24v batteries v 12v batts

cagey

cagey

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I’m looking at a boat to buy and she is 24v, I’ve always had 12v I’m wondering why and then I got thinking please what are the benefits or not, help me please through the thinking process
1 what are the benefits
2 what is the reason why
3 how involved Is changing back to 12v, she is due new batteries so if changing to 12v now would seem the time.
4 instruments and vhf etc is it straightforward fitting or have I got to find 24v toys and is there a premium for these
5 alternators etc are they dearer
Thanks everyone
K
 
probably more than 40ft?
imho you should be happy it's a 24V boat! means thinner cables to get the various loads to work, less voltage drop as a result.
Generally anything over 50ft is 24V, cable lengths and size power needs for certain components make things difficult, fe 8kW bow thruster at 12V?
changing windlass, bow/stern thruster (if available), possibly lights, freshwater pump, el.toilets (if avail), bilge pumps, battery charger, wiper motors, horns, etc (and I'm probably missing a dozen or so more...)
Fridges should be fine, run 12 or 24.

V.
 
You've not provided any information about the boat, it's engine, alternator or starter etc. It's likely that the starter and alternator will be 24V and will be expensive to swap. There could also be lots of 24V equipment. Most things are available 24V and for the few that aren't it's usual to have a simple DC-DC converter to run them. Very common setup on motor boats and some bigger sail boats.

The batteries will be 12V, connected in pairs, in series.
 
1. Lower current draw through wires fir equipment operating at 24V compared to 12V. For 1000W of power to lift an anchor a 24V motor will require less current.
2. Smaller electrical cables can be used compared to 12V power requirements.
3. You need to make sure that the installed electric wire size is big enough for new lower voltage.
4. You can run 12V stuff from a 24/12 DC/DC converter. I have this fitted on my boat.
5. Don’t know if 12v alternators are more expensive. Trucks tend to use 24V systems, so maybe not so much more.

In my experience, one issue I have is battery capacity. It’s easy to fit 2x12v batteries together in parallel to increase capacity at 12V. To get 24V the space for 2 x 12v batteries is used to wire together in series (or 4 x 6v) for 24V, so you can be stuck with the single battery capacity at whatever it is as there is no room to parallel batteries to increase capacity.

I also have a split voltage switch panel, so understanding that is important if adding any new equipment.

For me, it’s no big deal to keep, but 12v would be simpler.
 
Definitely stay with 24v.

Don't assume the start system is 24v it is not unusual for this to 12v.
 
Our boat also is primarily 24V, as mentioned above it's usually on bigger boats. As mentioned above, 24V will be made from 2 x 12V batteries.

The primary reason is due to cable length - the longer the cable run, the greater the voltage drop along the cable for a given size (diameter). The way to get around that is to increase the cable size, but after a point that becomes uneconomic and inefficient. The other way around it is to increase the voltage, this allows the cables to be reduced in size but still carry the same amount of potential.

There are still some systems on the vessel which run off 12V, so there will be a 12V system for these. Methods vary, some take 12V direct from one battery in the 24V bank (not ideal), some have a stand-alone battery for 12V, some use a voltage reducer (24-12V)

I would advocate keeping 24V if you can, it's a more robust system in my opinion. If you want to change to 12V, employ the services of a reputable marine electrician as there are lots of things to be aware of and the complexity needs someone with the right knowledge. It won't be cheap to convert a full boat, it will require a lot of work.
 
Older 24v boats tended to have multiple 12v devices, because 24v equipment was limited. These days virtually everything is available in a 24v version. Many devices will accept either 12v or 24v as standard.

If the boat is older it is worth considering updating any 12v equipment to 24v as it is replaced. It is usually, but not always, an easy swap. The voltage drop will be less and higher power devices run better on the higher voltage.

You should only be left with a couple of devices left on 12v, the NMEA 2000 bus power and VHF radio. These are easily powered with a 24/12 volt converter and these are not expensive.
 
PaulRainbow said:
It's usual to have a 24V boat, with the starter and alternator 12V ?
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Generally the engine will have dual alternators, usually with a high power 24v alternator added, keeping the original alternator charging only the start battery.

There are pros and cons compared to converting the engine to 24v, but this set up is not unusual on yachts in my experience.
 
noelex said:
Generally the engine will have dual alternators, usually with a high power 24v alternator added, keeping the original alternator charging only the start battery.

There are pros and cons compared to converting the engine to 24v, but this set up is not unusual in my experience.
Click to expand...

