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  • reed cundiff
    replied
    Our system does have fairly good BMS. Manzanita Micro monitor does show voltage of all 16 cells. I am to OCD to be happy without BMS and monitor

    Leave a comment:


  • Sunking
    replied
    OK PN but still at some point the cells will become unbalanced and need corrected.

    What I am driving at if you only monitor string voltage, all 16 cells in series, does not ell you what is going on with each cell. That can get you into trouble when battery voltage gets low because on eor more cells can fall below minimum threshold.

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  • PNjunction
    replied
    Exactly!

    Unlike an EV where space is at a premium, and capacity is paramount limiting the size / and trying to maximize the DOD of the bank, in a solar house bank where one still designs for a 50% DOD just like lead-acid, that large cushion of being able to go down to 80% DOD without harm allows you to do a slight tradeoff of running from 10-60% DOD, where balance (unless it is just whacko from the start) won't be much of an issue. It also cuts down on accumulative parasitic reactions, albeit slight every cycle. (electrolyte oxidation, SEI layer growth)

    Still, the warning here is that even a first timer who just throws a bare pack on a 13.8v charge source, still needs to babysit the very first charge just to make sure that the distributor didn't miss charging a cell close to the others. Stuff happens.

    It really is weird to deal with lifepo4 at first, since we are trained at birth to always achieve 100% SOC otherwise bad things happen. And with no sulfation, no penalty for psoc. I knew this going in, but once I got a first-hand taste of it, wow. It is all the options it opens up that freaks you out. You just figure out what tradeoffs work best for your installation.

    Leave a comment:


  • Sunking
    replied
    Originally posted by PNjunction View Post
    Nice.

    If that were my bank, I'd simplify by charging at no more than 56V (3.5v per cell max ideally), and not sweat small deviations, as long as they stayed under 3.6v under charge. I might tweak any outrunners by a simple individual discharge for a little bit, but that's about it.

    But I can understand those that need the assurance of an external circuit. Remember, I love to use my Flukes.
    OK so you are saying you never take your batteries to 100% SOC.

    Leave a comment:


  • PNjunction
    replied
    Nice.

    If that were my bank, I'd simplify by charging at no more than 56V (3.5v per cell max ideally), and not sweat small deviations, as long as they stayed under 3.6v under charge. I might tweak any outrunners by a simple individual discharge for a little bit, but that's about it.

    But I can understand those that need the assurance of an external circuit. Remember, I love to use my Flukes.

    Leave a comment:


  • Sunking
    replied
    Originally posted by PNjunction View Post
    This is an excellent example of what is not our application. High voltage - and high current.
    Huh? It is smaller than a solar 48 volt system. V1 is 48 volts @ 100 AH, and V2 is 96 volts @ 100 AH which is the equivalence of 48 @ 200 AH using the exact same batteries you are using. How is that any different?

    I charge both at C/2 but could easily drop that down to C/10 or lower if I desired. LFP batteries were developed for EV's like most of the R&D going into lithium chemistry. Solar is just a side show. When I cruise around in the cart I am only pulling 20 to 30 amps depending on grade of road surface. It only uses high amps when accelerating or climbing a tree. No offense but i am not sure what you are driving at. LFP is LFP regardless of how it is being used. Only difference in my mind is justifying the cost of using LFP. I cannot do that for solar application other than maybe a niche mobile application where weight is a concern. FLA cost 1/4th of LFP and only last half as long as FLA making them roughly 8 times the operating cost. So sorry if that were me using LFP on solar other than say small scale, dang right I will use a BMS to protect that investment and get as much life out of it as I can.

    So help me out on what I am missing?

    Leave a comment:


  • reed cundiff
    replied
    PNJunction

    You have provided quite a bit of useful information over the last few months of looking at this forum.

    The BMS charges at 57.6 V in absorb but cuts off charging at 54.4 volts. float. Maximum voltage of the battery bank would be 62.4 V but the BMS cuts it off (as noted) at 54.4 V.

    The Tri-Star monitor gives the charging rate in amps (48 V nominal) and watts.

    The Manzanita monitor gives: voltage of each cell (16) and of battery bank, charging (discharging) rate, Watt-hours above/below full charge. Happily, the Manzanita and Tri-Star Monitors give the same voltage values for the battery bank to tenth of a volt

    Reed and Elaine

    Leave a comment:


  • PNjunction
    replied
    Increasing capacity with multiple smaller cells

    Example:

    You ordered a 12v / 100ah lifepo4, but quickly realized you really needed 200ah.

    What would be the worst thing to do? That would be to order another 100ah battery, and merely parallel them at the ends, much like you would with a lead-acid 12v battery simply because you have no other choice.

    The rule of thumb here is:

    "Parallel your cells to build up capacity first into groups, and then series-connect those groups together to get your voltage."

    Schematically, our simple 12v / 4-cell would look like this, where "C" stands for a 3.2v cell, and "-" stands for a series link. Note that I'm not indicating any cross-connecting polarity needed when going from group to group to keep the visual simple.

