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Information overload Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 10 Feb 2004 13:31:07
In Reply to: voltage readout in dash display, RedAeroGirl, Tue, 10 Feb 2004 05:41:40 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The voltage display is useful, but you've got to know which 97% of the time you should completely ignore it. Then again, it's why you asked the question....
When you first start the car, the voltage display grabs the lowest voltage during starting, and holds that value until (1) you hit the info display, or (2), you drive about 50 feet (what Lu said). OK, what's the value of this number? It should give you an indication of the health of your battery. A low number means the battery is getting tired. OK, what's low? Well, that depends. Within a reasonable range (!?!), it isn't the number, but how it trends. Theoretically, the starting number should be in the 10 volt range, and anything in the 9's indicates a tired battery. That's theory. I've run through three 9000's, and each one has a different 'good' starting voltage. I've got one that shows 8.5 volts with a fresh battery, and it takes 8.0 or less to say the battery is tired. A different car, and anything under 10.0 is deadsville.
So, how do you know? Get to know your car. Observe the starting voltage, and don't obsess over it. You know when the battery is good - the engine turns fast. If the engine is turning slower, and you see the starting voltage is trending down over a period of days or weeks, then suspect the battery. But one low voltage on a frigid morning is, well, normal.
OK, enough for that non-answer. How about when driving around? Normal voltage runs from right around 13.0 up to 14.5 Why the difference? The voltage regulator, well, regulates voltage, but it can only do so much. The faster the engine, the easier it is for the alternator to put out current, so voltages tend to be higher. Electrical loads (headlights, fan, A/C compressor clutch, brake lights...) drag the voltage down. The Voltage regulator is temperature compensated, because warm batteries don't want to be charged as fast as cold ones, so the warmer it is under the hood, the lower the voltage will be.
So it's reasonable to see 14.5 volts on a cold day running down the highway, and as low as 12.9 volts at idle on a hot summer day with the AC cranked and the blower on 4. In between, well, in between. So, what do you look for?
If you see the voltage in the 12.X range when cruising down the highway, it's time for a new voltage regulator. If the BATT light comes on, expect to see voltages at 12.6 or worse. If the headlights are bright and you see 14.8 volts, the VR is shot and overdriving the system.
Again, the EDU voltage is useful in TRENDING the voltage system, but to trend, you need to have the same conditions. It's not fair to compare the voltage of the alternator at idle on a hot day to highways speeds on a cold one.
Frankly, the voltage display should be ignored most of the time.
I hope this helps.
posted by 192.249....
, Tue, 10 Feb 2004 13:31:07 <-- Viewing This Message
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