12v or 24v. pro's and con's

[AllanC]

I have read and seen that many boats are either 12volt or 24volt. What is the difference in terms of use? Which is preferable and can you convert one to the other if desired.

[Robbo]

24v can have thinner cable and is more suitable for the length of boats we usually have.  

24v high amp alternators are not as physically big in size as 12v ones.  Less current, better all around,etc.

Less voltage drop on the cables.

24v stuff can be more expensive, like pumps, etc.  Although lots of stuff is both 12v and 24v like lights and fridges.

if your engine is 12v, it’s not as easy to charge the main batteries from the alternator.  It’s best to have them on the same voltage for simplicity.  There’s ways around it, multiple alternators and 12-24v,etc.

yes you can get dc-dc transformers.

More non-marine stuff is more available 12v only like cheap inverters.  although I would only stick with decent inverter and chargers from the likes of Victron and MasterVolt.

if I was starting from scratch I think I would go 24v.

Edited July 27, 2017 by Robbo

[WotEver]

24V kit is generally more robust and reliable but sometimes more difficult to source and more expensive. I've not come across any 24V USB adaptors for instance. If you can't find a 24V starter for your engine then you'll have more complexities with a 12V engine start and 24V leisure. 24V installations require half the cable size as 12V for the same power. 

There's a few pros and cons to start you off. 

[OldGoat]

I don't subscribe to the idea that you should change the engine starter for 24v - don't forget the instruments and some switchgear would need to be converted as well. Why?

Most modern engines are supplied with a small 12v alternator that is not powerful enough to charge a reasonable sized battery bank. Therefore leave the engine side alone with its gear and fit a 24V alternator setup to deal with the domestics.

I've found 24v kit at reasonable prices - ebay has been a good source. Indeed Sterling has been selling returned items and I picked up several items at quite silly / affordable prices recently.

For me the killer was if you need to generate a reasonable amount of power from batteries, then 24 or even 48v is the way to go (that is if you can buy a 48v alternator  

[Detling]

For items like lights you can easily wire two 12 volt units in series on a 24 volt boat. Items like MTTP chargers for solar are cheaper for a 24 volt system as they are priced by the amps not the volts, so a 20A controller can control about 300 Watts at 12 volt and 600 Watts at 24 volts.

[Tony Brooks]

4 hours ago, Robbo said:

24v can have thinner cable and is more suitable for the length of boats we usually have.  

24v high amp alternators are not as physically big in size as 12v ones.  Less current, better all around,etc.

Less voltage drop on the cables.

24v stuff can be more expensive, like pumps, etc.  Although lots of stuff is both 12v and 24v like lights and fridges.

if your engine is 12v, it’s not as easy to charge the main batteries from the alternator.  It’s best to have them on the same voltage for simplicity.  There’s ways around it, multiple alternators and 12-24v,etc.

yes you can get dc-dc transformers.

More non-marine stuff is more available 12v only like cheap inverters.  although I would only stick with decent inverter and chargers from the likes of Victron and MasterVolt.

if I was starting from scratch I think I would go 24v.

1. rather misleading. you will get the same voltdrop on 12V and 24 volt circuits PROVIDING both have the correctly sized cables. I think I could easily produce a 12V circuit with less voltdrop than a 24 volt one by simply fitting oversized cables. However as 24 volt appliances need half the amps of 12V ones the thinner cable bit is correct.

2. Not technically correct, a simple transformer can not work with DC. However if you had typed "CONVERTER" I would completely agree .

Edited July 27, 2017 by Tony Brooks

[Robbo]

1. Yeah, blame iPhone and lazy typing. Should have clarified why.

2. As above.

[AllanC]

So, it would be possible to keep the engine at 12v with a separate battery, and add a 24v alternator to allow the domestic circuit to be 24v and charge the 24v battery bank.

I would then have to source 24v appliances and lighting. Or maybe just have the lighting at 24v and find an inverter to run the appliances.

I would not plan to have much in the way of appliances anyway. Perhaps just tv, laptop, twin tub washer, radio. Even as a house dweller, I don't find the need for a high tech existence. I can live a fairly simple life.

Of course I would have a genny for power tools, or find a hookup.

 

Edited July 27, 2017 by AllanC
to remove extranious word

[WotEver]

15 minutes ago, AllanC said:

I would not plan to have much in the way of appliances anyway.

Hardly seems worth the hassle then. 

[AllanC]

Maybe not. I'm just wondering if there is any real benefit to having 24v over 12v as quite a few folks have it.

So would you say it is more beneficial if you have a more power hungry lifestyle?

[WotEver]

24 minutes ago, AllanC said:

So would you say it is more beneficial if you have a more power hungry lifestyle?

Possibly. Like everything in life it's a balance. Look at what you want, check the availability and cost of items at both voltages and make the call. Cable costs will be lower but that's hardly a big percentage of the fitout costs. 

[AllanC]

Ok thanks. Plenty of time to think about these things and do the research.