HV Battery Headway 38120HP LiFePo4 70S pack

Discussion in 'Gen 2 Prius Main Forum' started by OBJUAN, Sep 15, 2021.

  1. OBJUAN

    OBJUAN Member

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    HOLD ON TO YOUR LUG NUTS:
    GOOD NEWS EVERYONE!
    I picked up 75 "USED" LiFePo4 cells 38120HP from battery hookup. 70 cells for the pack and 5 spares.
    The holders are poor and limit construction to a vertical array 5 x 14. Because of the configuration, extensive wiring changes were needed. With that in mind, I used another complete salvaged pack. As the compression clamp is no longer needed, the rods and 1 end plate were deleted. I lined the bottom of the frame assembly with FR4 2mm (blank PCB material, no copper or one side only) and a cutting pad on top of that. The cutting pad adds insulation, durability and cushioning. Inside edges of the frame were lined with 1x2 PVC trim board. One side needed about a saw blades width trimmed to fit the pack snuggly. Cannot speak to the burning of these materials should the worst happen, it is what I had on hand... The voltage sense harness needs to have the wires extended as the sensing posts will be on top and on the bottom of the pack. A new Batt (-) cable is needed, I used a length of #6 welding wire. The old negative wire and battery post was repurposed for use on the safety plug, which required salvaging the crimped terminal inside the safety plug socket. (not Fun) Also needed another run of #6 wire for the positive battery post. The new #6 wires needed new crimp terminals installed. The pack is held in place using 3 one inch cargo straps each rated 100-300lbs. The cargo straps are held with sailing 1" footman loop stainless anchors. Each anchor was tapped with an M6 cobalt tap and M6 bolts beneath the frame to hold them in place. The fit of the footman loop is perfect for the holes used to secure each of the NiMh blades. The top frame assembly uses more of the cutting pad for insulation and a couple rubber pads where the + & - HV battery posts are in close proximity to the metal. Some pool noodle foam was used to manage the air flow. The metal end plate has a teflon sheet RTV'd to it and some door 7 window foam strips to cushion against the batteries and also control air flow. The battery bus bar configuration is somewhat convoluted to get a shunt between array 11 and 12 for the service plug on top of the pack. Battery assembly weighs ~24kg, the whole pack is about 70% the original weight. Battery hookup said all of these batteries were 80-90% or greater of the new spec 8Ah. I tested a random sampling and was in agreement. I wired all the batteries in parallel and charged them over a 2 day period to 3.3V, how ever long it took for minimal current draw on the power supply. That yielded about 16.5v per 5 cell array, good range for the Prius to assume a valid SOC. Installed the pack and powered ON in accessory mode, everything is running AC as well and Dr. Prius App looks happy, batteries show <0.1v difference. On to READY... relays click ON and load PSST sound, smell of smoke. One battery failed under heavy load...this happened 3 times. 2 cells got very hot and one cell shorted out venting gas. Was not pretty and I was less than impressed. I pushed on, replacing the faulty cells then 2 others showed to be warmer than the others by 8C and Dr. Prius says 80.89% life. Once again, dismantle the pack and replace the 2 cells. My spares are gone...but the sucker works now! Has been up and down the mountain here dozens of times and the pack is tolerating the cycling. I've taken the pack out once to rebalance some cells and today I still have a few more to correct but knock on wood, promising so far... I am attributing the balancing drifting to poorly matched used cells. So looks like I will have to pamper the pack a while. I recommend NEW well matched cells... I'm on a crap pension so I have what I have and taking an exchange rate rip didn't help... The best array would be laid horizontally and stacked 3 high similar to the bamboo sticks NiMh from you know, "over there". That would have kept the wiring the same. Problem is the plastic holders. None available for that configuration, able to bolt to the metal frame and securely hold cells bolted end to end. I did talk to someone "over there" whether anything will come of it... If I had a 3D printer, I could have come up with something better. I think a dummy cell would be needed to clean up the layout, 3x2. Anyway, have a look see. I'll try to answer questions and post more pics when I sort them out. Cheers
     

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    #1 OBJUAN, Sep 15, 2021
    Last edited: Sep 15, 2021
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  2. james nancy

    james nancy Junior Member

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    I admire your crazy spirit, and I am curious whether the maximum allowable current of lithium iron batteries meets the needs?
     
