Voltage
Thread Starter
Racer
Joined: Oct 2009
Posts: 286
Likes: 0
From: Brooks GA
Voltage
I know i should see a little bit of voltage variance when I turn on the AC or Lights ect. But when I have no accessories running and it still goes from 14.2 volts to as low a 13.1 volts. Is that normal?
Racer
Joined: Mar 2010
Posts: 291
Likes: 1
From: Temecula Cali
could be a spastic voltage regulator... i just put a reman alt on my beast and it was doing some crazy voltage jumps for the first couple miles or so.
it was almost as if the regulator was trying to figure out what it was supposed to do. finally it settled down and now its seems to be more steady... 14.5 or so on startup and 14.1 when warmed up
rob
it was almost as if the regulator was trying to figure out what it was supposed to do. finally it settled down and now its seems to be more steady... 14.5 or so on startup and 14.1 when warmed up
rob
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Engine cold, the alternator output is 14.7 volts and this voltage drops with increasing temperature to 13.7 volts at the alternator's operating temperature. The dash voltmeter reads 0.3 volts lower because it measures the voltage after the ign sw contacts which have a 0.3 volt drop across them. When you turn on an accessory, there is normally a surge of current that drops rapidly to its steady state current and the voltage regulator in the alternator cannot instantly react to these sudden current rushes, so you will normally see a momentary drop in voltage and also observe the voltage recover.
Thread Starter
Racer
Joined: Oct 2009
Posts: 286
Likes: 0
From: Brooks GA
Engine cold, the alternator output is 14.7 volts and this voltage drops with increasing temperature to 13.7 volts at the alternator's operating temperature. The dash voltmeter reads 0.3 volts lower because it measures the voltage after the ign sw contacts which have a 0.3 volt drop across them. When you turn on an accessory, there is normally a surge of current that drops rapidly to its steady state current and the voltage regulator in the alternator cannot instantly react to these sudden current rushes, so you will normally see a momentary drop in voltage and also observe the voltage recover.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Recovery is fairly quick, like 1 second or less. The voltage regulator is inside the alternator and is replaceable. Even at 13.1 v, your battery is still being charged, although this is slightly low.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
......so how many watts are being generated in these contacts???Not really challenging you since I do not know....but without thinking about it a whole lot, 0.3 volts on this switch really sounds excessive
Thread Starter
Racer
Joined: Oct 2009
Posts: 286
Likes: 0
From: Brooks GA
OBTW thanks for the help. I am not trying to be a pest.
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Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
You aren't a pest, I come here to help. All cars potentially have grounding problems. If you have a voltmeter, engine running and accessories on, measure the voltage across the battery terminals AND the output terminal on the alternator. They should be the same and you can also compare the battery voltage with the dash voltmeter. Report what you find. If you don't have a voltmeter, go to Harbor Freight and buy their digital VOM (voltmeter, ohmeter, milliameter) test meter, its $8 (less on sale) and a decent meter. Report what you measure.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
And if you want to see the drop across the ignition switch, drop the column and measure it. Your Voltimeter is an ignition, not a battery feed. .3 is typical. Spray some Electrical Cleaner on the contacts and it'll come back for maybe a week or two, before corrosion sets in and it drops again.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Its a switch contact and a lot of current flows through it, E = I x R. I have measured switch and relay contact resistance many times, they are in the range of tens of milliohms. Ten amps times .01 ohms is a tenth of a volt. Three tenths of a volt drop across the ignition switch contacts is not excessive.
