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Old 08-02-2013, 21:05   #16
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Re: 48v 36v 24v and 12v system

I have a brand new sixty year old 6 volt bilge pump in my office.
I remember seeing 110 volt DC equipment for boats.

I expect we'll see higher voltage on boats as the automotive industry builds more hybrid and electric cars that operate on higher voltages.
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Old 08-02-2013, 21:11   #17
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
i understand now, so what's the safest daily discharge out of my 900 ah bank?
Do you mean depth of discharge? Then that would be around 50%.

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Originally Posted by Stumble View Post
The one issue with drawing down batteries is that lead acid prefer to be discharged slowly, particularly with the deep cycles we use on boats. This does result in an efficiency gain, so by drawing 6 amps at 24v you do actually get more usable power from the same batteries than if you draw 12amps at 12v.
For the same battery capacity in watt-hrs there shouldn't be a difference. You're drawing twice the current but from batteries in parallel so the amp rate out of each battery is the same.
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Old 08-02-2013, 22:50   #18
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Re: 48v 36v 24v and 12v system

Cal,

When you decrease the amp draw you are drawing more slowly out of each battery, which allows the battery to give up power more efficiently. Batteries are typically rated this way at standard discharge rates, so a 200ah battery is actually being rated as 200 amp hours when discharged at X rate. If you increase the rate, you decrease the amount of available power.

See Battery discharge current for a more in depth discussion.
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Old 08-02-2013, 23:57   #19
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Re: 48v 36v 24v and 12v system

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Originally Posted by Stumble View Post
Cal,

When you decrease the amp draw you are drawing more slowly out of each battery, which allows the battery to give up power more efficiently. Batteries are typically rated this way at standard discharge rates, so a 200ah battery is actually being rated as 200 amp hours when discharged at X rate. If you increase the rate, you decrease the amount of available power.

See Battery discharge current for a more in depth discussion.
Its rare I disagree with anything you post Greg, but for the same (physically sized) battery bank it does not make any difference in battery efficiency (in terms of the Peukert effect) if it is 12 or 24v.

For example if we 2 X 100 AHr, 12v batteries and a draw of 240w. We can wire these batteries as 12 or 24v.

In a 12v system we have 200 AHrs of battery with a current draw of 20 A. The battery is discharged at C10.

In a 24v system we have 100AHrs of battery with a current draw of 10 A.
The battery is discharged at the same C10 rate and battery efficiency will be the same.

( as others have said there are considerable gains in reducing wire size with the higher voltage systems, but not in battery effeciency)
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Old 09-02-2013, 00:15   #20
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Re: 48v 36v 24v and 12v system

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Originally Posted by noelex 77 View Post
Its rare I disagree with anything you post Greg, but for the same (physically sized) battery bank it does not make any difference in battery efficiency (in terms of the Peukert effect) if it is 12 or 24v.

For example if we 2 X 100 AHr, 12v batteries and a draw of 240w.
In a 12v system we have 200 AHrs of battery with a current draw of 20 A. The battery is discharged at C10.
In a 24v system we have 100AHrs of battery with a current draw of 10 A.
The battery is discharged at the same C10 rate.
Well I was only half way through my detailed description when your post popped up so I threw mine away.
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Old 09-02-2013, 00:26   #21
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Re: 48v 36v 24v and 12v system

To answer the original question.
The main advantage in running a higher voltage ( usually 24v) on a yacht is

1. Wire size ( and cost, weight) is reduced
2. High power appliances are not available in 12v. This is especially true of anchor winches, bow thrusters and large inverters. There are technical reasons why its not practical to make very large electric motors in 12v.
For example the maximum anchor winch size on 12v is about 3500lb. This anchor winch is suitable for yachts up to about 55-60 feet. Many cruising yachts like to fit a larger anchor winch than recommended ( my 47 foot yacht has a 3500lb winch). If I wanted to go bigger I would need to fit a 24v (or hydraulic) system.

