Another Perkins 4.108 Question?

[Dougal]

Some time ago, I blew the main (120Amp) engine fuse on my Perkins 4.108. Since then, the alternator has been upgraded to a higher output (75Amp I think). Should the replacement fuse also be unrated, considering I 'believe' that fuse is there to protect the alternator?

 

[ianj99]

Some time ago, I blew the main (120Amp) engine fuse on my Perkins 4.108. Since then, the alternator has been upgraded to a higher output (75Amp I think). Should the replacement fuse also be unrated, considering I 'believe' that fuse is there to protect the alternator?

Only one way to find out - suck it and see. (but I doubt it will blow)

I removed the fuses from mine and fitted a 50amp circuit breaker in the alternator cable for my 75amp alternator. Even with a digital regulator, I've never seen more than about 40amps from the alternator, ie, you can't assume that a higher current alternator will actually be able to deliver its rated output.
Ian

 

[sailorman]

fit an Adverc & a battery monitor, you will be amazed & know what you are producing & consuming too

 

[nimbusgb]

Sounds odd. 120 Amp is barely enough to run the starter on anything but a very, very worn 4-108. So is that really an 'engine' fuse?

And no there's no good reason to uprate the fuse. It may well be 120 Amp because that's what the main cable will support. Upping it may lead to the cables melting if something goes wrong.

If you are drawing more than 40 or 50 amps on a boat for anything but a starter motor or an inverter ( which should be close to the main batteries and on its own circuit anyway ) then you are in trouble! Putting in a bigger fuse is the wrong way to go.

 

[ianj99]

Sounds odd. 120 Amp is barely enough to run the starter on anything but a very, very worn 4-108. So is that really an 'engine' fuse?

And no there's no good reason to uprate the fuse. It may well be 120 Amp because that's what the main cable will support. Upping it may lead to the cables melting if something goes wrong.

If you are drawing more than 40 or 50 amps on a boat for anything but a starter motor or an inverter ( which should be close to the main batteries and on its own circuit anyway ) then you are in trouble! Putting in a bigger fuse is the wrong way to go.

The fuse is indeed not in the starter circuit - not much use when the starter takes 700+ amps.

There were 2 fuses on my 4108, one for the alternator and one for the rest of the boat electrics (the engine is from the days when boats only had one battery which supplied everything).

 

[nimbusgb]

The fuse is indeed not in the starter circuit - not much use when the starter takes 700+ amps.

There were 2 fuses on my 4108, one for the alternator and one for the rest of the boat electrics (the engine is from the days when boats only had one battery which supplied everything).

I wouldn't change the 120 amp fuse even if I'd put a 100 amp alternatpr in.

 

[Hadenough]

I wouldn't change the 120 amp fuse even if I'd put a 100 amp alternatpr in.

Why not?