How to keep NiFe Batteries Charged?

midijeep
midijeep Registered Users Posts: 102 ✭✭✭
in Solar Beginners Corner #1
HI,
I have a bank to 40 NiFe 200Ah batteries.  I only use 38 due to my solar setup.  I keep rotating two batteries but would like to at least keep a charge on the two 1.2 V NiFe batteries that I am not using.  The manual states to fully charge the battery needs 1.7 Volts. I just want to keep them charged (1.2V - 1,7v) so I don't have to keep rotating them in and out.  The other option, which I don't want to do is remove the electrolyte.
What equipment would you recommend to "trickle charge" the two 1.2v NiFe batteries e.g. solar panel with charge controller, battery charger, etc...... .
Thanks in advance!
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited March 2018 #2
    @midijeep
    It might be possible to use a LiFePO4 charger on 2 cells in series. I read, the maximum charge voltage is 1.8V per cell, so 2 in series would be 3.6V. The LFP charger is 3.65V. I don't know for sure if the 5 mV over recommended voltage would be a problem, if not, maybe a charge current of about 3% or 6 amps would be enough to keep them in a charged state. NiFe are not that efficient so it may take a little more current. Just an educated guess.

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    I went the route with a charger that has programmable set points and can use all cells. TristarMPPT-60
    But it looks like the LFP charger, applied 1x a week, would keep the 2 cells in  shape.  Too much voltage just boils off a bit more water
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #4
    For your stored cells... You generally want them to be somewhere around 1/2 charged (around 3.0 volts for typcial LFP... As always check the specifications)... Keeping them at 100% state of charge will age them pretty fast (lose significant capacity in 1-2 years).

    Also, the cells need to be disconnected from any loads or Battery Management Systems. If you cannot disconnect the loads, then you will need to check/recharge occasionally.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • midijeep
    midijeep Registered Users Posts: 102 ✭✭✭
    #5
    I wonder if this would work?
    I have a Drok Voltage regulator: 
    https://www.amazon.com/gp/product/B01MSJQAKY/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

    I'm thinking of using a spare solar panel I have and running it to a Solar controller by Battery Tender: 

    https://www.batterymart.com/p-021-1162-battery-tender-solar-controller.html?gclid=EAIaIQobChMIrPS-6fmD2gIVhYF-Ch08CAtPEAQYAiABEgJJWPD_BwE

    and then to the Drok voltage regulator then out to the two NiFe 1.v batteries in series.
    Would this be a bad idea?




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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited March 2018 #6
    The Drok looks like an interesting piece of gear.  It  would have to be powered by a battery, it is not capable of MPPT operation from a PV panel only.

    The battery tender is a 12V gadget, not adjustable to a pair of NiFe batteries. The batteries are likely tougher, and will just need a bit more water, more often.

    you are working outside the box here, and will have to learn what works and what burns your house down,
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #7
    @midijeep
    This charger should do the job. It's 32 dollars. You might have to put it on a timer to keep the SOC in the right range.

    http://www.batteryspace.com/Smart-Charger-6.0A-for-3.2V-1cells-LiFePO4-Battery-Pack-100-240VAC-CE.aspx

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • midijeep
    midijeep Registered Users Posts: 102 ✭✭✭
    #8
    Raj174 said:
    @midijeep
    This charger should do the job. It's 32 dollars. You might have to put it on a timer to keep the SOC in the right range.

    http://www.batteryspace.com/Smart-Charger-6.0A-for-3.2V-1cells-LiFePO4-Battery-Pack-100-240VAC-CE.aspx

    Rick
    Thanks Rick.  Bought the charger and works great for maintaining the two 1.2 NiFe batteries.
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