12v or 24V

[cmayflower]

Hello, I'd like some advice please about the benefits (or other) of using either a 12v system or 24v, we are looking into the options of both, we know 12v is widely used but 24v appliances etc. are becoming more available. Any advice greatly appreciated, this will be for a new boat build, we want to have explored both options before we get to the detail with the boat builder so we know what we are talking about.

 

ta muchly.

[Guest]

Biggest advantage I can see of 24V is the reduced volt drop on the longish cable runs. Most things appear available in 24V, but not sure if they are more expensive?

We went with 12V and would likely do so again.

[cmayflower]

Thank you catweasel.

 

I think it may come down to the overall draw on the batteries my understanding is that this would be less on the 24v system.

[by'eck]

Thank you catweasel.

 

I think it may come down to the overall draw on the batteries my understanding is that this would be less on the 24v system.

 

The power (volts x amps) taken from the batteries will be identical. You will need twice as many battery cells for 24 volts but half the amp hour capacity of the total; bank size, since the current draw from any load will be half, so the same say four 12 volt 110 Ah batteries could be used but wired series/parallel for 24 volts rather than all four in parallel.

 

There are pro's and con's with both voltages but on balance I would stick with 12 volts as Catweasel.

[peterboat]

If I was building from scratch it would be 24volts less voltage drop on long cable runs

 

Peter

[Guest]

If I was building from scratch it would be 24volts less voltage drop on long cable runs

 

Peter

True for a given cable size, but easily rectified with a larger cable CSA. Question is which is the most economical way to achieve the ideal voltage? Also practicalities such as availability of 24V spares when out and about may arise?

[Robbo]

Hello, I'd like some advice please about the benefits (or other) of using either a 12v system or 24v, we are looking into the options of both, we know 12v is widely used but 24v appliances etc. are becoming more available. Any advice greatly appreciated, this will be for a new boat build, we want to have explored both options before we get to the detail with the boat builder so we know what we are talking about.

 

ta muchly.

 

I would go with whatever the engine uses.

[OldGoat]

The cable run and consequent sizing / cabling costs to my mind are of relatively minor importance.

IME much, much more important is that 24V units are:-

 

• More reliable, especially inverters
• Many are available at much the same price as 12V models
• Alternators - physical size for size give at least 50% more power and are more robust - being designed for continuous high power output
• In general are more tolerant of voltage fluctuations.

 

Where some items 'have to be' 12V it's easy to take a tap in the battery bank at 12V, or even have a 24 to 12V converter (that latter is what I did for my car radios, but that was a complete overkill..)

 

Been there, got the T shirt.

[bottle]

6 * 110 amp hour 12v batteries wired parallel will give a bank of 660 amp.hrs @ 12v

 

6 * 110 amp hour 12v batteries wired series parallel will give a bank of 330 amp.hrs @ 24v

 

An appliance (1) of 12 watts will load the 12v system with 1 amp

 

An appliance (2) of 12 watts will load the 24v system with 0.5 amps

 

Appliance (1) running for one hour will 'use' 1 amp.hr

 

Appliance (2) running for one hour will 'use' 0.5 amp.hr

 

 

Over to the experts to shoot this down.

[Guest]

The cable run and consequent sizing / cabling costs to my mind are of relatively minor importance.

IME much, much more important is that 24V units are:-

 

• More reliable, especially inverters
• Many are available at much the same price as 12V models
• Alternators - physical size for size give at least 50% more power and are more robust - being designed for continuous high power output
• In general are more tolerant of voltage fluctuations.

 

Where some items 'have to be' 12V it's easy to take a tap in the battery bank at 12V, or even have a 24 to 12V converter (that latter is what I did for my car radios, but that was a complete overkill..)

 

Been there, got the T shirt.

Don't know much about alterbnators so can't comment, but would be very surprised if 24V inverters were "more reliable." In what way?

Also, and I believe relevant, what voltage are the majority of hire boas, and why?

Edited August 14, 2015 by Guest

[dmr]

24 volts is obviously more "technically sensible" on a boat, but looking around me now there are several items that are readily and cheaply available at 12 volts but would be difficult, expensive or almost impossible to obtain in 24 volts.

 

If you go 24volts you will probably need to install a 12v circuit as well which is electrically less sensible.

 

If you go down the Trojan battery route then 4 (or 6) works nicely for a 12 volt system.

At 24volts you would need all 4 in series so have no redundancy against a failed cell, or else you would need 8 which might be a bit over the top.

