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DIY Lifepo4 charge cycle

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    DIY Lifepo4 charge cycle

    I thought some of you who are considering Lifepo4 might be interested in seeing an actual charge cycle. This is a 560ah 2p4s [2 cells in parallel / 4 cells in series] config. I installed them June 2020. They were represented to be 280ah EVE cells, 1st quality and matched. I don't know if these are EVE but the capacity is over 560ah. They are not 1st quality or matched - and I didn't expect them to be for the price I paid.

    The graphics below are from the REC BMS dashboard and show today's charge cycle and a 150a load. When I left the boat Monday the Lifepo4 battery was at 95% SOC. Returning today SOC was 51%. I leave the frig and security system on.

    I've been off the boat since Monday - so 6 days. I wanted a some heat and hot water so fired up the generator.

    This is the BMS dashboard when I got onboard today:
    51.5% SOC
    13.05V
    -6.90A

    The BMS also monitors each cell voltage. The variance among cells here
    is 0.003 volts.

    Click image for larger version  Name:	Screenshot 2021-10-09 130825.png Views:	0 Size:	46.5 KB ID:	633399
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    Here are some of the settings for the system. They are the most critical. All settings can also be configured via command line.

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    The charger is a Freedom 25 130amps set for cool wet cell @ 14.4v. The battery is accepting 120a. Voltage jumps a bit and there is a 0.030v variance among cells [more in this later].

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    ---------------
    Around 92% SOC the first cell passes 3.45v. This is my setpoint to initiate cell balancing. This BMS employs active balancing @ 2amps. This can be seen by the high cell #4 resistance as the charge is shunted by 2amps and lower voltage cells receive more charge. This was 3hr 4min after starting the charge cycle. The battery is at 13.72v accepting 102a. There is a 0.036v variance among cells.

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    ------------------
    The charger transitions to constant voltage - absorption, and amps start dropping around 14.25v and tail to about 5a at 14.30v and 97% SOC. This was 3 hr 17min after charge started. Note the rapid voltage increase that occurred within 15 minutes. Cell voltage variance gap closes as amps drop.

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    The cell voltage variance under 150a load was 0.047v.

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    The cells are really out of balance when under high charge / loads. These cells didn't pass the 1st QC and landed in the secondary market. There are fewer paths for a consumer to purchase top quality cells and much more expensive. The EVE cells need to be top balanced every year.

    I will be disconnecting the system next week so will wait until spring commission to top balance the cells. The voltage variances are not an issue for my current use. But if my use were to change where I need to discharge 100a+ for prolonged period of time - like the convection oven for 3 hours for a roast - I would be replacing these cells with Winston 700ah or 1000ah cells [for well over 3x the cost].
    Irony
    1989 Bayliner 4588 - EH700TI
    Portsmouth, NH

    #2
    The technology is interesting. I installed my fridge in the boat last week, a small Norcold, and wanted to test it. I had the radio playing with Navionics using the radio's wifi to download new maps. It was raining, my solar panels were still able to keep the 100AH battery fully charged. Next test is to let the fridge run all night, but fall conditions are not representative of warm summer, so that will wait. So far I am quite happy with the system.
    This was the state of batteries few days ago:
    Attached Files
    1989 2159 Trophy Hardtop
    5.8L OMC Cobra
    2 1/2 year restoration project after "all you need to do is put the rebuilt engine back in".
    Mountlake Terrace, WA

    Comment


    • Kwood
      Kwood commented
      Editing a comment
      Looks good. Is that 13.0v float?
      ETA - You don't want to let them sit at full charge for too long.

    • Metrodriver
      Metrodriver commented
      Editing a comment
      Once the lead acid reaches float the charger stops charging, and monitors the voltage until it drops below 12.7 at which point it will charge again until 13.2 V

    #3
    That is Very cool!!!!!

    KEVIN SANDERS
    4788 DOS PECES - SEWARD ALASKA


    Whats the weather like on the boat
    https://www.weatherlink.com/embeddab...59665f4e4/wide


    Where am I right now? https://maps.findmespot.com/s/2R02

    Comment


    • Kwood
      Kwood commented
      Editing a comment
      I have another set of 8 - 280ah Gang Feng cells. The story - I ordered these in January 2020 as COVID hit. They had not arrived by April & the seller could not provide tracking so I exercised Alibaba's buyer protection and got a full refund. I purchased the EVE the same day. The following week the Gang Feng arrived I considered installing these also - they take less room than 2 golf cart batteries - but the system gets more complicated. These tested better than the EVE so I may swap them over to see how they work in operation. Anyone interested in a set of 8 280AH cells?

    #4
    Kwood , do you leave the LiFePO4 batteries on the boat over the winter? I know they don't take too kindly to charging below freezing, I just wasn't sure about storing them under no load/use. I bring all of my batteries inside the house for the winter here in Michigan. I have a LiFePO4 for my motorcycle, the three lead-acid batteries from the boat, and all of my lawn and power tool rechargeable batteries.
    Justin
    1984 2150 Ciera "C-ya"
    AQ225D w/ 280
    MMSI 338355691
    St. Joseph, Michigan

    Comment


    • Kwood
      Kwood commented
      Editing a comment
      I discharge to about 50% SOC and disconnect the cells from each other completely. I keep them in the battery box on board. Sub freezing weather is the norm here for 3 months. That won't hurt the cells. There is no charge or load. Only individual cell self discharge. In spring I wire all 8 cells in parallel and charge that bank to 3.65v and hold it there until tailing current approaches zero. I use a 50amp variable voltage charger for this with a high voltage disconnect set at 3.66 volts. The top balance procedure takes about 4 - 5 hours including disassembly and reassembly to the 560AH 12v config.

    • C-ya
      C-ya commented
      Editing a comment
      Kwood, I bought a set of four B cells to play with and learn on. Top balancing will be done soon, and I'll just play around with it/them over the winter powering various and sundry things to learn about the settings for the high and low cutoffs. I have a BMS, just no BT to see what it is doing. I know the presets, so I'll see if they are sufficient first. BT BMS may be the next thing to buy.

    #5
    My charger has a temperature probe that is sitting on the battery. If temperature comes close to freezing it cuts off the charging. It also protects at high temperatures.
    1989 2159 Trophy Hardtop
    5.8L OMC Cobra
    2 1/2 year restoration project after "all you need to do is put the rebuilt engine back in".
    Mountlake Terrace, WA

    Comment


    • Kwood
      Kwood commented
      Editing a comment
      A marine charger? The BMS should monitor cell temperature and disconnect at setpoints. The charger temp sensors I'm familiar with will vary charge voltage. You do not want that.

    #6
    I have a Renogy system with their 100AH smart battery, and a DCC30S charger with the MSDCDC monitor, 2 100W solar panels. The charger is a DC to DC charger and one of the first that has the MPPT option for solar and has charge profiles for Lithium, SLA, FLA or AGM batteries. It cuts off charging at 1C, and starts again at 3C.
    I was looking at what Kwood did, buy cells, buy a bms and set it up yourself. For a larger system that is a good idea, for just one battery and my knowledge level I thought it was safer to go with off-the-shelve components that are proven in many camper / rv installations. Most marine installations are on sailboats or larger boats with large battery banks, and many are put together from components sourced from everywhere.
    1989 2159 Trophy Hardtop
    5.8L OMC Cobra
    2 1/2 year restoration project after "all you need to do is put the rebuilt engine back in".
    Mountlake Terrace, WA

    Comment

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