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    Fast attack craft
    by Martin555 πŸ‡¬πŸ‡§ ( Commodore)
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    63 Posts 62 Replies 16 Photos 107 Likes
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    Nerys
    Lieutenant Commander
    πŸ“ Fast attack craft
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    I like my bottled gas for cooking and if we get a power cut have three Tilley lamps for lighting. Don't like relying on the utilities!
    1
    When the winds before the rain, soon you may make sail again, but when the rain's before the wind, tops'l sheets and halyards mind
    Martin555
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    Thanks for that DG,
    Luckily we still had gas to boil the water, but I remember when I was much younger we used to get power cuts extremely regularly, I expect you do too.

    Martin555.
    1
    If it looks right it probably is.
    DodgyGeezer
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    "...I charge them up occasionally and as luck would have it we recently had a power cut so I was able to power up a couple of car headlights so That we could see...."

    A very clever idea! You can get car accessories like immersion coils for boiling water, which may also be useful in the future.

    I have a number of old Uninterruptible Power Supplies sitting around with dead batteries - these will run off 12v car batteries very nicely and give me 240v if I need it - though at the cost of some efficiency. The last power cut we had here was 2 days ago, and if we keep running our energy strategy in the way we are currently doing, I expect they will become a regular feature of life. Luckily it wasn't long, so the web servers stayed up on their UPSs.....
    1
    Martin555
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    Thank you DG,
    That explanation has made it clearer to me.
    I still have a few sealed lead acid batteries that are mainly used just to weight things down with.
    I charge them up occasionally and as luck would have it we recently had a power cut so I was able to power up a couple of car headlights so That we could see.
    We used one and the other we took around to an elderly lady who lives on her own, plus a flask of hot water for her to make a cup of tea.
    So now I make sure that they are charged more often now.
    They certainly came in handy then.

    Martin555.
    1
    If it looks right it probably is.
    DodgyGeezer
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    ".....it seemed to generalise without mentioning the the decisive parameters involved, including cost difference!..."

    Um. Tricky to cover everything, in a 4 sentence comment!

    There seems to be a grave shortage of balanced advice in all aspects of modern life - though no shortage of advice per se at all! In a field where technological change is proceeding it is even harder to gather a useful view. Comparisons which were true one year are incorrect the next, and I suggest that it would be very useful to update any advice on the board which covers batteries....

    Luckily there is one reasonably independent place we can go for a balanced view - the market. Although it is not perfectly unbiased, we can deduce that if some battery technologies are surviving in that marketplace there must be a demand for them, and hence that these technologies are likely to be the best available ones for some specific task. We only need to determine what that is.

    As a quick example, if you look at a major UK battery supplier to the model hobby - Component Shop - you will find available:

    NiMH - both standard and low self-discharge
    LiPo
    LiFe
    Lead Acid (sealed)
    Alkaline (probably Manganese)
    Silver Oxide

    All of these will be the 'best choice' for some application. Our interest is probably mainly with the first four.

    There are many battery features to take into account. The energy capacity that the battery contains is one common figure, usually measured in amp-hours, but most people do not realise that that is only correct for a particular delivery rate. To make a motor go fast you need a battery with a high current delivery rate - able to put out a lot of amps over a short time. Dry batteries, for instance, do not usually have a high delivery rate - hence the poor performance available to us in the 1960s!

    My top-of-my-head generalisations are below, though I am sure exceptions can be found in all cases! 'Robust' refers to a mix of physical strength and resistance to misuse, such as over-charging or excessive drain. I will try to use the words 'capacity' for the amount of energy stored in a battery, and 'delivery' for the maximum rate at which that energy can be released...


    SLA Very robust. Cheapest for high amp-hour capacity at 6 and 12V. Can do high delivery as well, Very heavy. Use for displacement boats, where the ballast weight is a positive benefit. Can do heavy discharge as well, but many small SLAs are designed for emergency equipment use, and expect to support a light discharge over 10-20 hours.

    NiMH Fairly robust. Quite cheap for medium amp-hour delivery, and reasonable capacity. Low self-discharge costs are dropping and that technology seems to be expanding in the market, though they tend to be low amp delivery types. Some types can compete with Lipos for high amp delivery in the 30-40A range. Fairly heavy. Make sure that you buy a high-delivery type if that's what you need for motors. Low self-discharge types are good for emergency flashlights and RC transmitter/receivers...

    LiPo - Less robust. Best current choice for high amp delivery with low weight. Only readily-available type offering current delivery in the 100+ Amps range. Light, and available in very small sizes. More expensive than NiMH, high capacity very much more, and you need a special charger, though these can be quite cheap nowadays. You should really be using a charger optimised to your battery type anyway. Remember that each LiPo cell is 3-4V, not 1.2V...

