T&T: Big Alternator and Dual Pulleys

Sat Dec 30 22:38:12 EST 2006

I'm designing a 2500 watt inverter and larger alternator set  up for a  
single diesel I'd like to have installed in a Monk  36.

I know I have seen a thread on the optimum manner of hooking up  and  
switching such a system, but I can't seem to find it. I also need  to  
decide how big an alternator I need, and if the serpentine  belt  
(looks about 1" wide) will handle it.

Any  help?

John LeRoy
Pensacola, FL

I am catching  up on the digest; sorry it took so long to  reply; I had such 
set up on a previous boat; hooked all this up to a Ford Lehman  120----

A big alternator is a good thing; you will need an external  regulator; you 
also should think about a dual shiv (double pulley for two  serpentine belts, 
not one) there is a HUGE start up load.

You can control this to some extent by the external regulator,  gradually 
asking for more amps from the alternator as the belt warms and you  bring the 
revs up.

You have to calculate the diameter of the alternator pulley(s) and  the 
engine pulley (s); you need to know how fast you need that alternator to  spin to 
give you the amps and you cannot overspin it if your cruising rpm is a  certain 
figure, you can't exceed that spin on the alternator; although most of  the 
time the problem is getting enough alternator spin at idle or moderate rpm  for 
charging on the hook.

Charging on the hook at idle or moderate rpm: Ok for a big dumb  diesel like 
the Lehman 120, not such a good idea for a main engine diesel of  higher 
horsepower like a 3208 or the new type common rail Cummins etc. Probably  not a 
good idea for anything with a  turbo.

Absolutely you should figure out how to have the alternator  pulley(s) spin 
off the main engine pulley not the same belt and pulley what runs  the water 
pump; the side load is just too much and you will blow the water pump  bearings.

Machine shops can make pulleys no sweat; it may take some  experimentation.

How big an alternator; kind of what you can afford and what space  you got; 
also the more amps the more load the more belts you gonna  need.

I never really got it right, I sold the boat before I went to dual  shiv; I 
was running a one inch serpentine off the main engine pulley not the  shared 
water pump pully but I had to wrench it really tight because of slippage  and 
squeal at high amp load;  destroyed about a half dozen belts along the  way.

You seriously need double shiv. Double shiv serpentine, not the  other kind 
of belt; use the new flat ones.

Just saw other posts by other listees re this same topic; they are  right on 
re size of alternator and house battery bank size; I kind of assumed a  house 
bank of about 800 amps; and charging on the hook when you're hanging out  for 
a few days; I assumed you don't have a genset; I kind of concentrated on the  
mechanical end of it; the invertor will work off the battery bank like always, 
 the external regulator and big alternator will take care of charging the 
house  bank when shore power (or a genset ) is not available for the charge side 
of the  invertor to charge the house bank.

Best John Houts.
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In a message dated 12/3/2006 9:00:57 P.M. Pacific Standard Time,  
trawlers-and-trawlering-request@lists.samurai.com writes:

Message: 6
Date: Sun, 3 Dec 2006 07:21:38 -0600
From: John  Leroy <johnl2003@earthlink.net>
Subject: T&T: Wiring diagram for  adding inverter to DC system
To: Trawler World List Post List  Post
<trawlers-and-trawlering@lists.samurai.com>
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I'm designing a  2500 watt inverter and larger alternator set up for a  
single diesel  I'd like to have installed in a Monk 36.

I know I have seen a thread on  the optimum manner of hooking up and  
switching such a system, but I  can't seem to find it. I also need to  
decide how big an alternator I  need, and if the serpentine belt  
(looks about 1" wide) will handle  it.

Any help?

John LeRoy
Pensacola,  FL

I am catching  up on the digest; sorry it took so long to  reply; I had such 
set up on a previous boat; hooked all this up to a Ford Lehman  120----