Alternator slow to start charging

[Reluctanse]

2000 k3500, 7.4 vortec with 0411 sap:

It got cold out, and the truck was weak to start— but it started. Battery was probably a little weak but it did start.

However the alternator didn’t start charging right away. It was as of the alternator wasn’t doing anything, verified by 11.2 volts at the battery.

After about 20 minutes it started charging like normal, and was fine on the drive after that.

It’s done this exact thing 3 times now. I put the battery on the charger just in case, but it didn’t seem to make a difference.

Any ideas what’s up with this behavior? Do I need a new alternator or is there something simple going on?

 

[AuroraGirl]

It got cold out, and the truck was weak to start— but it started. Battery was probably a little weak but it did start.

However the alternator didn’t start charging right away. It was as of the alternator wasn’t doing anything, verified by 11.2 volts at the battery.

After about 20 minutes it started charging like normal, and was fine on the drive after that.

It’s done this exact thing 3 times now. I put the battery on the charger just in case, but it didn’t seem to make a difference.

Any ideas what’s up with this behavior? Do I need a new alternator or is there something simple going on?

sounds like the regulator is failing or there is an internal break that once it warms up it makes connection. I would say its time to replace. did your voltage light on dash stay lit up till you got it to start working? And what year truck, model alternator is it

 

[454cid]

You might check the wiring to the alternator before replacing it.

 

[movietvet]

Yes, basics first. Inspect both battery cables for corrosion under the insulation. Check for tightness. Check for corrosion at battery connections. Check wiring at back of alternator for loose, corroded. When you say, "charging like normal", do you mean according to dash gauge? Those are notorious for just being close. Need to try and duplicate the problem with a DVOM attached. Are we talking about the 1 ton? It would help if you put in the post, what we are looking at. Were you in the deep freeze and ice storm here in Oregon?

 

[Drunkcanuk]

When you say cold, how cold?
Batteries don't like it when it starts getting below freezing and not getting driven daily.
Here when it's -40, most vehicles are ok as long as they are driven or started for a while daily.
But if they sit for a day or more, that's when the trouble start.

 

[Reluctanse]

Thanks for the replies, yeah its the truck in my sig.. 2000 K3500.

Yes, basics first. Inspect both battery cables for corrosion under the insulation. Check for tightness. Check for corrosion at battery connections. Check wiring at back of alternator for loose, corroded. When you say, "charging like normal", do you mean according to dash gauge? Those are notorious for just being close. Need to try and duplicate the problem with a DVOM attached. Are we talking about the 1 ton? It would help if you put in the post, what we are looking at. Were you in the deep freeze and ice storm here in Oregon?

I am kind of relying on the gauge, but I checked the before voltage with my meter and it showed low, the gauge on mine is *fairly* accurate, at least when its pointing straight up I know its charging. Yeah here in Oregon with snow pocalypse... except see below

When you say cold, how cold?
Batteries don't like it when it starts getting below freezing and not getting driven daily.
Here when it's -40, most vehicles are ok as long as they are driven or started for a while daily.
But if they sit for a day or loy, that's when the trouble start.

"cold" was around 20*F maybe, again keep in mind it did start fine.
But the alternator had the same behavior today, and it was 60 out.

I do think I need to go through all the wiring, BIG 3 is on my list, it just seems like there's some warmup switch that is kicking in to charge mode once it hits full temp. It's been pretty consistent, the 3 times I've driven it now, for the first 15 min after startup its not charging, then bam it flips over. I also noticed it was squeaking slightly today, for whatever thats worth.

 

[Drunkcanuk]

Thanks for the replies, yeah its the truck in my sig.. 2000 K3500.


I am kind of relying on the gauge, but I checked the before voltage with my meter and it showed low, the gauge on mine is *fairly* accurate, at least when its pointing straight up I know its charging. Yeah here in Oregon with snow pocalypse... except see below




"cold" was around 20*F maybe, again keep in mind it did start fine.
But the alternator had the same behavior today, and it was 60 out.

I do think I need to go through all the wiring, BIG 3 is on my list, it just seems like there's some warmup switch that is kicking in to charge mode once it hits full temp. It's been pretty consistent, the 3 times I've driven it now, for the first 15 min after startup its not charging, then bam it flips over. I also noticed it was squeaking slightly today, for whatever thats worth.

Cold has a tendency to expose any weakness in a vehicle at the most inconvenient time.

 

[AuroraGirl]

Thanks for the replies, yeah its the truck in my sig.. 2000 K3500.


I am kind of relying on the gauge, but I checked the before voltage with my meter and it showed low, the gauge on mine is *fairly* accurate, at least when its pointing straight up I know its charging. Yeah here in Oregon with snow pocalypse... except see below




"cold" was around 20*F maybe, again keep in mind it did start fine.
But the alternator had the same behavior today, and it was 60 out.

I do think I need to go through all the wiring, BIG 3 is on my list, it just seems like there's some warmup switch that is kicking in to charge mode once it hits full temp. It's been pretty consistent, the 3 times I've driven it now, for the first 15 min after startup its not charging, then bam it flips over. I also noticed it was squeaking slightly today, for whatever thats worth.

Respond to my questions especially about do you have a charge light on when its not charging and it would be a lot better if you had a DVOM in hand and could tell us what the voltage at the battery on startup is vs when it starts running

Also would like to know your model alternator, probably a CS130D but can you send a picture please?

 

[AuroraGirl]

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[1990Z71Swede]

The way most 12V old school alternators work is by means of a rotating magnetic field (the "rotor") in close proximity to a three phase winding(the "stator"). That Magnetic field is usually not a permanent magnet but an electromagnetic coil.

For this coil, the "field coil" to become magnetic it needs a small initial excitation current, this current is normally sourced from the battery through the charge light as per the drawing in the previous post.

As soon as charge current starts to flow, this initial current is no longer needed because now the charge current is taking over the task of creating the current in the field coil.

This is also what takes care of the charge light function. When the light is on it means current is flowing into the field winding, when the alternator starts to charge the light will go out, and it does this because it now has the same voltage on both sides of the bulb and current is no longer able to flow through it. Normally this is a split second process and the bulb does not have time to light up before the Alternator starts charging.

This also means that on some vehicles, when the bulb goes out, a perfectly functional Alternator may not start to charge. Some has a bypass resistor in parallel with the bulb to take care of that issue. Some vehicles just need you to rev the engine a little bit past idle to start self excitation etc.

So that's where I would start, in the circuit for that bulb, provided it is not lit when the alternator is not charging that is. Oh yeah, proper grounding of the Alternator to, in the end, the battery negative terminal is also a must for that excitation current to be able to flow. so verify that first. If there is a
grounding issue the bulb will not light up and as a consequence no initial excitation current will pass.

After those simple tests it becomes slightly more complicated. The regulator circuit is in the field coil current path for example.

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