Alt.not charging.help please

[Lild]

1986 m1009
did the roscommon 12v conversion back in the summer. I did the one where u remove the drivers side alt.

Drove home today, & notice the the wipers barely want to move, lights seem dim. When i got home, turn truck off, & tried to restart, no go. Had to go some where for a while. So a few hrs had pass, jump started the truck, fired right up. Got out my digital volt meter, checked batters, & alt, each read 12.v running. Figured the alt was going bad. So i changed out that one with the drivers side one i took out back in the summer, jumped again, batteries read 12.2 & alt read 12.2, took it for a quick drive to charge things up, notice lights got dim. Got home, 5 mins later, rechecked, 9.8 for every thing.

So i assume that both alts are bad, i may take the other to have tested, & my question is,
1- is there any thing that would keep the alt from charging, & why would it go from 12.2v to 9.8
2-will a reg civi alt work in place of the current alt. the batteries are wired in parallel, so is the isolated ground thing an issue, & i noticed that the replacement alts had no mounting point on them for the ground wire (like i have on the current rosco setup to the block.)
3-what amps is required, i see 78 & 108 amps. Most threads i see say 100 but again not sure since i converted to 12v system.

Thank you for any help

 

[Keith_J]

Burned out alternator lights will do this. You know how a Delco SI alternator works, right? If the "idiot" light burns out, the alternator is dead.

Since you have converted to single battery, a non-isolated ground alternator should work IF ground is negative with respect to the batteries.

Current of the alternator just relates to how fast it will charge the battery, the alternator wants to keep the battery voltage around 14.5 volts. If the battery voltage drops, the regulator increases the output voltage of the alternator. A 100 ampere alternator will be able to charge faster and sustain higher loads, any alternator between 50 and 100 amperes should be able to handle your loads.

 

[Lild]

Ok, so I didn't know about the "idiot" light being out meant that the alt was shot. I assume that of there was a problem the light would come on.

So I checked the bulb, it's good. Guess a new alt is in order.

 

[Keith_J]

Have you checked the wiring between the idiot light and the alternator? That could be an issue. In the STOCK configuration, power for the idiot light is switched by a relay and there is a diode (one-way valve for electricity) in this circuit. The bulb should illuminate with key on and engine off, this means the regulator is getting power and is maxed out on field current so it should work if the pulley is turning. Once the field current drops, the light goes out but there is still a small voltage signal going through the bulb's filament. When you shut the vehicle off, the key switch interrupts this voltage signal, turning the regulator off to prevent battery drain. Likewise, if the bulb is burned out, the regulator is shut off and it will not charge even if spinning.

I have zero experience with 12 volt conversions since I stock an overhaul kit for starters and alternators and know how to rebuild the things. 24 volt starters last longer as they need less current. Yes, they can go through solenoid contacts and plates but those are easily swapped.

 

[M1008driver]

double post

 

[M1008driver]

2-will a reg civi alt work in place of the current alt.

DL7157

Get the Duralast/Alternator from Autozone and make sure your alt light is working to energize the alt when you start the vehicle.

 

[lostintexas]

Warthog post a good article in this thread when I had similar no charging issues. In my case the idiot light had been removed altogether and the alternator wouldn't charge. You could apply power to the brown wire with white stripe and it would begin charging, remove power to brown/white and no charge. Read the article lots of good info.