Voltage drop - normal?
Thread Starter
Melting Slicks
Joined: Dec 2004
Posts: 2,560
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From: La Quinta CA
Voltage drop - normal?
When I turn on my air conditioner the voltage drops down to 13.5 from 14.2, is that normal? I thought alternators supplied constant voltage unlike the old generator days.
Drifting
Joined: Apr 2006
Posts: 1,276
Likes: 5
From: Ambler Pa.
Pro
Joined: Oct 2008
Posts: 735
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From: New Harmony IN
St. Jude Donor '09
Especially at idle, you will see this voltage drop. Now as the RPMs come up the voltage should come up with it a little, mine sees .2-.4 drop from normal which is 14.2-14.4 at cruising speeds with the A/C on. At least this appears normal for mine. 
Le Mans Master
Joined: Jan 2005
Posts: 5,611
Likes: 5
From: Thousand Oaks California
The A/C compressor clutch, engine cooling fans and the HVAC blower motor, ignition module and other on board modules, plus the DRLs do require a significant amount of amperage. The generator can not always meet the demand at engine idle speeds, so you have the battery as a "buffer".
Le Mans Master
Joined: Sep 2003
Posts: 8,847
Likes: 795
From: Longview Texas
Also, if your battery is fully charged and in good condition, the charging voltage will be less. Mine usually gets below 14 volts (13.9 or 13.8) even with nothing else on. When my fans come on, it drops a couple more tenths.
