Designing an electrical system for a 30ft boat.

[burgundyben]

Twin engines have 24 volt starters and alternators.

There is a need for 12v on the boat. I'm not keen on those voltage dropper units. I had a mascot one on the previous boat which was reliable enough but they look like inefficient and unnecessary risk to me so I'd like an alternative.

I know of a boat with 24v starters, one engine has a 24v alternator which charges the battery starting bank. The other engine has a 12v alternator charging the domestic bank. If you go this route then you need a battery charger with both a 24v output and a 12v output. Presumable the exciter wire for each alternator is different, one at 24 and one at 12, so how do you switch on the ignition for the engine with the 12v alternator and send 12v to the exciter and 24 to the starter?

I am starting from scratch, so there is an opportunity to get it exactly how I want it.

 

[halcyon]

Presumable the exciter wire for each alternator is different, one at 24 and one at 12, so how do you switch on the ignition for the engine with the 12v alternator and send 12v to the exciter and 24 to the starter?

I am starting from scratch, so there is an opportunity to get it exactly how I want it.

24 volt relay, 12 volt on contacts.

Brian

 

[MapisM]

B, I guess it's the new to you FH you are thinking about. Whose engines, I suppose, are not electronically controlled in any manner.
And if this is the case, your one and only 24V requirement could be for the starters, right?
Now, if this is the case, and if you are sure that you can run anything else on 12V, a possibly silly idea popped to my mind:
Keeping two 12V battery banks, fit 12V alternators on both engines, and use a switch to momentarily put the two banks in series at startup.
Mind, I might well be missing some major drawbacks of such solution, as I said it's just a thought which popped to mind....

 

[P4Paul]

Twin engines have 24 volt starters and alternators.

There is a need for 12v on the boat. I'm not keen on those voltage dropper units. I had a mascot one on the previous boat which was reliable enough but they look like inefficient and unnecessary risk to me so I'd like an alternative.

I know of a boat with 24v starters, one engine has a 24v alternator which charges the battery starting bank. The other engine has a 12v alternator charging the domestic bank. If you go this route then you need a battery charger with both a 24v output and a 12v output. Presumable the exciter wire for each alternator is different, one at 24 and one at 12, so how do you switch on the ignition for the engine with the 12v alternator and send 12v to the exciter and 24 to the starter?

I am starting from scratch, so there is an opportunity to get it exactly how I want it.

12 volt switching wire from the starter switch to 12v and 24v relays in the engine bay?

 

[P4Paul]

Blimey, those guys are quick on the keyboard. ^^^^^there were no replies when I started typing!

 

[superheat6k]

Ben

The Bluesea range of low voltage fuse distribution blocks are excellent, and can be bought from Barden Batteries for a reasonable price (tell them you are 'trade' to get a decent discount - they don't question this too much, but an advantage if you can buy them through a company name).

For the diagrams the layout on my previous Fairline Turbo was pretty well thought out, but was 12 volt only.

The distribution details are available here ...
https://www.dropbox.com/s/sr7y05cydioeeyo/Ocean Belle Dist Wiring 2014.xlsx?dl=0

 

[David2452]

One way to have what you want, and I have done it a few times quite satisfactorily is:
24v bank supplying 24v kit and charged by alternator(s) and shore power charger.
12v bank supplying 12v kit and charged by a battery to battery charger from the 24v bank, this will mean one type of alternator and one mains charger only.
Personally if starting from scratch as you are I would make the whole extra low voltage DC install 24v.

 

[dustywings]

Could you just convert the engines to 12v and forget 24v altogether. I installed a pair of Sabres in my boat and did this with new starters and alternators and you are halfway there with the alternators. I sold the old ones to help fund the new ones so wasn't too painful. Probably a really good reason for keeping 24v but it has worked well for me.

 

[burgundyben]

24 volt relay, 12 volt on contacts.

Brian

Thanks, I can see how that would work, but it feels like a whole load of potential failure points.

Ben

The Bluesea range of low voltage fuse distribution blocks are excellent, and can be bought from Barden Batteries for a reasonable price (tell them you are 'trade' to get a decent discount - they don't question this too much, but an advantage if you can buy them through a company name).

For the diagrams the layout on my previous Fairline Turbo was pretty well thought out, but was 12 volt only.

The distribution details are available here ...
https://www.dropbox.com/s/sr7y05cydioeeyo/Ocean Belle Dist Wiring 2014.xlsx?dl=0

Thanks Trev. Useful.

Could you just convert the engines to 12v and forget 24v altogether. I installed a pair of Sabres in my boat and did this with new starters and alternators and you are halfway there with the alternators. I sold the old ones to help fund the new ones so wasn't too painful. Probably a really good reason for keeping 24v but it has worked well for me.

Since P=IV we can provide the same power to the starter motor using half the current if we use double to voltage.

I note that the fridge I am likely to install is 24, so really perhaps only the chart plotter and instruments are 12v, maybe its best to use mostly 24v and just had the voltage dropper for the limited 12v.

 

[vas]

I note that the fridge I am likely to install is 24, so really perhaps only the chart plotter and instruments are 12v, maybe its best to use mostly 24v and just had the voltage dropper for the limited 12v.

Ben,

that's what I also have, 24V led lights all around, 24V navlights, 24V fridges, 24V engines, gauges and bilge pumps.

You only need 12V for chartplotter and NMEA2K network (if you install such a thing), VHF and car stereo. Even USB charging sockets (which I urge you to install!) can be fed from fernell's 24->5 xformers 1, 1.5 or 2A ones and they work fine.
I have a smallish 24->12V dropper (20A iirc) and keeps up with all that just fine.

cheers

V.

PS. where are the pics of the new boaty arrival?

