Lithium Ion Batteries

bobbypat
bobbypat Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
in Grid Tie and Grid Interactive Systems #1
I currently have a 100 AH 48 volt "Humless" Lithium ion battery with the specs as follows:
Nominal voltage: 51.2V
Bulk/Absorb: 55.2V
Cutoff: 46V

Can I safely add in parallel a 100AH 48 volt "EG4" Lithium ion battery with the specs as follows:
Nominal voltage: 51.2V
Bulk/Absorb: 56.8V
Cutoff: 44.8V
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,594 admin
    edited September 29 #2
    Do you have links to the batteries and their specifications?
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bobbypat
    bobbypat Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    #3
    No, but the critical specs for each battery are given in my post.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,094 ✭✭✭✭✭
    edited September 28 #4
    There are many Lithium chemistries. When you say "Lithium Ion" it raises a flag in my mind. Are you sure the batteries you have aren't LiFePo4, or otherwise known as Lithium Iron Phosphate? All the different chemistries have different charging requirements. The voltage numbers you give is where the flag is risen.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • bobbypat
    bobbypat Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    #5
    Both batteries are LiFePo4.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,870 ✭✭✭✭✭✭
    #6
    Yes but both have different BMS and that is your problem as they will not communicate!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • bobbypat
    bobbypat Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    #7
    I appreciate your advice. I thought that each BMS would act independently of each other, keeping the individual batteries balanced separately, and then combining their voltages afterwards. From what you are saying, that's not the case. It appears that's not the case. Rather, the 2 different BMS's will be "thrown off" by their non-consistent programming parameters, and I'll have a mess on my hands?
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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #8
    You should be fine putting those two batteries in parallel. You are correct that the main thing each BMS is there for is to protect the one battery it is part of. Your older battery may have less capacity than the new one (just due to age), but it won't be a problem. Lots of people have 100Ah LiFePO4 batteries in parallel with 280Ah batteries, and it all works fine.

    The hard part might be to find the right charging profile to use, since the two manufactures have different bulk / absorb recommended voltages.  I would just go with the lower 55.2V. If your charging source has a tail current setting, just set it to 0.02C (4A for your two parallel 100Ah batteries). Unlike lead acid, LiFePO4 batteries don't really care if they don't get completely full, so even if you stop charging before the newer battery is at 100% SoC, it all should be fine. Fact is, I've seen some battery science people claim that LiFePO4 batteries actually last longer if you don't charge them to 100%.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • bobbypat
    bobbypat Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    #9
    I'm really glad to read your comment that my basic premise is correct, in that the 2 different BMS won't affect each other negatively.  As for finding the right charge setting it makes perfect sense to go with the lower bulk charge setting, and "so what" if the newer battery comes up a bit short of full charge. The plus side is that it gets extended life.  I've read so many negative things about using LiFePO4 batteries of slightly different charging specs in parallel. It didn't make sense to me, unless the one BMS would try to "corrupt" the other one. It would appear now that's not the case, if the 2 batteries are connected in parallel. I can now pursue the new battery that I want (from a different manufacturer), and I can save some hard-earned dollars that way. Much thanks !!
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