voltmeter drops/raises

Need some opinions.
I put a new alternator in 3 weeks ago.
The old one died. Limped home on battery.
Anyway, twice I've noticed the voltmeter dipping down.
One night at a light it was low, so I reved the engine and the meter went up. The headlights also got brighter. So I know it is not the gauge.
With this new alternator I have also noticed the voltmeter is running
a line or 2 above the 14 volt mark. I have owned the blazer since
99 and it was always steady at 14 volts.
Checked/cleaned the battery terminals.

Any ideas. IS my new alternator bad?

First, the voltmeter on the dash isn't the most accurate gauge in the world. When the idle is low (sitting at a light) with accessories on (high load) the voltage will normally drop. Alternators are tested for output of voltage and amperage at 2000 rpm not idle.

It sounds normal from here, but if you have any doubt have it tested for output.

Need some opinions.
I put a new alternator in 3 weeks ago.
The old one died. Limped home on battery.
Anyway, twice I've noticed the voltmeter dipping down.
One night at a light it was low, so I reved the engine and the meter went up. The headlights also got brighter. So I know it is not the gauge.
With this new alternator I have also noticed the voltmeter is running
a line or 2 above the 14 volt mark. I have owned the blazer since
99 and it was always steady at 14 volts.
Checked/cleaned the battery terminals.

Any ideas. IS my new alternator bad?

Take a voltmeter out and check the battery voltage when the engine is off and when the engine is running.

Please tell me you recharged the battery back up before you installed the new alternator.

Take a voltmeter out and check the battery voltage when the engine is off and when the engine is running.

Please tell me you recharged the battery back up before you installed the new alternator.


Yep, I charged it up for the 1-2 hours it took to replace the alternator.
Hopefully that was enough. (it started the truck)

Yep, I charged it up for the 1-2 hours it took to replace the alternator.
Hopefully that was enough. (it started the truck)

No, it wasn't enough, the battary should be charged for 5 hours on 10 amp if it is completly dead.

The alternator is not a battery charger and you will end up ruining the alternator again.

No, it wasn't enough, the battary should be charged for 5 hours on 10 amp if it is completly dead.

The alternator is not a battery charger and you will end up ruining the alternator again.


You are the "man".
I just threw my charger on the battery.
I am just below 75% and will leave the charger on as needed.

Do you think I damaged the alt?

You are the "man".
I just threw my charger on the battery.
I am just below 75% and will leave the charger on as needed.

Do you think I damaged the alt?

Is your charger automatic or manual?

How many amps are you charging with? 10A/6A/2A?

Did you take the battery out of the truck when you were charging it?

How many amps was it drawing when you hooked it up today?

Good luck with this. I have the same exact problem. Gone through 2 reman alternators already and a new battery. Still does it. NEVER did this with the original alternator.

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