The only reasons I can see for doing this are availability (no 24V option - unlikely) or cost. For many reasons, it is almost always cheaper for the boat builder to put on a 24V secondary alternator than order a 24V engine.

From a technical perspective, there should be no reason to have a 12V starter motor as this is one of the largest current consumers. It would be like having a 12V bow thruster - makes no sense practically.

I agree that this is seen more common on smaller/midsize yachts than full 24V systems, but make no mistake about the reasons - it is cost that is the driver, not practical or technical reasons.
 
There are many reasons to stick with 24v. The biggest though (IMO) is the cabling. The current flowing through them will be sized for 24V. If you put 12v though them to power the same device (let's say a pump) then the current will be twice as much.

That is a potential fire hazard.
 
Moodysailor said:
The only reasons I can see for doing this are availability (no 24V option - unlikely) or cost. For many reasons, it is almost always cheaper for the boat builder to put on a 24V secondary alternator than order a 24V engine.

From a technical perspective, there should be no reason to have a 12V starter motor as this is one of the largest current consumers. It would be like having a 12V bow thruster - makes no sense practically.

I agree that this is seen more common on smaller/midsize yachts than full 24V systems, but make no mistake about the reasons - it is cost that is the driver, not practical or technical reasons.
Click to expand...

It is less expensive to keep the start system on 12v. The other advantage is all the vital components such as the starter, alternator, senders, engine panel and gauges are kept as standard, so parts are easy to find and are also inexpensive.

The main drawback, as you note, is the high draw of starter motor is kept at 12v rather than the more preferable 24v. Starter motors certainly run better and cooler on 24v, but unlike a bow thruster or anchor windlass the duty cycle is very short and cable length can often be made short reducing the voltage drop issue. The standard engine 12v alternator only has to charge the start battery so has an easy life. The house bank will usually be charged using a high output 24v alternator so the advantage of 24v alternators ( higher output and less heat build up ) is still seen despite using an electrically standard 12v engine.

The overall engine size is a large factor. Larger motor boats will use commercially rated engines. These are commonly fitted to 24v work boats so 24v engine spare parts are not an issue and the starter motor becomes large enough that 24v is not only better it may be the only practical option.

For smaller yacht engines many 24v boats use 12v start systems so the demand for 24v engine parts is less, making them hard (but not usually impossible) to find, skewing the advantages more towards keeping the engine 12v, but as I indicated there are pros and cons and both options can work well.
 
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noelex said:
It is less expensive to keep the start system on 12v. The other advantage is all the vital components such as the starter, alternator, senders, engine panel and gauges are kept as standard, so parts are easy to find and inexpensive.

The main drawback, as you note, is the high draw of starter motor is kept at 12v rather than the more preferable 24v. Starter motors certainly run better and cooler on 24v, but unlike a bow thruster or anchor windlass the duty cycle is very short and cable length can often be made short reducing the voltage drop issue.

The overall engine size is a large factor. Larger motor boats will use commercially rated engines. These are commonly fitted to 24v work boats so 24v spare parts are not an issue and the starter motor becomes large enough that 24v is not only better it may be the only practical option.

For smaller yacht engines many 24v boats use 12v start systems so the demand for 24v engine parts is less, making them hard (but not usually impossible) to find.
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Our engine is commercially rated. 24v starter. 24v alternator. 12v control circuit and 12v fuel pump. 4.4 litre engine but just 86hp and enough torque to tow a beach
 
geem said:
Our engine is commercially rated. 24v starter. 24v alternator. 12v control circuit and 12v fuel pump. 4.4 litre engine but just 86hp and enough torque to tow a beach
Click to expand...

Sounds like another good option. There are many possible permutations that can be used with a 24v house system and an engine that is kept at 12v, or partially at 12v. Another one I have seen is having a 12v engine with a single large 24v alternator using a 24v to 12v battery charger to keep the start battery charged.
 
noelex said:
Generally the engine will have dual alternators, usually with a high power 24v alternator added, keeping the original alternator charging only the start battery.

There are pros and cons compared to converting the engine to 24v, but this set up is not unusual on yachts in my experience.
Click to expand...


Would you care to share what you base those statements on ? What exactly is "your experience" ?
 
PaulRainbow said:
Would you care to share what you base those statements on ? What exactly is "your experience" ?
Click to expand...
14 years of full time cruising.

Most boats we visit and socialise with offer a “boat tour”, and as I have an interest in anchors (sorry about that :)) and boat electrics these systems and people’s experiences with this equipment is of particular interest.
 
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