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Another electrical question

Stumpalump

NAXJA Forum User
Location
Franktown Co.
If one were to replace the mechanical fan on a XJ with an electric fan wouldn't the extra drain on the battery cause the alternator to put an equal amount of mechanical drag back on your engine? I would think you would only see gains when the engine was cold.
 
If Im thinking correctly, the alt. has the same drag no matter the load. It's not clutched or anything. If it needs more output Im guessing the regulator adjusts for that. However there is no evidence that Im thinking correctly, either.
 
technically, you are correct, with one exception.
the "drag" from the alternator will differ slightly at a given speed due to the higher current draw (picture running a battery through it backwards, it would try too turn the other way). however... depending on the electric fan you use, it may be more efficient at moving air through the radiator than the mechanical one.
 
The fan draws it's power from the battery which has a reserve capacity. The current required to recharge the battery is spread out over some time so it will not put a huge load on the alternator unless you really drain the battery down. The fan runs intermittantly so it does not drain the battery enough to cause a huge load.
 
The electric motor is more efficient at applying torque than a mechanical linkage, meaning it takes less mechanical load on the engine to make the current that runs the fan motor. Hence the reason trains have a diesel generator set to power the electric motors that run the wheels. And yes, the battery provides a big surge for the starting current. Saves the altrernator bearings wear and tear.
Just a newbie trying to help :read:
 
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