LFP’s Voltage Curve…

[3_tons]

As I’ve previously posted, my 200a drop-in LFP battery bench tested at 215a (so about 7% more than the shelf rating), yet I was able to brew Keurig coffee at 125a even at zero % SOC, without a single low voltage alarm on either the inverter or the Victron BMV 712…

I have no way to know how ubiquitous this ‘over capacity’ feature might be regarding other vendor’s LFP’s, but in this case (possibly unique - I donno?) it nearly translates to 100% of advertised rating as potential usable capacity…And this kinda explains my buddy’s scenario when using his single 100a/h LFP he inadvertently ran his air cond down to 6% SOC without a low voltage alarm (was at a dang 6% before noticing SOC!)…

So (speculative forensics here only), although his Victron was displaying 6% SOC, then based upon my above example (same maker battery, assuming 7% surplus), in reality he may have had about 13% SOC (say, < > 6a + 7a) still remaining reserve…In retrospect (admittedly assuming such…), his voltage at that time was likely at around 12.0v - thus, explains why no low voltage alarms…

Voltage/SOC chart link:

https://footprinthero.com/lifepo4-battery-voltage-charts

Whether or not this potential (say unadvertised?) over capacity is a wider-spread feature among other battery makes (??), still, it’s this nearly flat voltage characteristic that provides LFP’s their far greater usable capacity, and though often somewhat difficult to convey, where actual practice very much mimics ‘a near’ shore power experience…

It would be interesting to hear other LFP users points of view!

3 tons

[Cptnvideo]

Good to know, 3 tons. I may do that. But, hopefully, I never experience another shut down - it was pretty chilly when we got up that morning. 😉

[3_tons]

Well, I spoke to my battery’s in-house tech-engineer and he said that IF a BMS shutdown scenario were to happen, to disconnect the positive battery cable for 15 sec then reconnect, and this will reset the BMS…I simply installed a copper knife disconnect switch (from Amazon) at the battery’s positive post - Just saying 🙂

3 tons

[Cptnvideo]

We have 3 206 AH LFPs. According to my Victron BMV, our deepest discharge was 559Ah.
However, we did encounter a battery shut down once. But we were boondocking in the midst of Ponderosa Pines (very tall trees) and not getting a full charge. Plus we have a residential fridge that draws 120Ah daily. Admittedly, I should have paid more attention to the battery voltage before going to bed (and I could have turned off the fridge breaker).
Anyway, I now think the battery shut down feature of the LFPs is nice to have.
However, there is also a "Catch 22". Since we wouldn't get sunlight on the solar panels until about 9AM (and no coffee), the generator wouldn't charge the batteries since the inverter/charger was also down. So we had to jump the LFPs with the truck battery to "wake" them up.