12v lifepo4 battery installed and testing!

Discussion in 'Gen 3 Prius Accessories and Modifications' started by abubin, Oct 6, 2021.

  1. abubin

    abubin Member

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    I have successfully built a 12v lifepo4 battery with 50aH. 4s x lifepo4 cells of 50ah each. EVE brand cell.

    I have a BMS rated at 100A supposedly able to work on cars with cranking amp requirement. This part is a bit iffy if you know how cheap parts from China always exaggerate it's ratings. The BMS will handle things like overcharging, low voltage discharging. The ability for it to handle cranking amps...I am not putting hope in that. Also, a Prius doesn't need cranking amps which save a lot of cost in building such ability on the battery.

    So anyway, I have been running it in the car for 3 weeks now and have driven around 100km with it.

    Here are some information I gathered so far:
    - the voltage would stay stable around 13.3v - 13.5v (I read this is the nominal voltage for each of the lifepo4 batteries at 3.325 - 3.375)
    - the battery does get charged up to 14.4v after each long drive and battery will slowly goes back to nominal range above after some time (haven't measured how long)

    I have yet to take out the batteries to check if each of the cells are in balance. Will be installing a cell monitor soon that can also do active balancing.

    BTW, I have also installed a 30amp fuse on the battery which so far have not blown yet. I am thinking is that fuse size too small? Should I change it to 50amp instead?

    As for the cost, since this is initial experiment I had to buy few things to test it. Like some active balancers and BMSes and voltage monitors and cables and tools and casing. However, once I got everything sorted out, I would put the cost at around the same as buying a standard AGM battery for it.

    Anything else you guys think I should be checking or experimenting with the battery? I would like to do more experiment before I create a video out of it.
     
    #1 abubin, Oct 6, 2021
    Last edited: Oct 6, 2021
    Russell M Jedinak Jr likes this.
  2. black_jmyntrn

    black_jmyntrn Member

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    What active balancers, BMSes and voltage monitors did you use? I use the victron bms 712 on the second 85A AGM battery I added, also have an 85AH AGM battery for my main 12V.

    My plan is to replace both AGM batteries with two 100Ah lifepo4 I can make fit where both of my current batteries are.

    The question is, what changes did you have to make to the Prius to use lifepo4 versus AGM?
     
  3. abubin

    abubin Member

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    No changes done on the car. Just direct swap the 12v AGM with 12v lifepo4. The only mod I need to do is changing the battery cable terminal connector from small to big.

    Didn't know how your plug-in works but for a normal gen3 Prius, the 12v battery is only used to power-up the car and the accessories. No cranking amp required to crank the engine. Once the car is started up, the high voltage will start powering the 12v.

    As for the active balancer, bought 3 different unit. All are these cheap no name brand from China. Going to experiment to see which one is suitable.

    Also very important thing to note is wiring for active balancer and BMS is totally opposite. BMS uses positve to negative whereas AB uses negative to positive. I was careless with the first AB and stupidly used the BMS cable to connect the AB. When I connected, it sparked and burnt the AB circuit.
     
    #3 abubin, Oct 6, 2021
    Last edited: Oct 6, 2021
  4. burrito

    burrito Member

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    How much would this all cost, minus the testing equipment? Is it less than the Ohmmu battery ($350)?
     
  5. black_jmyntrn

    black_jmyntrn Member

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    The battery I will use has built-in BMS, do you have a wiring diagram for the active balancer and BMS on the car?

    Working on that now...
     
  6. abubin

    abubin Member

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    It would cost around USD143 including BMS, AB, voltage monitor, manual on/off switch, cables and wooden crate made of plywood.

    If op for ready made battery plastic case, add USD30. This will looks much better if you care about the outlook.
     
  7. black_jmyntrn

    black_jmyntrn Member

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    can you list out the components? If I paid today the $143, when will the items ship? How do I make payment?
     
  8. abubin

    abubin Member

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    Sorry, I am not a seller. I am doing it as a hobby only. Also, to make youtube video. Once I am ready, I will make a video of it and list the components. As it is not finalize yet, I need to do further tests. This is to confirm which components I am going to use.

    You should be able to order those parts from Aliexpress. Amazon should also have those parts but probably at 10-15% extra.
     
  9. abubin

    abubin Member

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    upload_2021-10-8_11-15-29.png

    Here is a sneak peek at the active balancers I am testing.
     
  10. Russell M Jedinak Jr

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    Proof of concept
     
  11. abubin

    abubin Member

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    Lifepo4 have a flat voltage from 20% to 90%. As such, it is quite difficult to know the actual percentage. That is why I am still monitoring the voltage. So far, even at 1 week of not driving the car, voltage still hover around 13.2-13.3v.

    upload_2021-10-13_11-3-52.png
     
  12. abubin

    abubin Member

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    The battery was working fine for few weeks. But now seems to be getting a strange issue.

    The car will have no power at all but when I check the battery, it still have 13.2 volt. I just tried turn-off and on (i have a battery switch) and it work again. Or I just unplug the -ve and plug back and it will work again. Very strange. Need to test further.

    When it work again, I have no problem driving it and after shutdown down the car, power will go away again after few hours.

    Right now, I have swapped back the 12v AGM and seems to be no shutdown issue. The lifepo4 12v is being tested and no issue.

    Very strange.
     
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  13. bisco

    bisco cookie crumbler

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    13.2 volts is incorrect if the car is off. battery might be defective
     
  14. ASRDogman

    ASRDogman Senior Member

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    The two different batteries are charged differently. And the ECM is trying to charge the battery in
    the manner in which it was designed to charge the AGM battery. I imagine you will have problems
    until you reprogram the ECM to charge the different battery.
     
  15. abubin

    abubin Member

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    That is one of my concern actually going into this experiment. LFP4 does have slightly higher voltage. Let me try reducing the voltage to 12.8 to see if things will improve. If, that is even possible.
     
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