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Best way to manage this LFP house battery

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  • #61
    Originally posted by max2k View Post


    That and also in another thread I was asking karrak details of his data logger and came to realization AC inverter must introduce AC component on the current shunt at double AC frequency, should look similar to the AC component on top of DC coming from common diode rectifier connected to a capacitor. I never worked with LFP batteries myself but I think hooking up scope there and checking how big is that AC component relatively to DC is worth the trouble. In karrak's case his data logger is taking samples at about 1 Hz intervals and if 120Hz AC component is present it would be also present in the measured data but at much lower frequency due to aliasing. Depending on AC 'noise' amplitude it might present a problem or not.
    Take a look a @BackwoodsEE's mppt thread for evidence of this. He is plotting the input side of the mppt at 4096 Hz sampling, but if you can see it there, you can be sure it is on the battery side as well.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #62
      worth a thousand words. These burnt battery boxes were not DIY:

      Li-IonFires.png
      Attached Files
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #63
        Originally posted by max2k View Post
        Mike's examples are different as I believe they show relatively fresh banks and it is hard to tell the exact reasons for those failures. My concern with Mike's cases is the empty battery cabinets- looks like there were no design measures taken to prevent chain reaction.
        At the end of the day, certainly, everyone will have a different safety level that allows them to sleep at night. Myself, I'm primarily worried about something so exothermic and rapid that it prevents me from physically escaping a runaway before it becomes deadly. I'm convinced LFP can't achieve this, while conversely I think the cobalt chemistries are all too risky. There are plenty of other combustion mechanisms on board my RV that can also result in the whole thing ending up on fire; I can't fully eliminate all of the risk in any case.

        I'm underwhelmed by the LFP combustion evidence that's available so far. I want to see documented examples of thermal events in LFP systems that we can show are reasonably-managed, and then those events need to exhibit the kind of high-speed reactions that differentiate them from traditional electrical fires or propane fires or similar, common occurrences to really justify an aggressive additional layer of physical protection.

        That and also in another thread I was asking karrak details of his data logger and came to realization AC inverter must introduce AC component on the current shunt at double AC frequency, should look similar to the AC component on top of DC coming from common diode rectifier connected to a capacitor. I never worked with LFP batteries myself but I think hooking up scope there and checking how big is that AC component relatively to DC is worth the trouble. In karrak's case his data logger is taking samples at about 1 Hz intervals and if 120Hz AC component is present it would be also present in the measured data but at much lower frequency due to aliasing. Depending on AC 'noise' amplitude it might present a problem or not.
        You're talking about AC bleeding back into the DC side of the system? I would expect that to be well-filtered, but also I think if it were causing measurement issues we would hear about them (?). My DC SOC estimator seems very, very accurate so far at least at 1/6-scale (AC and DC) loads. I can put my scope on my shunt to see what we see, but practically speaking I don't think there is much of an effect, if I'm understanding what you're saying. I'll put it on the list to test, though... it's easy enough.

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        • #64
          Originally posted by Mike90250 View Post
          worth a thousand words. These burnt battery boxes were not DIY:
          It's certainly effective marketing...


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          • #65
            Originally posted by nebster View Post

            At the end of the day, certainly, everyone will have a different safety level that allows them to sleep at night. Myself, I'm primarily worried about something so exothermic and rapid that it prevents me from physically escaping a runaway before it becomes deadly.
            OK, that's your choice

            Originally posted by nebster View Post
            I'm convinced LFP can't achieve this, while conversely I think the cobalt chemistries are all too risky. There are plenty of other combustion mechanisms on board my RV that can also result in the whole thing ending up on fire; I can't fully eliminate all of the risk in any case.
            there's a difference- other 'dangerous' things on board of your RV probably passed certain certification before you bought them. That would mean they have history of things going wrong and those certifications reflecting this. You creating LFP bank yourself and I simply wish you to avoid learning one or two small details the hard way. I have no doubt you know what you're doing electrically but safety is different kind of expertise often learned off failed designs.

            Originally posted by nebster View Post
            You're talking about AC bleeding back into the DC side of the system? I would expect that to be well-filtered, but also I think if it were causing measurement issues we would hear about them (?). My DC SOC estimator seems very, very accurate so far at least at 1/6-scale (AC and DC) loads. I can put my scope on my shunt to see what we see, but practically speaking I don't think there is much of an effect, if I'm understanding what you're saying. I'll put it on the list to test, though... it's easy enough.
            In abstract sense- yes, AC bleeding. What I meant is inverter feeding AC loads would consume energy according to sine wave on the load side. It would cause equivalent unipolar sine wave on DC side in the consumed current as the voltage would remain relatively constant.

            Depending how big that AC component on top of DC component of the current going through shunt is it could be ignored for the purposes of coulomb counting or not. If you could hook up scope parallel to the shunt you'd see this right away.

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