12 to 24 volts

[eidiohir]

Just thinking of changing a few electrical things on board and twenty four volt stuff seems to work better and can be obtained cheaper than twelve,So I thought why do boats have twelve?and why not change it? I can understand that the starter motor would have to go and the alternator also but everything else seems to work on either 12 or 24.So where is the big drawback?I know from bitter experience that there has to be one so what is it?

 

[Ludd]

Just thinking of changing a few electrical things on board and twenty four volt stuff seems to work better and can be obtained cheaper than twelve,So I thought why do boats have twelve?and why not change it? I can understand that the starter motor would have to go and the alternator also but everything else seems to work on either 12 or 24.So where is the big drawback?I know from bitter experience that there has to be one so what is it?

Depending on engine there may/may not be a 24v starter available,though you could have it rewound.Possibly have to change engine instruments. Could be costly ,but you'd then be able t o use lorry gear.

 

[Sandyman]

24v was the standard long before 12v came along. Why 12V ??? Maybe battery sizing or the fact that the auto industy went 12v ??? Does anyone know ???

 

[William_H]

Battery voltage

Well I would disagree with sandyman. I think 6V was the original standard for cars and some trucks.
Probably for a cheaper battery. It was in fact the starting and headlights that suffered with the high current needed at 6V.
I think for a boat it is the engine start then anchor winch and inverter that will be big current drawers hence the reason to go 24v.
It is possible that the 12v engine starter will be OK on 24v. This because the current drawn drops rapidly as the starter begins to crank. You should enquire of the makers. Obviously you will need to convert the alternator to a 24v type. So if you have problems with your existing system 24v may solve them and as you say for high current items 24v will be much better. good luck olewill

 

[LadyInBed]

So where is the big drawback?I know from bitter experience that there has to be one so what is it?

I inherited a 12 and 24v system. Two alternators and Five Batteries!
Not all kit will work off 24v, so you will probably have to use a series - parallel battery setup or use two batteries of different or equal (large) capacity AH with a center tap to power the 12v kit. This isn't ideal as the larger / parallel battery(s) won't get fully charged.
The alternative is to use three batteries - Two large capacity in series for the 24v plus a 24 to 12v converter / charger to charge the 12v battery, Waeco also do one.

Starting from where you are, this isn't a route that I would go down!!

 

[mikefleetwood]

So much possibility for problems with mixed 12/24V systems.

A friend of mine spent half the weekend on a "10 minute" job on fishing boat. He was asked to replace the all-round white light that got damaged on delivery. Fastened down the new fitting to the mast/gantry and found cables getting hot and other lights coming on - with nothing switched on! System was two 12V batteries in series, but the 12V circuits were taken off the wrong taps. Negative for the 12V was actually +12V to the engine and finding a current path back via the steel braiding in hydraulic hoses!

Better to have a single voltage system if at all possible IMHO

 

[eidiohir]

I am not really going down that route as I am happy enough with things as they are and I am only a diy electrician .It's just as someone without any more than the basics of elelectrickery I wondered why 12v when it seems to be a lesser system than 24v.Then I wondered if it is better why not change and if you do change what stands in your way.To me changing the starter and alternator doesn't seem like an insurmountable hurdle to overcome if everything else was ok.I didn't think of the engine instruments so thats one other thing but the winch will work on 24 the fridge ,the gps, radio and radar all will so what is left?

 

[eidiohir]

I should have added that all the light bulbs would have to be changed from 12 to 24 and that could cause a problem with nav. lights I suppose

 

[bigwow]

It is possible that the 12v engine starter will be OK on 24v. This because the current drawn drops rapidly as the starter begins to crank. You should enquire of the makers. ter. good luck olewill

In my youth I raced a special saloon car with a BDA engine. The cars system was 12v but the 12v starter was rigged to use 24v so it turned the engine over fast enough to start.

