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How much voltage drop is normal when the radiator fan turns on? by masospaghetti
Started on: 08-27-2013 08:49 AM
Replies: 3 (1358 views)
Last post by: theogre on 08-27-2013 10:14 AM
masospaghetti
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Report this Post08-27-2013 08:49 AM Click Here to See the Profile for masospaghettiClick Here to Email masospaghettiSend a Private Message to masospaghettiEdit/Delete MessageReply w/QuoteDirect Link to This Post
I lose about 1.5v (from 14.3v to 12.8v) when the radiator fan turns on. Is this typical? I am running a power pulley with the CS alternator. Or does this indicate a bad ground?

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Report this Post08-27-2013 08:55 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
Typical. The stock fan draws a lot of amperage when it kicks in.

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Marvin McInnis
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Report this Post08-27-2013 09:49 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
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.


 
quote

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.


 
quote

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).]

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theogre
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Report this Post08-27-2013 10:14 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierosound:
Typical. The stock fan draws a lot of amperage when it kicks in.

Typical but not normal...

Fan draws 10-11 Amps at ~14 Volts.

Mainly Points to:
bad ground(s) in engine bay or anywhere.
Iffy wire(s) for alt... Bad wires, loose/dirty connections, etc.
Alt has problems and/or belt is loose. (Alt Case is Alt Ground. check/clean case and bracket)
Under rated alt (too small for the job)
use "power pulley"

Low volts can kill Fan motors, Fuel Pump, causes Dim HL, etc.

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