24v vs. 12v - any advantages?

Discussion in 'Electrical Systems' started by Lady Sophie, Nov 26, 2012.

  1. Lady Sophie
    Joined: Aug 2007
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    Lady Sophie Junior Member

    I am near the point of construction where I need to be planning the electrical. Is there any advantage to 24v vs. 12v for house bank and mechanical systems? My primary cruising area is Asia - Thailand to New Zealand with home base in Malaysia. Starting motor is 12v.

    I previously posted this to the electronics and controls forum - my mistake. I apologize for having to post twice.
     
  2. Frosty

    Frosty Previous Member

    Most things you can buy is 12 v-- if you want 24 --( for what reason ) then you will not have such a choice of products made in 12v.

    If you boat is not commercial and is under 60 foot most things bought can be 12v
     
  3. Stumble
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    Stumble Senior Member

    The advantage of 24v is that you can use smaller wire, and there is a lower voltage drop with the higher voltage. But as Frosty mentioned a lot of accessories are not as available in 24v. The larger the boat the more important the voltage drop can be.
     
  4. Frosty

    Frosty Previous Member

    Wow I wasnt suggesting that you would /could economize on wire guage to the extent that it would not carry 12v.
     
  5. michael pierzga
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    michael pierzga Senior Member



    A combination system with 12 and 24v is complicated and non redundant. Stick with a complete 12 v or 24 v system .

    If your boat has powerful equipment like ac dc inverters, electric winchs, bow thrusters , 24v is the way to go.
     
  6. Frosty

    Frosty Previous Member

    Its not complicated at all . 2 alternators on one engine can supply 12 and 24 even with the block as common earth for 2 voltages.

    Just look in the parts book and see what your get in 24 volt.

    I dont think there is a 12v depth sounder or GPS or 12 volt fuel guages or temp senders. Its the small stuff that dont need 24.

    Yes you can get it sometimes it may be special wound but it is not a common voltage.

    Therefore if it were my choice 12v is the way to go.
     
  7. CDK
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    CDK retired engineer

    With a 24V house bank, the cross section of all wiring can be reduced by 50%, so that saves a lot of copper.
    The downside is that nearly all 24V appliances are more expensive or not available at all.

    If you really want to reduce wire size, go for a 230V AC system with the inverter installed close to the batteries.
     
  8. michael pierzga
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    michael pierzga Senior Member

    Ac power is a good choice for many pieces of equipment. Its cheap and readily available.

    In the end its all about the size of the boat and the level of sophistication .

    For a small boat Id go 12v and keep it simple. Once you got to 45 or 50 ft Id investigate different solutions.
     
  9. SPARK1
    Joined: Nov 2010
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    SPARK1 Junior Member

    I have been looking into the same thing. It seems to me a lot depends on the size of the boat. The bigger the boat, generally the heavyer the current draw will be. Especially things like windlass and bow thruster. From what I have been able to find out, by doubling the voltage, the current more than halves. I suspect that this has do do with higher voltage moters being mor effecient. Also at 24 volts, the wire is less than half the size than 12 volts.

    You can get 24volt to 12 volt dc converters for any thing that must run 12 volts. Bigger inverters work better at higher voltages and chargers are smaller and need to produce less current.

    Hope this helps
     
  10. CDK
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    CDK retired engineer

    SPARK1, it is simple arithmetic. 24 watts load on a 12V system draws 2 amps, on a 24V system it draws 1 amp.

    P = V x A
     
  11. SPARK1
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    SPARK1 Junior Member

    Yes I agree! But remember that you always get less power out than you put in. A higher voltage motor will always be lighter and also more efficient, all other things being equal. When you are looking at motors above 2000 watts, there wil be a significant difference in current draw and power out put. On large dc bow thrusters, look at the same power output for 12 volt and 24 volt and you will see that 24 volt is less than half the current draw.

    Also because permisible voltage drop is defined as a persentage of supply voltage, the higher the voltage, the higher the amount of volts that may be "dropped". This also will then allow you to use a smaller cable for same current at 24 volts.

    All this 24 volt does often cost more for some equipment, but I have seen a lot of equipment for the same price as 12 volt.

    I think 24 volt only makes sense if current draw is high, which usually means a larger boat.
     
  12. Lady Sophie
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    Lady Sophie Junior Member

    Saving on wire size for small appliances and instruments is not worth the bother. There are good arguments to be made for 24v windlass, bow thruster, watermaker, and autopilot tho. West Marine and the popular suppliers don't list 24v equipment as there is such low demand here (USA) but if you call the manufacturer everything (that I've checked on) is available in 24 and only a very modest markup. I think perhaps the biggest argument for 24 volt systems is battery life. Battery life is dependent on amp draw and of course 24 pulls half of 12.

    I started my engineering career at Delco-Remy (GM Division) as a process development engineer (many years ago - I had an AGM in my Chevette before anyone had ever heard of them). I worked closely with the product boys in developing prototype processes to manufacture the new style batteries before they went into full production. GM had a push on to try to get automakers to convert to 24 volt systems. Everybody said it was only for GM to save money on wiring but the big reason was battery life and more robust components. GM offered 24v as an option for several years in the Cadillacs but consumers didn't buy and the initiative was dropped.
     
  13. michael pierzga
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    michael pierzga Senior Member

    Gee, Ive been working with 24v on yachts for decades. Plenty of gear around.

    As you say West Marine is 12v and they are also expensive.


    24v gear tends to be commercial ,professional. Check with a fishery supplier . The advantage of this is service life.

    In the end its a consumer choice. Best if you draw out your reguiements for both 12 and 24, then make the final choice.

    As I noted ,a dual voltage system is troublesome...either 12 or 24, not a combo.
     
  14. Lady Sophie
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    Lady Sophie Junior Member

    I have a (former) brother-in-law that is a commercial salmond fisherman out of Bristol Bay, AK. His boat is all 24v.
     

  15. portsmouthmarin

    portsmouthmarin Previous Member

    And you have to use twice the number of battery cells to get the 1/2 reduction in amp draw.

    There is no free lunch here.
     
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