Good Morning Volvoers - (DL 240 '86) I am having a hard time getting my new alternator to charge a new battery - with a new starter and new coil on the line. The battery has been tested and charged a few times so far and the alternator has been tested. The car starts and runs fine - but is not charging.
With the engine running - tight belt - I get the same V reading on the B+ and on the D+ post as the straight reading on the battery.
I've replaced the biodegradable wire from the D+ post on the alt to the junction box on firewall where the D+ wire from alternator joins its counterpart headed for the battery/alternator charge light on the instrument panel. Yes I'm sure I replaced the right wire. The alternator is grounded - three times!
Could it be that the new alternator only becomes activated when the battery reads 12.5 or above?
Is it possible that the ignition key tumbler is not making the right electrical connection at starting position? Inside that there is the hot wire that is linked to the wire that goes to the coil/ distributor as well supplying juice to the starter solenoid?
I've received The Answer - the route of electricity in the full circle from battery/alternator/key/warning light - from The Master but the Master only answers once and then it's live and let die! : )

 

Even though your "New" alternator tested good out of the car and you have voltage at B+ and D+, off hand I'd say you have either a bad " Regulator" or the brushes are hanging up in the holder. By taking the alternator out and having it tested may have allowed the brushes to make contact and start charging on the bench. Try and rap on the regulator with a screwdriver handle and see what happens.

 

Thx. Madman, I'll try that.

 

what V reading are you getting with the engine running? it should be about 1.2 volts higher than the battery rest voltage.

 

I was getting the exact same reading at D+ as on the + battery post when engine running and alternator hooked up. No charge.
Saw a video on 'parasitic drain' from circuits that hadn't blown their fuse and I think I found a circuit like that - #3 down - either radio or wipers - so I took the fuse out and ran the engine. The V reading on battery went from 11.9 to 13 in about a minute and I thought all was well. Then it started going down down down - with engine running.
My next bright idea was that the key mechanism - only 4 years old - was jiggling too much so I suspected the D+ wasn't connecting to the battery juice . . . which is what the key in position 2 does right? So - I tried linking the D+ line from alternator straight to the + post of the battery bypassing the key. But took a V reading first, without starting the engine and the battery went from about 12.06 to 11.9 so I shut it down and disconnected. Why didn't that work?
The alternator did begin to charge and the battery is holding it's -now - low charge.
Are these clues?

 

I believe what you have is still a bad alternator regardless that it tested good, that said ,I'm thinking you have a bad "rectifier bridge" within the alternator, these diodes in the bridge will break down and cause current to flow in the wrong direction and will cause a 'parasitic drain' also if you able to look at B+ with a oscilloscope you would should see a flat line output, with a bad rectifier you would see a "ripple" indicating one or more diodes are bad.

Here's a good video on testing:

 

You could Be right but that seems a long shot. Do you know if what i descrbed i did - linking d+ line from alt to + post on battery is safe? Can i start the engine safely? I want to check that the key isn t a dud electrical link. Another wierd possible as i saw on yt vid is that the buttefly on intake valve isn t closing properly because of carbon deposIts this was the solution in one case. You d think auto zlone's alt test would spot a bad diode?

 

Hi Madman - just wanted to let you know I watched the video you sent the link to to test the diodes on an alternator. Simple! Still looking for a 'yes' answer on linking the D+ (tickler wire) on the alternator straight to the battery - to test my theory that the key mechanism may be the weak link in the current flow from alt to battery?

 

Yes you can go from the battery terminal or you can go from the B+ to D+ post on the alternator but be careful not to short against the alternator frame, a jumper wire with insulated alligator clips on the ends would be the best way.

 

[QUOTE=Dagaan;454654]Hi MaDman - great. Thanks.