24 Volt System and alternators

[Stranded Mariner]

I am still in the stage of designing / selecting systems for my boat. For the electrical system I would prefer a 24 V system. Now when looking at engines, I observed that most have alternators for 12 V only, and also the starter on most is 12V. Are engine manufacturers able to supply their engines with 24V systems, or is it easy to convert?

Or is it possible to keep the engine starter, alarm and control panels etc. on 12V, but fit an extra 24 V alternator for the rest of the boats' system?

Thanks in advance!
Andreas

[jscott]

24 Volt alternators are certainly available, and are used on larger truck engines and stationary engines.

A 12 V alternator can also be made to put out 24 Volts be changing the voltage regulator, (i had an old kit that jumped one up to 120 V to run drills and saws etc.)

24 Volt starters are available but probably not for your smallish engine....it would be possible to rewind it for 24 volt service but this would be difficult, check with an alternator repair shop, and I don't think the brushes would be last very long.

[Rick]

I believe that it is the other way around: The brushes on a 24V starter rewound to be a 12 V starter would not last as long. The brushes on a 12V starter rewound to operate on 24V would last longer than it would have on 12V. The reason is that in both cases the starter must have the same peak power. For the same peak power the current is half when operating on 24V and, therefore, the brushes are taking it easy, relatively speaking.

It is not uncommon to add an additional 24V alternator to an engine. AS was mentioned before one can change a regulator to make a 12V alternator work at 24V or vice-versa. The stator magnetic saturation will not be optimum for a given rotor field winding current maximum rating and so the power rating of the alternator will have to be derated some in both cases.

[never monday]

The smaller engine are predominantly 12v. Yes you could do a second 24v alternator for the house system and keep the engine 12v

[Stranded Mariner]

Thanks for all your input! I guess keeping the engine system at 12V, and run a separate alternator for the 24V house system, would be the best way to go then. I will check availability of 24V alternators for the engine arrangement I have in mind (Yanmar)