The Stovebolt Site Forums The Shop Area The Electrical Bay Low voltage

I just replaced my alternator because it was showing a discharge on the ammeter. It also had a bearing that was going bad and had started squealing. My ammeter would always show negative at first start, as soon as I accelerated the engine it would jump to the positive and after a few seconds level out to the mid point on the ammeter gauge. Now that I have changed the alternator I am still getting a slight discharge. It is showing 12 plus volts at the alternator and the battery. What am I missing here. It starts fine each time and the battery is fine.

Sorry guys the truck is a 58 Apache with a 235 12 volt system.

Is this the same issue you were having 10 years ago?
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/981646/charging-system.html#Post981646

No this is a different issue. Before I went from a generator to an alternator. This time I am replacing a bad alternator.

Your voltage regulator could be malfunctioning.

"Alternator" covers a lot of territory. Can you be a little more specific about which one was involved in the conversion from generator to alternator? The most common one is an internally regulated Delco 10-SI, but there are others that have an externally mounted voltage regulator. The wiring and diagnosis procedures are totally different.
Jerry

It is the 10-SI and it has the internal regulator.

Use a small blade screwdriver in the D-shaped hole in the back of the alternator housing to bypass the regulator. It should go to a minimum of 15 volts at 1500 engine RPM if the alternator is good. If the voltage goes up with the regulator bypassed, either return the alternator as defective, or put a new regulator in it.
Jerry

Thanks I will try that

Just solved my low voltage problem. I bought a new alternator from Orillys and discovered it was bad after having it tested at another store. swaped it out for another and it was bad only produced 12.5 volts. Picked up a third alternator and it was the same issue with the same voltage. Always showed a negative on the amp gauge. took it back and got a refund and went to Advance auto and purchased one from them, everything is right on point. Alternator is producing around 13.5 to 14 volts running. I am 74 years old and have replaced lots of parts over the years and this has never happened before. So beware guys, just because it is marked new does not mean a thing.

Most rebuilt alternators are designed to work with an idiot light only, and will not work without either a light bulb, or a resistor simulating a light bulb. I learned this the hard way many years ago. It can drive you crazy. I'm not suggesting that was your problem. I'm just posting it in hope that it might help someone later down the road.

Mike, a little misleading there. When an alternator is "rebuilt", like say a 10si Delco, it is rebuilt to be a 10si Delco. Which will operate on an indicator or an ammeter/voltmeter or neither. 10si alternators were available with different outputs at idle and different max outputs. (12si,15si, 27si) But basically the same alternator. Some case size differences. At first they called the 10si a Delcotron Generator.

10si does not need a light or resistor to operate. An idicator light is very nice to have. Neither the light nor a resistor in the "key on" wire is for "kick starting" the alternator.

Speaking solely about three wire 10si install.

The "Delcotron" was a model 52D, produced from 1962 to 72, and used an external regulator.
Jerry

GM tried to get people to use the term Delcotron as a generic term like "Kleenex" to refer to Alternating Current Generators.

Chrysler was using the term Alternator. Of course Alternator stuck and nobody ever walked into a parts store and asked for a Delcotron for anything.

As I said, Chevy referred to the 10si internally regulated, solid state, integrated circuit, System Integrated unit as a "Delcotron Generator" into the late 70's early 80's. Used the name on DN and others.

Mike Burns Have always overhauled my own delcotrons,would get a pile of "defective parts" put them in an alternator,take-off and work fine !! Over the years made my own test equipment,have a way to externally test regulators just shuck em thru there.

When they "reman" these alts. & some other parts they take out the quality original equipment parts & put in cheap parts sold to reman companies in mass amounts. The quality is poor & the failure rate is heavy. I always did the GM alt. & starters myself. They are so plentiful you can cannibal some for parts.

George

Wrenchbender Ret. My local junkyard has kept my alternator inventory up in good shape so I have a place to get original goodies. Can find the right stuff to make a unit that will prime at reasonable RPM then charge at idle,while you get around,neat and simple.

Please tell us or describe what test equipment you have made up! Very interesting!