 

[Bodach na mara]

I am surprized that you can find 24 volt stuff cheaper and more easily than 12. Thay has not been my experience. The Watermota engines of circa 1970's had a 24 volt alternator and battery system simply because, to spin them fast enough to start, they used a 12 volt starter and hit it with 24 volts. This works provided you do not operate the starter for more than 15 seconds at a time.

Having a 24V battery bank has advantages, but it has meant finding ways to get 12 volts for lights, radios and instruments. Tapping off the battery bank is a bad idea and I use a DC/DC convertor. Right now however, I have two problems: Finding replacement 24V bulbs for the fridge warning light and compass, both of which have really strange holders.

 

[fuss]

Just thinking of changing a few electrical things on board and twenty four volt stuff seems to work better and can be obtained cheaper than twelve,So I thought why do boats have twelve?and why not change it? I can understand that the starter motor would have to go and the alternator also but everything else seems to work on either 12 or 24.So where is the big drawback?I know from bitter experience that there has to be one so what is it?

I see your boat is 34ft and so the cable runs are not long enough to need 24v. 24v is for larger boats with long cable runs.
My boat has 12v motor and generator and 24v house systems. I used to wonder why the whole thing was not 24v as it seemed silliy to have both. But now I like it... the generator and the engine use the same 12v start batterys and both charge them. the generator and the engine both charge the 24v system as well. i could imagine that if all was 24v I would have lots of problems finding parts in remote places.
Another point, I think I would need more battery space if starting was 24v
As it is at the moment I need 2x 750 cold cranking amp batts in parallel to start my perkins sabre.
John

 

[eidiohir]

I think you misunderstand me.I'm not complaining about my present system or making plans to change it.I was just wondering why 12 when 24 is better.By the way i don't think that you need extra batteries to provide more power for a 24 volt starter as the energy needed to turn the engine will be the same and the 24 volt starter will be more efficient so the total power needed will stay more or less the same but the starter will work better.
I think one of the reasons to up the voltage is power taken overcoming resistance goes down as voltage goes up.That's why power transmission lines for the national grid are at hundreds of thousands of volts not that I want that much voltage running around anyones boat.
The main reason is that motors are more efficient at 24 volts a good example is a cordless drill would you prefer a 12 volt or a 24 volt to do a difficult job?

 

[Bobobolinsky]

I have a seperate 24v system for my anchor winch as I did not want 24v start for my new engines, but have a 24v alternator on one engine and two batteries way forward, so cranking runs are not long Since I have a large Simpson Lawrence winch I didn't fancy the cost of a 12v motor

 

[William_H]

Re Wight Dawn finding special globes

For small indicator lights I think a series resistor would be quite appropriate to run the 12V globes on 24v.
You need to know the wattage of the lamps probably 3w which takes 1/4 amp at 12v you need a resistor of
R=E/I 12v/.25 is 48 or 50 ohms at 3or more watts rating. Just a few pence at an electronics supply like RS. good luck olewill

 

[RedAdmiral]

I wouldn't worry too much about the starter motor. Many years ago when some cars had 6volt electrics we often swopped them to 12volt changing only dynamo, battery and bulbs (possibly wiper motor as well unless you had a Ford and electric fuel pump if you had a Morris). I never heard of a 6volt starter burning out with 12 volts across it, probably because when pulling a couple of hundred amps out of the battery the actual voltage was about nine!

