What is a 'normal' voltage drop for an alternator at idle with accessories on (A/C, radio, seats, rear defogger, lights)?

I'm seeing 14.4 at the battery at idle with no accessories on and 12.9 at the battery with the accessories above on.

I checked the FSM and searched and read but no results.

2001 Maxima, battery is ~1 year old.

 

I believe the alternator output voltage should be between 14.1-14.7.

12.9 is pretty low with those accessories on. I don't think it should ever really drop below 13.7. Sounds like an alternator or belt slippage problem as opposed to a battery issue considering it's fairly new.

Also, may want to inspect or upgrade the main grounds (manifold to chassis, alternator to chassis, etc.)

 

"I'm seeing 14.4 at the battery at idle with no accessories on..."

That seems really high to me. How's your battery life?

"...and 12.9 at the battery with the accessories above on."

Does the 12.9V reading increase when you rev the motor?

 

FSM says alternator regulated voltage is 14.1 to 14.7 (SC-31) - so I that's right in the middle of the range.

I forgot to check the voltage when reving the motor, I'll do that tonight and report back.

 

What is alternator slippage? Do you mean slippage of the belt at the alternator? Can there be slippage without hearing a squeal/noise?

I don't know where the grounds are located. Should I check the voltage drop from the alternator to the battery to rule out the grounds?

 

On my 2000, the voltage at idle was 14.1. Turning on every possible thing I could think of and running the windows up and down, the voltage only dropped to 14.0. And this was still at idle.

Dropping to 12.9 volts says there is something wrong with the voltage regulator.

 

^This. I'd say your alternator is on its way out.

 

Thanks Dennis. Empirical evidence is best evidence

I've also been hearing a rattling from the wheel well that must be from the alternator bearing going bad (since it's not the AC pulley or the idler) - so it's definitely time to get it rebuilt or replaced.