New alternator not charging new battery

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Dagaan
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Joined: Mon Feb 12, 2018 5:10 pm

New alternator not charging new battery

Post by Dagaan » Fri Feb 16, 2018 3:26 pm

Hello to the brotherhood of electrical problems! My first post here.

'86 Volvo DL240. For starters, the ECU on this model has nothing to do with the charging system so eliminate that. This is the simplest of alternators - one B+ pst, one D+ post and one ground wire from case to engine block. I've done every primary test; ohm resistance on positive and negative cables to the NEW, tested, battery; and hot wire from starter to alternator; traced the D+ wire to the dash warning light - if I ground D+ wire while engine and alt running, light does goes on; tested that alt casing matches ground of engine block;

The alt was tested with a computerized system before it left the store. This is the 3rd new rebuilt alt; also tried a non rebuild NEW alternator and still no charge. New alt #2 charged up to 14+ V's but then went back to match the charge of the battery. This alt initially went up to 12.8 and then back down to match the battery charge. After each of those initial charging events, the B+ post on Alt never went back up again but only matched the current battery charge.

The only thing I can think of that could be wrong is that the hot wire from starter to Alt tested ok for correct resistance BUT is actually, for some reason, only made of a couple of copper strands that won't conduct 12 to 14 + volts. But - as with alternator spinning, the charge at the B+ post only matches the current charge of the battery, that doesn't seem relevant.

I've read that a 12V charge straight from the battery + post to one side of the warning light, on the D+ circuit, will excite the alternator, but have not tried this. I assume that 12 volt charge should go to the lightbulb contact farthest away from the fuse?

Really baffled. Could there be something informing the internal regulator to NOT produce a charge???

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Dale M.
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Re: New alternator not charging new battery

Post by Dale M. » Mon Feb 19, 2018 10:08 am

How is ground cable from battery to chassis and is there good ground strap from chassis to engine block? Are all connections clean and not corroded?

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

Ol'fogasaurus
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Joined: Tue Nov 14, 2006 1:17 am
Location: Just north of Seattle

Re: New alternator not charging new battery

Post by Ol'fogasaurus » Mon Feb 19, 2018 11:55 am

Dale M. wrote:
Mon Feb 19, 2018 10:08 am
How is ground cable from battery to chassis and is there good ground strap from chassis to engine block? Are all connections clean and not corroded?

Dale
If you are still using one of those "woven/braided ground straps" :evil: they have a long history of being a problem as they were often used on cars, especially with positive grounds, here in the states back in the late 40's and earlier. I just did a search on braided ground straps and some cars still have them even today and they are still having problems with them (porche and Suburu et al are still are having problems with them) Unless one is in contests for restoration I recommend bi-passing these monstrosities and go straight to the block with a conventional ground cable or, if you are still using padded mounts straight to the block then use the strap or cable as a secondary ground to the chassis.

Those small strands through age and bouncing around so they then have a tendency to break apart reducing the ability of the strap to work as they should, especially around the clamps at each end of the strap. I think you could do a load check on them to see if it is the strap that is the problem. Try a jumper cable from the battery's ground directly to the trans or block.

Proper grounding on older cars is another problem in its self because old metal, quesionable welding, etc..

Lee

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