So for cruising yachts above 50 feet especially with an electric bow thruster I would fit a 24v system. Below this size the complication is generally not worthwhile.

Electronic 24 to 12v reducers are available for those appliances that will not work of 12v, but many bits of marine equipment, like instruments can be run from either 12 or 24v.

Most larger boats also have a 110 or 240v system via an inverter or generator, but the house system is normally 12 or 24v for the sized cruising yachts. CF members are likely to use.
Yachts with electric propulsion are the rare exception.
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Old 09-02-2013, 00:28   #22
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Re: 48v 36v 24v and 12v system

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Well I was only half way through my detailed description when your post popped up so I threw mine away.
You have got to be quick on this forum
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Old 09-02-2013, 01:43   #23
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Re: 48v 36v 24v and 12v system

There are a lot of savvy OPs on this thread, and they are not even Electrical Engineers. I'm very impressed! Just a word of caution, when replacing/upgrading an electrical system, have it done by a pro. It is neither as easy as it sounds, nor it is just a weekend project. Mauritz
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Old 09-02-2013, 02:05   #24
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Quote:
Originally Posted by drousy88 View Post

i understand now, so what's the safest daily discharge out of my 900 ah bank?
50% or 450Ah
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Old 19-01-2016, 03:30   #25
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Re: 48v 36v 24v and 12v system

I realize that this is an old thread, but no one had yet mentioned that inverters are slightly more efficient when the input voltage is higher (up to the output voltage). So, for example, a 24V to 120V inverter will be more efficient than a 12V to 120V inverter (of an otherwise identical model from the same manufacturer). The most efficient inverters produce AC from a DC voltage that is higher than the target AC voltage, for example 144V DC to 120V AC.
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Old 17-04-2016, 13:57   #26
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Re: 48v 36v 24v and 12v system

The arguments for which voltage to run in a boat seem to boil down to wire size and the savings associated with it, since the same amount of work can be accomplished by any of the voltages used.

What I get out of the posts seems to be summed up by saying, look at all the electrical loads current and future that will be on the boat and choose the highest voltage that the engine and all loads will function at.

Is that a good assessment?
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Old 17-04-2016, 14:39   #27
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Re: 48v 36v 24v and 12v system

Chessyman you're close. The thing that decides the a boats DC voltage is the starter motor. If you have 12 volt starters the most practical way to wire your boat is 12 volts.

If you have the choice of 24 volt starters, by all means wire the boat for 24 volts.

If you have the option of higher voltage starters, don't choose them. You won't be able to find the right voltage auxiliary equipment such as bilge pumps and blowers.

Some 32 volt equipment is still available but it will soon disappear from the market.

Yes you can have multiple DC voltages but why bother? It just complicates things.
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Old 17-04-2016, 14:41   #28
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Re: 48v 36v 24v and 12v system

Chessy,

As a practical matter most systems are 12 or 24v because that's what most consumer grade equipment is available in. Going to a 48v backbone with voltage converters is possible but far less efficient than a pure 12/24 system. It works on big boats with very high electrical demands, and where equipment is available in 48v.
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Old 17-04-2016, 14:51   #29
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
i dont understand the point of having anything but 12 volt on a boat.... all motor and appliances i have seen are 12 volt. what is the purpose of wiring batteries and having chargers in 24 volt or higher? what possible electrical devices could i use that isn't 12 volt?
Higher dc voltages are used when high current demands with stable voltage are needed that 12V cant meet.

Military comms and weapon systems are one example.

High power winches, pumps and hydraulics are another for larger yachts.

Way back when 8V batteries were common in tractors. This led to multiples of 8 for static battery powered applications on farms.

If you have a boat under 50' then you shouldnt need anything other than 12V.


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Old 17-04-2016, 15:20   #30
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Re: 48v 36v 24v and 12v system

I am planning a rewiring job, getting a high out put alternator, and going to 24 volts, but had been wondering about higher voltages. Thanks for the help.
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