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mcp

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Posts posted by mcp

  1. 18 hours ago, K4309 said:

     

    Question @Island Time, how many people actually charge or have alternators big enough to charge LiFePo at 1C? 

    It's not that difficult or vastly expensive to spec an engine with big alternators. The picture below is of a recent install of mine with a lithium bank being happily and safety charged at 5.8kw off a 110hp engine with 2x large frame alternators. The Alternator setup including electronics and my time was just over $1 a watt. This was excluding a mount bracket that needed to be made.

     

    Totally agree with Islandtime about the comparison with lead carbon, and ill add that lead carbon have pretty bad voltage sag under high load draw in my experience. 

    Screenshot_20231024-110540~2.png

  2. On 4/02/2023 at 8:10 PM, Black Panther said:

    Has anyone used it? With all the recent damp the decks and canvaswork both growing things.

    Would it work? Is runoff likely to damage my awlgripped hull?

    Active ingredient in wet and forget is benzalkonium chloride, also found in the cheapest disinfectant in pak n save at a similar concentration minus the surfactants.  

    image.png

    • Haha 1
  3. On 15/01/2022 at 11:57 AM, Psyche said:

    my existing system with a carbon foam LA

     

    IMG_0507.thumb.jpg.35f2be96a8d93dc4961ea30bd43d49dc.jpg

    I would be very surprised if your existing gear can be programmed to suit carbon foam batteries, and then not be programed or made to work with lithium.  Carbon Foam batteries do not share the same bulk, absorption, float voltages with any of the other LA batts.  What brand Carbon Foam are you looking at?

  4. On 15/12/2021 at 3:24 PM, Island Time said:

    OK, here is my current level of knowledge. I'm not a LifePo4 specialist, and currently experimenting!

    Why would you want LiFePo4 batteries. 

    1. Light weight - for my tests, I've put in 2 120 a/h batteries giving  192a/h useable at 80% depth of discharge. They can each be carried easily in one hand. They replaced 2 200 a/h VRSLA batteries weighing 62KG each, and gave 200 A/h useable capacity at 50% dod.
    2. Life span - the VRSLA's give 400-1000 cycles - the LiFePo4 about 3000 cycles, both at the manufacturers recommended dod.
    3. Charging abilities. A good LiFePo4 battery can accept huge charge rates right until full - no bulk/absorbtion/float required. It is amazingly quick to charge (provided your charging system is up to it - an alternator designed for lead acid may quickly fail. 
    4. Voltage stability - LiFePo4 batteries keep very stable voltages until almost empty, when it drops VERY fast... 

    Why not?

    1. Your charging system will need careful consideration and planning - for all charge sources, Aternator, Solar, Wind, Shore Power, Genset - whatever you have will need to be set up for the right voltages - EVEN WITH DROP IN - because they are not! LiFePo4 is different. All these things either have to be set up correctly, or, if they cannot be, then replaced.
    2. LiFePo4 batteries, especially drop ins, are not starting or high current batteries. Check the specs for max discharge rates for high loads. Sometimes this can be overcome by several smaller capacities in a parallel bank rather than one larger one.

    LiFePo4 batteries don't need - or want - to be kept at full charge all the time, so you have to change your mindset about this. Also, other stuff may change - like on Island Time for example, the watermaker draws 24a at 12v when in production, so we used to only use it when the engine was running. However, now, as the batteries can take the full alternator output (around 90-100a continuous in our case) it is now better to run  it off the batteries, and top them up if needed. 

    The NZ regs state among other things, that lithium batts must have audio and visual warnings, at the normal operational station of the vessel,  before battery shutoff. This is a problem for virtually all drop in batteries.  So, at this point, there is no way to use a drop in battery and comply with the law. There is no device I'm aware of that will talk to a drop in system's internal  bluetooth BMS (Battery Management System) and facilitate this.

    Next, the drop ins are normally made from cheaper grade cells, that may not be matched or balanced. Balance is the voltage control of the internal cells in the battery, normally 4x 3.2v cells for a 12.8v battery. Proper cell balance allows equal charging and discharging of the battery, as well as actual capacity. More on that below. 

