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rws 08-08-2005 12:28 PM

Question about alternators
Will a 100 amp alt require more horsepower to operate than a 70 amp? Are there there any disadvantages to using a one wire (self exciting) alt?

Thank You

Big Block Billy 08-08-2005 12:54 PM

Re: Question about alternators
Yes , But I can't tell you how much. Basically, think of it as a torque converter and the electricity is transmission fluid. Alternators go into an electrical torque stall, which puts a load on the engine and drive belt . A 100 amp alternator may need to be revved higher than the 70 amp unit to produce adequate output. It may not have enough output at a prolonged idle. I feel this would be especially true of a one wire alternator that does not have the same field winding excitation as a 3 wire unit. Do you really need the 100 amp unit ? You could however swap pulleys to spin it up faster if you do alot of idling. BBB

Cord 08-08-2005 01:06 PM

Re: Question about alternators
Only when a full 100amps is required. Otherwise there is no difference. A boat should only need a very small alternator, say 30a.

Gary Anderson 08-08-2005 03:36 PM

Re: Question about alternators
What cord said, except I think the standard merc is around 60amps.

scarrab30 08-08-2005 05:34 PM

Re: Question about alternators
I use marinized one wire on mine. Mine are 60 amp and have no problem keeping up with the load. I also have custom pulleys to slow them down. I have no charging under 1500 rpm. I have a large electrical load I use electric water pumps on my motors along with other items. If a one wire goes bad ,theyre easy to repair or replace at a fraction of the cost of the merc junk. Brian

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