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Prop shaft alternator conundrums

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by SkipperColin, Aug 21, 2017.

  1. JimB

    JimB Super Moderator Most Helpful Member

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    The method of uncoupling the drive belt as suggested by TCM has merit, as does the suggestion to use a bigger lower speed alternator.

    However, there is a big difference between coupling/uncoupling a drive belt in a field or workshop and doing the same thing on a boat in a rough sea.
    When Old King Neptune is giving me a hard time, I think that I would prefer to just push a lever to engage/disengage the alternator rather than fiddling trying to refit a v-belt.

    JimB
     
    • Agree Agree x 1
  2. Les Jones

    Les Jones Well-Known Member

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    Hi Colin,
    Some questions to try to understand your setup. (These are refering to how it has been used up to now.)
    1 Is the system a single battery system where the battery is charged from a alternator on the engine when the engine is running and charged from the alternator driven from the propeller when sailing ?
    2 Assuming the answers to question 1 are yes then what is connected to to the propeller driven alternator when the engine is running ? Are the two alternators charging the battery at the same time ?

    Les.
     
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

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    If it were me, I think I'd introduce a layshaft driven by a 1:1 ratio belt drive and supporting a home-brew dog-clutch which engages the big pulley, something like this :-
    ClutchDrive.PNG
    The layshaft speed would then be 2500rpm max and the big pulley would be idle when not required. I think a simple dog-clutch could be made from a disc keyed to and slidable on the layshaft. Pegs on the disc could engage holes in the big pulley, which would be freely rotatable on a bearing on the shaft.
    Excuse the drawing: LTspice isn't the best of graphic editors :).
     
  4. dave

    Dave New Member

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  5. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    I think you can or could get a mod for a lucas Acr which might be similar, to protect it if the battery was disconnected, transient suppressors or something like that.
     
  6. Les Jones

    Les Jones Well-Known Member

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    A thought on elecrto magnetic clutches. The type used for the drive to the air con compressor on a car might be suitable. I don't know how much current they take so it is possible it could take significant part of the alternator output.

    Les.
     
  7. SkipperColin

    SkipperColin New Member

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    Hi all, thanks for the great replies.

    I have used the classic engineering approach of going for a walk and then a beer to think through the problem.

    The alternator was working well. Since then I have reduced the pulley size and also put new cutless bearings on the drive shaft.

    This has led me to think the following:

    Rather than the diodes breaking down on regulation, I may have been stalling the prop shaft in the quest for more power.

    If the battery bank is reasonably full, then the load on the alternator is small.

    However if the batteries are low, and the boatspeed high the alternator is creating too much torque, slowing the shaft, and cycling like that. Too much torque, stall, build up speed, repeat

    This is exacerbated by surfing down a wave, (fast) then slowing at bottom of trough stalling shaft at same time, almost like a double whammy.

    In the interim, I have gone back to original pulley giving me a ratio of 4.8 to 1 (down from 6.9:1)

    This has the effect of de-rating the power of the alternator and hopefully not stalling the shaft.

    This idea came from a great blog on the subject

    http://lifepart2.info/equipment/prop-shaft-driven-alternator

    I've got to do the remainder of the calculations for my setup but I am slightly hopeful!

    I also probably will redo wiring to the battery bank over the winter, and install a sense wire to the house bank.

    Many thanks for the ideas and suggestions. If money was no problem I would modify a manual jabsco pump, coupled to a pma with external regulator, however there are other more pressing improvements on Emerald of a higher priority!

    I will report back on the success of the de-powering. The alternator should still provide a useful 5-8amps at our cruising speed.


    Once again thanks for all the input and ideas. What a great forum!
     
  8. SkipperColin

    SkipperColin New Member

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    Hi Dr Pepper, just seen your post. I'll see if I can track those down thanks!

    Les, that was my original thought, but the power would wipe out the generating capacity. However, it might be worth considering if I go for a pma, as I don't need the 3amps of field current.
    Cheers everyone.
     
  9. Les Jones

    Les Jones Well-Known Member

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    I have recently been working on a remote voltage and current sensing unit that may be of interest to you. It uses Texas instruments INA219 current and voltage sensor, a PIC12F1840 (Microcontroller.) and an HC-12 RF module at the remote sense end. At the receive end it is just an HC-12 module and an FDTI serial to USB convetrter plugged into a PC. The PC just runs a terminal emulator program. To get a reading you just type the # character followed by a letter. The letter is to identify the remote sensor as the system can read fron a number of remote sensors. It would be useful to confirm your theory by taking current and voltage readings. Is the alternator charging a different battery to the one used for starting the engine ?

    Les.
     
  10. SkipperColin

    SkipperColin New Member

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    Hi Les yes is the simple answer.

    We have a single 110AH start battery charged through a battery combiner (set at 14 volts)

    Our house bank is 675AH of six trojan t105 6volt batteries in series parallel.

    We have a very accurate shunt meter which gives volts Amps and amp hours for house bank for monitoring based on peukert's equations.

    The key for me will be finding the sailing conditions to do the tests on our way from northern aegean Greece to southern italy over the next few months.

    Best wishes
    Colin & Nichola
     

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