Mppt performance and Lifepo4 SoC%

[CaptainRivet]

Originally Posted by PaulCrawhorn

You really should base your cutoff on per cell/group voltage not bank voltage.

Anywhere in the 3.41V to 3.49V range is fine.

Even if you are sure your balancing gear / process is working well, 50mV variations are normal even in a top notch set, and in less than ideal contexts much higher deltas are common.

cheap BMS in drop-in mostly start at 3,5V to balance and that passive with 100-200mA max. so you need to have your cutoff at least at 3,55V or 14,4.
that his battery is at 13.9 and imbalanced is a cause of that he avoids the cutoff and stops charging at 13.8V where no balancing can happen.
all guess one cell is at 3,7V but what about the others....one at 3,65 and 3,25V and 3,3V??? or all 3 at 3,4V...nobody knows...
And when that battery is at 13.8V the SOC is definitely not 100%....and yes it still can measure full capacity.
you actually don't know the SOC before all(!) cells hit at least 3,45V. Only in the steeper part you really can determine SOC and top balance. before at egop} 3,40V a cell can have 40 or 80%SOC, you simply don't know. A good BMS also measures charge current total and per cell/block and can very well do an interpolation, the more full cycles, the more precise SOC is.
your cutoff must be at 14,4V lowest, so you can cut charge at 14,3V...

[SOLAR SUPPORT]

Bms circuits placed in Drop-in Lifepo4 batteries are not very advanced. I'm not sure if it has an active or passive cell balancing function. This issue is not specified in the technical documentation. I am not sure even if low profile bms should have built without the cell balancer.

I will send an e-mail to the company that manufactures "RITAR" brand Lifepo4 batteries in China. If there is no active stabilizer in the battery, then I am thinking of opening the batteries and adding a 4s active balancer to both of them.

In order to add a cell balancer, it is necessary to cut and open the box. This is something I never want to do because the warranty hasn't expired yet. The watertightness will also deteriorate. I hope the cell balancer is exist in the battery.

[goboatingnow]

Originally Posted by SOLAR SUPPORT

Bms circuits placed in Drop-in Lifepo4 batteries are not very advanced. I'm not sure if it has an active or passive cell balancing function. This issue is not specified in the technical documentation. I am not sure even if low profile bms should have built without the cell balancer.

I will send an e-mail to the company that manufactures "RITAR" brand Lifepo4 batteries in China. If there is no active stabilizer in the battery, then I am thinking of opening the batteries and adding a 4s active balancer to both of them.

In order to add a cell balancer, it is necessary to cut and open the box. This is something I never want to do because the warranty hasn't expired yet. The watertightness will also deteriorate. I hope the cell balancer is exist in the battery.

I agree some cheaper drop ins are noting of the sort and shouldn’t be anywhere near a boat much less a amateur and a boat

[SOLAR SUPPORT]

Upper and lower SoC% are important for healthy and long-lasting use of Lifepo4 batteries. In Lifepo4 batteries, which are used between SoC 10-90%, the possibility of cells being damaged due to the problems caused by the cells that are out of balance is reduced. There is an informative video about this.

https://youtu.be/iN4ok93hhWY

Working with balanced cells is ideal for Lifepo4 batteries. For the cell balancing process in question, Lifepo4 batteries must be in the SoC 0-10% or SoC 90-100% regions. In these regions, energy is transferred between cells very sensitively by using discharge-charge current balancing circuits along with the cell voltage.

This process therefore takes a very long time, as the transfer currents used for intercellular balancing must be quite low. It is also important that there is no consumption during the balancing process.

Sometimes it is necessary to isolate Lifepo4 batteries from the system for balancing charging that takes days. Therefore, it is not possible to do the balancing charge at frequent intervals. However, when the conditions are suitable, it is necessary to make an equalization charge.

Here is an other video link related with Lifepo4 battery balancing from "off-grid garage"

https://youtu.be/wvmf4xPqmrw

[goboatingnow]

Well “ he “ **** my pants “ which about sums up that guy

[SOLAR SUPPORT]

Originally Posted by goboatingnow

Well “ he “ **** my pants “ which about sums up that guy

Is there any benefit in directly trying to vilify people instead of questioning their thoughts? If you have an idea about the subject, you must put it out.

