I've checked through the archives and found a few on this subject but
none that clearly state if there is any real advantage of running a
24V system.

Obviously the current draw for a given load will be less but I've
not seen any mention of 'standard' instruments that run on 24V. I've
read somewhere that fishing trawlers use higher voltage systems
(24/36V?) but do they have DC-DC conversion (36-12V) for their
instruments? Or do they use 24/36V instrumentation? I assume, as 12V
is 'standard', that costs of higher voltage instruments will be more
expensive than 12V ones.


Thanks,

Peter

If I had it to do over again I would have gone 24V in a New York minute.
Wire sizes can be smaller but mainly voltage drops on long runs are
a lot less of a problem and charging cycles are a lot shorter.

A DC/DC converter is the best way to drive any 12V electronics. You can
tap 12V off the batteries but that results in uneven discharging and
creats a whole new set of problems.

PeterV wrote:

I've checked through the archives and found a few on this subject but
none that clearly state if there is any real advantage of running a
24V system.

Obviously the current draw for a given load will be less but I've
not seen any mention of 'standard' instruments that run on 24V. I've
read somewhere that fishing trawlers use higher voltage systems
(24/36V?) but do they have DC-DC conversion (36-12V) for their
instruments? Or do they use 24/36V instrumentation? I assume, as 12V
is 'standard', that costs of higher voltage instruments will be more
expensive than 12V ones.


Thanks,

Peter

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

PeterV wrote in message
om...
I've checked through the archives and found a few on this subject but
none that clearly state if there is any real advantage of running a
24V system.

Obviously the current draw for a given load will be less but I've
not seen any mention of 'standard' instruments that run on 24V. I've
read somewhere that fishing trawlers use higher voltage systems
(24/36V?) but do they have DC-DC conversion (36-12V) for their
instruments? Or do they use 24/36V instrumentation? I assume, as 12V
is 'standard', that costs of higher voltage instruments will be more
expensive than 12V ones.


Thanks,

Peter

***

You are right, there is no reason to put 24V instalation in boat smaller
than 60ft. All boats with higher voltage than 12V have **V/12V inverters for
audio/video/instruments/??lights. El. current in 24V instalation is 1/2 of
12V instalation with same load so all wires can be thinner but voltage is
higher so insulators must be better and higer voltage instalation is much
more sensibile to electro-corrosion than 12V.
The bigest loads on boat are motor starter (motor batery is usually close to
motor so wires are short and there is no problem), bow-thruster and anch.
winch (use only 2 large wires to connect "+" and "-" of service battery with
relays mounted close to thruster or anch. winch) command wires are not
problem.

By.

Many marine electronic pieces are rated for 8-48 volts, having
internal regulators to extract the power they require. Many boats are
24 or 32 volts to match the requirements of the engines in them. A
friend had a Hatteras 56 FBMY with twin 8V92TA DD diesels in them. I
called them "Train Engines" because everything was 32VDC.

He like to had a heart attack when we had to replace the bad battery
banks (3 banks of 4 batteries each, each battery 4 cells (8VDC) in
series to get 32VDC per bank) Each 4-cell battery was $300! You do
the math.....(c;

Inside the Hatteras' main helm was a couple of BIG 32V to 12V analog
regulators that very inefficiently reduced 32 to 12 at great heat for
the 12V Only instrumentation and accessories at the helm and on the
flybridge above. Power isn't much of an issue when twin V-8 diesels
are chugging away at 2200 RPM in the bilge.

Your assumption about 24V using half the current of 12V is correct. I
think 12V cars was as big a mistake as 6V cars were. We should have
converted the whole damned country to 24 or even 48VDC when we had the
chance, saving millions of pounds of copper in the process.



On 18 Dec 2003 01:34:19 -0800, (PeterV) wrote:

I've checked through the archives and found a few on this subject but
none that clearly state if there is any real advantage of running a
24V system.

Obviously the current draw for a given load will be less but I've
not seen any mention of 'standard' instruments that run on 24V. I've
read somewhere that fishing trawlers use higher voltage systems
(24/36V?) but do they have DC-DC conversion (36-12V) for their
instruments? Or do they use 24/36V instrumentation? I assume, as 12V
is 'standard', that costs of higher voltage instruments will be more
expensive than 12V ones.


Thanks,

Peter

Larry W4CSC

NNNN

Hallo Miljenko,


You are right, there is no reason to put 24V instalation in boat smaller
than 60ft. All boats with higher voltage than 12V have **V/12V inverters
for
audio/video/instruments/??lights. El. current in 24V instalation is 1/2 of
12V instalation with same load so all wires can be thinner but voltage is
higher so insulators must be better and higer voltage instalation is much
more sensibile to electro-corrosion than 12V.

