12V vs 24V electrics

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EricJ

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I noticed that with the facelift from V39 to V40 Princess have changed the on board electrics from 12V to 24V. I thought that normally around 45 ft 12V is replaced by 24V systems. Navigation equipment, pumps etc are mostly available in 12 and 24V. Is there apart from weight of the batteries another reason why 24V is not used for any type of cruiser, from 30 ft upwards? Would that not be more efficient?
May be weight is the simple answer but I would be interested to hear your views.
Thanks
 
I'm not sure to understand why you think that weight should be a factor.
Afaik, the reason for using a higher voltage is just that it allows, for any given power requirement, the use of smaller diameter cables.
And larger boats need higher power windlass, thrusters, etc. (all the way up to three phase AC motors, in very large boats where the builder prefers an all electric solution to the hydraulic alternative), hence the opportunity to use 24V equipment.

But if you wish to run say a 1000W bow thruster, cables aside, you can either have:
- two 12V batteries in parallel, capable to deliver the required ampage at 12V (i.e. 80A or so), or
- exactly the same batteries in series, who will deliver half the ampage (hence smaller cables) at 24V.
The net result is the same, as is the total weight.
 
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Not necessarily Mapis, with the newer cables to the market they can use much smaller cables with much thinner insulation with improved performance, it is becoming standard practice to use this lightweight cabling in everything these days, and boats are no exception. Weight can be a factor, but the mental attitude of using lightweight materials is becoming endemic among designers, and of course the lightweight cabling used in wiring looms is now cheaper than standard wiring.
 
I wasn't aware of these new cables, what are they made of? Not copper, I suppose.
Anyway, my observation about the overall battery bank size/weight required, which AOTBE is still the same regardless of whether connected for 12 or 24V, still stands, I reckon.
 
MapisM said:
I wasn't aware of these new cables, what are they made of? Not copper, I suppose.
Anyway, my observation about the overall battery bank size/weight required, which AOTBE is still the same regardless of whether connected for 12 or 24V, still stands, I reckon.
Click to expand...
You’re right on the weight. I had overlooked that you need less amps if you power the same equipment from a 24V battery. That would make it easy to use 24V as standard. Particularly with bow thrusters.

I had a 12V socket overheat when a camping gaz 12V cool box was connected to it. It was not enough to trip the fuse but still enough to melt part of the inside of the socket...
 
I suppose that given 24v would require a minimum of 2 engine batteries each side and 2 house - total 6 in a smaller boat that does not need the amps 12v would reduce this to 3 which will help with space and costs
 
jrudge said:
I suppose that given 24v would require a minimum of 2 engine batteries each side
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Why each side? I never had any twin engine boat where each side had its own starter battery.
Redundancy is granted by the possibility to put domestic batteries in parallel, anyway.

Besides, the number of batteries are a bit of a red herring.
I've been using for years the Trojan T-105 as domestic batteries, because their price/performance is in my experience the best among lead acid batteries.
And they are 6V, so I've got 2 banks in parallel, with 4 of them in series each (225Ah/battery, 450Ah @ 24V total).
In fact, imho the choice of batteries is more driven by weight considerations, with anything above 30Kg or so beginning to be a proper PITA to handle.
The T-105 is a 28Kg battery, and a decent 12V service lead acid battery of similar weight is (unsurprisingly) approximately half of its 225Ah.
So, unless you don't mind fitting much heavier stuff, for any given total capacity you're going to have just about the same number of batteries, regardless of whether they are 12 or 6V.

Mind, my old boat was factory installed with 4 huge (almost 80Kg each!) Exide NG-2 batteries, capable of 280Ah @ 12V (560Ah @ 24V in total). So, that is indeed a possibility.
But it's no coincidence that the yard used to build fishing trawlers, equipped with deck crane, etc.
I wouldn't suggest anyone to go for such monsters in a pleasure boat, though - in fact, also in that boat, I replaced them with the above Trojan, trading a bit lower capacity for a much safer handling and less overall weight.

All that said, I agree that with small boats where smallish 12V batteries are enough, it's convenient to stick to 12V.
40 footers are a bit borderline in this respect, but when in doubt I'd rather go for 24V, even if some 12V-only stuff (VHF or whatever) require a converter.
 
P,

that must be a UK thing, IIRC most builders have separate starter batteries, maybe wrong though.
BTW, Trojan now have a T105RE (for Renewable energy) which I'm fitting in a couple of weeks. Meant to be slightly better than the normal T105.

cheers

V.
 
Good to know V, thanks. Just curious, how new are those "RE" exactly?
My supplier didn't mentioned them last year when I bought eight of the things... :ambivalence:
Anyway, if previous experience is anything to go by, I'm expecting to be good to go for the next 5 years at least, also with the "old" stuff! :encouragement:
 
not sure P.
I know I did have problems getting prices from other places, so seems that either it's newish (2yrs or so) or the dealers just stick to what they know and sells...
if you see the specs at trojan site the RE is slightly better and having 600W of solar on MiToS I was keen on making the most out of them. Although I'll just install 4XT105RE for now and decide if I add another 4 next year, probably wont need them unless I go silly and get enough juice to run the stabs (when I finish with their config) running silently for an hour or so at lunchtime in certain locations.

V.
 
Although Mapism is correct in his original post Id also have thought battery efficiency comes into play. i.e. Most deep cycle house batteries and "half way house" (the correct term escapes me) cannot deliver high amperage effectively without affecting capacity adversely. Better to have a higher volatage lower amperage drain to maximise capacity efficiencies.
 
Why larger boats and some newer have 24 volts I'll make the presumption that there is a greater reliance on electric luxuries and electronics
 
elton said:
Bigger boats have longer cable runs, and there's less heat loss in the cable with a 24V supply than 12V because the current is halved.
Click to expand...

I think it's much more to do with voltage drop at the far end rather than heat loss along the cable.
 
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