Lithium Battery Bank 12v Motorhome

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  ocular on 11/09/2022 - 07:20

  Do you have a 12V DC DC charger in your system that can charge LiFePO4 batteries? Whats the physical space you have for the batteries. If you have had AGM 3x120Ahr ideally for longevity you shouldnt use greater than 30-40% of their capacity. Has 120-150Ahr useable capacity been enough? https://mullerenergy.com.au/product/muller-energy-12v-200ah-…
  would give you 80% x200Ahr=160AHr useable capacity and more efficient charging. Ruben has a good reputation and is on OZB. There is another guy Power Paul on facebook that had good reports with LiFePO4. IMHO you need a monitoring system where you can see what is happening to each cell voltage of the LiFePO4 pack (usually blue tooth connection to smartphone app). Not just the overall voltage

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    fishing on 11/09/2022 - 15:21

    Thanks for your response. The DC DC charger is red arc and manages where the power comes from. This then enters via the Enerdrive system which manages how fast and how high the batteries charge. The Enerdrive system has a Bluetooth connection for monitoring. It is capable of being programmed for dealing with AGM or lithium.

    The current battery system has failed and rather than replace with AGM I thought now was the time to jump to lithium. Current system allows me to be off grid in rain for 7 days running laptops, pumps, fridge, lights and inverter for microwave in required.

    Are there Different kinds of lithium batteries or are they all LiFePO4?

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  Euphemistic on 11/09/2022 - 07:36

  Check out some caravanner forums. Lots of good knowledge there specific to off grid van life.

  3x100 has advantage of ability to remove one battery if it falls over or to distribute the weight more efficiently.

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    fishing on 11/09/2022 - 15:23

    Thanks. Many many many opinionated people on caravanning forums and very confusing so I’ve been avoiding them so far while looking at what on eBay etc. thought I need to upskill do I don’t get confused In the forums

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      Euphemistic on 11/09/2022 - 17:09

      And you think there aren’t opinionated people here?

      Unfortunately you’ll get all sorts of responses online and it gets hard to weed out the accurate and helpful information.

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  rooster7777 on 11/09/2022 - 08:53

  12V 100Ah lithium should weigh minimum 11-12Kg. (so about half a similar AGM) Anything less is most likely not 100Ah. Size should be similar to AGM (with a fair bit of spare space in the battery case)
  12V 300Ah SHOULD have all cells balanced, with no chance of imbalance. 3x 12V 100Ah SHOULD have cells of each battery balanced, with no balancing between batteries -which may lead to imbalance across the batteries with increased load on an individual battery and subsequent battery damage. (Speaking of balancing, if you have batteries in parallel it's important how you connect them (in terms of wiring lengths, and equal loads - otherwise you can have real problems with charging and loads being shared unequally leading to failure)
  12V lithiums require a different charge profile than lead batteries - any lithium marketed as a "drop in replacement" should be viewed with cynicism.
  I'm not familiar with enerdrive equipment, but a quick internet look indicates a wide range of stuffs. You do need to be able to charge them at voltages the battery manufacturer/ retailer advises.

  Matters you haven't asked about, but may/may not be aware of:
  As ocular mentions above, lithiums have a far greater effective capacity than lead, and also charge far more quickly. If you have found 300Ah of AGMs completely sufficient, and haven't been strangling them by discharging down past say 12.3V, then you are likely to have significant surplus battery capacity with 300Ah of lithium. If you have been strangling them, or running out capacity before strangling them, then 300Ah of lithium will help you with your problems.
  I used AGMs and held off lithiums for a few years because of price (motorhome and "small" off grid battery bank for some of the house load)
  I finally bought 4x 12V lithiums for the 48V off grid battery bank, and 1 to eventually replace the motorhome AGMs (which I haven't done yet) I've had mixed fortunes with those lithiums - in 1 year's constant use of between say 4-8KWh per day (recharged by a much larger solar array than yours) I've had 2 batteries fail and be replaced under warranty (depth of discharge is usually round 60%, and has never been 100%). The bank of 5 was sold to me for a "special price" of $2500. I don't wish to name the batteries because their quality could be considered bad because of those failures, but the supplier has been good and replaced them.
  The more solar you have, the easier things are with batteries, but I recognise limitations on how many panels you can fit on the roof of a motorhome… though if you've managed to fit 2x300W panels you must have a bit of roof size. If you have a bus and lots of roof I'd strongly suggest more panels as a priority. If you have significant periods not travelling, then having panels on the ground alongside the vehicle/ home base would benefit you well.
  If you enjoy the topic rather than it being a chore, I'd recommend collyn rivers book/lets on the subject. They are somewhat dated, but the concepts and information a beginner can learn … I found invaluable some years ago.
  Good luck.

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  fishing on 11/09/2022 - 15:38

  Thanks for your thoughtful reply

  Was full time in Motorhome until beginning of the year , now only use it once a month regularly. There is no more real estate for more solar panels. I found the Collyn River books not as easy as people suggested. I understand the homes 12v electrical system and am capable enough to follow power issues and find hidden fuses etc.

  I don’t have any knowledge of lithium, the quality or reputable sources. I understand there are a lot of dodgy suppliers. My location prohibits travelling to most suppliers. I’m Desert based and there are no suppliers within at least 1500 klm, which is a bigger trip then my leave and RDOs would allow, to facilitate Purchase and return to work in a timely fashion.

  I think you are saying lithium is heavier than AGM and although may be smaller, the casing may be the same size. Would you mind expanding on cell balancing. I don’t understand This.

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  ocular on 11/09/2022 - 22:04

  If you want to waste hours and find some good references about LiFePO4 go to diysolarforum.com
  Balancing is making sure each cell is at the same state of charge (SOC). Understanding the relationship between voltage and SOC is the key. Fig 1 shows it. https://www.researchgate.net/figure/Relationship-between-the…
  The cells require precise monitoring where the control system will isolate the cells if <2.8V or > 3.6V - this is the function of the BMS (battery management system). Balancing is also required to keep the cells all at the same SOC. This is done by monitoring all the cell voltages. This comparison can't be done at the middle-SOC section because a cell voltage of 3.2V could represent a SOC of 30-70% So top balancing is done at the High-SOC section where the cell voltages diverge and better represents SOC. Before a pack is put together all the cells can be put in parallel and charged to 3.6V and they will be balanced. A pack with cells in series can be balanced by passive/active balancer circuit. Cell voltage is measured to 1/1000 of a volt and charge is taken from the higher cells and distributed to the lower cells. When in the High-SOC section the aim is to get the difference between lowest and highest to <10mV. In an ideal system with high quality cells once top balanced cells should stay balanced. But as cells age it is likely balancing will be required. Thats balancing in a nutshell for LiFePO4

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  fishing on 12/09/2022 - 07:23

  Is balancing for LiFePO4 different from ensuring SOC in AGM? I have reached out to Enerdrive and asked what factors I need to talk into account if I move to lithium. Thank you for your time. It is appreciated

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  ocular on 12/09/2022 - 08:06

  The principle is the same - adjusting voltage to determine SOC. It gets much more complicated when cells are in series and you're dealing with such precision measurements and tolerances.