alternator wiring question

[loren]

yep, another one!!!

72 blazer. pretty sure my alternator went out last week. picked up a new one, only to discover the PO put in an internally regulated alternator. the one i got was externally regulated.

this is how the old one looked (delco remy 3 wire), with terminal #2 jumped to + pin:



now the weird part is terminal #1 had a 5" length of wire (the "brown wire") that went nowhere. I did lots of reading on the 3 wire alternators and it looks like that terminal is supposed to go to voltage meter or ammeter or ignition or something of the sort. mine goes nowhere. it seems like it has been this way for a while (wire end is dirty, looks old) and functioning properly. i've been driving it for a year and haven't touched any part of the charging system.

seems like i had a 3 wire alt that was functioning as a 1 wire alt. this a pretty good explanation. so, was a conversion done, like this one? must have been, right, because it worked for this long?

 

[chulisohombre]

72 had a external regulator that sent signal through brown wire to harness and then to ammeter. I switched to single wire summit alt and so I don't have a ammeter working anymore. I would like to figure out how to get that working again. My alt is powered by rpm. Has to get above 1500 to start charging so it is self excited giggity. But you're sounds to have a jumper to the + to excite the stator to get it to charge. It takes the signal to figure out internally by the regulator how much output it needs to charge your battery. With mine it is constant 14 volts at 100 amps because of strait one wire hookup direct to batt.

 

[diesel4me]

To have a internally regulated alt. work right,you need to have all 3 wires hooked up right...

The big stud terminal on the back goes to the battery via the thick red 10 gauge wire in the harness,which is hot all the time..

The #1 wire on the two prong plug needs to go to a 12V source thats only hot when the key is "on",and you need to put a #194 bulb or use the stock dash warning lamp in between the power source and the #1 terminal wire,or else it will put out full amperage constantly,and eventually cook the battery and possibly damage bulbs and other acessories..you need the resistance the bulb provides to reduce the input voltage to the proper level to "sense" when the battery needs more amps..

The other #2 terminal can be directly jumped to the stud terminal thats always hot...the reason yours worked with the #2 wire dissconnected is the altenator stator can either retain enough residual magnetism to let it kick in and start charging once it goes over 1500 rpm or so by itself,or just a voltage surge can activate it,sometimes just one faulty diode in the trio letting some voltage get to the stator is enough to energize it and make it start charging.....its not good for the regulator to get "zapped" that way,it can damage it and the diode trio eventualy..

There are kits available that convert a 3 wire altenator to a one wire,it could be someone did just that to yours already..it consists of a special regulator and some other things you replace internally..

 

[loren]

thanks for the help guys. i did a bit more reading on the 1 wire alternators, and i got to thinking maybe i didn't test properly.

that 1500-2000 rpm charging for the self exciting 1 wire alts... i think that threw off my diagnosis. i'm used to being able to check voltage at idle (newer cars!). all signs pointed to bad alternator and the low voltage (and slow battery drain) at idle just confirmed it.

now i'm thinking the battery might have just been pretty drained and i didn't drive around enough to give it a good charge. i idled several times to charge it up (like i normally would for a drained battery), but now i realize that just made my battery drain even more!

so i returned the new externally regulated alternator to oreillys, got my old alternator back, and properly charged the battery (out of the truck). i'm gonna throw the old alt back in there with the charged battery and see how it goes. maybe i'm in luck and nothing is broken

 

[chulisohombre]

Once a one wire alt goes over 1500 rpm to energize it, it will then charge at any rpm until you turn off the engine and start it up again. If you don't rev the engine a little bit on startup and just let it idle it won't energize and you will still be running on batt power alone. After you rev above that it should jump volts up from 12 from the battery to around 13.9 to 14.5 depending on how dead your battery is.

 

[diesel4me]

Your doing the right thing by charging up the battery before hooking it up to the new altenator...many get fried by using them to revive a totally dead battery,they aren't meant to be battery chargers,they are instead intended to maintain the charge of a battery ....they will recharge a dead one,but it pushes them to the limits and will eventually do some harm to it...so if you need a jump start,its always a good idea to let the other vehicle run a few minutes with the jumpers hooked up to boost the dead battery up some before starting yours,it will take some load off the altenator...

Another "bad" thing to do to an altenator is to "test" it by removing the positive battery cable with the engine running,this can blow diodes and on cars with computers,send a voltage surge thru the system that can harm the computer and sensors...it was a common test method back in the day,but was never "reccomended"..