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Old 11-20-2012, 02:43 PM   #1
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24 volt or 12 volt?

I am new to this forum and this is my first post. I have been using this forum as a resource to help me with the purchase of a trawler type boat. My current boat has a 12V system but a few of the trawlers I have looked at are 24V. My question i : Are 24 volt systems good or bad/ advantages or disadvantages?
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Old 11-20-2012, 02:48 PM   #2
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The principal advantage of 24v is smaller gauge wiring to deliver the same amperage compared to 12v. On a larger boat, this can be a material savings. Principal disadvantage is that some 24v electronics are more expensive than their 12v analogs since fewer of them are made. If the boat already has 12v the advantage of smaller gauge wiring with 24v is immaterial because somebody else already paid for the wire. Bottom line, on a used boat, I don't think you care.
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Old 11-20-2012, 03:18 PM   #3
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Thanks for the info. I been told if you have to ask the price you cannot afford it. Checking the price difference between 12 and 24 v blowers for example, it appears that 24v parts are higher than 12v.
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Old 11-20-2012, 04:00 PM   #4
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The big disadvantage is that wire sized for 24 volt, is generally under sized for 12 volt. So it better to have wire sized for 12 volts as the wire is over sized for 24 volt. As mentioned be for most 12 volt items cost more.

There are only a few items that 24 volt might be better; starters, windless, and bow thrusters.
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Old 11-20-2012, 05:21 PM   #5
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On many newer boats the alternators are 24V and 175 to 200 amps. This is great for house battery charging while underway. Many 24V boats have 12V electronics to avoid the 24V premium.
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Old 11-20-2012, 07:41 PM   #6
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sunchaser;"On many newer boats the alternators are 24V and 175 to 200 amps. This is great for house battery charging while underway. Many 24V boats have 12V electronics to avoid the 24V premium."

I always understood that batteries liked a 'gentler' charging rate than the 175/200amp units. However I happily admit to a high degree of ignorance when it comes to electrics.
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Old 11-20-2012, 08:02 PM   #7
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Good point. Normally a 24 volt vessel could be running a good sized fridge, freezer, ice maker, cooking bagels, running the microwave, charging batteries for engines and thrusters and running a variety of 12 V systems. All this in addition to charging up the house set. My guess is the house set would take less than 1/2 of the available amps at best.

R Widman or Bofofthenorth could give a good description of how the regulator and inverter/charging system would protect the house batteries so they don't get too juiced up too quickly.
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Old 11-20-2012, 08:41 PM   #8
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While essentially a 24-volt boat, the Coot has 110 AC, 24-volt DC, and 12-volt-dc. The air compressor and water heater are on AC. Radar, plotter, interior lighting, water pump, fuel-polisher pump, engine-room exhaust fan, deck lights, toilet, wipers, refrigerator, search light, and bow thruster are on 24-volts. Running and anchor lights, VHF radio and depth finder are on 12-volts. There are both AC and 12-volt plug outlets.

As said earlier, 24-volts are better for longer wire-runs. All the other boat models made by this builder are larger, so I presume the builder went with 24-volts on the Coot to simplify manufacturing even if it resulted in an "overbuilt" electrical system.

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Old 11-20-2012, 09:07 PM   #9
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My current boat has a 3000 inverter hooked to 6, 6v golf cart batteries. Which I charge with the generator, on the lake we travel short distances and set on the hook for the weekend. I have noticed that trawlers like to charge the inverter batteries while moving to the next anchorage with the alternators..
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Old 11-20-2012, 10:47 PM   #10
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Jollyvo

Yes we do like to charge house batteries while running. To whit, on my all electric appliance vessel we have about 1700 hours on the mains and 440 hours on the genset. But in the hotter climes where you reside, AC use at anchor would drive this ratio up
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Old 11-21-2012, 07:03 AM   #11
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24 V for charging and engine start is great .



The real question is if 24 is used for operating equippment , would Hydraulic for the bigger loads have been a better solution?

Bow thruster, Windlass , Cruise generator , Water maker?
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Old 11-21-2012, 10:27 AM   #12
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50 or so years ago, auto manufacturers switched from 6 volt to 12 volt systems in cars and light trucks. The advantages were that smaller gauge cables could be used, saving cost and weight, less voltage drop from long cables and connections, and smaller and less expensive motors.

A 24 volt electrical system in a boat wuld have the same advantages over a 12 volt system. But:

24 volt boat parts are pretty uncommon. Go to your favorite marine store and look for 24 volt bulbs, pumps, radios, etc. Chances are, you will find few or none. Parts will be special order and the selection will be small and the price high.

Basically, you pay your money and take your choice, but I think the standard 12 volt system is the most practical until you approach 40 or 50 feet in boat length.

