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  1. #1
    Join Date
    Dec 2007
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    Default 12 Volt Battery System; Nickel-Iron Batteries.

    Hi,
    I am fitting out a workshop and I want to generate and store 12 volt DC power.
    Today I first heard of nickel

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  3. #2
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    May 2012
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    Woodstock (Cowra)
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    Default

    Lithium ion Li is the preferred battery and you would be hard pressed to find any cordless tool new now that uses NiCd batteries.

    If you can give us an idea of the type of cordless tools you are going to use and for what purpose, we can give you a better idea
    The person who never made a mistake never made anything

    Cheers
    Ray

  4. #3
    Join Date
    Dec 2007
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    Lindfield
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    Default

    Thanks Ray,
    I am hoping to end up with an off grid solar powered workshop.
    Regards,
    Phillip

  5. #4
    Join Date
    Oct 2007
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    Alexandra Vic
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    Default

    For off grid, ideally you want a higher voltage battery pack to reduce the current drawn from or fed to the battery pack for a given power level.
    If possible, avoid all forms of lead acid storage, as they have very limited life if you draw down on their capacity significantly. To operate a nominal 1HP (750W) motor at full load, the inverter needs to draw at least 750W from the battery bank, plus additional to covering wiring and inverter losses. All up around 65 A, which needs substantial cabling etc, and would flatten a nominal 100AH battery bank in about 40 minutes. (Lead acid batteries amp hour ratings are normally calculated for discharge over 10hrs, so a 100AH battery is rated to supply 10A for 10 hours. As the current demand increases the capacity available decreases rapidly, so for a 50A discharge rate, the capacity is more likely around 50AH rather than 100AH. Plus at this sort of load rates, the batteries could well have a lifetime of 100's of charge/discharge cycles, instead of 1000's. If you want to preserve the potential lifespan of LA batteries, you size the pack so that you don't discharge them more than 10-15% of their rated capacity in any anticipated cycle, which should give new batteries a life of around 3000 cycles or more.

    If you can up your battery voltage to 24V you halve the charge /discharge currents for a task, at 48V you cut it to 1/4 what it would be for 12V.

    The current way to go really is Lithium Iron Phosphate, which are dearer than LA, but have significantly less charging losses so can better utilise the input from your solar panels. They can also be discharged to about 80% of rated capacity regularly without impacting on the lifespan of the pack, so 3000 cyles to 80% discharge is a realistic expectation. These batteries are common in the modern electric vehicle sector, and are popular in the off grid and grid connected battery storage sector and are available in a range of cells to 400AH. As an indicator, the two Mitsibishi EV's use 16AH cells in packs around the 300V mark. These give the Outlander Plugin Hybrid a 45km battery only range, and the I-miev pure electric a range of over 100km. Aussies are actually importing used EV packs from wreckers in Europe and the US to reconfigure for domestic use packs.

    If you want to connect with the solar users/experimenters/designer/installers, Energy Matters operate a very good forum dedicated to the topic.

    Re Nickel Iron, I am not aware of anything in the market at the current time that is viable, but did used to have a Military Surplus 24V 10AH pack about 50 years ago. These were purchased dry and used a saturated caustic soda solution as an electrolyte. Individual cells were in enameled steel cases with moulded hard rubber tops, and produced 1.2V nominal, with the capacity rated for 20 hr discharge. Weight wise, a pack assembled from these was way heavier than an equivalent capacity LA motorbike battery.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  6. #5
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    Dec 2007
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    Lindfield
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    Many thanks Malb for your informative reply.
    Do you have any comment on the longevity of nickel-iron batteries?
    Weight is not an issue, once they are installed in what I am doing because whatever battery I use it will stand on a 100mm concrete slab.
    I see there are nickel-iron batteries advertised on e-bay.
    Again, thanks for your comments,
    Phillip.

  7. #6
    Join Date
    Oct 2007
    Location
    Alexandra Vic
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    I looked at the listings on ebay and the main difference between the 10AH units there and the ones we had 50 years ago would be the transparent cases that allow a visual check of electrolyte levels vs the older style enamelled steel cases. The ones we had were mil surplus from a disposals store in QLD, and were date stamped in the 1940's to very early 1950's, the ebay ones appear new. Ours were bought abt 1973, and operated spasmodically until abt 1978, although their was a fairly linear failures vs time during that period, i.e they all worked but probably below nominal capacity initially, about half had dropped off their perch midway, and they weren't worth charging by the end, but we had no knowledge of their former use. Beyond that, I can't comment about expected lifespans, but the technology appears very similar to that of the 1940's, but despite the supposed benefits, they haven't replaced LA in the 70+ years since. A bit of time on google or similar might turn up better results for you.

    It is very bad form to leave any wet cell system resting directly on a concrete floor for long, as the colder floor and generally warmer electrolyte cools the lower levels of electrolyte and tends to cause the electrolyte concentrate at floor levels to the point where the electrolyte comes out of solution and crystalises at the bottom of the case, reducing the concentration and capacity. I note that the ebay vendors photos for high power sets have support frames that keep the cells well clear of the floor.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  8. #7
    Join Date
    Dec 2007
    Location
    Lindfield
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    Default

    Thanks for your further thoughtful and much appreciated reply.
    If you think of more comment, I would be pleased to read it.
    Meantime, I need to more homework.
    Regards,
    Phillip.

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