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Let's talk alternators

AH64ID

By AH64ID
in 3rd Generation Dodge

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AH64ID

AH64ID

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So I am pretty sure my alternator died. 

I left for work this morning and noticed the headlights were a bit dim. I assumed it was frost on the lenses so I fired up the high beams/fogs and it got dimmer. I then noticed voltage was holding about 11.4 at the ECM (from my touch). I gave it a mile or two to see if maybe it was low batteries and the voltage never came up so I turned around. 

When I got home I separated the batteries, hoping to find one bad one, and both were at 11.3ish. Then I disconnected the alternator wire and fired the truck back up. With a voltmeter the alternator output started at 9v and dropped to 6v just holding the volt meter on it. 

I also put a 10A charger on the batteries for about 10 minutes and the voltage came up to 11.6 so it appears the batteries will accept amperage but the alternator isn't supplying any. 

I never got a charge light or CEL... does anyone know the threshold for a charge light?

I will do a continuity check of the fuseable link when I get home tonight. 

I had the alternator checked out in Nov of '13 and the brushes/bearing were replaced. I was told it was very rare for the windings to fail. It only has 30K miles on it since then, but maybe a new armature brush contact is needed??

Thoughts?

Anything else I can check? 


 

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Tractorman

Tractorman

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Posted (edited)
1 hour ago, AH64ID said:

So I am pretty sure my alternator died. 


Then I disconnected the alternator wire and fired the truck back up. With a voltmeter the alternator output started at 9v and dropped to 6v just holding the volt meter on it. 


Anything else I can check? 

 

 

A couple of thoughts: 

 

  *  What happened to the alternator 30,000 miles ago that it needed brushes and bearings? 

 

  *  Disconnecting the alternator output wire and then running the engine is never a good idea.  The field circuit for the alternator is controlled by the ECM and could easily damage the ECM.

 

Before you remove the alternator you can inspect the alternator output wiring and fusible link as you mentioned, as well as inspecting the ground circuit and the field wire to the ECM.  You could use a jumper lead from the alternator case to a battery ground as a test to bypass a potential ground circuit problem.

 

- John

Edited by Tractorman
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AH64ID

AH64ID

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2 hours ago, Tractorman said:

A couple of thoughts: 

 

  *  What happened to the alternator 30,000 miles ago that it needed brushes and bearings? 

 

  *  Disconnecting the alternator output wire and then running the engine is never a good idea.  The field circuit for the alternator is controlled by the ECM and could easily damage the ECM.

 

Before you remove the alternator you can inspect the alternator output wiring and fusible link as you mentioned, as well as inspecting the ground circuit and the field wire to the ECM.  You could use a jumper lead from the alternator case to a battery ground as a test to bypass a potential ground circuit problem.

 

- John

 

Engine was out so I had the alternator freshened up. Nothing was wrong with it. 

 

The field circuit is controlled by the ECM but there shouldn't by any additional feedback to the ECM with the alternator output disconnected. 

 

The ground circuit seemed fine this morning. 

 

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AH64ID

AH64ID

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Well there is a new development. 

I was getting ready to move it around to the shop and park it so with it running I started wiggling the connection from the ECM and got my voltage back! 

It didn't stay back but the alternator is able to output power when I am applying sideways pressure to the connection. I tried wiggling wires and pushing them in and it didn't work, the only way to get power was to either push up or down on the connection. 

Thoughts on that? I am guessing I have a loose connection in the alternator side, which means the rebuild kit from Geno's should fix it.
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pepsi71ocean

pepsi71ocean

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On 4/20/2017 at 6:09 PM, AH64ID said:

It doesn't feel like the pig tail. It feels like the alternator side is loose. 

 

the pinch side of the connector is on the pigtail side, not the alternator, it just is a simple set of metal probes that go to the charging field circuit. At least on the Denso ones.

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AH64ID

AH64ID

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I just went out and played with it a little more. It's the first chance I have had in 10 days since I have been out of town. 

 

I know you guys want it to be the pigtail side but it's not acting that way at all. With the truck idling I can wiggle the pigtail wires and get nothing, but as soon as I put pressure on the armature brush housing it works. That's pressure anywhere on it, so even away from the connection. 

 

If I apply pressure to the truck side of the connection and wiggle it nothing happens until I apply enough pressure to move the armature brush housing. 

 

Everything is pointing to a loose connection in the replaceable armature brush housing.

 

I am going to order the rebuild kit from Geno's today. 

 

 

Update: So I went and pulled the armature brush housing and the issue is that the brushes are all worn down and out of play. The reason it works with pressure is I am getting the brushes to contact. 

 

My slip ring also shows some wear that I didn't anticipate for 126K miles. Maybe a replacement is in order. 

Edited by AH64ID
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AH64ID

AH64ID

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I pulled it apart last night and they aren't as worn as they looked, but now is the time to replace them. They would still accelerate the wear of the new brushes. 

 

I had had a failing winch motor two winters ago and it was putting a major electrical strain on the alternator. I wonder if the high current started the wear. 

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pepsi71ocean

pepsi71ocean

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19 hours ago, AH64ID said:

I just went out and played with it a little more. It's the first chance I have had in 10 days since I have been out of town. 

 

I know you guys want it to be the pigtail side but it's not acting that way at all. With the truck idling I can wiggle the pigtail wires and get nothing, but as soon as I put pressure on the armature brush housing it works. That's pressure anywhere on it, so even away from the connection. 

 

If I apply pressure to the truck side of the connection and wiggle it nothing happens until I apply enough pressure to move the armature brush housing. 

 

Everything is pointing to a loose connection in the replaceable armature brush housing.

 

I am going to order the rebuild kit from Geno's today. 

 

 

Update: So I went and pulled the armature brush housing and the issue is that the brushes are all worn down and out of play. The reason it works with pressure is I am getting the brushes to contact. 

 

My slip ring also shows some wear that I didn't anticipate for 126K miles. Maybe a replacement is in order. 

 

best to also pick up a set of slip rings as well, as that will eat a brush very quickly.

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Mopar1973Man

Mopar1973Man

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8 hours ago, AH64ID said:

I had had a failing winch motor two winters ago and it was putting a major electrical strain on the alternator. I wonder if the high current started the wear. 

 

Very possible. Because as load goes up pulling the voltage of the system down the field leads go to full 12 volt and current goes up on both the field and the charge output. So the stronger the magnet field on the armature the more charge current from the alternator. If the period of time of the high load could of heat damaged the brush holders. (Thinking out loud...)

Edited by Mopar1973Man
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