A friend of mine was called to work on a boat with a 32 volt electrical system. You won't find those parts at your local West Marine store.
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Old 11-21-2012, 10:47 AM   #13
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Even on 60+ ft bts 12 volt works just fine. It might be OK to have both 12 volt for house and 24 volt for start, thruster, windless. But no just 24 volt. As mentioned be make sure the wire is sized for 12 volt, and usually wire for 24 volt is not sized large enough for 12 volt because the amps are double. DC 1 amps 24 volts = DC 2 amps 12 volt. Basic forumula is Amps X volts = Watts.


If you have a high torque need, might look at installing a hydraulic system before a 24 volt. However, it should be noted in some parts of the world 24 volts is more common than 12 volts. So it might depend where the boat was mfg and/or going to be used.

True story.

I bought some light bulbs to replace in the dome lights, and they where very dull. I spend several hour tracing things out before I realized they where 24 volt.
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Old 11-21-2012, 01:12 PM   #14
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Quote:
Originally Posted by Andy G View Post
sunchaser;"On many newer boats the alternators are 24V and 175 to 200 amps. This is great for house battery charging while underway. Many 24V boats have 12V electronics to avoid the 24V premium."

I always understood that batteries liked a 'gentler' charging rate than the 175/200amp units. However I happily admit to a high degree of ignorance when it comes to electrics.
Andy, the amount of current a battery can accept is a function of its type and size. AGM have a higher acceptance rate than wet cell, so can benefit from higher initial charge rates without damage. Some of the very new technology batteries that have corresponding price tags will accept a lot of current right up to the point where they are almost fully charged. And, the larger the bank, the more current can be accepted by whatever type battery you have. Large charging capacities are only useful for a relatively short period of time since for most batteries, after 30 minutes or so, the acceptance rate drops quite a bit, meaning the higher capacity of the charging system isn't needed. Modern 3 stage regulators use temperature sensing at the battery to detect when too much current is being supplied during the bulk charging phase.

The lesson is that simply putting a really big charging system online doesn't hurt the batteries if properly regulated, but may not be of much use most of the time as the acceptance rate of most types of batteries drops as the voltage of the bank goes up.

By way of reference, I put a 1380 amp hour 24v house bank on board and between the genset and the alternator can get the AGMs to accept around a peak of 200 amps, slowly tapering off after 45 minutes or so to below the capacity of just the alternator, so if I have also spun up the genset to accelerate charging, it goes off. The next 4 hours of run time on the alternator brings the batteries up to nearly 100%. In other words, I have greater capacity to charge than I can use for all but around 20% of the time.
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Old 11-22-2012, 07:35 AM   #15
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Folks with a modern marinized engine will frequently have 24V as is normal today in the transportation industry.

IF only 60A or so of 12V is required for operation Vannier makes a converter that uses the 24V pair of 12V batts to create 12V.

This is properly done (not just a center tap) and is common on most any bus in the USA. Vannier units are quite reliable and have been doing this for decades.

Since 200A and 300A/24V driven with flat belts alternators are also common , a large inverter could create air cond sized power while underway.

Perhaps a simple way to go?
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Old 11-22-2012, 08:14 AM   #16
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Folks with a modern marinized engine will frequently have 24V as is normal today in the transportation industry.

IF only 60A or so of 12V is required for operation Vannier makes a converter that uses the 24V pair of 12V batts to create 12V.

This is properly done (not just a center tap) and is common on most any bus in the USA. Vannier units are quite reliable and have been doing this for decades.

Since 200A and 300A/24V driven with flat belts alternators are also common , a large inverter could create air cond sized power while underway.

Perhaps a simple way to go?
No, the "simple way to go" is tp have everything 12 volts. Anything else complicates matters.

By "everything", I mean all the DC eqipment. You'll still have 120 volt shorepower and either an inverter or genset to power it when away from the dock.
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Old 11-23-2012, 06:49 AM   #17
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the "simple way to go" is tp have everything 12 volts. Anything else complicates matters.

Fine but for recharging a large battery bank the 12V alternators seldom go over 200A.

A large 12V bank may be able to absorb more , so extending charge times .

Many modern good sized engines with electronic injection control are not made in 12V.

Having a 24V,,4000W inverter (or two) is a simple way to have power from the main engine to operate as a cruise generator.4000W in 12v requires an alternator of unusual size.In 24V/300A its OTS.

SIMPLE is defined by the power systems that are required during the vessels cruise, and their usefulness at other times.

EG a good large inverter will frequently have a match or limit function.

So starting a second air cond from a smallish noisemaker is no hassle, the inverter fills in the required current.

Additionally its easy to operate from an extension cord (15A) from a dock , or buddy plug rafted , and still function well.

Every boat is a complete SYSTEM , and the "easy" way out may or may not be .
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