    C - C - C - C

    But now you've received your additional cells. Merely expand upon this theme:

    CC - CC - CC - CC

    In this case, we are still at 12v nominal here, but the capacity is doubled. Now you have to make sure that they are banded / strapped together properly too.

    One can expand upon this theme and come up with some operational advantages, (like a ship at sea that needs extreme redundancy) but this goes beyond the realm of KISS, and of course actually introduces more points of failure. At some point, it becomes ridiculous, much like trying to make your own bank out of hundreds of small cylindrical 18650's. If you want to retain your sanity and safety, don't go there.

    Ideally, from a KISS standpoint, reduce your cell count if you can. Note that unlike lead-acid, an error in over-capacity won't cost you in battery life due to sulfation. It will just be heating up your wallet instead.

    Leave a comment:


  • PNjunction
    replied
    Reed - that's a nice collection of CALB cells for sure.

    While I don't recommend you change your existing setup, nor have any comment on the quality of Manzanita Micro, it does add an additional point of failure and cost, even though it may work until the end of time. I'm sure it wisely includes an LVD and HVD, along with balancing.

    The overall message I'm portraying here is that extreme balancing can be excessive when all we have to do is lower our overall charge voltage, and given the abundance of capacity we build into our systems as solar users, we also don't need to go nuts at the bottom like EV'ers do, stopping at a relatively conservative 80% dod maximum. That way if one cell is truly at 85% DOD due to a slight imbalance, we aren't going to worry too much since we don't plan on hitting an LVD every day. One may very well find that if the cells are properly charged at the factory, an extreme balancing procedure under OUR typical house-bank conditions may not be necessary at all.

    In the case of KISS, an external LVD, along with the HVD as set by the CC or ac charger, may be all one needs.

    Still, you have what appears to be a very nice setup.

    Leave a comment:


  • reed cundiff
    replied
    Vince

    There are a lot of threads on permanently fixed on roof (flat versus tilted) versus ones you place on ground. The best reasons for ones placed on ground is that you can site your RV in the shade and place the panels in the sun - and then move them and tilt them as required. The main reason for fixed is convenience and the fact that they are charging battery bank while you are traveling.
    Reed and Elaine

    Leave a comment:


  • SunEagle
    replied
    Originally posted by reed cundiff View Post
    Hmm, wish it were not a typo, or I could be running an EV down the road at 60 mph as long as the sun shone.

    We are currently almost fully in the shade otherwise we would be charging around 500 W rate since the Fort Collins area is cloudy and rainy this week. We have gotten 1300 W to controller at mid-day in mid-summer and are to absorb by late morning. As noted in earlier post, we run Dometic refigerator (power hog) on AC 24 hours a day when dry camping in desert. This results in a -3 kW deficit by morning.

    We have 1420 W of solar panels (6 x 235 W panels). They just do not do well in tree shade. I wrote on another thread (or earlier on this one) that we spent 6 days in Olympic Rain Forest and dropped about 50% DOD. Did call a NP CG and asked if they had any solar friendly sites. I was gently chided "Sir, this is a rain forest, your solar panels will not be very effective!" But the LFP battery bank does hold us well for quite a few days in shade using micro-wave and some forced air heater in the morning (in winter). Lasted another six days in deep shade at Portal NF CG in SE Arizona with no problems. We turn off the inverter when it is not in use in these situations since it draws around 60 W phantom

    You have to choose your sites carefully for sun when dry camping. We do a lot of boondocking in western NM and eastern Arizona and there are few problems there (no trees, no shade). If there are trees, then we look for a site that will give us solar insolation through early afternoon and then shade in the mid afternoon to evening. Most FS CGs have a few sites with solar. Dispersed camping sites can be found in open terrain. Most folks want shade. Had great solar on beach in Yucatan and about two hours of solar when camped in jungle at north end of Lago Bacalar (it was sufficient with older 700 W solar system).

    Dry camping/boondocking is what we prefer: quiet/solitude, wildlife, interesting people of the same general attitudes and interests. Almost everyone that boondocks has 100 to 1500 W or more of solar. Have had delightful times with these other folks. Battery banks are from two x 6V batteries to more than we have.

    Please contact us if you have further questions on boondocking. RV.Net has a lot of threads on this as well.
    Reed and Elaine
    I appreciate the info. My wife and I will probably not "rough-it" in the beginning and go to places that have utility hook ups but I want to prepare for the day when we do go dry camping and understand what my small "solar system" might be able to do for me in case fuel becomes an issue.

    I currently have about 500 watts of panels in various wattage (4x40, 2x80 and 2x90) with the 4 big ones (see pics) mounted to bases that fold down and can be stored in the RV. They then can easily be set up close enough to the batteries for charging. Not the best equipment but I purchased before I came here and read about what I really should have gotten.

    Thanks for your help.
    Vince
    340 watts of pv panles.jpgBehind PV panels.jpg

    Leave a comment:


  • reed cundiff
    replied
    Hmm, wish it were not a typo, or I could be running an EV down the road at 60 mph as long as the sun shone.