  3. OBJUAN

    OBJUAN Member

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    200A, 80A charge ;o)

    batteryhookup.com/products/used-headway-38120-hp-3-2v-8ah-lifepo4-battery
     

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  4. TMR-JWAP

    TMR-JWAP Senior Member

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  5. james nancy

    james nancy Junior Member

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    The charging current of 80a seems a bit small, but it is still a good idea. You can connect the battery cells in parallel to improve the charge and discharge performance, and the capacity can be doubled. But the volume will become larger, I hope it can be placed in the car.
    I have monitored the charging current. It can reach 100a under the condition of strong regenerative braking on a downhill. Normal braking regeneration also has a current of more than 20a. During high-current regeneration, the battery ecu seems to relax the highest requirements for battery voltage, sometimes even reaching 19v, which means that each cell is 19/12=1.583v.
    You used 70 lithium-iron batteries, and each cell can reach 19*14/70=3.8v during strong regeneration. I don’t know if this exceeds the best voltage of lithium-iron batteries. In addition, the module may be as low as 12v when discharging. The minimum cell voltage of each lithium iron battery is 12*14/70=2.4v, and the conservative point is 12.9*14/70=2.58v, which seems to be lower than the minimum requirement of 2.8v for lithium iron batteries.
    But these are all imaginations. I am not sure whether the battery ecu determines whether the charging is based on the measured capacity, or the voltage of the module, or both. If the lithium battery has a high capacity based on capacity consumption or regeneration, it may not be used at the limit. state.
    Is your lithium iron battery loaded into the car when it is fully charged, or is it empty or a certain voltage value?
     
    #5 james nancy, Sep 15, 2021
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  6. OBJUAN

    OBJUAN Member

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    Batteries had been parallel charged to 3.2v then assembled into the pack. The maximum voltage the LiFe can charge at is 4.2V but it only adds 1% capacity from 3.65V, so they spec 3.65V and minimum 2.5V(worst case). Never saw the battery go down to 12V. The car complained when it got to 7.8V. Then about 7.4V it lit up alarm lights and would not start. Turning it off and then back to READY it started up. ECU will keep the 70S LIFe in a comfortable range relative to the NiMh specs. I didn't see >90Amps charge with the Dr. Prius app, limits of the polling I guess. Hopefully it can handle the brief extremes. Dr. Prius group is selling a LiFe pack ~2KUS. I expect they are using similar strategy with 5S blocks, no clue what cells the use. Anyway, all experimental. I have a Meanwell LED driver coming tomorrow, more experiments...
     
  7. OBJUAN

    OBJUAN Member

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    Hi Admittedly, I am pampering it, seeing 40-60A with ~80A peak regen and charging is the weakest part of it. It is rated to 200A continuous discharge according to one spec, another one says 120A pulse! I am not confident on a highway run yet. I am curious as to what cells Dr. Prius uses in their LiFe solution.... fingers crossed:eek:P
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    If you didn't get a chance to look at that thread in post #4, here's a clip of the post showing the highest values I achieved during a test drive following a battery replacement. I was not gentle with the car. At all. And it was fun......

    I took it for about a 10 mile drive, and put the hammer down a few times to get a high discharge rate and got on the brakes to get a high regen rate. The highest logged discharge was 172 amps and the highest regen was 104 amps.

    I'm not sure how I achieved 174 amps, because I read somewhere on the internet (a website selling a new style battery) that the OEM battery is only capable of 100 amps.

    Normal driving likely shouldn't put any strain on your battery at all. It's just going to be an emergency stop scenario from >50ish mph that may get you into the scare zone.
     