 

[DownWest]

Same experience as RedAdmiral, as the max recommended time for starter use then was 10sec, 12v into a 6v didn't make a lot of difference apart from the faster start. VW Bugs were a case in point. 24v systems halve the wiring cross-section, usefull for high consumption items (anchor winches), but only if a new fit. Many American boats have 32v, but I think that is going out of fashion.
Our big company ketch had 12v for engine start, 24v for most everything else. 240v genset, which could charge the lower voltages as well though a shorepower unit. One engine had 24v alternator, the other 12v. Worked fine. One start battery per engine (Detroit 4cyl 2-strokes) and around 4 domestics IIRR, plus the dedicated genset 12v start.
A

Just reread the OPs last post. I expect that the marine industry (leasure) has drifted into the auto world, where 12v is the standard. Probably because the electrics are auto based (cost) as are many of the engines. Commercial vessels tend to use higher, more efficient voltages as the advantages are worth the extra cost.
A

 

[grumpy_o_g]

I think you misunderstand me.I'm not complaining about my present system or making plans to change it.I was just wondering why 12 when 24 is better.By the way i don't think that you need extra batteries to provide more power for a 24 volt starter as the energy needed to turn the engine will be the same and the 24 volt starter will be more efficient so the total power needed will stay more or less the same but the starter will work better.
I think one of the reasons to up the voltage is power taken overcoming resistance goes down as voltage goes up.That's why power transmission lines for the national grid are at hundreds of thousands of volts not that I want that much voltage running around anyones boat.
The main reason is that motors are more efficient at 24 volts a good example is a cordless drill would you prefer a 12 volt or a 24 volt to do a difficult job?

You need 12 cells to make a 24 volt battery regardless of the capacity so there'll be a cost and weight penalty in the battery if you don't need the extra voltage to overcome the high current resulting from using lots of Watts.

Once you get to a certain point, whether from long cable runs introducing resistance or from high loads in the system, the cost and weight of upgrading the cables and the devices they're powering as well possibly, outweighs the added cost/weight of a 12 cell battery. I suspect it's that simple - it usually boils down to money.

 

[eidiohir]

I'm not trying to nitpick,so don't get me wrong.You are right of course you do need twelve cells for 24volts The thing is most if not all of us with cruising boats have at least two batteries connected in series for the domestic and a hefty starter battery as well.The domestic battery bank could just be changed to parallel whereas the starter battery would have to be 1,joined in parallel with a equal battery or 2, separated and charged at twelve volts or 3,replaced with two smaller batteries.I think the cost and weight end of things is low.My Colvic Watson 34 comes in around 12 ton so one more battery means little.
So the question I was putting forward is not the cost of changing but why 12 and not 24.It seems to be more or less universally agreed that 24 is better so why not 24.
I suppose it comes down to the size of your boat and the number of motors you have.You see my better half has told me that I must have a bow thruster fitted for next summer and I was looking at them on the internet and noticed that for the same money you can get a 24 volt instead of a twelve volt and the 24 gives you more power and needs smaller cables.Then I said to myself it must be better to go 24 so why not,what are the problems, they must be there somewhere.So forgive the long winded reply I hope you know where I'm coming from now at least.

 

[halcyon]

I am not really going down that route as I am happy enough with things as they are and I am only a diy electrician .It's just as someone without any more than the basics of elelectrickery I wondered why 12v when it seems to be a lesser system than 24v.

Back as recent as the 1990's 24 volt private ( not commercial ) equipment was rare. Even spare 24 volt bulbs were a problem, remember Westerly stripping new light units for spare bulbs on the Whitewater Sea Wolf.

Also back in 1985 30 foot was a big boat, and thus 12 volt was not a problem with cable runs. Once you get to 50 foot, volt drop can be a problem, so 24 volt same wattage halfs current, and reduces volt drop to acceptable levels.


Brian

 

[eidiohir]

Back as recent as the 1990's 24 volt private ( not commercial ) equipment was rare. Even spare 24 volt bulbs were a problem, remember Westerly stripping new light units for spare bulbs on the Whitewater Sea Wolf.

Also back in 1985 30 foot was a big boat, and thus 12 volt was not a problem with cable runs. Once you get to 50 foot, volt drop can be a problem, so 24 volt same wattage halfs current, and reduces volt drop to acceptable levels.


Brian

So that's why it is the way it is now and I suppose that's the way it will remain for the future.Things tend to carry on the same old way until something major happens to upset the apple cart.