    We are currently almost fully in the shade otherwise we would be charging around 500 W rate since the Fort Collins area is cloudy and rainy this week. We have gotten 1300 W to controller at mid-day in mid-summer and are to absorb by late morning. As noted in earlier post, we run Dometic refigerator (power hog) on AC 24 hours a day when dry camping in desert. This results in a -3 kW deficit by morning.

    We have 1420 W of solar panels (6 x 235 W panels). They just do not do well in tree shade. I wrote on another thread (or earlier on this one) that we spent 6 days in Olympic Rain Forest and dropped about 50% DOD. Did call a NP CG and asked if they had any solar friendly sites. I was gently chided "Sir, this is a rain forest, your solar panels will not be very effective!" But the LFP battery bank does hold us well for quite a few days in shade using micro-wave and some forced air heater in the morning (in winter). Lasted another six days in deep shade at Portal NF CG in SE Arizona with no problems. We turn off the inverter when it is not in use in these situations since it draws around 60 W phantom

    You have to choose your sites carefully for sun when dry camping. We do a lot of boondocking in western NM and eastern Arizona and there are few problems there (no trees, no shade). If there are trees, then we look for a site that will give us solar insolation through early afternoon and then shade in the mid afternoon to evening. Most FS CGs have a few sites with solar. Dispersed camping sites can be found in open terrain. Most folks want shade. Had great solar on beach in Yucatan and about two hours of solar when camped in jungle at north end of Lago Bacalar (it was sufficient with older 700 W solar system).

    Dry camping/boondocking is what we prefer: quiet/solitude, wildlife, interesting people of the same general attitudes and interests. Almost everyone that boondocks has 100 to 1500 W or more of solar. Have had delightful times with these other folks. Battery banks are from two x 6V batteries to more than we have.

    Please contact us if you have further questions on boondocking. RV.Net has a lot of threads on this as well.
    Reed and Elaine

    Leave a comment:


  • SunEagle
    replied
    Originally posted by reed cundiff View Post

    Currently in an RV park (oh the shame and humiliation) and we are in total shade (get back about 600 kW-hours a day). Have paid attention to PNJunction and only hook up the 15 amp cord through the battery chargers when we get down -3500 W-HOURS

    Reed and Elaine
    That 600 kWh a day is probably a typo so I guess you are talking about 600 watt hour a day.

    I am also curious as to how many watts of solar panels you have and how they are charging your batteries being in the shade or are the panels in the sun and your RV in the shade?

    I'm not trying to be sarcastic. Just trying to understand what limitations I might see when my wife and I decide to do more RVing in the future that might take us to some dry camping places.

    Leave a comment:


  • reed cundiff
    replied
    China Aviation Lithium Batteries

    Just checked the fabricator of our batteries, Manzanita Micro. They primarily produce battery packs/banks for EVs. The cells are China Aviation Lithium Batteries (CALB). It turns out that CALB makes Manzanita small.jpg lithium battery banks of up to 200 kW-hours. Attached is photo of a battery (4 cells) similar to ours. "...Available in 180Ah packs. Includes: 4 Lithium Ion Cells, Aluminum Battery Box, Lexan Top, Fully Assembled Reg Deck, All necessary hardware, and Regulator..The battery box is 8" wide, 12.5" long, 13.5" tall (without lugs). Total weight with 180Ah cells is 63 lbs/ 28.5 kg."

    Mazanita Micro designs for the high power demands of EV but work well with the lower requirements of RV living. We have four of these in series for a 48 V (nominal) system. We do have room for another two batteries and 700 W more on roof, but this would cost quite a bit more, require redesign and configuration, and we can see no reason to do such.

    Currently in an RV park (oh the shame and humiliation) and we are in total shade (get back about 600 kW-hours a day). Have paid attention to PNJunction and only hook up the 15 amp cord through the battery chargers when we get down -3500 W-HOURS

    Reed and Elaine

    Leave a comment:


  • PNjunction
    replied
    Don't cheap-out!

    Yeah, I too would like to see the prices of lifepo4 prismatics come down. Just don't be tempted to go with fly-by-night or no-name manufacturers just to save a buck here and there. Personally, I'd stick to GBS, CALB, Winston, and perhaps Sinopoly or Hi-Power.

    Why? Aside from possibly of using poor quality chemicals, and maybe shoddy exterior construction, little concern may be placed upon the precision of how it's made INSIDE, and that's important.

    What I'm talking about is precision alignment and size of the materials themselves. Essentially the cheap ones may have little knowledge of what is known as "overhang", or purposely making one set of plates if you will, larger than the other. This is to help prevent dendrite formation. They also need to be aligned inside. Some of the counterfeiters of the small cylindrical 18650's may cut corners in just this fashion - leaving you with a dendrite short later.

    This is also the reason that once you have a bulged / swollen cell, and somebody thinks that all you have to do is squeeze it back together again is wrong. Sure, you may be able to do so physically, and the cell may even appear to operate ok - for the time being. BUT, you may have lost the internal alignment, and now you face the great possibility of future dendrite growth, and an eventual internal short.

    Leave a comment:

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