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LiFeP04 - two SIMPLE tips.

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  • LiFeP04 - two SIMPLE tips.

    Instead of writing 300 message threads, I'll try to keep these TWO tips practical and short.

    I don't care if you have gone DIY, or purchased a "drop-in" with all the goodies. Were not going to go there. We are going to assume you are top-balancing, which most drop-ins do, or most people who are not EV'ers do. Not going to argue top/bottom here. We've already done that for years.

    What I will address are two of the most common concerns, and how easy it is to perform without any special gear.

    1) Charging to less than 100 % capacity. And for beginners, I'll use the typical nominal 12v battery rather than individual cell voltages but with comments of course. This is a popular option for many concerned about always taking their cells to full charge.

    Set either your SCC / solar charge controller to NO MORE than 13.6V as your CV. When a cell is charged to no more than 3.4v individually, it will act like normal, but will not charge to the full rated capacity. Simple. Now you will never get charged to full, and that's what a lot of people want. 13.6 EVERYWHERE, so that means BULK = ABSORB = FLOAT are 13.6 if you can set all 3 the same. If you can't get as many as you can set.

    DONE! Now you will never charge your battery to full capacity. But DO READ the comment below!

    Not using solar but a charger? Same deal. Charge with no more than 13.6v. That's 13.6, NOT 13.7 or 13.8v. This is a knife-edge setting. Use a good quality multimeter to verify!

    2) LVD or low-voltage disconnect with inverters
    Most of the drop-ins have an LVD to protect you from going too far. Mostly, these are very low in my opinion, so for you dc-purists, add your own external lvd to stop earlier if you like. Standard knowledge be it lead-acid or LFP.

    But here's the good news for those of you using ac-inverters!

    Nothing extra to buy! Normally inverters have their own LVD's and they tend to fire off at 11.7v or thereabouts. Normally using these "dead-man" inverter disconnects with lead-acid is a bad thing. You don't want to take lead down that far, but it's better than nothing. Pretty common mistake for newcomers to lead to think this is a good LVD. It's not, it's just a catastrophe-saver, not good engineering practice.

    BUT - with LifeP04, that is actually usable because we have a different charge/discharge profile than lead-acid, which all the inverters are designed around.

    So now, if you get your kicks out of cycling, or are running an inverter and forget, not a major deal to let the inverter just shut off near it's 11.7v point.

    Obviously in the real world, some inverters might have set theirs too low to 10.7v, but get this - at least that's .7v higher than what is in the battery's own lvd. So while I don't like to go down this far, it's .7v better.

    So common sense here - don't even go that far in either situation if you don't want to. Standard knowledge, but a total-worry factor can be relieved for many.

    The 13.6v (or 3.4v/per cell) is a knife-edge setting to ensure you never get to full.

    If you go any higher, anywhere from 13.7/13.8 to 14.6, you will eventually charge your battery fully - it just takes much longer at 13.8 than it does at 14.6v

    Drop-In users:
    The first time out, just to ensure your BMS balancers have actually attempted to top-balance your battery, it takes a higher voltage for those weedy little resistors to kick in. That's usually somewhere at 3.5v or higher individually.

    So that means to just charge and use your battery a few times by charging to full. A charge controller setting of 14.4 to 14.6v will do it.

    Then, if you want to stop going that high and are willing to sacrifice some overall capacity, reset to 13.6v MAX. No further.

    Here I've tried to present an easy and practical way for beginners not to actually charge to full if they want to go that route without a lot of hoo-ha. But a tip to charge normally at first a few times to make sure the balancer they paid for did it's job initially.

    Second, if using an inverter, you can let it go into it's catastophic "dead-man" lvd cutoff, and not worry about it much like if you were constantly doing that with lead, because the discharge profile for LFP is different.

    Ack - still too much to read when I look back on it. Wish I knew how to be more concise!
    Last edited by PNjunction; 05-02-2021, 04:18 PM.

  • #2
    It may seem long to you but it is hard to communicate in text. I think you have written a great simple post that gives good info.

    I originally asked what I should set my LVD at but since then I have the battery and a good spec sheet with it. Rereading you post I have it under control.

    Last edited by Bala; Yesterday, 03:31 PM. Reason: New info