my limited knowledge, absorption needs to be about 15-90 minutes and the voltage is held at the set point as the amperage slowly and consistently reduces. If you have any passing clouds or what not affecting solar production, that will upset your absorption phase. How much this matters I don’t know.

What I do know is while lifepo4 C 12v CAN be charged to 14.6v, many on this forum don’t bother for a number of reasons. One being is the theory that charging to the top most voltage is stressful to the cells. Think about it. You have a suitcase that can hold 14.6 liters of clothing. You pack 14.0 liters and dang the thing is pretty full, it’s getting hard to pack any more in there. You then spend another hour packing in the last 0.6 liter and then when you try to zip up the suitcase (this is now the absorption phase), the thing is bulging and you might be a bit concerned about the stress being put on to the zipper.

I have my solar charge controller set for bulk (also known as boost on some devices) to 14.0v. I don’t need the extra few bits of juice and it’s theoretically a bit less stressful on the cells.

My shore charger I only use a couple times a week or less and I set it a bit stronger to 14.25v. An occasionally fuller charge is less stressful than daily. In theory.

Thank you very very much for all these informations, I learnt more reading your message than watching many videos on the subject! I will dig more about all of this, and use what you said and a great starting base thanks again.