Alternator spinning too fast?

[Niander]

Alternator spinning too fast?
the setup on my boat has an alternator driven off the big engine flywheel this means it will be spinning very fast
could this be a problem as ive noticed other set ups have a smaller pulley driving alternator
so it will be spinning a lot slower.

 

[pvb]

Alternator spinning too fast?
the setup on my boat has an alternator driven off the big engine flywheel this means it will be spinning very fast
could this be a problem as ive noticed other set ups have a smaller pulley driving alternator
so it will be spinning a lot slower.

Is this the MD1 you mentioned in other posts? If so, it has a Dynastart, not an alternator, and it's designed to work off the flywheel.

 

[earlybird]

Don't know any exact figures, but I'd guess that an automobile type alternator must be capable of well over 14-15,000 rpm before it self destructs, so, if your pulley ratio is <4:1, it's OK, and you will get good output at low engine revs.
OTOH, my pal's Volvo (MD2 ?? ) has an arrangement like yours with a 6" dia alternator pulley, (which I've just modified for him to suit a new alternator). This keeps the ratio ~2:1, but I doubt that it really matters except that the alternator will suffer less mechanical wear.

 

[halcyon]

Don't know any exact figures, but I'd guess that an automobile type alternator must be capable of well over 14-15,000 rpm before it self destructs, so, if your pulley ratio is <4:1, it's OK, and you will get good output at low engine revs.
OTOH, my pal's Volvo (MD2 ?? ) has an arrangement like yours with a 6" dia alternator pulley to keep the ratio ~2:1, but I doubt that it really matters except that the alternator will suffer less mechanical wear.

My MD6a runs dynastart on two flywheel grooves, and alternator on the third, and it's run like that for many years without alternator damage.

Dynastart charges engine battery, alternator the service battery.

Brian

 

[TrueBlue]

My MD6a runs dynastart on two flywheel grooves, and alternator on the third, and it's run like that for many years without alternator damage.

Dynastart charges engine battery, alternator the service battery.

Brian

Some alternators have to run incredibly fast to get any output e.g. Balmar and many are designed to run at 10,000 rpm; at least that's what the output curves imply.

Don't fret

 

[VicS]

What pvb says if this is the Dynastart.

This is necessary to enable the Dynastart to crank the engine ... an ordinary starter motor drives the ring gear on the flywheel.

 

[nigelmercier]

Alternator spinning too fast?
...

If you change it, your tachometer [EDIT] may be wrong.

 

[VicS]

If you change it, your tachometer will be wrong.

Only if its a tacho taking its signal from the "W" terminal of an alternator. Older VP engines had a sensor on the hand cranking gear although they did not all have tachos.

 

[Rigger Mortice]

Alternator spinning too fast?
the setup on my boat has an alternator driven off the big engine flywheel this means it will be spinning very fast
could this be a problem as ive noticed other set ups have a smaller pulley driving alternator
so it will be spinning a lot slower.

Most manufacturers publish the specifications for their alternators and, if you can find that, you'll be able to see what speeds it is supposed to work at.

Try their website or, failing that, try the nearest Lucas (or whatever they are called nowadays) depot. Mine were very helpful when I wanted some information on an alternator a couple of years ago.

 

[Niander]

Is this the MD1 you mentioned in other posts?
fear not i know the difference from dynostarter , starter motor and alternator

no this is my inboard petrol at the moment
the md1 is a possible future install
so sounds like its not a problem then spinning fast
good for charging at tickover?
there is also a smart regulator job connected
and i notice a wire that feeds into back of alternator
appears to have an on/off switch to it?

 

[pvb]

Is this the MD1 you mentioned in other posts?
fear not i know the difference from dynostarter , starter motor and alternator

no this is my inboard petrol at the moment
the md1 is a possible future install
so sounds like its not a problem then spinning fast
good for charging at tickover?
there is also a smart regulator job connected
and i notice a wire that feeds into back of alternator
appears to have an on/off switch to it?

Is this some sort of guessing game, then? Wouldn't it be useful if you were to say which petrol engine it is, which alternator is fitted, which "smart regulator job" is fitted? You never know, you might get meaningful answers.