Boats with 12v and 24v systems on board.

[Minerva]

I went to have a second viewing of a boat today. Something I missed first time around was the boat has both a 24v and a 12v system on board.

I get why one may want a 24v system; amp draw for given wattage being lower, lower voltage drop, smaller cables etc.

Question I have is how does that work in Practice? Would you expect to have engine start battery, 24v domestic bank and then a third 12v bank of batteries? That feels an awfy lot of batteries!

Alternatively do you just take the 12v load off one of the batteries in the middle of the 24v bank?

Or would you have a 24v to 12v dc-dc charger going from 24v bank to a 12v busbar?

Thanks.

 

[Sandy]

Personally, I'd be asking the current owner why they have overcomplicated things and listen to the explanation. Then make a judgment is you should walk away from the sale or spend time and money moving everything to one voltage or another.

 

[Minerva]

This looks very much like it was originally built with the two systems but in the intervening decades there have been a few DIY hands having a say in its operation…

 

[ChromeDome]

I've seen 18 or 24 volt for starting (big engines, no chance on 12 volt), then 12 volt for the rest.

Explained in practice here
Mixing 24 Volt & 12 Volt Systems

 

[Minerva]

I've seen 18 or 24 volt for starting (big engines, no chance on 12 volt), then 12 volt for the rest.

Explained in practice here
Mixing 24 Volt & 12 Volt Systems

Thanks. That suggests my idea of a 24v domestic bank and a 24v-12v converter feeding a 12v busbar would be an acceptable foundation.

 

[tjbrace]

Good friends of mine have 24 and 12 volts circuits on their Dunkirk Little Ship, I think the 12 volts is for the electronic equipment. On one trip the newly installed n2k network failed. I was able to jury rig a 12 volt supply to the network which bypassed the box that converted 24 to 12 volts and the trip continued. The conversion box was under rated for the load.
The ship was subsequently rewired by Paul Rainbow successfully.

 

[dunedin]

I believe that 24V and 12V systems are common on bigger boats, and as supplied direct from the factory.
24V (or 48V as boats get bigger) better for high power items such as bow (and stern?) thruster, anchor windlass, electric sheet and halyard winches, electric furling etc. Lots of these on bigger boats.
But many electronic and domestic items more widely available as 12V so also have a 12V system for this.

Clearly as electric propulsion starts to be introduced, there will be many more boats operating with a variety of voltages, high and low. Best not to muddle them up.

 

[melvynpatrick]

Hello. My boat was built from new (1978) with a 24v and 12v system. The engine starter battery is 12v and has its own alternator. The 24v house system also has its own alternator. All lights, fridge, heater, nav systems are 24v. I have fitted a Victron 24v to 12v converter for the few more modern items that run only on 12v. It all works very well and isn’t really very complicated. The engine is a beta 50hp by the way with twin alternator system. Biggest issue I’ve had though is charging off solar to the 24v. 24v solar panels are too big

 

[RunAgroundHard]

My boat was built with 24V, alternators, starter, battery, lamps, autohelm, windlass, extractor fans, bilge pump, heater. There was the 24v switch board and everything else plotters, vhf, instruments 12v fused circuits and odd switches.

At some stage a DCDC 24 to 12 converter was added for 12V stuff. In my ownership, the boat was rewired and there is only one switch panel but with two bus bars at the back one for the 12v and the other for 24v.

Likely it will be a similar set up. It is not complicated. I always buy 24v equipment if possible as the DCDC converter has a limit on it.

 

[ProMariner]

I wouldn't be put off a boat just because it has 12v and 24v, one mans overcomplexity is another mans redundancy. You can usually find good deals on 24v equipment, which is often higher spec than the light duty yachty / caravany 12v equivalents. We already have 12v and 230v, the addition of one more system doesn't really add complexity in use. If you like everything else about the boat, and the electrical systems are sound, go for it. Just keep a multi meter handy....

 

[tillergirl]

12v and 24v systems side by side are fine. My boat was originally fitted with 24v electrics for the engine. Later domestic systems with 12v were added. The boat now has:

'Start' Bank' 2 x 12v in series
'Services Bank' 2 x 12v in parallel
'Auxilliary Bank' 1 x 12v for the auxilliary engine

24v alternator and 12v alternator on the main engine
12v alternator on the auxillliary engine
2 solar panels in series with a 24v controller
1 solar panel for the 12v with a controller that split product 80% to the sErvice Bank and 20% to the auxilliary

The windlass is 24v. All other kit is 12v. Instrument gauges have some 24v and a couple 12v. A relay handles the power to both (as taught me by Paul Rainbow on the forums)

The advantage apart from lower amps, I can run down the Services Bank without risk of no power on the Start Bank. On the other hand I always start the engine before using the windlass.

 

[RunAgroundHard]

… You can usually find good deals on 24v …

That is a very good point. Truck and Lorry accessories can be very low cost at 24V. A surprising amount of cabin stuff as well for truck cabins. I bought a lot of 24V LEDs for locker illumination for pennies, also 24V microwaves for truck cabins, for example.

 

[Minerva]

That's great. Thanks folks

 

[Hermit]

Hello, I have a mixed 12/24v system on my 1977 Moody. She came out of the factory as such and all seems fine, but I do have a lot of batteries but mainly because a previous owner was very risk averse. Buy kit is fine (and the truck stuff is good). My 12v are only charged by shore or solar but only run the raymarine kit so really not an issue. All of the 24v stuff is easier as smaller cabling (bow thruster and windlass).

 

[Seven Spades]

I have both 12 and 24V systems on the boat. The engine and generator have 12V starter batteries. 24V runs the winches and bow thruster, fridge, freezer and watermaker and lighting. 12V runs the nav, VHF, TV and radio. I can't remember what the heater works on.

When we had lead acid I think that they took 12V from 6 of the 2V batteries but when we converted to Lithium we fitted a 24V to 12V Victron voltage dropper, I amn not sure but I think it is rated at 100A

 

[MontyMariner]

That feels an awfy lot of batteries!

Yes, I lived with a dual voltage boat for about 18 years, a 24v WG kept the system topped up with a 24 to 12v converter for the 12v battery bank. I then added Solar for the 12v bank.
The WG finally needed a major refurb to the point that it should be replaced! That was too expensive, so I ditched the WG and put the two batteries supplying 24v into the 12v bank, I fed the items that needed 24v from a 12 to 24v converter. It's proved to be a much better solution, I wish I had done it years ago as I could also ditched the 24v alternator. The engine is 12v and I have 160w of solar to top up the 3x 120ah batteries.

 

[geem]

Our boat was built as a 24v boat. We have several 24/12v droppers to provide power for electronics, vhf, cooker ignition, USB chargers. The generator has its own 12v starter battery. Both engine and domestic banks are 24v. The domestic bank being lithium. 24v really comes into its own when you go lithium. Especially for high loads like electric cooking.

 

[14K478]

On my former boat I had 24v navigation lights, and a step up transformer from the 12v system.

 

[JayDomK]

Our boat was also built as a 24v boat. And it also has 12v systems. I personally never saw it as a problem until I read this thread. I always thought it was the way it was supposed to be.

 

[Minerva]

Our boat was also built as a 24v boat. And it also has 12v systems. I personally never saw it as a problem until I read this thread. I always thought it was the way it was supposed to be.

I don't necessarily see it as a problem, but something I've not worked with and am ignorant of the day to day operation of a bi voltage DC system boat.

Seems like most have agreed with you that it's not a problem and I shouldn't be put off the purchase...