 

[Why Not]

I would recommend that you get yourself a copy of the “The 12-Volt Bible for Boats”.
It a clear introduction to the 12-volt electrical systems used on boats to power everything
from reading lights to bilge pumps.
It is written by Edwin Sherman, and the current edition is thoroughly updated
with respect to modern batteries, breaker and panel design, alternative energy sources,
and troubleshooting equipment.

Notwithstanding that it retains the fundamental simplicity that has made it
one of the most popular books on the market for boaters.
It will keep certain marine electricians from pulling the wool over your eyes,
and enable you to work out exactly the maths involved - always go the full nine yards.

Why Not

 

[halcyon]

Thanks, I can see how that would work, but it feels like a whole load of potential failure points.

You must have a vivid imagination, coil feed from common 24 v ign switch, contacts feed 12v alt warning light, relays normally have working life of a few 100,000 operations, intrigued ?

Brian

 

[macnorton]

Use 2 x 12v batteries for the 24v and take the 12v of 1 of the batteries. (yes it will and does work!!)

 

[kashurst]

The various chart plotters and instruments I have used/fitted over the years all worked from 12 to 30 V dc. I would keep everything at 24V, to keep it simple. Mixing voltages across the boat is bound to cause a serious cock up sooner or later. Also at 24v the currents are all pretty much half so less stress on all the various connectors etc. If you find an item that will only work on 12V - use a modern switch mode converter. They are very efficient, don't create much heat (unless you use a really big one and work it hard) and reliable. I have 3 on my boat for the stereos and something else I can't remember. You can run 12v by making a connection at the join of two 12v batteries but over time the two batteries don't always charge evenly. If you decide to do that make sure you get the negative from the common negative connection.

 

[jfm]

Hi BB. I have exactly this on current and previous boat: a 24v boat basically, but need for 12v for some appliances and a dislike of droppers. The "needed" 12v consumers are things that just don't come in 24v like VHF, N2k and similar backbones, Recaro electric seats, Fusion radios and amps, cameras, KVH sat gear, and a few others I have forgotten

I use the following set up, though it aint hugely cheap and if you only want say VHF then it is worth considering a dropper, dislikeable though they might be:

1. separate 12v battery and distribution board feeding the 12v consumers;
2. separate 230v - 12v charger eg this http://www.mastervolt.com/products/chargemaster-12v/chargemaster-12-25-3/; and
3. a "24-12v" charging dropper, to charge the 12v battery in a proper "3step" process off the main engine 24v alternators http://www.mastervolt.com/products/mac-magic/dc-dc-converter-magic-24-12-20/

 

[MapisM]

Wow, that's possibly the most sophisticated dual voltage DC setup I've ever heard of!
Just one thought: assuming that you have AC available at all times, either through dock, genset or inverter, wouldn't it have been easier to connect the 12V charger to the inverter (as I guess is the main fridge, for instance ) and get rid of (3) altogether?

 

[burgundyben]

1. separate 12v battery and distribution board feeding the 12v consumers;
2. separate 230v - 12v charger eg this http://www.mastervolt.com/products/chargemaster-12v/chargemaster-12-25-3/; and
3. a "24-12v" charging dropper, to charge the 12v battery in a proper "3step" process off the main engine 24v alternators http://www.mastervolt.com/products/mac-magic/dc-dc-converter-magic-24-12-20/

Agree with 1 and 2, but not sure how different 3 is to having a dropper?

The problem on Playtime was that the cabin lights we're 12v running off the dropper, at night, I could put my book down, reach up and turn off the cabin light, but the dropper would still be on, I had to leave it powered up all night or get out of bed to switch off the 12volt and clamber back into bed, which is of course, exactly what you don't want to be doing when preparing for level 10 snoring!

I think a dropper is the solution, it just needs to be positioned in a different place in the circuit.

24v starters, alternators, cabin lights, heating, fridge, nav lights, cabin lights.

12v is for echosounder and plotter only, an 'instruments' switch on the 24 panel with the dropper in the line to the instruments.

Phone charger! Mustn't forget phone charger!

 

[kashurst]

are you sure the echo sounder and plotter won't run from 24v ? might be worth asking the manufacturer if they are not marked.

 

[Dick Atcherley]

Agree with 1 and 2, but not sure how different 3 is to having a dropper?

The problem on Playtime was that the cabin lights we're 12v running off the dropper, at night, I could put my book down, reach up and turn off the cabin light, but the dropper would still be on, I had to leave it powered up all night or get out of bed to switch off the 12volt and clamber back into bed, which is of course, exactly what you don't want to be doing when preparing for level 10 snoring!

I think a dropper is the solution, it just needs to be positioned in a different place in the circuit.

24v starters, alternators, cabin lights, heating, fridge, nav lights, cabin lights.

12v is for echosounder and plotter only, an 'instruments' switch on the 24 panel with the dropper in the line to the instruments.

Phone charger! Mustn't forget phone charger!

A couple of USB ports and a cigar lighter point takes care of most portable electrical devices these days...

 

[vas]

Agree with 1 and 2, but not sure how different 3 is to having a dropper?

The problem on Playtime was that the cabin lights we're 12v running off the dropper, at night, I could put my book down, reach up and turn off the cabin light, but the dropper would still be on, I had to leave it powered up all night or get out of bed to switch off the 12volt and clamber back into bed, which is of course, exactly what you don't want to be doing when preparing for level 10 snoring!

I think a dropper is the solution, it just needs to be positioned in a different place in the circuit.

Ben,

why do you believe you HAVE to switch off the dropper? I also have one and never bother to turn it off (even when away...) Cannot be any serious consumption when idle.

Other option is to pick off one battery and balance loads (like one batt does VHF and radio, the other does plotter/sounder) but it's not elegant

V.