12v vs 24v which and why?

[CharlesM]

Hello all

the boat I have recently purchased has a 24v system.

Could anyone enlighten me as to why one may decide to rig the house batteries to provide 24 volt rather than 12 volt.

What do I do when I need to run 12v appliances?

Thanks for any advice

Regards
Charles

 

[srm]

How big is your boat?

24v will cause less of a voltage drop on long wire runs, such as to a tricolour light at the mast top.

My last boat had a 24 v supply, which may have been dictated by the ex-aircraft generator that the previous owner ran off the main engine. I soon discovered that taking 12 volt off part of the 24 v bank was not a good idea, even with 2 different 12v supplies to try and balance the load as the previous owner had. It was difficult to keep both sides of the bank charged but also potentially dangerous as 0v on one side could be +12v on the other with 'interesting' results.

Eventually, I fitted a 24v to 12v converter for the VHF and other 12v appliances.

Incidentally, what voltage is the engine start?

Have fun

Sean.

 

[andrewbarker]

I've got 2*300 hp engines, so 24v, lower resistance, means much faster engine turning over for starting.

 

[wooslehunter]

Interested to hear what people use for the 24>12 conversion. I have both & 2 alternators - 24v for the engine start & 12v for the domestics. I'd like to add another battery to get 24 for the domestics simply so I can use the domestic bank to start the engine if I really have to.

Also the 12v alternator is a bit of a bodge since it doesn't sit on the engine but on the engine mounts. Hence it doesn't vibrate with the engine. It's actually only a Fiesta 1100 unit so when it dies a replacement is really cheap.

 

[VicS]

[ QUOTE ]
24v will cause less of a voltage drop on long wire runs, such as to a tricolour light at the mast top

[/ QUOTE ]
Just a few words to explain that:
For the same power a 24volt piece of equipment will only draw half the current. For example a 12volt, 25 watt bulb will draw just over 2 amps but a 24volt, 25watt bulb will draw just over 1 amp. It is because the current is halved that the voltage loss on long cable runs is halved.

 

[Benbow]

Most boats with 24V systems have 'droppers' to supply 12V to some of the electronics (eg VHF, sailing instruments, GPS) whereas higher power systems (eg radar, windlass) are almost certain to be 24V versions.

Good droppers here http://www.alfatronix.co.uk/

 

[CharlesM]

Hey srm

The boat is 43', so I guess the bit about long wires makes sence.

Perhaps it has to do with the generator, not sure what the output of the generator is.

Also, I believe the engine start is wired to the house batteries, so is probably 24 volt.

Charles

 

[CharlesM]

so it seems 24volt house is not a bad idea then...

 

[Piers]

The use of a 24v to 12v dropper is the correct way to go. Bear in mind that the unit you use will then be the weak link - if it fails, you lose all your 12v supply to all your 12v kit.

I am about to use droppers from Mastervolt, but with two in parallel in case one fails - I am told they can be used in parallel without interference.

Mastervolt DC to DC

 

[Benbow]

If its useful, I have a lot of experience with the alfatronix units. They are very good and have a lifetime guarentee. I have once had to claim on this and there was no quibbling at all. (I am reluctant to say how it was blown, but the words, "Falmouth Boat Yard" and "arc welder" are not irrelevant)