The electro-corrosion is dependet on the resistor or the cable and the
current so the effect is smaller
with lower current as is in 24V systems.
The isolation should not realy be a problem at 12 or 24 Volts.

The needed wire size is for a given device 1/4 of the 12Volt wire. The
reason is
that you need 1/2 of the current and you can accept the double amount of
voltage to be lost on
the way.
To make it clear i´ll try to give an example.
at 12 Volt you need 100 Watt. The wire has 0,1 Ohms for the plus wire and
0,1 Ohms for the return line
you see 10 Amps and lose 2 Volts at the wire. The 100 Watts are drawn from
10 Volts at the user.

At 24 Volts with 100 Watts you see 20 Volts at the user at 5 Amps the wire
could use 2 Volts each witch means
a resistance of 0,4 Ohms each so you need 1/4 of the copper.

The bigest loads on boat are motor starter (motor batery is usually close
to
motor so wires are short and there is no problem), bow-thruster and anch.
winch (use only 2 large wires to connect "+" and "-" of service battery
with
relays mounted close to thruster or anch. winch) command wires are not
problem.

Heavy Inverts for 120/240 Volts at 3000 Watts are very difficult to run on
12 Volt.

The reason for my boat to use 12 and 24 Volt systems was that i was not able
to
get a warm water heater around 24 to 30 KWatts at 12 Volts because this
things
are made for trucks and busses and so they are using 24Volt systems. The
heater
runs with fuel but has a high pressure pump and some electric inside.

Michael

I am building a Cape George 38 sailboat. The large house bank is about 750
Amp/Hours at 24 volts. I also have a smaller 12 volt house battery and a 12
volt engine starting battery. I don't believe you need a very large vessel
to take advantage of a 24 volt system.

I have found the following items for 24 volt systems.

Large frame 140 amp secondary alternator
External regulator
4000 watt inverter / charger
Refrigeration and air conditioning system
Hydronic diesel furnace
Fans for heating and air conditioning systems
Radar
Chart plotter
All interior and exterior lighting
Lighting dimmers
Battery volt and amp meters
Anchor windlass
Halyard winch
Autopilot control system
Autopilot steering motor
Electric flush toilet
Sewage treatment system control
Bilge, pressure water, and fuel transfer pumps
Bilge and gray water pump controllers
Cabin fans
Bilge and exhaust fans
Tank gauges
Automatic self-cleaning raw water strainer
Water maker

Items only available in 12 volt, that I know of, are these:

Automotive style stereo
VHF radio
HF SSB radio
Propane control panel
Instrument system
Engine starting system for 51 HP Yanmar

Even the instrument system could be powered from the 24 volt autopilot
control system. It has an output for that.

Anything with a motor will run cooler, and last longer, on 24 volts as
opposed to 12 volts. Any item, at the same wattage, will use half the
current at 24 volts as at 12 volts. Since power loss in your wiring, and
heat in your motors, is based on the square of the current, the loss at 24
volts will be 1/4 the loss at 12 volts. You can take advantage of that by
having a much more efficient system with smaller wiring. And smaller wiring
is cheaper and lighter.

I have heard the auto makers are thinking about going to a nominal 48 volt
system. The higher the voltage, the greater the efficiency. This is why
industrial motors are 480 volt three-phase, high speed trains draw 12,500
volts or more from overhead lines, and long distance power transmission
lines run up to one million volts.

A down side is setting up a large 24 volt battery system. I have 12 Trojan
industrial cells in the bilge. Another good method is to use four of the
Rolls 6 volt batteries or three of their 8 volt batteries. A 24 volt system
with all the cells in series is going to be a lot easier to maintain than a
large 12 volt system with batteries in some combination of series and
parallel.

All Ancor marine wiring is rated for 600 volt service, so using it for 24
volts is no problem. Most 12 volt switches also have a 24 volt rating,
although it might be a few amps lower.

An interesting note: The Blue Sea brand DC light dimmers are rated by
current draw. So you can control twice the wattage at 24 volts as you can at
12 volts, with the same dimmer.

Rusty O'Shaughnessy
S/V Lorgadoir Eolais

Thanks for all the replies; it seems there is an advantage as long as
there is not too much 12V 'only' stuff to replace.

Peter

In article ,
(PeterV) wrote:

Thanks for all the replies; it seems there is an advantage as long as
there is not too much 12V 'only' stuff to replace.

Peter

One of the things that I have used on multi-voltage vessels, is to
setup the 32-24/12 VDC Converter as a Battery Charger. Then have it
charge a large (D8 type) battery that then supplies the 12 Vdc Buss.
This way you can have Large Current devices, that are intermitant in
nature, on the 12 Vdc Buss but still keep use a fairly small current
converter to keep the battery charge up.

Bruce in alaska
--
add a 2 before @