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  1. #21
    vyv_cox's Avatar
    vyv_cox is offline Registered User
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    Quote Originally Posted by greenalien View Post
    As mentioned earlier, batteries only last if they are kept fully charged, and never discharged more than 20% of their capacity. Any more than that, and they will expire after 2 - 300 charge / discharge cycles.
    I have read that theory many times and no doubt most others have too. My own experience is very different. I have completed seven seasons of six months aboard in a warm climate. My two domestic batteries were bought in the first season of this period, my ex-starter battery, now added into the domestic bank, was bought in the previous year. All three are 'leisure' types. My refrigerator runs continuously from May to October.

    Until a couple of years ago I had two domestic batteries and 70 watts of solar panel. Overnight my domestic battery voltage used to fall to below 12.0 volts every night. Since uprating my panels to 125 Watts and adding the starter battery to the domestic bank the voltage is usually at about 12.2 or 12.3 first thing in the morning. All three batteries appear to be in good condition, they hold their charge well and are normally used to start the engine.

    At a conservative estimate two of these batteries have been discharged by 40% or more around 600 times. The bank of three has been discharged by more than 20% more than 200 times, so two have accumulated 800+ cycles.
    Answers to some technical queries at http://coxengineering.sharepoint.com

  2. #22
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    Quote Originally Posted by Bajansailor View Post
    So maybe the electric motor was not such a good idea after all....... has anybody got a copy of this month's Classic Boat?
    Yes. The reason for ditching it are the same reasons why the idea has never caught on generally. It simply did not do what was claimed. Insufficient capacity to be usable and the regenerative bit (which is what could make it practical in a sailing boat) did not work.

    Given that (as the OP says) electric power has been with us for over 100 years, the fact that nobody has been able to make it work except in limited situations suggests it is a bit of a blind alley!

    Clearly there are some applications where it works - low speed inland waterways where range is not too important and there are suitable recharging points being the most obvious. Hybrids might have a wider application, but size weight and cost limit their application.

  3. #23
    DaveS's Avatar
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    As a number of contributors have pointed out, an electric auxiliary propulsion system is attractive in theory but tends to fall down in practice over the inability to generate sufficient "free" energy to adequately recharge the batteries. Wind generators do not remotely approach "24/7" operation and, cost apart, there is a practical limit to how much solar cell area can be accommodated on a boat's hull. Unless the boat is already at hull speed and driving hard, extraction of energy from the water will slow the boat down.

    One major technical breakthrough could change things, however. Consider the possibilities if photo-voltaic sail cloth was available. The hugely larger solar capture area might well solve the energy balance issue - at least in the sunnier parts of the world.

    Of course photo-voltaic sail cloth doesn't exist. Yet. I did, however, attend a lecture a few years ago where researchers from Heriot Watt were looking at developing textile based photo-voltaic material. They envisaged an application consisting of tents for disaster relief which would also generate electricity. It struck me then that yotties might be a more lucrative market, even for conventional auxiliary powered boats. The further possibility of making elimination of the diesel practical would IMHO make the idea well worth exploring.

  4. #24
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    I believe that post does mean 20% from fully charged and 80% of charge remaining.
    Yes, that's what I meant - some degree of sulphation will occur at any level of discharge, but becomes more significant after 20% discharge. A lot depends on how much they are discharged, and for how long they are left in a partially discharged state. The 2-300 cycles life is quoted from manufacturers info on semi-deep discharge batteries (i.e. typical leisure batteries)

    All three batteries appear to be in good condition, they hold their charge well and are normally used to start the engine.
    Unfortunately, although all these batteries are charging properly and appear to be working OK, there is no mention of the change in capacity - you can't find this out by measuring voltage alone, the only answer is to apply a known load from fully charged until the battery voltage falls to 10.5 volts - (taking them any lower could be permanently damaging)
    it's then possible to work out the capacity of the bank - and after 600 charge / discharge cycles, my guess is that it will be considerably less than when they were first installed.

  5. #25
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    Quote Originally Posted by greenalien View Post
    Unfortunately, although all these batteries are charging properly and appear to be working OK, there is no mention of the change in capacity - you can't find this out by measuring voltage alone, the only answer is to apply a known load from fully charged until the battery voltage falls to 10.5 volts - (taking them any lower could be permanently damaging)
    it's then possible to work out the capacity of the bank - and after 600 charge / discharge cycles, my guess is that it will be considerably less than when they were first installed.
    Sorry, I'm a practical boat owner, not a theoretical one. The fact is that my 6/7 year old batteries do exactly what I want them to do, i.e. running all my requirements for half the year, including lighting, instruments, refrigerator, engine starting, etc, with absolutely no problem. Am I bothered if your instruments and calculation tell me that their capacity is lower than it should be? Not in the slightest.
    Answers to some technical queries at http://coxengineering.sharepoint.com

  6. #26
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    This is a company that manufactures a complete electric drive system from Motor through to the running gear, prop etc, they also include a few examples of boats they have been fitted into.

    http://www.ozmarine.se/OZecoDrive/En...oDriveEng.html

    My personal thought's would be that some form of backup generator if you needed to motor for an extended period of time, the system can regenerate power from the prop when under sail.
    I'd certainly like to give it ago on one of my future boats.

