b body charging system..

Hey guys lots of into floating around about the charging systems but i have a couple questions-first its a 66 charger just put it back together after 10 years of sitting in the shop with no engine. anyhow
it had the old style regulator with the dual field square back alt.. it worked 10 years ago but after firing up the new engine it wasnt charging i had the alt tested -ok so i replaced the old regulator with a "new" style one. rewired it and it was charging at 13.5 at idle-perfect

200 km trip and i started to smell battery.. sure enough its charging at 15.5v at idle now and was cooking the battery.
so while idling if i unplug the blue field wire from the alt it stops charging, the green wire seems to have no effect weather its plugged in or not.

now with both blue and green field wires unplugged engine off, if i test for continuity between bat neg and either field terminal on the alt i have continuity, is that normal? also unplugged the regulator and i dont have any continuity between regular posts if that means anything.

some help would be great
thanks

If I understand your setup, you are running the newer dual field terminal charging system.

If that is so then neither terminal should be shorted to ground. Once side, blue wire, should be a switched 12v and the other side, green wire, is controlled by the voltage regulator.

Sounds like the alternator has a short in it and is full fielding, which would be consistent with the 15.5v you are seeing.

Sounds like you were running the square back alt on a pre-’70 application. Likely one field terminal is intentionally grounded by the removal of a brush assembly insulating washer, substituting a metal washer. As mentioned, on a later isolated field system, there can be no continuity from either field brush/terminal to the case. Check the washer under the mounting screw head that the green wire currently connected to, make sure it’s an insolating washer.

It sounds like when you rewired it you missed something As a minimum you have to run an additional wire from the alternator to the voltage regulator when you change from the grounded field to the ungrounded field alternator.

Charging Circuits

its wired just like the 1970 and up diagram,

sounds like you may be right... i can take it apart and have a look but still strange how theres continuity between either field terminal and the case?

Not strange at all. If one terminal is grounded, there is direct continuity. The other terminal is grounded through the field winding to the other field terminal which is grounded, indirect continuity if you will.

I'm missing something cuz the 2 field terminal alt would not work with the old style "box" reg but you said it was charging in the 13's way back so I missed something there. DO you have the flat one or the box? if either of the male field terminals on the alt are grounded then there is an alt issue, as said start by checking the brushes, grab your vom. EDIT I see that you have the later system (flat reg), something inside the alt is grounded with there being continuity from one or both alt field terminals to the batt neg

i had a cracked brush holder do that to me one time. when i discovered it and took the holder out, it broke into pieces.

Now if the green wire is normally grounded thru the flat reg case with it not running (I dont know) then the field terminals being grounded at that point in time would be normal. so the full fielding is somewhere else. with the alt checking out OK at the parts house (not always 100% but close) I think the reg is full fielding.

Controlling the field strength controls the output of the alternator.
The old 1 wire alternator's used a variable signal through the blue (+) wire to control the field strength They were direct grounded.
The newer 2 wire alternators use a continuous power through the blue wire and control the field by varying the ground through the green wire.

If it is over charging you either have a grounded field wire inside the alternator, a short to ground in the green wire or the VR (Voltage Regulator) bit the big one.

Disconnect the field wires from the alternator and the regulator.
Check for a ground from the green wire to the engine/negative terminal. If it is disconnected at both ends and has a ground then there is a short.
Check for grounds from the field ternimals to the alternator housing WITH THE WIRES DISCONNECTED. If there is a ground you have a shorted alternator field.

If it isn't grounded it sounds like the Voltage Regulator took a dive.

I carry extras in my glove box because the new ones are garbage.

OP " the green wire seems to have no effect weather its plugged in or not."
This statement in the original post would eliminate anything external to the alternator brushes.

point taken

I missed that one. Sounds like a bad alternator (Internally grounded field) or there is a hokey wiring setup that wasn't described but I believe him when he says it was wired correctly.

Disconnect both field wires from the alternator. If there is a connection from the terminals to the alternator case there is a short.

if one of the brushes is grounded ( intentionally or accidentally ) we must say thanks God is not the one getting the blue wire, because if so, will inmediatly short out and burn the wire as soon you put the key in RUN.

Very Very true

It's still important to disconnect both field wires when checking for shorted fields. If you leave the blue one hooked up when checking for a shorted field you will almost always get a false positive. The blue wire also directly, or indirectly, connects to solenoids, coils and such so it will tell you there is a ground when it is just current finding its way home through another device.

My apologies if I didn't explain why.

so just to clarify, this alt was used 10 plus years ago on the car when it had the old style regulator, after removing the alt this evening and having a better look at it the field terminal where the green wire goes has no plastic washer under the screw, the terminal where the blue wire goes does have the plastic washer.. so the field terminal with out the plastic washer is grounded to work with the pre 1970 regulator, make sence? that was my over sight, however the other field terminal with the plastic washer still has continuity to the alt case its self,

with the car running when i would go to plug the blue wire in it would spark you would hear the idle drop slightly and it would be charging ar 15 volts up to 18 off idle. i decided to try plugging the blue wire onto the other field terminal and it instantly shut the car off..

You were seeing continuity through the field winding to the grounded terminal from the insulated terminal. And as mentioned, connecting the blue wire to a grounded terminal normally results in a lot of burned up wiring, you’re lucky it stalled it first. Find a fiber washer for the grounded terminal screw, problem solved.

May have been stated earlier; but the new style double field alternator can be used with the old style regulator. You just ground the brush with a wire or to the case by removing insulator. When you swapped to electronic regulator, you had the control feature shorted. Not sure what your battery state was, but if drained, it is possible that was dragging down voltage as the alternator was charging at full from such a low initial charge.

Then the battery finally fully charged on your trip and then over charged as you had no voltage regulation. You were at full.
So take the alternator to an auto parts store and they will test it. Chances are it is fine.
Then have the second field winding brush set back up correctly insulated. Frankly, do that before you have it tested.

Then get a new regulator. I am sure it is toast. You should not be pulling and attaching under power. You also grounded the field winding that should never touch ground.
Inspect your harness closely, put the tested alternator, and new regulator in an try it.

What you did was unknowingly ground the blue wire. The blue wire is the positive field wire which also connects to the ignition system, various solenoids and such.

The only fuse in the blue wire circuit is the fusible link. Check the fusible link for damage.



The field (Rotor winding's) inside the alternator is just a large continuous coil of wire. If either end is grounded then both ends will be grounded.

just like a bulb... will read ground on either terminal because the filament makes the bridge. A bulb is not more than a controled short to become it on a light source thanks to oxigen absence to burn it out like it was a complete short to burn. Well, an alt is more less the same, with the rotor just like the filament in a bulb

put a new insolation washer under the second field terminal screw, and shes fixed thanks for all the help guys even tho this should have been pretty obvious. always learnin!

thanks
connor

happy to hear it was a simple fix !