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Thread: 12 to 24 volts

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    eidiohir's Avatar
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    Default 12 to 24 volts

    Just thinking of changing a few electrical things on board and twenty four volt stuff seems to work better and can be obtained cheaper than twelve,So I thought why do boats have twelve?and why not change it? I can understand that the starter motor would have to go and the alternator also but everything else seems to work on either 12 or 24.So where is the big drawback?I know from bitter experience that there has to be one so what is it?
    Things are never so bad that they couldn't be worse

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    Quote Originally Posted by eidiohir View Post
    Just thinking of changing a few electrical things on board and twenty four volt stuff seems to work better and can be obtained cheaper than twelve,So I thought why do boats have twelve?and why not change it? I can understand that the starter motor would have to go and the alternator also but everything else seems to work on either 12 or 24.So where is the big drawback?I know from bitter experience that there has to be one so what is it?
    Depending on engine there may/may not be a 24v starter available,though you could have it rewound.Possibly have to change engine instruments. Could be costly ,but you'd then be able t o use lorry gear.

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    24v was the standard long before 12v came along. Why 12V ??? Maybe battery sizing or the fact that the auto industy went 12v ??? Does anyone know ???

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    William_H is offline Registered User
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    Default Battery voltage

    Well I would disagree with sandyman. I think 6V was the original standard for cars and some trucks.
    Probably for a cheaper battery. It was in fact the starting and headlights that suffered with the high current needed at 6V.
    I think for a boat it is the engine start then anchor winch and inverter that will be big current drawers hence the reason to go 24v.
    It is possible that the 12v engine starter will be OK on 24v. This because the current drawn drops rapidly as the starter begins to crank. You should enquire of the makers. Obviously you will need to convert the alternator to a 24v type. So if you have problems with your existing system 24v may solve them and as you say for high current items 24v will be much better. good luck olewill

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    Quote Originally Posted by eidiohir View Post
    So where is the big drawback?I know from bitter experience that there has to be one so what is it?
    I inherited a 12 and 24v system. Two alternators and Five Batteries!
    Not all kit will work off 24v, so you will probably have to use a series - parallel battery setup or use two batteries of different or equal (large) capacity AH with a center tap to power the 12v kit. This isn't ideal as the larger / parallel battery(s) won't get fully charged.
    The alternative is to use three batteries - Two large capacity in series for the 24v plus a http://www.reuk.co.uk/24V-12V-DC-DC-Converter.htm to charge the 12v battery, http://www.sailgb.com/p/Waeco_Perfec...12v_converter/ also do one.

    Starting from where you are, this isn't a route that I would go down!!

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    Exclamation

    So much possibility for problems with mixed 12/24V systems.

    A friend of mine spent half the weekend on a "10 minute" job on fishing boat. He was asked to replace the all-round white light that got damaged on delivery. Fastened down the new fitting to the mast/gantry and found cables getting hot and other lights coming on - with nothing switched on! System was two 12V batteries in series, but the 12V circuits were taken off the wrong taps. Negative for the 12V was actually +12V to the engine and finding a current path back via the steel braiding in hydraulic hoses!

    Better to have a single voltage system if at all possible IMHO

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    eidiohir's Avatar
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    I am not really going down that route as I am happy enough with things as they are and I am only a diy electrician .It's just as someone without any more than the basics of elelectrickery I wondered why 12v when it seems to be a lesser system than 24v.Then I wondered if it is better why not change and if you do change what stands in your way.To me changing the starter and alternator doesn't seem like an insurmountable hurdle to overcome if everything else was ok.I didn't think of the engine instruments so thats one other thing but the winch will work on 24 the fridge ,the gps, radio and radar all will so what is left?
    Things are never so bad that they couldn't be worse

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    eidiohir's Avatar
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    I should have added that all the light bulbs would have to be changed from 12 to 24 and that could cause a problem with nav. lights I suppose
    Things are never so bad that they couldn't be worse

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    Quote Originally Posted by William_H View Post
    It is possible that the 12v engine starter will be OK on 24v. This because the current drawn drops rapidly as the starter begins to crank. You should enquire of the makers. ter. good luck olewill
    In my youth I raced a special saloon car with a BDA engine. The cars system was 12v but the 12v starter was rigged to use 24v so it turned the engine over fast enough to start.

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    I am surprized that you can find 24 volt stuff cheaper and more easily than 12. Thay has not been my experience. The Watermota engines of circa 1970's had a 24 volt alternator and battery system simply because, to spin them fast enough to start, they used a 12 volt starter and hit it with 24 volts. This works provided you do not operate the starter for more than 15 seconds at a time.

    Having a 24V battery bank has advantages, but it has meant finding ways to get 12 volts for lights, radios and instruments. Tapping off the battery bank is a bad idea and I use a DC/DC convertor. Right now however, I have two problems: Finding replacement 24V bulbs for the fridge warning light and compass, both of which have really strange holders.
    Ken

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