    What controls the balance, and can switch the battery on or off is the internal BMS (There are some drop ins without this - don't go there!). Most of the low(er) cost drop ins use FETs for control. A FET is like a solid state relay, it's not bright, it's just a switch. The cheaper FETs will not carry much current, so the ability of the battery to charge, discharge, and balance is or can be restricted. Look at the spec sheet on any battery you are considering, and ensure that the charge rate is good - at least 1c (1x the capacity of the battery in amp hours, so 100a for a 100a/h battery), the discharge rate is workable (what's your highest load the battery could ever see? - electric winches, inverters, anchor winches etc for your boat, and if you can, the balance current for the BMS. That last one can be hard to find! Also, a good manufacturer will be able to provide vibration test data for a marine battery. The most common drop in (therefore the cheapest) around are actually made for LED street lights - so the output can be low amps, the charge by solar low amps as well, and the balance currents can be small. 

    So, the BMS. The BMS will switch off the battery during use if

    1. A single cell voltage gets to low (under about 3 volts)
    2. A single cell voltage gets too high (over about 3.65 volts)
    3. The battery total voltage gets too low (some under 12v, some under 10v)
    4. The battery total voltage gets to high (around 14.6v)

    Some further data first. V=IR so the cells voltage will rise = to the current x resistance of that cell - the other cells may be different.

    A battery can switch off well before full charge, and in fact never get charged if one cell is out of balance, and that cannot be remedied.

    The BMS is supposed to balance the cells, usually either during charging or when the battery is resting. Good BMS units can control how much current goes to each cell, and even bleed from one (higher) cell to top up another. Cheap ones cant do that, they can simply add a little resistance to one cell to reduce the current to that cell, and bleed off the excess energy into heat. If the BMS cannot control sufficiently the voltage of a higher voltage cell during charging, then that cell voltage will rise to the cut off voltage, and the WHOLE BATTERY will shut down at least it's charge side (it likely, but not always, will keep the discharge side turned on). That means that the battery may stop charging when nowhere near its total capacity. 

    This issue is why quality Lifepo4 battery manufactures select matched cells (virtually identical resistance and voltage at the fully charged state). The process of fully charging and measuring the cells is known as top balancing, and is done by individually charging the cells.

    Unfortunately in a drop in, you have no access to the individual cell terminals to do this, and the cells are not usually matched at production either. So you have to rely on the internal BMS to do it for you. This means some will NEVER manage to balance the cells at full charge, and they wont produce the capacity that they should, as the BMS is not capable of correcting the imbalance, depending on time and their balance current. Some of the cheap BMS systems are only capable of a 50ma or less balance current. More info here http://www.liionbms.com/php/wp_balance_current.php for any geeks. Please note that a 1000a/h battery with a 10ma balance current wont balance in YOUR lifetime! This is why balance current of the BMS matters. I learned this with my experimental system - the internal BMS balance current is totally inadequate :-( . 10amp balance current in a 100 a/h batt would be good...and balance in 10 hours from one flat cell.

    Remember from above - one cell can turn off the rest, so one cell at 3.65v then switch off when the others are at 3.4v means  the battery was only around 85% charged when the charging shut down due to poor balance.

    When a LiFePo4 battery switches off without informing the alternator first, the alternator can fail immediately, blowing the diode pack. As the drop in units dont normally have the ability to do that, another method must be employed. I use an Argo Fet based battery splitter, and a SLA start battery, so that the circuit is never simply cut off. Works ok so far....

    There's probably more to say, but this post is long enough, and tests are continuing...

     

    Just a couple of points,  without picking at your post. 