  7. #27
    Madhatter's Avatar
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    Quote Originally Posted by DaveS View Post
    As a number of contributors have pointed out, an electric auxiliary propulsion system is attractive in theory but tends to fall down in practice over the inability to generate sufficient "free" energy to adequately recharge the batteries. Wind generators do not remotely approach "24/7" operation and, cost apart, there is a practical limit to how much solar cell area can be accommodated on a boat's hull. Unless the boat is already at hull speed and driving hard, extraction of energy from the water will slow the boat down.

    One major technical breakthrough could change things, however. Consider the possibilities if photo-voltaic sail cloth was available. The hugely larger solar capture area might well solve the energy balance issue - at least in the sunnier parts of the world.

    Of course photo-voltaic sail cloth doesn't exist. Yet. I did, however, attend a lecture a few years ago where researchers from Heriot Watt were looking at developing textile based photo-voltaic material. They envisaged an application consisting of tents for disaster relief which would also generate electricity. It struck me then that yotties might be a more lucrative market, even for conventional auxiliary powered boats. The further possibility of making elimination of the diesel practical would IMHO make the idea well worth exploring.
    http://www.idealstar-net.com/idealstar_news.html

  8. #28
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    Quote Originally Posted by greenalien View Post
    Yes, that's what I meant - some degree of sulphation will occur at any level of discharge, but becomes more significant after 20% discharge. A lot depends on how much they are discharged, and for how long they are left in a partially discharged state. The 2-300 cycles life is quoted from manufacturers info on semi-deep discharge batteries (i.e. typical leisure batteries)



    Unfortunately, although all these batteries are charging properly and appear to be working OK, there is no mention of the change in capacity - you can't find this out by measuring voltage alone, the only answer is to apply a known load from fully charged until the battery voltage falls to 10.5 volts - (taking them any lower could be permanently damaging)
    it's then possible to work out the capacity of the bank - and after 600 charge / discharge cycles, my guess is that it will be considerably less than when they were first installed.
    Methinks that you may have your 20% at the wrong end of the scale........

  9. #29
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    Some interesting posts here, again split between the very encouraging and the no-hope outlook. I love the photo-voltaic sailcloth idea!! Imagine raising sail in a dead calm, and getting enough amps to hit hull-speed...

    My instincts are those of a dinghy sailor, inclined to make maximum use of any available advantage, and to be glad of them, whilst not relying on any power-plant more complex than oars, to help out when wind and tide don't play in my favour.

    On that basis, I'd enjoy a part-renewable/hybrid electric drive as an absolute boon, when nature not only blew my boat to the destination I desired, but powered anything and everything electrical on board, with stored power from renewable sources. If the journey itself consumes most of the cells' usable power, I'll be no worse off than any sailboat-owner in need of a battery charge; and if I'm in no hurry, I'll get mine for free.

    If the batteries require occasional (or even regular) reboosts from an I/C source aboard, no problem. Aren't we all quite used to running the donkey for a few hours now and then, for the batteries' health? There's no shortage of choice - diesel or petrol/LPG - generators are out there in every size and needn't be immobile or inaccessible or horrifyingly costly and heavy. Concievably the generator may even drive the motor directly, if the batteries are flat. After all, that's the basis of road-going hybrids.

    But this concept is surely only a real possibility if demands placed on the system are made with some sympathy for its weaknesses. If these are understood, and restraint shown in the system's use, then a fairly green, reliable, very peaceful, flexible and enduringly workable power supply is available.

    I get a feeling that the habits we've learned from prolonged diesel dependance, seem to have addicted many of us to its imperfect yet robust, uncomplaining output. Pity, if the necessity to think even a few hours ahead about our use of power, detracts most of us from trying an alternative source.

  10. #30
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    Quote Originally Posted by dancrane View Post
    Pity, if the necessity to think even a few hours ahead about our use of power, detracts most of us from trying an alternative source.
    NO, its the low cost, convenience and reliability of a small modern diesel that makes it so attractive. If electric power ws really so superior it would have taken over already - but it isn't because of the fundamental inefficiencies of storing the energy in sufficent quantity to be independent of outside sources. Just compare the usable energy in a 50 litre fuel tank compared with a huge battery bank and the ease with which the tank can be supplemented and topped up.

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