Lithium batteries

Discussion in 'Boat Design' started by Capn Bogbrush, Oct 2, 2019.

  1. Deering
    Joined: Feb 2005
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    Deering Senior Member

    You might be able to get past the temperature limitation by incorporating a pre-heater for the times that you need to cold charge. Some of the battery management systems have a safety shutoff to prevent charging below freezing. Others have charge current limiters.

    I installed a LFP house bank this year, replacing my old AGM’s. I didn’t appreciate the complexity of the change. LFP batteries have a very different charge profile than lead acid, so your charging system needs to accommodate that. Also, when the batteries are full they simply shut off abruptly which can damage your alternators. If I did it again I’d probably go with an integrated system that allows everything to communicate with each other (alternators, chargers, batteries...). A lot of the internal battery mgmt systems lack the capability to communicate with other components of the charging system. I’d probably go with Victron batteries and management system and Balmar alternators with lithium-smart regulators.

    That being said, my current system seems to be working well, but I need another season to fully evaluate. I saved about 300 lbs in the switch.
     
  2. portacruise
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    portacruise Senior Member

    This site has good general information on some of your questions, including comparison tables and specific data comparisons

    BU-216: Summary Table of Lithium-based Batteries – Battery University https://batteryuniversity.com/learn/article/bu_216_summary_table_of_lithium_based_batteries

    Look under super caps for your capacitor question, and under specific battery types for specks on low charging temperatures.

    There is conflicting info on the web regarding LTO cycle life with some sources listing 1000 cycles and others listing more than 20,000 Cycles, perhaps all don't reflect the current state-of-the-art.
     
  3. gonzo
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    gonzo Senior Member

    The amount of cycle life depends hugely on the quality of the battery construction. You would not expect a Ford Fiesta to compare in reliability and performance Toyota 4 Runner. Check the reports of the brand you are buying. Usually, you get what you pay for. Many of the no brand items sold online have either no warranty, or the requirement that the buyer ships the items to China where they will decide whether the warranty applies or not.
     
  4. portacruise
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    portacruise Senior Member

    Agree Gonzo, but I have never seen that large of an estimated range from 1 to 20000, compared to most of the others with usually a factor range of well under 5X, for a commercial product- available to the public. LTO charging and charging amps allowed below freezing estimates also seem to vary widely. Of course there are other factors that affect the cycle life which is usually stated for the most perfect and Optimum conditions. Undesirable ambient temperature operating conditions, High rate of charge and discharge, and especially depth of discharge can greatly affect cycle life.

    As I understand it, nicad batteries are one of the few chemistry's that thrive or at least tolerate deep discharge down near 0 volts, so long as cell reversal is avoided. The first satellites used specially purpose-made nicads as I recall, and some of them may still be operational to this day. Hobbyists have been using recycled Prius nimh batteries for their custom EVs because of their very high quality and great specs. These nickel systems are generally lighter, smaller, than AGMs, and with comparable prices, so might be worth a look by the OP?
     
  5. Dejay
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    Dejay Senior Newbie

    I think you should decide if you really need operations in freezing temperatures first. Then make a spreadsheet with the cost of usable energy stored over lifetime. Deep discharge would just be how much usable watt hours you have in the battery. It's not an advantage in itself. Depth of discharge will also influence how long they last. Number of recharge cycles is makes your battery cheaper compared to others - but maybe you don't really need the batteries to last that long. But lithium is already cheaper than lead acid. Don't know about nickel. LTO is definitely more expensive.

    It's no use speculating, just try to find the numbers and compare them.

    Here is another video about the cost comparison.
     
  6. Capn Bogbrush
    Joined: Oct 2019
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    Capn Bogbrush Junior Member

    This is very useful :)
    I think I will have to try to find someone to collaborate with on LTO research - as you say they are considerably more expensive than other Li cells but they do have the extended temperature range which is very tempting.
    Unfortunately the water does sometimes freeze around my boat. The frost stat on the cabin heater is set to come on at 3.5°C so, in theory, the batteries could be installed inside the cabin but that could prove difficult and I'd still be concerned that the local temperature might get too low. I guess a thermostatic heating mat would afford some additional peace of mind.
    Are you making a distinction between capacity and current? As I think I already said; I don't know a great deal about batteries but have observed that LA batteries can struggle to start a vehicle at lower temperatures. I assume this is due to the chemical reaction being affected by temperature but I don't completely understand whether the reduction in capacity is reversed once the temperature rises.
    I'm failing to understand what makes Li-ion cells more like a capacitor than, say, LA cells. Don't both work in a similar way - transferring ions (charge) from the electrolyte to the electrodes?
     
  7. gonzo
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    gonzo Senior Member

    Capacity is measured in watts/hour. Current is measured in Amperes. They are two very different parameters.
    Lead/acid batteries have a Redox chemical reaction that transfers electrons from one compound to another. The reaction is reversed when the battery gets discharged
    A Li Ion battery has an initial chemical reaction (formation done at the factory) that generates free ions. The ions are transferred from one electrode to another through the introduction of a charge, like in a capacitor. The physical characteristics of the electrodes are important, particularly the crystalline structure. Basically, the electrode needs holes for the ions to be stored. There is also a passive layer created at formation where Li ions are trapped and not free to be used for charge/discharge. At the end, the specifications, warranty and reviews if available are what should matter to you.
     
  8. Capn Bogbrush
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    Capn Bogbrush Junior Member

    Thank you. Very useful info. And a chemistry lesson too :)
     
  9. gonzo
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    gonzo Senior Member

    I spent a few years in battery research. Some of the chemistry stuck with me.
     

  10. Dejay
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    Dejay Senior Newbie

    Gonzo, this is totally off topic but I'd love to hear your take on the Molten-salt battery (or liquid metal battery) for stationary gridscale energy storage. It sounds brilliant to me but there doesn't seem to be much investment. Lecture for anyone interested.
     
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