    #8 TMR-JWAP, Sep 16, 2021
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  9. OBJUAN

    OBJUAN Member

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    Yes I did go through that list, very informative albeit scary on regen, thanks. Hopefully it is a short duration pulse.... I found the H-Assistant not H-Reporter. My initial woes (3 bad smokey cells) were no where near those levels for them to baulk the way they did. Just cheap-used-unmatched cells. I undoubtedly will be pulling the critter out many more times, at least it is not the back buster it was.
     
  10. Isaac Zachary

    Isaac Zachary Active Member

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  11. james nancy

    james nancy Junior Member

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    I'm sorry that I made a mistake in the description of the characteristics of the lithium iron phosphate battery. It can work normally in a wide range of voltage ranges. It should work normally under 2.5-3.8v. I have an idea. Supercapacitors have excellent power density, lifespan, and temperature range. Can supercapacitors be connected in parallel to balance instantaneous discharge and regeneration. However, it has a lower pressure resistance and a smaller conversion capacity. It may require a large number and volume, so you have to consider how to put it in the vehicle.
    Using a super capacitor, I think it will improve the comfort of the power battery. The clockwise current flowing through will be shunted by the super capacitor, and the temperature can be lower, its capacity is used.
     
  12. OBJUAN

    OBJUAN Member

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    No worries, should be in a happy voltage range as far as the Prius S/W is concerned. Regen maybe biggest issue. Supercaps, may work but shoe horning it into the car would be a problem, at least 2x the size. Trying to keep it stock... Converted my old grid tie charger H/W-S/W to use the MEAN WELL LED driver that arrived today. I just put it on the original NiMh pack for now, set to stop charging at 240V. Will check in a hour...cheers
     
  13. james nancy

    james nancy Junior Member

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    Very meaningful work, I really hope to hear the news of your success.
     
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  14. T1 Terry

    T1 Terry Active Member

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    A very interesting experiment. I steered away from using LiFeP04 (LFP) chemistry because they don't handle anything much more than 1CA charging and discharging without the voltage going either high on high current charging and low on heavy current discharging. The voltage going outside the 3.8v upper limit and 2.5v lower limit generates heat inside the cell, so cylindrical cells would need some form of heat transfer to keep them below the 60*C mark where things get real serious as far as electrolyte separation and the higher volatility elements boiling off, that smell you get from LFP cells when they get hot ......sort of a sickly sweet smell ....
    The issues you will have is the cells you are using are only 8Ah capacity when new, 10CA is 80 amps so heat will be a serious concern
    here are the specs
    Headway 38120HP 8Ah LiFePO4 Battery Cell


    Specification

    Nominal capacity

    8Ah @ 1C

    Minimum capacity

    7.5Ah @ 1C

    Nominal voltage

    3.2V

    Max Charging voltage

    3.65 ±0.05 V

    Discharge ending voltage

    2.5 ±0.05 V

    Charge current

    Standard charge: 3C

    Max charge: 10C when T≥10 ℃

    Max charge: 3C when 10 OC≥T≥0 ℃

    Max charge: 0.1C when 0 OC≥T≥-10 ℃

    Discharge current

    Standard discharge: 5C

    Max continuous discharge: 15C

    Max instant (30s) discharge: 30C

    Charge and discharge cell surface

    temperature rise

    5C continuous discharge:≤15 ℃

    10C continuous discharge:≤25 ℃

    Recommended charge and discharge
    cell surface temperature

    Charge: 0~45 ℃

    Discharge: -20~60 ℃

    Maximum allowable charge and discharge cell surface temperature. Charging and discharging at these conditions will shorten cell cycle life.

    Charge: 60 ℃
    Discharge: 75 ℃

    Humidity range

    0~90%RH (non condensing)

    Internal resistance

    ≤4mOhm (AC Impedance, 1000HZ)

    Cell dimension

    Height: 136 mm Max

    Diameter: 38.5mm Max

    Note that 10CA discharge temperature limit, equal to or less than 25*C but must be above 15*C or the discharge current must be reduced. Trying to maintain that 10*C operating range will require some really trick heat transfer, the temp can run away to 60*C but there is a real risk of cells boiling the electrolyte if you reach that 60*C mark, the 75*C mark is where the end caps start to leak and the cells are seriously damaged.

