|Originally posted by masospaghetti:|
How much voltage drop is normal when the radiator fan turns on?
10% max voltage drop (from battery to the load) is the usual design limit.
I lose about 1.5v (from 14.3v to 12.8v) when the radiator fan turns on. Is this typical?
Where are you measuring the voltages? At what engine RPM? The voltage should be very stable when measured at the battery, but up to 10% (max) voltage drop is acceptable at the load (i.e. at the fan motor). If the voltage is dropping at the battery, that indicates insufficient alternator output. If the voltage remains relatively steady at the battery but drops more than 10% at the fan motor, then a wiring fault is likely ... poor connection (hot or ground), degraded (e.g. corroded) fusible link, fan relay failing, etc.
I am running a power pulley with the CS alternator.
If the voltage is dropping at the battery at low RPM, then the pulley is the most likely suspect. A failing alternator is also a possibility.
[This message has been edited by Marvin McInnis (edited 08-27-2013).]