 

Thicker cables for a 12v system are a once only cost, 24volts will be an ongong extra cost.

24 volt becomes more sensible if you plan very heavy electrical use.

 

............Dave

 

edited to make it make sense

Edited August 14, 2015 by dmr

[Chewbacka]

I went for 24v as it is thinner cables and lower currents.

I also use LED lights and most of them are domestic rather than car based which requires 12v and not 14.4v So I use a regulator which is 90%+ efficient ( I think). The regulator works well at 24v, but on a 12v system it may not be stable as the battery voltage drops to below 13v. so for me 24v works well. I also use a 230v fridge through the inverter, so again a lower cost than a 12v or 24v fridge.

My radio is at the front of the boat, where I have a small 12v leasure battery charged by a 24v to 12v regulator. I tried to run the radio from a switch mode supply but the tuner was flooded by rf from the supply, hence the battery. If I was doing the boat again I would go for 24v, but not use a car radio, either finding a 24v radio I liked or go for mains radio as the inverter is on running the fridge.

[Arthur Brown]

Possibly 24v would be better from a volts drop point of view, but 12v gives you a much bigger range of accessories from the car and caravan market.

 

The MOST critical single unit is the starter motor! If the engine has 24v then you need 24v to crank it.

[cmayflower]

Thank you very much for all your replies so far, this is really helpful.

[Keith M]

I design and install electrical systems for for sorts of vessels both inland and choppy waters

 

If the new build does not require and inverter and is less than 50 feet I would select 12-volts

 

So if an inverter or combi is to be be installed I would select 24-volts every time

 

I find 24-volt equipment to have a much greater reliability. Items likes pumps etc

 

24-volts is widely used in the UK and Europe in the commercial markets

 

Purchase the 24-volt products from the commercial supplies very much cheaper than using chandlers

 

Keith

[Chewbacka]

If you have a dedicated battery and small alternator for the engine then it doesn't matter if the domestic circuits are 12v or 24v. In my case I have a 45a alternator for the engine battery and a separate 24v alternator for the domestic batts.

 

I suspect there are those that like 12v systems and those that like 24v systems and both have pros and cons. There isn't a compelling reason to select either, just go with whichever you fancy.

Edited August 14, 2015 by Chewbacka

[cmayflower]

Much appreciated Keith M for neatly summarising the choices given your experience; on-line research has shown us that any DC voltage equipment we require can be had in a choice of 12v or 24v or even dual 12/24v selectable. The 12v LED lighting by Chewbacka is well considered and the engine will have its own starter battery and engine driven alternator so should not be an issue I believe. A 24v system may not be cheap but as always you get what you pay for and as it’s a new build narrow boat over 60ft we’d rather do it right first time for us, without regrets. All these excellent posts are helping with our decision making.

[ditchcrawler]

Much appreciated Keith M for neatly summarising the choices given your experience; on-line research has shown us that any DC voltage equipment we require can be had in a choice of 12v or 24v or even dual 12/24v selectable. The 12v LED lighting by Chewbacka is well considered and the engine will have its own starter battery and engine driven alternator so should not be an issue I believe. A 24v system may not be cheap but as always you get what you pay for and as it’s a new build narrow boat over 60ft we’d rather do it right first time for us, without regrets. All these excellent posts are helping with our decision making.

I don't think it will cost you much more. The only thing you may struggle with is a 24 volt car radio. many charging leads are now 12/24 for phones etc.

[Timleech]

Smaller 12V kit can easily be run from 24/12V droppers, eg Alfatronix, they give the benefit of stabilised output and there are usually a few on ebay at decent prices.

Don't buy cheap ubranded ones.

 

Tim

[bag 'o' bones]

I think there are pros and cons of both systems.

 

I was under the impression that when converting voltages that the closer the voltages are to one another the more efficient the conversion. Converting from a higher voltage to a lower one is also more efficient than the other way round. Something to do with entropy? Although I could be wrong so would be interested if an expert agrees.

 

24 volt appliances are reasonable common - most lorries are 24 volt and have been for some time.

 

Some cars are going over to 24 volt so perhaps 24 volt will be the norm in a few years time perhaps?

 

 

[Alan Saunders]

Surely a single voltage for all devices and systems is the simplest solution. An alternator ~300V DC may be the ideal?

