RWD - Exciter wire voltages

Volvo RWD 900 Forum

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Exciter wire voltages 900 1992

Hi Tim,

I’m a little confused with the posts. You had higher voltages in the first one and now you are to low with a load applied.
This means to me, like you said, curious, that current flow out of the alternator is not correct.
It’s acting like one diode or two are not working at full capacity.
You see the alternator puts out three waves of pluses in one rotation. That’s why they are more efficient than the old DC generators before 1965.
You could short an output into the regulator or from the stator windings.

You said you “essentially” have a new alternator? I don’t relate to essentially. Is it off a scrapyard car, a rebuilt one from a parts house or what?
Bench testing is only as good as the person testing it with good connections.

Are you sure that housing of the alternator is grounded with a wire to the engine? Remember Volvo uses those rubber mounts! You are not the first person to find a faulty wire down there.
Of course, I assume that the 900’s still use rubber mounts? I not up on the 900’s.

On used or rebuilt alternators there can be a snafu using either! Rebuilds are not always completely refurbished or assembled with due diligence!
If the rotor brushes or the slip rings on the rotor are not conducting current into the rotor the magnetic field will not get stronger and therefore less current output.
In other words, the middleman, the regulator & brush pack can not deliver the goods!

I suggest you pull the alternator off the car because something is not right and you are going to have to do it anyways!
If you remove the regulator & brush pack, you can verify their condition. The regulator is held in by two screws. It’s a straight forward job to inspect it’s contact spring and brush lengths. The brushes must slip freely in their spring loaded holders.
You can look into the hole and observe the slips rings for wear. If the brushes are short or a deep groove can be felt with your finger in the slip rings, there is a problem!

Checking diodes are more difficult as they are on a heat sink plate but can be replaced individually.
If need be, by automotive electrical shop. Most people get another alternator, especially, if there are signs of wear as mentioned above. Just use a reputable shop!

I wish I knew what we are dealing with, you know, like a warranty?
You can rebuild it yourself, as that is how people in the business, get started in the business!
This way, you know what you have in a good reliable alternator!
This is a recently changed site that you can learn a lot from and they have god part descriptions and prices the last I knew. Some people on the Board have used them in years past!


Let’s see what you have and we will come out on the other side, more knowledgeable!
If it’s hot or cold outside it’s a good bench project tearing these things down.



New Exciter wire voltages [900][1992]
posted by  someone claiming to be Tim  on Wed Jun 5 13:49 CST 2019 >

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