[RE-wrenches] Lithium battery charge rate

[Steve Higgins]

For many LFP batteries, while some say you can charge at the C1 Rate, most
want you to charge at the C2 or C3 rate.

While you don't have to get them full all the time like lead, as long as
you are cycling regularly, it is still a good idea to get them to full
regularly.   Now if they are a backup system or not being cycled, they
should not be held to full all the time. This can accelerate damage to the
cells.

Where we see the major mistakes are the absorb timer settings.   Too many
people are setting the absorb timers too short, especially if they have
parallel modules and are not running closed-loop communications, or the
batteries can't communicate with each other or the chargers.

In these cases where you have 2,3,4... more batteries in parallel, the
absorb timers can help balance them as the batteries that don't need
balancing stop charging, while the cells that need the extra time get that
time if you have longer absorb timers.

We advise for our LFP drop in's that you have the following.   Assuming
that you are charging at least the C2 Rate.

1 Parallel Connection = 30-45 mins absorb timers.
2 Parallel Connections = 45-60 mins.
3 Parallel Connections 60-90 mins.
4 Parallel Connections 90-120 mins




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On Mon, Jun 26, 2023 at 6:51 PM Darryl Thayer via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi Jay, Larry says is correct.  My experience, with cells and there BMS is
> they need to get up to top balance voltage then the BMS will stop charging
> the full cells and bring the remainder of cells up to fill charge.  My
> oldest set is about 6 years old, since I understood they have been fine
>
> On Mon, Jun 26, 2023, 3:58 PM Jay via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> Hi All
>>
>> I’m wondering if minimum charge amps for lithium is common or not?
>>
>> Or does it have to do with the cell shape: cylindrical vs prismatic vs
>> pouch?
>>
>> A client purchased some EG4 batteries and they are getting a bit out of
>> balanced. Tech support didn’t suggest higher volts or longer absorb but did
>> mention they need 30-50 amps charge. It’s not in the manual.
>>
>> Wondering what you all think and know
>>
>> Thx
>> Jay
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