 

I cannot seriously object to 24V starter motors. Trying to start a truck engine (Albion Reiver) it turned over slowly and there was a 'fizzing' sound. A poor connection to the 24V battery had resulted in arcing that melted a battery terminal; +'ve and -'ve terminals have a slightly different diameter and the wrong one had been fitted. I have never seen this problem with a 12V starter; a poor battery connection usually fails open-circuit with no apparent arcing or heat sufficient to damage or destroy a battery terminal post.

 

Alan

[Chalky]

I design and install electrical systems for for sorts of vessels both inland and choppy waters

 

If the new build does not require and inverter and is less than 50 feet I would select 12-volts

 

Keith

 

I'd agree with that (I work in the research dept for a vehicle manufacturer). Our boat is 40" and we went for 12V. Main reason was that the engine came with 2 x 12V alternators as standard. When I did the calculations 24V used smaller wire sizes however I bought cable in 100M lengths and by the time I'd standardized the cable sizes there was nothing in it. Most circuits were wired in 2.5mm CSA, the tunnel light and horns in 6mm to cope with the current and volt drop. What I did do was to have 2 fuse boxes. 1 was in the engine room and ran the back of the boat, the second was in the middle of the boat and ran most other circuits. This was connected to the rear of the boat using 40mm CSA cables but meant that I could downsize other cables. Some circuits are run off the middle fusebox but switched by relays with the coils driven off the rear.

 

One thing to think about is what wire size your electrical fittings will accept. Going to 24v will allow you to drop the wire size for a given volt drop. Most screw terminals will accept 2.5mm or 1.5mm without any problems. Dropping to 0.75mm or 0.5mm may result in problems. Volt drop, temperature rise in the harness bundle and current rating are only part of the problem.

Surely a single voltage for all devices and systems is the simplest solution. An alternator ~300V DC may be the ideal?

 

 

300V DC is absolutely lethal and is covered by lots of regulations. 300V AC is a lot safer.

[Keith M]

Much appreciated Keith M for neatly summarising the choices given your experience; on-line research has shown us that any DC voltage equipment we require can be had in a choice of 12v or 24v or even dual 12/24v selectable. The 12v LED lighting by Chewbacka is well considered and the engine will have its own starter battery and engine driven alternator so should not be an issue I believe. A 24v system may not be cheap but as always you get what you pay for and as it’s a new build narrow boat over 60ft we’d rather do it right first time for us, without regrets. All these excellent posts are helping with our decision making.

 

They are many 24-volt Led lights available I am using a company near Telford

The lights that I am using are design for the commercial vehicles. They are far superior than what can be found chandlers

 

Regrading 24-volt radios

There are two ways to approach this problem first a 230-volt AC radio all modern commercial vehicles have a radio normally via a small DC / D converter

 

Keith

[OldGoat]

Much appreciated Keith M for neatly summarising the choices given your experience; on-line research has shown us that any DC voltage equipment we require can be had in a choice of 12v or 24v or even dual 12/24v selectable. The 12v LED lighting by Chewbacka is well considered and the engine will have its own starter battery and engine driven alternator so should not be an issue I believe. A 24v system may not be cheap but as always you get what you pay for and as it’s a new build narrow boat over 60ft we’d rather do it right first time for us, without regrets. All these excellent posts are helping with our decision making.

 

There's a limit to the power that you can extract from a 12V alternator commonly available on the market. Many of these require high speeds to achieve that output.

When I built Beta fitted a girt big Leece-Neville 24V unit designed for a truck 145 amps @ 24V

That equates to 290 amps @ 12V

You can't do that with a 12 unit. Cos £450 quid though...

 

There a number of bus / truck units available on eBay a sample here:-

http://www.ebay.co.uk/itm/Alternator-24v-AC203RA-120A-Dennis-CAV-Prestolite-PSV-Bus-/181589857784?pt=LH_DefaultDomain_3&hash=item2a479955f8

 

£295 - you'd pay that much for a Balmar 12V unit at half the capacity

 

or this one for £170 being a 'marine unit' you get shiny black paint for no extra cost

http://www.ebay.co.uk/itm/24V-60AMP-MARINE-ALTERNATOR-66021532-/191634165967?pt=LH_DefaultDomain_3&hash=item2c9e4950cf

 

Both the above rotate at reasonable speeds so the pulley arrangements don't get silly

Being designed for trucks and buses they are designed for continuous output rather than intermittent use in a car.

 

a

[GUMPY]

 

Regrading 24-volt radios

There are two ways to approach this problem first a 230-volt AC radio all modern commercial vehicles have a radio normally via a small DC / D converter

 

I have some ViTronix 10amp 24>12v converters in my lockup that I can exchange for Beer.