[goboatingnow]

Originally Posted by SOLAR SUPPORT

Is there any benefit in directly trying to vilify people instead of questioning their thoughts? If you have an idea about the subject, you must put it out.

This is what he said not me

[PaulCrawhorn]

Originally Posted by wholybee

I expect that when the battery reaches 13.9 and stops charging, you have a cell at 3.7V

Even if all the cells are perfectly balanced, it is best to stop well before 13.9V

If the C-rate is low, 13.8V gets the pack to 100% Full, there is no additional usable storage capacity, no useful purpose served going any higher in voltage, you are just shortening lifespan.

[PaulCrawhorn]

If a drop-in vendor chooses to "design" their product so that the user cannot care for it properly, then that product should be avoided.

Saying that longevity promoting care protocols should be thrown out the window just because their product is poorly "designed" does not serve the community.

Going all the way to max spec voltage is just silly.

If you know the start-balance voltage, then sit at 20mV above that at a current rate just above the balance current level.

If the vendor makes you guess what these parameters are, then it is not smart to buy their product.

[SOLAR SUPPORT]

Originally Posted by PaulCrawhorn

If a drop-in vendor chooses to "design" their product so that the user cannot care for it properly, then that product should be avoided.

It is the fact that not all Drop-in Lifepo4 batteries are the same quality. By labeling drop-in Lifepo4 batteries as out of quality you imply that the local authorities that test and approve these products are also not doing their job.

Saying that longevity promoting care protocols should be thrown out the window just because their product is poorly "designed" does not serve the community.

I think it would be more logical to do this using a smart device. There are smart active balancing devices that can perform top balancing charging in a shorter time and more precisely. I bought one and will use it for this job.

Going all the way to max spec voltage is just silly.

Forcing the Lifepo4 batteries to charge over 90% SoC using mppt or alternator or AC charger available onboard is quite risky. There is a consensus on this issue as well.


If you know the start-balance voltage, then sit at 20mV above that at a current rate just above the balance current level.

The biggest shortcoming of some of the Drop-in Lifepo4 batteries is the lack of hardware that enables communication with the external environment. Having a port for active balancing of cells inside the box would also save people the hassle of cutting them open.

......

[MVDarlin]

Wow. I plan to replace my 250ah AGM Optima bank with 3x 100 amp Lithium batteries. I am located on the baja in Mexico and power my house bank with 6x 150 watt solar panels conneced with Victron mppt controllers. that run a freezer and refer through a 3,000 watt inverter during the day. I shut down refer and freezer in the evening and only use incidental AC power. Batts also supply dc power for watermaker 1 hr a day. I also have a 4.5kw gen detcI can use to top up batts or run high demand AC appliance when needed like water heater or dryer.

What is the best recommended lithium battery for this system?

[Pete7]

If the budget allows why not install a pair of 160Ah or single 300Ah Victron. Built with high quality Winston cells but you are paying for the name too.

Pete

[CaptainRivet]

Originally Posted by Pete7

If the budget allows why not install a pair of 160Ah or single 300Ah Victron. Built with high quality Winston cells but you are paying for the name too.

Pete

That is a bit too less AH considering 3kw inverter, fridge freezer running 24/7 of the 3kw inverter and a watermaker…curious how he made it with 250AH optimas…
I would use 8 cells of EVE 304AH and a REC BMS, making your own 608AH LFP bank. Costs 50% of the Victron which still needs a BMS…their smart BMS in drop in sucks…

[goboatingnow]

I fully support the system architecture that the bms controks all charge sources rather then individual settings in separate chargers. It’s the architecture I’m aiming at

[Pete7]

Originally Posted by CaptainRivet

That is a bit too less AH considering 3kw inverter, fridge freezer running 24/7 of the 3kw inverter and a watermaker…curious how he made it with 250AH optimas…

He has a generator.

However, an energy audit should come first to assist in calculating the house bank size required and then size the solar or solar and genny to charge it all.

Pete