[RE-wrenches] Lithium battery charge rate

Tue Jun 27 09:07:00 PDT 2023

Hi Steve,

My experience is different. First, I don’t know of any stationary battery systems that have C2 charge ability, many not even C1. A 20kWh bank C2 rate would be 40kW or over 770Amps @ 52V. I have 10 years experience with Li batteries, (hundreds of Li installations, mobile and off grid), and thousands of LiFeBlue Battery customers, low current charging works without issues. Most of these systems charge at the high end 0.35 C rate or less. Jay did not mention the bank size so we don’t know the C rate for the 30-50 Amp recommendation. But I guess it is far lower than 1C.

Long absorb (CV) times may cause a cell to saturate resulting in rapid voltage rise and the BMS protection inhibiting input current. This sudden loss of load (essentially a battery disconnect) can cause havoc with some inverter/chargers and PV solar controllers. In our experience, the best method to set Absorb times for any Li system is by trial. If the cell voltages are staying relatively close during discharge (6mv in the attached image), then balancing time (> 3.55V CV) is sufficient, whether it is 0.1 hours or much more.  

Larry Crutcher
Starlight Solar Power Systems
(GM, LiFeBlue Battery)

On Jun 27, 2023, at 6:33 AM, Steve Higgins via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:

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 

 <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/> <http://www.rollsbattery.com/>Steve Higgins ⋅ Technical Services Manager
t +1.902.597.4020  m +1.206.790.5840
f +1.902.597.8447  e steve at surrette.com <mailto:steve at surrette.com>
 <http://www.facebook.com/RollsBattery> <https://www.youtube.com/user/RollsBattery> <https://www.youtube.com/RollsBatteryEngineering> <https://www.youtube.com/RollsBatteryEngineering> <https://www.youtube.com/RollsBatteryEngineering> <https://www.linkedin.com/company/rolls-battery-engineering> <https://www.linkedin.com/company/rolls-battery-engineering> <https://www.linkedin.com/company/rolls-battery-engineering> <http://www.instagram.com/RollsBattery> <http://www.instagram.com/RollsBattery>
CONFIDENTIALITY: The information transmitted herein is intended only for the addressee and may contain confidential, proprietary and/or privileged material. Any unauthorized review, distribution or other use of or the taking of any action in reliance upon this information is prohibited. If you receive this email in error, please contact the sender and delete or destroy this message and all copies.

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

http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230627/78af8f45/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 32ED5403-8A66-4ED5-AFFD-E308D5FC48C6_1_105_c.jpeg
Type: image/jpeg
Size: 123914 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230627/78af8f45/attachment-0001.jpeg>