24v batteries v 12v batts

[PaulRainbow]

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.

Wasn't a loaded question, i was genuinely interested, as my experience differs and i wondered what these boats were that "generally had twin alternators" and had 12V starters and alternators.

I have worked on boats with dual alternators, but (in my experience) these tend to be both the same voltage, either 12V or 24V, although i'm aware that some have DC alternators and AC ones too. I've worked on lots of 24V boats too, but in every single case, the starter and alternator have both been 24V, with lots of 24V equipment and varying amounts of 12V equipment.

Have the ones that you have visited had those 2nd (24V) alternators fitted aftermarket to power things like bow thrusters and windlasses etc ? The 24V boats that i have experience with were built as 24V, with 12V subsystems (mostly motorboats, i see very few 24V sailboats).

 

[noelex]

Wasn't a loaded question, i was genuinely interested, as my experience differs and i wondered what these boats were that "generally had twin alternators" and had 12V starters and alternators.

I have worked on boats with dual alternators, but (in my experience) these tend to be both the same voltage, either 12V or 24V, although i'm aware that some have DC alternators and AC ones too. I've worked on lots of 24V boats too, but in every single case, the starter and alternator have both been 24V, with lots of 24V equipment and varying amounts of 12V equipment.

Have the ones that you have visited had those 2nd (24V) alternators fitted aftermarket to power things like bow thrusters and windlasses etc ? The 24V boats that i have experience with were built as 24V, with 12V subsystems (mostly motorboats, i see very few 24V sailboats).

They were all originally built as 24v boats. Very few owners contemplate changing their house bank voltage, with the rare exception of owners who have also converted to electric drive.

I suspect part of the reason for our different experiences may be the type of boats we see. Long distance cruising yachts tend to be larger than coastal cruising yachts. 24v systems are common, but they frequently have typical yacht engines from manufacturers such as Yanmar and Volvo. These engines are often not easily or cheaply converted to 24v (although it is possible), and the ready availability of spare parts is an issue, hence the popularity of 12v engines with a 24v house system.

I see fewer power boats. There are less power boats involved in long distance cruising and commercial and recreational mariners don’t frequently socialise together. This is a pity because I suspect we could learn a lot from the equipment chosen, especially on commercial boats. Most long distance cruising power boats have larger commercial engines and for reasons I have outlined a 24v house bank is nearly always combined with a 24v start system, whereas with yachts 24v house systems are more commonly combined 12v start systems. I suspect with your profession you see more power boats with 24v hence our different experiences.

 

[Deleted member 36384]

It may the that many old cruising boats still have twin alternators from when it was a thing to have twin alternators. My own has twin 24V alternators and it is an old cruising boat, fitted with the larger engine option (4236), 24V starter, internal lights, navigation lights, windlass, fridge, bilge pumps and water pump, bilge alarm, gas detector, ACU 400 and Neco Motor. Plotter, VHF, Instruments, USB sockets and Navtex are all wired to 12V Interestingly, at Attainable Adventure Cruising (www.morganscloud.com, a subscription service), they claim a single, large case, modern alternator, correctly installed is far better than twin alternators, they make the case on their web site for single alternators and recommend this approach. They have solid figures for reliability and it is about 3000 hours (caveat, I may be remembering wrongly) that they replace theirs, with a refurbished unit, with the removed one going for refurbishment.

 

[PaulRainbow]

They were all originally built as 24v boats. Very few owners contemplate changing their house bank voltage, with the rare exception of owners who have also converted to electric drive.

I suspect part of the reason for our different experiences may be the type of boats we see. Long distance cruising yachts tend to be larger than coastal cruising yachts. 24v systems are common, but they frequently have typical yacht engines from manufacturers such as Yanmar and Volvo. These engines are often not easily or cheaply converted to 24v (although it is possible), and the ready availability of spare parts is an issue, hence the popularity of 12v engines with a 24v house system.

I see fewer power boats. There are less power boats involved in long distance cruising and commercial and recreational mariners don’t frequently socialise together. This is a pity because I suspect we could learn a lot from the equipment chosen, especially on commercial boats. Most long distance cruising power boats have larger commercial engines and for reasons I have outlined a 24v house bank is nearly always combined with a 24v start system, whereas with yachts 24v house systems are more common combined 12v start systems. I suspect with your profession you see more power boats with 24v hence our different experiences.

That's interesting and i'm sure you are correct, the differences are likely to be down to the boats we typically see. With the 24V boats that i get to work on all being motor boats, recreational and commercial, the engine are all big lumps that would have been typically produced with 24V electrics.

 

[jwfrary]

It's usual to have a 24V boat, with the starter and alternator 12V ?

Looking at a halberg rassey tomorrow with exactly that! Though its really not ideal is it!

24v equipment is easy to get and the alternators tend to be cheaper in my experience.

One thing to note is the nmea 2000 bus is 12v so interfaces with some things need careful consideration.

24v is better in almost every conceivable way.

