why 24 volts and not 12?

Burnham Bob

Burnham Bob

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a frieind has bought a boat that is being rewired to take 24 volts. 12 volts i understand but 24 i don't. All my instruments work off 12 volts and all cigar lighter plug in chargers work off 12 volts. its an ex-tug ro be used as a liveaboard so its a heavy boat but i'm at a loss to understand the justification for 24 volts. please enlighten me!
 
I think on larger boats the resistance in the cabling can be too much for 12 volt systems to work properly in all circumstances. All systems on a boat, if not able to accept two different voltages should be available as both 12 or 24 volt versions.
 
It may well be that with a big powerful engine on a tug, the starter motor is 24v. If you're using 24v for that anyway, it's just as easy to have everything else the same.
 
As said primarily it is for the starter motor of the engine. (but is good for anchor winch too) Big engines need big pwer to start. So larger trucks and boats with big diesel engines use 24v batteries for starting.
The higher voltage means less voltage drop in wiring because current is less for same power but also voltage drop is less significant to total voltage.
Some of us oldies might remember car sytems that were 6 volts. Engine starting was always a problem with huge volt drops on cranking. hence they went to 12v but 24v would have ebeen even better. I understand some cars have gone to 48v for same reasons.
Anyway for your friend I would suggest a 24v system with power coverter to 13.75volts to charge a 12v battery used for domestic services. So only the 12v battery is susceptible to discharge with lights fridge etc. A 27 volt VSR would turn the charger on when the engine is running.
generally i think your friend is fortunate to ahve a 24v system for the engine. good luck olewill
 
Rally cars had a trend for 24 volt starters at one time when they were naturally aspirated with high compression ratios. Slow turnover and big carbs and they flooded. Spin em fast and off they went.
 
It's the same reason as mains voltage is 130,000 volts on the pylons, instead of 240. Less power loss (as heat from the cables) at lower current/higher voltage.
 
elton said:
It's the same reason as mains voltage is 130,000 volts on the pylons, instead of 240. Less power loss (as heat from the cables) at lower current/higher voltage.
Click to expand...

I suspect being able to suspend much lighter cables from the transmission towers is also a factor.
 
my boat is 24v starting. Engine is 4.4 Litre so takes a bit to turn it over. In reality we have a number of drop down devices to make 12v as well. windlass is 24v and a 2kw motor. the wires are already large. This would be a problem at 12v.
 
24V = better system

Best to use a switch mode dropper for 12V rather than wiring to one battery unless the current is minor.
 
Lakesailor said:
Rally cars had a trend for 24 volt starters at one time when they were naturally aspirated with high compression ratios. Slow turnover and big carbs and they flooded. Spin em fast and off they went.
Click to expand...
I think the starter was still 12V, putting 24V into a 12V starter does make it spin quickly, have done this occasionally with a tight newly built engine to get it to go initially.
 
I did drive a 6v beetle ( or classic as they are now known) for a few weeks one summer..
One passenger ( not averse to taking serious on board risks with 240v and leaky decks) actually insisted we stop to verify that the headlights were actually working one night. Bloody cheek..

Funny little battery too( two would a been better for the cold cranking)
 
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