    LiFE - Similar to LiPo, but more robust. Slightly lower voltage, but very flat volt delivery. Typical current delivery in the 30A range rather than 100+. More expensive than LiPo at the moment, but may displace them eventually.


    LiPos are essential if you are using a very high consumption motor - perhaps a racing boat? But when using such currents you usually require cooling systems and quite a specialist drive train. Brushless motors can take high currents, so LiPos are often associated with them, but you can use any battery with any motor if you want - just so long at it delivers the amps! There is no reason why you should not use brushless with SLAs, or LiPos on a low-drain application - though a LiPo may be more expensive than you need for that...

    NiMH are perfectly capable of making a boat plane - IF you ensure that the max amp delivery is adequate. You can, for instance, buy NiMh batteries designed for wireless phones with max output 500mA or less - these will disappoint you if you try to use them for motor power!

    A handy rule of thumb for estimating optimum battery discharge is to look at the capacity in Amp-hours. A low-drain battery is probably designed to put that out over 20 hours, so divide the Ah by 20 to get an estimate of optimum current draw. A high-drain battery is usually designed to output over 1 hour - so divide the Ah by 1 to get optimum amps. That's only a generality, of course, and the battery spec sheet is the definitive place to look...



    "...more likely that HE had shares in a LiPo company to be able to afford them back then..."

    When it comes to electrical equipment I do have connections. 😊

    If you think LiPos were expensive in the 2000s, you should try buying NiCad pen cells in the 1960s. Probably the most unusual battery I have used was a pack of saline/manganese oxide cells from ex-RAF life jackets, where the battery was open to the water underneath the boat and you could speed it up by scattering salt in front of it....
    2
    jbkiwi
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    Re-Yes I agree that you require a certain amount of knowledge
    I understand what you are saying Martin but young people these days have grown up with electronics and I don't think they will be scared off to easily. If my son (for example) wants to know anything, it's straight out with the smart phone and looking up everything to do with the subject (wouldn't bother to ask one of us fossils, except as a last resort😐).
    I've been using computers for around 33 yrs, and he's 26 and knows way more than I do. Like most people now, he has a computer (smart phone) in his pocket every day. All we had was a phone glued to a wall and later (if we were lucky) a brick.
    JB
    1
    RNinMunich
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    Hi Peter,
    "One thing this conversation has resulted in is a much better understanding of alternatives to LiPo. "
    Thanks! Then I have achieved my objectiveπŸ˜‰
    What irritated me about Dodgy's initial post on the subject, and apologies to Dodgy if my response was a little over the top, (must remember not to answer such posts so late at nightπŸ€”) was that it seemed to generalise without mentioning the the decisive parameters involved, including cost difference!
    Sure there are better low discharge NiMhs thse days, but at higher cost, as I believe I mentioned. E.G. for the fast electrics market.
    LiPos have also improved their safety record tremendously (thanks partially to the Boeing Dreamliner mini disaster) in the 15 years that Dodgy has apparently been using them.
    Seems more likely that HE had shares in a LiPo company to be able to afford them back thenπŸ˜‰
    In fact most of the earlier problems with Lithium batteries were with Lithium-Ion.
    Was a big nuisance when we wanted to export some of our mobile/portable tactical radio kit.
    Had to send the batteries separately under special (expensive) conditions 😠
    Seems about time I updated the Battery charging sections in the 'How Tos' on this site to match current products! Been meaning to do that for yonks. So much to do, so little time πŸ€”
    Cheers, Doug
    2
    Young at heart - slightly older in other places πŸ˜‰ Cheers Doug
    redpmg
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    Any battery when abused causes problems - even good old Ni-cads - there were a few pictures of exploded boats in MB magazine - one a Sun tug split in half when the owner tried to fast charge non fast charge Ni-cads.
    I had a melt down with two dissimilar Ni-cad packs using a Graupner servo type switch speed controller - the smaller pack burst into flame - fortunately on a test rig.

    Possibly what is different about Lipos is they take far less abuse than the other types - so if you are careless with your batteries it would probably be safer to avoid them...

    Has anyone any knowledge of the Lipo's which look like double sized AA batteries ? I have 4 and a charger - not sure how to use them ........
    4
    MouldBuilder
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    One thing this conversation has resulted in is a much better understanding of alternatives to LiPo. I must admit that I turn to LiPo without even considering the application. I will retrain my thought process in future.
    3
    I promise I will finish a boat project before I start another......Maybe.
    Martin555
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    Basically for the benefit of the new guys to this hobby.
    It is important that you know what type of batteries you have and how to look after them properly.

    If in any doubt then please seek advice.

    We have some very knowledgeable members on this site so don't be afraid to ask.

    Martin555.
    2
    If it looks right it probably is.
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