 

[noelex]

Interestingly, at Attainable Adventure Cruising (www.morganscloud.com, a subscription service), they claim a single, large case, modern alternator, correctly installed is far better than twin alternators, they make the case on their web site for single alternators and recommend this approach. They have solid figures for reliability and it is about 3000 hours (caveat, I may be remembering wrongly) that they replace theirs, with a refurbished unit, with the removed one going for refurbishment.

Large case alternators are always better if you have the room. Especially on 24v they can produce heaps of power (ours is rated at 175A @24v or 4.2 kw although I have derated this to 120A ).

There are many inexpensive large frame 24v bus and commercial vehicle alternators available and these are designed to work continuously at high output so are usually very reliable on pleasure boats. The combination of the large case and 24v alows for much cooler operation increasing reliability and permitting this type of high power output with a relativly simple and inexpensive design.

 

[jwfrary]

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Large case alternators are always better if you have the room. Especially on 24v they can produce heaps of power (ours is rated at 175A @24v or 4.2 kw although I have derated this to 120A ).

There are many inexpensive large frame 24v bus and commercial vehicle alternators available and these are designed to work continuously at high output so are usually very reliable on pleasure boats. The combination of the large case and 24v alows for much cooler operation permitting this type of high power output with a relativly simple and inexpensive design.

Paid 360 quid for a new prestolite 175 amp at 24v a few weeks ago. If your motor takes a j180 mount theres loads of options out there.

Much above 175 the cost spirals a bit!

 

[PaulRainbow]

Looking at a halberg rassey tomorrow with exactly that! Though its really not ideal is it!

24v equipment is easy to get and the alternators tend to be cheaper in my experience.

One thing to note is the nmea 2000 bus is 12v so interfaces with some things need careful consideration.

24v is better in almost every conceivable way.

From scratch, i'd install all 12V navigation electronics on a dedicated DC-DC converter. I did a refit on a large motorboat a couple of years back where the electronics were a mix of 24V and 12V, even down to two VHF sets, one 12V and one 24V. Made the rewire "interesting".

 

[jwfrary]

From scratch, i'd install all 12V navigation electronics on a dedicated DC-DC converter. I did a refit on a large motorboat a couple of years back where the electronics were a mix of 24V and 12V, even down to two VHF sets, one 12V and one 24V. Made the rewire "interesting".

We use quite a few DC to DC converters on our vessels at work, all victron 10 amp ones and then carry one in the spares.

I thought about feeding a 12v bus with a couple of larger converters but in the end it was cheaper to use more single ones.

The biggest single point of failure for us would be the 24v to 12v converter on the nmea 2k and that has a change over with a second converter on standby service.

I recon it must be 3 or 400 kg we save in cable being 24v over 12v. Minus the extra converters which is prob only 10 kg at the most.

I should say out of the 12 converters on board one of our vessels, I have had none fail, the vessel is in constant commercial use covering 4000 miles and circumnavigating the uk over the last few months so I would say I'm happy with the result!

 

[LadyInBed]

My boat came with dual voltage systems, some kit on 24v, some on 12 and it was a pita! If it had been all one or the other, there would have been no problem.
The main issue was the way it was put together, Engine was 12v with a piggyback 24v alternator, which put a lot of strain on the 12v alternator belt.
Dual secondary charging was an issue, 12v via solar 24 via WG, two mains chargers.
Battery footprint was large if you wanted a large 24v capacity.
I eventually worked out that the kit on 24v could be handled by a dc to dc 12 to 24v convertor so I changed , I was pushed into making the change because the 24v WG had reached end of life and they are expensive to replace! My secondary charger is now just solar.
If you are just 24v stay with it, as switching to 12 is bound to entail rewiring for high draw devices and replacing working 24v kit with 12v kit is expensive.

 

[Bodach na mara]

I have been reading this with interest as my last boat had a 24V system. I have been hoping that the OP would tell us what type of boat he has. My own was not at all like some of the ones speculated on by some posters. It was a 31 foot Westerly Renown with the Watermota diesel engine. The story behind that engine is that it originated as a Ford crossflow petrol engine that was modified to run on diesel but there was no way to get heater plugs into the head, so a 12 volt starter was fitted with a 24 volt alternator and battery bank. When the starter was hit by the 24 volts it got the engine spinning fast enough to start without heaters.

Whether that is true or not, the 24 volt system worked well an as has been said, allowed various high current devices to operate at half the current that they would usually draw to give the same power. Thus the fridge, domestic water pump and central heating were all 24V. For the rest a DC-DC converter was fitted.

 

[ryanroberts]

12v is definitely a step down, even with a much shorter boat than the 24v one. Only disadvantage is it can be trickier to source 24V components quickly in chandlers, keep a spare water pump.

 

[jwfrary]

12v is definitely a step down, even with a much shorter boat than the 24v one. Only disadvantage is it can be trickier to source 24V components quickly in chandlers, keep a spare water pump.

Commercial chandlry tend to be the other way around, but your right the likes of force 4 probobly dont carry much 24v stuff