Wattcycle BMS, toggling charge and discharge

[bjojoh]

Hi,
I planned to buy the Wattcycle 280 Ah Mini with Bluetooth (the updated 300Ah), when I read the FAQ:

Q: Can I use the battery while it is charging?
A: Unfortunately, WattCycle’s deep cycle LiFePO4 batteries currently do not support simultaneous charging.

I don´t follow at all, so I e-mailed the support I got the following answer:
"We don't recommend that charging and discharging at the same time. Which will shorten LiFeO4 battery's lifespan."

I mean, isn´t this the normal usage? Have a solar controller charging your batteries when you simultaneously use them? Sometimes the charge current is too low compared to the load, so you discharge, sometimes the opposite?

Do I misunderstand something, or is the BMS useless? Any comments/experiences?

Kind regards
Björn

 

[robbob2112]

you are missing that it is pretty much impossible to both charge and discharge at the same time with a common node BMS.... the charge and discharge MOSFETs are connected to the same battery post ...

So if you have a higher current than your load from the charge source your load runs from the charge source... If you have a load that is lower than the charge source, part comes from the charge source and part is used to charge the battery.

 

[bjojoh]

Hi,
thanks for answering.
I was a bit unclear in my question, but I agree, this is exactly my point. The BMS can´t see what is going on outside the battery with its two terminals.
Either we charge or discharge. The current sums up in a net current, in or out.
The strange answer is from the Wattcycle support: "We don't recommend that charging and discharging at the same time. Which will shorten LiFeO4 battery's lifespan."
Do I miss something here? Is it the toggling between charging and discharging that is the problem (if the sun is out or fade)?

 

[robbob2112]

This explains in good detail what happens inside a battery while you are running a SCC that matches the load -- there are still currents induced in the battery --- and the battery with the single terminal BMS will automatically switch between charge and discharge as needed....

charge/discharge eddy currents inside the battery

You can get BMS that have separate charge and discharge terminals --- so there would be 3 terminals on the case... a positive, a charge negative and a discharge negative --- so you would be able to charge at the same time as discharge --- but they are not popular or much in use these days....

There is a resource from @FilterGuy that goes into great detail about the different types of BMS and how they work.

 

[AmpD]

Betting it was a miscommunication or interpretation. Batteries either charge or discharge.

 

[Chuck7454]

Hi,
thanks for answering.
I was a bit unclear in my question, but I agree, this is exactly my point. The BMS can´t see what is going on outside the battery with its two terminals.
Either we charge or discharge. The current sums up in a net current, in or out.
The strange answer is from the Wattcycle support: "We don't recommend that charging and discharging at the same time. Which will shorten LiFeO4 battery's lifespan."
Do I miss something here? Is it the toggling between charging and discharging that is the problem (if the sun is out or fade)?

Your statement suggests a level of competence on the part of "WattCycle support".