when replacing alt on 5.0.... does it need to be excited?

[PUR PONY]

I am in the process of rebuilding a smashed explorer I bought. I got a junkyard alt and installed it... but the needle on the dash didnt show it was charging.... I removed the alt and took it back for another.... its doing the same thing.... When the truck is at idle the battery is putting out 11.49 Volts... my ranger pickups battery at idle shows 15 volts.....

The battery in this explorer is brand new and the wiring "seems" to be fine....

Maybe the junkyard alts are really junk??? or is there some type of way the alt needs to be excited before it will start charging?

thanks for any help

 

[vrytired]

no, ALL alternators are self exciting. if it didn't excite itself it would be a generator not an alternator. check the alternator field fuse. you may have to start at the fuse box and work back with a dmm.

 

[Eneurb]

Your Explorer is not charging... your Ranger is overcharging.

 

[Doug904]

I am in the process of rebuilding a smashed explorer I bought. I got a junkyard alt and installed it... but the needle on the dash didnt show it was charging.... I removed the alt and took it back for another.... its doing the same thing.... When the truck is at idle the battery is putting out 11.49 Volts... my ranger pickups battery at idle shows 15 volts.....

The battery in this explorer is brand new and the wiring "seems" to be fine....

Maybe the junkyard alts are really junk??? or is there some type of way the alt needs to be excited before it will start charging?

thanks for any help

Look at the three wire connector going to the alternator, two of those wires should be hot with the key on.

www.4.0performance.com/explorer/alt.jpg

As in this photo from the EVTM the Regulator has two wires that are hot on it, in this photo the wire from the distribution box Yellow/White and the wire from the guage Light green/Red. The White/black wire just routes back to the stator from the regulator.

I can tell you this for sure because I had the same problem one time. Yes, the alternator must have a switched 12v source going to the regulator or else it won't charge.



Thanks, Doug.

 

[410Fortune]

Also check the battery to frame/to engine ground connection/strap.

Often when replacing engines it is easy to forget...usually the starter wont crank easy if at all but its worth checking...

 

[PHL Flash]

I had my alternator sieze, and purchased a new one. It wouldnt charge the system. I returned to the store, where they found a blown fuse in the fuse box right near the battery. One of them was very small, and IIRC it said 'alternator'. Replaced the fuse, and been nicely charging ever since. Cheap fix, and worth checking out.

 

[PUR PONY]

well i have not been about to figure this problem out yet and its starting to get to me. Alternator is BRAND NEW..... I checked all the fuses... all fine, checked the wiring and grounds and everything seems fine... STILL NOT CHARGING....

There are only 2 wires going to the alt...ones yellow and ones green/red. One of these has power all the time and the other only has power when the key is on...

then there is a big wire coming off the alt going to the starter solenoid.....

When the truck is running the big wire coming off the alt is only showing 11.3 volts.... and the battery is only showing 11.3 volts....

truck starts and seems to run fine.

Also I can get the blower motor for the heat-a/c to work.....

I am totally lost now.

 

[gish]

What year is the truck? Also , when you say that you are reading 11.3 volts coming off the alternator ,are you reading directly off the alternator terminal or the solenoid point you mentioned beforehand? Also check that your battery is not actually drawing so much current that it is loading the alternator down. You may want to charge the battery with a charger to start off with. An alternator is not intended to charge a dead battery it is supposed to maintain a charge. A low or dead battery will take as much current as you can supply it until the charge starts to equalize.

 

[PUR PONY]

the explorer is a 1996 V-8

On the alternator is a plug and a post... the wire coming off the post goes to the solenoid on the drivers side fender where is splits and goes to the battery and starter.

When the truck is idleing the post on the alternator is only showing 11.4 volts, the solenoid is only showing 11.4 volts, and the battery is only showing 11.4 volts..... I would think that if the alternator was working correctly the post on it would be putting out 14.4 volts or so....... I will go out and fully charge the battery right now.

 

[gish]

According to my haynes manual, with key on engine not running, there should be 12 volts at terminal "A" of the regulator(looks like yellow/white wire)and1 volt at the "I" terminal( light green /red wire) .When the engine is running, there should be about 14.0 volts at the "A" terminal and roughly a volt less at the "I" terminal. It says if the voltages are not as specified check the wiring harness,if the wiring harness is not defective, replace the alternator. Hope this helps.