6hp Tohatsu "Sailor" Charger output

Discussion in 'Outboards' started by sailerboy, Dec 26, 2015.

  1. sailerboy
    Joined: Dec 2009
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    sailerboy Junior Member

    One of the reasons that I bought 6the Tohatsu "Sailor" model was to charge the 40amphr battery on my trailer sailor.However I have been very disappointed in this regard.
    (It has the full kit with the rectifier, so is not just a "lighting kit") Its an MFS 6B model, about 4yrs old.

    Measuring the open circuit voltage at the charger output terminal at 2-3000rpm I am only getting about 12.6-13.0V. Barely enough to overcome the back EMF of the battery I thought.
    With a battery voltage of 12.8V (ie about 50%charged) and the charger connected I was only getting a charge current, (measured with a multimeter in series with the +ve lead) of around 1 to 1.5amps at max cruise revs (3800rpm)

    The specs rate the alternator at 60W so by my calcs it should be putting out some where around 5 amps, dependant on battery charge.

    The dealers are now help and say this is about normal. Barely a trickle as far as I'm concerned.

    What have other people with this motor found?
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Small outboards do not have a real alternator/charge controller, just an extra coil in the flywheel and a bridge rectifier. The 60 Watts are a peak value, which is totally meaningless without reference data like voltage and rpm.

    The number of turns of the coil is calculated to provide a little over 13V at 0 charge current, so the battery cannot be overcharged at any rpm. A handful of extra turns would give much more charge current but would require a complicated controlling circuit because unlike an alternator there is no field current, just a permanent magnet.
     
  3. sailerboy
    Joined: Dec 2009
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    sailerboy Junior Member

    Thanks for the reply CDK. I understand why I got the results that I did now. I was running the output through a 5A solar panel regulator, but this is probably throttling the current even more.
    I was considering some extra turns on the charge coil. How many would you recommend if I was to still run the output through the regulator? Would this give me any extra charge current?? Or am I best to just leave things as they are and connect directly to the battery, not going through the regulator? I have a voltmeter in parallel on the battery and do monitor the voltage, so could just unplug if it gets up around the 14.1+
     
  4. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Running the output through a solar regulator was not a good idea. There is a voltage drop from a series diode you do not need and the only thing the regulator can do is short the input. Fortunately the input voltage wasn't high enough, so nothing happened.

    You could wind some extra turns on the coil if it is an open one (some are potted), I guess the ratio is approximately 15 turns per volt.
    I would leave things the way they are and hook up a small solar panel.
     
  5. sailerboy
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    sailerboy Junior Member

    Thanks for the comments.
     
  6. Justaguy
    Joined: Nov 2015
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    Justaguy Junior Member

    As an aside, at what horsepower level do outboards begin having real alternators/charge controllers?
     
  7. CDK
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    CDK retired engineer

    In general when they begin having an electric starter and a battery as standard equipment.
     
  8. Justaguy
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    Justaguy Junior Member

    So, if I understand you right, you're saying that having those components is more indicative than any HP level (10hp, 20hp, etc)?
     

  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    There is a relation with HP level of course, everything over 20hp comes with an electric starter and must be equipped to fully charge a battery. But there are/were some weird exceptions like 15-20hp outboards with optional electric starter but no regulated charge current.
     
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