SHAFT DRIVEN ALTERNATOR
Mention of a shaft driven alternator brought up
memories of such a thing that we put on a few Newporters in Dorchester. I remembered seeing drawings of Ack’s and
since I have a lot of “stuff” from my Newporter days a search through my
collection produced three drawings of the design and one of the electrical
setup to make it functional. (At least I
think that’s what it is so I’m including it here for the use of anyone who can
understand it.)
This shows the total unit on what must be the engine
beds and one frame. The lower pulley is inserted between the two halves
of the shaft coupling. Above that is an
idler shaft with two pulleys side by side.
This shaft is turning faster than the propeller shaft. Off to the side is the alternator, turning
faster than the idlers.
Of all the other pictures and drawings of the various shaft alternators I’ve seen, this is
unique. Those were all rigged with
the belt going from the propeller shaft directly to the alternator. The idler on this setup provides a place to change the speed
of the alternator just by changing one or both pulleys on the idler.
The alternator is mounted on the outboard edge of an
angle iron. On the inboard edge is
mounted a bracket that holds the idler and the adjustment arm for the
alternator. The adjustment arm for this
bracket is on an engine bed. These
adjusters vary the tension on the belts.
Here
is the side view and top view of the setup.
The upper drawing shows the relative positions of the shaft pulley and
the idler.
In the top view we see the back of the transmission with
the coupling and its pulley over the fiberglass drip catching pan under the
engine.
At the bottom of the drawing is the angle iron alternator
mount, fastened to a frame member at one end and the engine bed at the other.
The dashed lines indicate the bracket on which the idler
(not shown) is mounted.
Here we have some details of the construction of the
unit. A good study of these details will
give an understanding of how to build this unit.
I think the genius in Ack’s design is the idler that gives the unit a fairly simple means of changing the speed of the alternator. In a forum found in a web search it was said by one person that the alternator had to turn at 1000 rpm to produce a charge. If you can only get that speed at ten knots it won't be of any help. The first step in the design of your own unit is to find the rpm of your shaft at various speeds of your boat under sail. From there it is only simple math to find your needed pulley diameters.
I think the genius in Ack’s design is the idler that gives the unit a fairly simple means of changing the speed of the alternator. In a forum found in a web search it was said by one person that the alternator had to turn at 1000 rpm to produce a charge. If you can only get that speed at ten knots it won't be of any help. The first step in the design of your own unit is to find the rpm of your shaft at various speeds of your boat under sail. From there it is only simple math to find your needed pulley diameters.
And finally here is the electrical schematic of how to wire things up. This sheet was found separately from the drawings above and I am only guessing it has something to do with the shaft/alternator unit. It does include a “sailing alt.”
