Voltage drop
Thread Starter
Racer
Joined: Oct 2002
Posts: 395
Likes: 4
From: Addison Il
Voltage drop
I have a 89. When I am on the brakes and with the headlights on, I have between 13 to 14 volts on the digital dash readout. If I turn on the rear defroster or the ac, my voltage drops to around 11.5 to 11.2. I put a NEW Delco alternator (old one died) in and cleaned the grounding block last summer. I am worried that the car is going to drop too low and die out. Any idea's on what I can do so it would drop so low?
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
Re: Voltage drop (Steve's89)
Steve, what is the rated amperage output of your new alt? What is the condition of your Batt? Have you inspected the wiring for any defects?
As you obviously are aware, you should have a reading of 12+ volts from your batt with the engine OFF, and 14+ volts with the engine ON, even with most accessories ON. The reading you are getting (11+) signifies that either your alt/reg is/are not providing sufficient output, or that your batt may be drawing more amps to stay charged. My '93 has an alt rated at 120 amps, and I see no voltage drop with accessories in use, even at idle.
[Modified by Oldman, 7:43 AM 2/24/2003]
As you obviously are aware, you should have a reading of 12+ volts from your batt with the engine OFF, and 14+ volts with the engine ON, even with most accessories ON. The reading you are getting (11+) signifies that either your alt/reg is/are not providing sufficient output, or that your batt may be drawing more amps to stay charged. My '93 has an alt rated at 120 amps, and I see no voltage drop with accessories in use, even at idle.
[Modified by Oldman, 7:43 AM 2/24/2003]
Thread Starter
Racer
Joined: Oct 2002
Posts: 395
Likes: 4
From: Addison Il
Re: Voltage drop (Oldman)
I have checked the wire's and seem to be ok. The battery is an AC Delco that is less than a year old, but I will check the voltage when I get home to see where it is at.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Voltage drop (Steve's89)
The rear window defroster draws 24 amps, but shouldn't cause the voltage drop you observe unless the engine is at idle with a heavy electrical load. The alternator cannot deliver full current rating with low rpm such as idle. Measure the voltage across the battery terminals to see if the cluster voltmeter is being subjected to voltage drop by the defroster.
