Questions about battery/alternator voltage

[ricky50]

I have a gauge that tells me the volts when the engine is running and the battery voltage when resting.

I wanted to know if it is normal for the alternator to put out 12.2 - 13.3 at idle at a light from time to time and then go 12.5 - 13.5 with only the a/c running in the daytime? (non-electric fan)

Also the battery at rest (engine not running) will go from 12.5 - 12.2 with nothing on ?

The car starts fine and would not suspect a thing if it was not for the gauge.

Do i have a bad battery or am i concerned over nothing?

Anything you can tell me about batteries and alternators would be helpful!!

 

[HISSIN50]

If you have the stock 2G alternator, that can be normal. Some basic guidelines:

With the car off, the battery should be around 12.6 volts (this is the break-even point for the charging system. A voltage reading of more than this = charging. A reading of less = discharging or draining the battery).

At start up (cold idle) look for 13+ volts.

At hot idle with an accessory on (this is a 2G joke), it can be normal to see volts drop below 12.6. If this occurs for short periods (e.g., sitting at a red light), most dont mind it. You just wanna see more than 12.6 volts once the car is moving.

A 3G conversion would help this issue, but if you dont mind it now, it is not a huge deal.

Underdrive pulleys (if you have them) dont help, as they slow the alt down.

Random thoughts. Good luck.