Isboys306

Just wanted to know when do you realise your alternator is going bad. Some of my buddies with lexus IS alternator have been going bad lately.

mandyfig

You can google it.

If you have a multi-meter, your charging voltage should be around 13.5 to 14.4 Volts. And the voltage across the terminal should read 12.60 volts, on a fully charged battery.

Snipped:

The rule of thumb that states 12.6 volts equals a fully charged battery and 12.2 volts means it is 25 percent charged, is starting to change with some modern batteries and charging systems. If there is a dead or weak cell, normal charging voltage can't be achieved on a battery with a bad cell.

Bichon

Autozone will test your alternator and and load test your battery for free. (everywhere but California)

Also, if your alternator gets weak enough, the charging system warning light (looks like an icon of a battery) illuminates.

maeveLexi

Car will feel sluggish during acceleration and your music through your aux will sometimes cut off.

2013FSport

iTrader: (2)

Electronics go bazerk, PS light comes on, you loose power assist.
You end up walking as car shut off.....


In short when running the gains need to outweigh the losses.
As stated above, if the charge voltage is not higher than the cell voltage (2.125v X6 = 12.75v), your charging system is not adequate. i.e. if at idle, lights and A/C on and your voltage is less than 12.9v chances are you're in trouble.

Last thing, it is current that charges a battery not voltage. So volts above nominal cell voltage result in current flow to the battery that charge the battery.

IS-MIKE

^^^^ Do not wait until you see the charging system warning light to swap the alternator since it doesn't come on early enough.

I didn't get a charging system warning light until alternator voltage dropped below 10v.
So my the first charging system warning light I got also coincided with power steering failure. Very scary. Don't wait so long like I did. lol

You do need to see the alternator under load.
My last alternator when it was going bad would give a normal 13.5v or better when the car was cold but would drop down below 12v after the car was on the road and warmed up.
When the alternator is outputting under 12.6v, you're draining the battery. (you don't want that)

To test the voltage when driving I bought a Cigarette Lighter Adapter displays battery voltage. You get to see voltage as you drive the car on the road. The one I bought also had USB charging.

*** edit ***
Another thing you could do is fully charge the battery overnight. In the morning with the car off and cold check the battery voltage (should be around 12.6v if battery is good). Do your normal daily driving, park the car. The next morning with the car off and cold check the battery voltage. If the second reading for voltage is significantly down the alternator is probably going bad.