    Low balance current on BMS's in the 10 - 40ma range is perfectly sufficient for balancing small to medium lithium batteries. It's just not working how most people assume, as the majority of people are assuming you are removing current from each cell, while the other cells are receiving charge current. In fact what is happening, it the balancing is resistive [yes you do get a current measurement] and works from a voltage drop standpoint. The cells being balanced have a slightly lower voltage, therefore less charge acceptance, with the other cells are charging at a higher current, so they are catching up and not the out of balance cell having current removed. Balancing should only occur during charging and there is very little point is balancing happening until you are getting above 3.45v a cell, as below that the charge curve is to flat and you do need a difference in potential to be effective. 

    FETs,  or MosFETs as in the case of what is used in most BMS's have very low resistance when full on,  they also are perfect for this role as because once the gate charge is applied there is no further current draw from the device,  also the resistance between on and off is such that they can be used as variable resistor, to resistively balance the cells in the pack. 


    You can top balance your drop ins. Bring them slowly up to 14.6v, from 14.2 over a few days on a bench top power supply should do the job perfectly. There is no real capacity to be gained here, but is will equalise the cells if you are worried about voltage difference between them.


    With regard to starting engines and running high loads, lithium batteries are vastly superior if the BMS can handle it. The fusing requirements for lithium based batteries is an indicator of this as you need an arc interrupt capacity of 20,000amps and currently, Class T fuses are the only accessible marine fuses I know with this rating. A lead battery of any type can not sustain the current output and voltage stability of most lithium battery types of equivalent capacity.  


    Audio and visual warnings, a battery monitor like a Victron 712 would be sufficient and this is what I use. 


    Perfectly matched cells is another internet myth that is persistent. It is true to a degree, but the internal resistance is such that you would need to be pushing some pretty massive current or likely have faulty cell in order to have a real world issue and that might be a couple of percent lower capacity for the total pack in most circumstances. If you have a faulty cell, you just have a faulty cell like any battery.  Failures can happen.

    • Like 4
  5. 11 hours ago, Island Time said:

    Issues with Tablets are

    1. not normally waterproof
    2. If in a waterproof case they can't be charged/plugged in without compromising the waterproofing
    3. The screens are not great in direct sunlight
    4. Some don't dim down sufficiently for night use, without compromising your night vision
    5. Can be fairly easily broken if not actually mounted in a bracket
    6. Can be an issue to get instrument data, radar, AIS, sonar data connections, depending on what you have
    7. Can be difficult/impossible to use in poor weather, water, snow, etc

     

    I have a Samsung Galaxy Tab Active running OpenCPN.  Its waterproof, can be charged when wet, as it has Pogo pins on the side (docks are avalible), screen isn't the best in direct sunlight...But I just move it, DIMs down fine at night, Its tested to MIL-STD 810G US military standard for ruggedness, I use signal K sever [can run on almost any device]for AIS Sonar Data and can run radar this way, Has a S Pen that works when device is wet....but to be fair it works pretty well when wet with your finger anyway. 

    Comes in a 8inch [i have this one] and 10inch sizes.

    https://www.samsung.com/nz/tablets/others/galaxy-tab-active-8-inch-black-16gb-lte-sm-t395nzkaxnz/

    Example of one of the numerous charing mounts for these using the Pogo Pins https://www.rammount.com/part/RAM-HOL-SAM60PU

  6. 19 hours ago, darkside said:

    My boat won't pass the new rules. Nor would the one we circumnavigated in.

    However I would be reluctant to go through any documentation process for the sole reason of avoiding a safety inspection or requirement. That would open a huge can of worms for any insurance claim or third party liability should something go wrong.

    Once offshore you can register your boat back to New Zealand?

  7. 18 hours ago, Black Panther said:

    Industrial strength curls are burning out the pump.

    A diaphram bilge/shower pump wouldn't be bothered by even the most industious of curls.   Could be worth a look for next time.

  8. If you are using a Victron Smart Solar MTTP,  you do not need a relay or a switch for a BMS.  You just need someone to program the Victron properly for you. PM me if you need help.

    Also what BMS are you using?   Most are overly complicated for little reason. 

    @Island Time Solid state relays generate heat when closed as well,  because of high internal resistance.  A mechanical latching relay would be the most idea relay for this instance,  if it can be controlled from the devices. 

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