    T1 Terry
     
  15. james nancy

    james nancy Junior Member

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    The recommended value is charging 3c and discharging 5c, that is, charging 24a and discharging 40a. This is the recommended value, and the instantaneous current should be larger. I think if allowed, it’s better to make a 70s2p, that is, 70 series and 2 parallel, the current endurance can be shared, and the capacity can be doubled, but another battery box is needed. I think I need to connect 4 power lines and 15 battery voltage detection Wire, 6 temperature sensor wires.
    Since the current is shared, the current of each cell is in a comfortable range. I am not sure whether the temperature is high or low. This requires experiments to observe. If the temperature rise is very low,
    It is not necessary to use a fan.
     
    #15 james nancy, Sep 17, 2021
    Last edited: Sep 17, 2021
  16. OBJUAN

    OBJUAN Member

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    Thats a far more comprehensive spec! I may well be on the edge... I need to move the temp sensors to the output side of the airflow. That should be the worst case condition. No way to monitor the whole pack. The fan is set to run all the time, hopefully that will help plus we have cooled off considerably from our record heat, drought and wild fire summer. 16C and rain today. I will pull the pack today for some balancing, move sensors and put in the grid tie PS harness.
     
  17. OBJUAN

    OBJUAN Member

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    Agreed if space is not an issue. Not two separate packs in parallel but integrated where each pack is 35S2P and put in series. Double the height perhaps (custom boxes), stacked back on itself keeping power lines short. Extend the existing V sense harness, temp sensors and safety plug.

    I used sweethome 3d to make rough models. This is the pack (basically), showing top bus bar pattern and pink tops highlight the V sense points. Bare in mind, along the centre, those are the even numbered point (2,4,6,8,10,12) which are on the bottom side of the pack. Positive post is upper left and Negative post is upper right. Sense wires start (#1) at Negative post and end (#15) on the Positive post. SW won't allow underside view, can't show bottom bus bars... Site does not allow SH3D files, stuck with Jpegs...cheers
     

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  18. OBJUAN

    OBJUAN Member

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    Batts were pretty close so I didn't pull the pack.
    Got the grid tie working.
    Meanwell driver runs through my old grid tie PS.
    It manages the output, no battery no output and cut off is at 240v for now.
    Hermetic relay flaked out, put an exercise routine in on startup to clean the contacts.
    Relay provides the mechanical isolation, it switches on first if the batt voltage is over 180v.
    Then a mosfet turns on to supply charge power. We'll see how that goes.
     

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  19. T1 Terry

    T1 Terry Active Member

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    I plan to build a 55Ah LTO battery for my Prius that had the traction battery go up in smoke (and flames and bangs and pops) It will take up the whole area where the traction battery lives now, the spare wheel well and that space above the spare wheel but under the rear hinged floor section ...... 55Ah LTO cells are big :lol:
    These cells can handle high CA rate charging and discharging without serious voltage change ..... but I will still need to monitor cell temp. I'm looking at building a sealed box out of Lexan sheets (so the cells can be seen :)) and flooding the box with an E fluid that boils close to the temp I want to maintain the cells at, then suck this vapour out the top of the box and compress it a bit and push it through an air to fluid heat exchanger, then return the fluid to the bottom of the box. Sort of the same method as air conditioning uses, just not near the pressures associated with that sort of heat pump.
    The idea is, a lot of heat energy is required to change a liquid to a vapour, so the process should virtually suck the heat out of the hot cells without affecting the cells that haven't reached that temp ..... theory is there, just gotta put it to the practical testing :lol:

    T1 Terry
     
  20. james nancy

    james nancy Junior Member

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    I think this is a very complicated project. It is difficult to complete by an individual. It is difficult to seal well. If there is a leak, there will be problems. You can also consider oil cooling, which does not conduct electricity. If the battery needs liquid cooling to dissipate heat , Then it should not work in a comfortable area, ordinary prius (non-plug-in), its motor power is not as high as a pure electric car like Tesla, it should not need a complicated heat dissipation system
     
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