"slow" alternator

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Nov 18, 2003 | 11:21 PM

laynrubber

Thread Starter

Laughing Gas

Joined: Apr 2003

Posts: 936

Likes: 25

From: La Ronge Saskatchewan

"slow" alternator

Now that the temps are below freezing i am noticing something on this truck and i'll throw it for anyone with an idea.

My truck has a one wire GM alternator and it works great......but.
When i first start it in the morning the alternator doesn't "come on line" right away.
I'll explain; i have a voltmeter instead of an ammeter in the dash and once the truck is started and running at warm up speed (1500rpm) i look at the guage and it is reading battery voltage....12 v, it takes a minute or so and then the lights get brighter, the fan speeds up and i see that now the voltage is at 15.5 or so.
My 79 did that when it got cold and i found that the ignition switch needed a jiggle (till i lubed it)
I have jiggled the ignition switch and tried to "surge" the electrics by switching on the lights and heater on high but to no avail. It's almost like something in the charging system needs to warm up.
So far as long as the system starts to charge i can live with this.

Any ideas ??

Nov 18, 2003 | 11:47 PM

texasbob

Tuned

Joined: Oct 2000

Posts: 262

Likes: 4

From: Lake Jackson, Texas

I had a similar problem a few years back, the lights would get brighter and dim at random, and the ammeter would show it. Turned out to be the alternator going out. take it to the local parts house, they should be able test it for you.

Bob

Nov 19, 2003 | 04:56 AM

Jim VA.

Senior User

Joined: Feb 2003

Posts: 150

Likes: 0

From: Western Shore of Virginia

Shaune; The GM alternators with internal regulators, will have to reach a certain RPM before they will start to have output. Have you tried increasing RPM on inital start up ? Perhaps after your cold engine warms up and gains RPM the regulator kicks in and everything would work ok. Jim VA.

Nov 19, 2003 | 03:35 PM

BobJonesSpecial

Senior User

Joined: Sep 2003

Posts: 233

Likes: 0

From: Silverthorne Colorado

Jim VA is correct that GM alternators have to reach a certain RPM before they self energize and lite up. A solution might be to go to one slightly smaller pulley size on the alternator to speed it up without having to wrap the engine to higher RPM.

BobJonesSpecial

Nov 20, 2003 | 12:50 AM

laynrubber

Thread Starter

Laughing Gas

Joined: Apr 2003

Posts: 936

Likes: 25

From: La Ronge Saskatchewan

Well the alternator is new....less than a year.
It should be on line at 1500rpm, and yes it has reved higher on start up and still not clicked on.
I think for amusement one day i will put a heater on the alt and let it prewarm up, then start the truck just to see if the alt needs to "warm up" before producing.

Nov 20, 2003 | 08:38 AM

GreatNorthWoods

Lead Driver

Joined: Apr 2002

Posts: 8,813

Likes: 13

From: Littleton, New Hampshire

Having to bring the rpms up to begin charging is a normal trait of the one wire alternator. One of the wires eliminated is the "exciter" wire which in a 3 wire makes it start charging immediately. However, I would think 1500 rpm would be enough to bring it online. I've never heard that they have to warm up. Perhaps you got a bad one...