Voltage surge at start-up
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Race Director
Joined: Oct 2000
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Voltage surge at start-up
Year - 1987
When I start my car, I see 14.4-14.5 volts, for about a minute. After the car warms up, it goes to a much more comfortable 13.9 volts.
Is this caused by the cold? The highest temperature I've started it at in the last two weeks was 40 degrees F, most temps are much colder.
I don't want to split the battery, is there anything I can do? My roomate said he heard something about an adjustable zeniar(sp?) diode, so that you can regulate the voltage coming out of the alternator. Is 14.5 volts going to hurt anything if its only on for a minute? Thanks.
When I start my car, I see 14.4-14.5 volts, for about a minute. After the car warms up, it goes to a much more comfortable 13.9 volts.
Is this caused by the cold? The highest temperature I've started it at in the last two weeks was 40 degrees F, most temps are much colder.
I don't want to split the battery, is there anything I can do? My roomate said he heard something about an adjustable zeniar(sp?) diode, so that you can regulate the voltage coming out of the alternator. Is 14.5 volts going to hurt anything if its only on for a minute? Thanks.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Voltage surge at start-up (NoWorries)
Its just a start up transient and will not harm the battery or the alternator. My 87 doesn't do this , but your alternator has this quirk. The alternator is designed to maintain 14.3 to 14.7 output volts but does not have tight temperature compensation and as the alternator warms up its output voltage falls to about 13.3 volts or thereabout. The alternator regulator also has output current limiting to its rating (105 amps) and achieves this by decreasing its output voltage to limit the current to 105 amps. Yes there are adjustable zener circuits (not really a zener diode, but an integrated circuit) , but since the voltage regulator is a molded device, adjustment of the voltage control circuits is not possible. Also, connecting an external zener across the alternator to limit its output voltage would cause high currents when the alternator is trying to put out a voltage higher than the zener is set for (like when you first start your car). Just do as Bugs Bunny says, "Unlax Doc".
Melting Slicks
Joined: Feb 1999
Posts: 3,261
Likes: 9
From: sonoma ca
Re: Voltage surge at start-up (NoWorries)
My 95 does the same thing, 14.7 at startup & usually drops to 14.2 after about 20 minutes. Has been doing that forever. Sounds normal to me.
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Advanced
Joined: Oct 2000
Posts: 59
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From: The Woodlands TX
Re: Voltage surge at start-up (NoWorries)
With my truck, when I start it my gague reads about 14-15 volts, but when it warms up, it drops down to about 10 at idle, due to my underdrive pullies. But the reason for mine being that high when I first start it is cause I told my computer to idle higher at colder coolant temps. I'm assuming the stock computer does the same, so if the engine is turning more revs at colder temps, then the altenator is also turning faster, producing more volts.
Instructor
Joined: Nov 2001
Posts: 164
Likes: 0
From: Columbus oh
Re: Voltage surge at start-up (NoWorries)
when you use the starter, especially in cold weather, starter takes off the 'top' charge on battery, so alternator will charge higher than normal for a few mins till it replaces that. Then goes back to normal charge. Anything in the 13.5-14.5 volt range is considered normal.
Burning Brakes
Joined: Dec 2000
Posts: 1,161
Likes: 0
From: Orangeburg, NY
Re: Voltage surge at start-up (NoWorries)
WHat your are experiencing is normal. The starter takes a heavy draw of amperage from the battery, especially if it is cold (or extremely hot). Once the aperage is drawn (the car is started and the starter off ) the alternator attempts to replace the amperage/voltage back into the battery in a quick and efficient manner. As the battery is recharged the amperage needed is reduced. 14.7 initial voltage dropping down to 13.3-13.7 is ok.
