Alternator problems

[padgett]

On spare car, not a Reatta but a 10SI is a 10SI right ? Circuit looks the same.

Am just about stumped by the sudden loss of the alternator. Everything checks out good, voltages are in the right places, took the alternator to PepBoyz and tested fine, put on car and nada.

Idiot light is on when engine off, goes out when starts but no voltage gain (has both light and meter). Am wondering what the shop tested (nice printed readout, no amperage just volts).

Be easy if I had a spare alternator to swap but connector looks different.

Anyone see anything like this?

[Ronnie]

I'm thinking you have a bad diode in the bridge rectifier. The alternator has the ability to produce AC current and may test good at 12 volts DC without a load but if you have a bad diode it will allow reverse (AC) current flow through the rectifier which will give a net voltage of 0 volts under load.

[Guest simplyconnected]

Worse than that, Ronnie, a shorted diode IS an internal load, causing the belt to labor (with no output). Pep Boys should have noticed the mechanical load on the pulley. With no electrical load, the pulley should free-wheel even at full field strength.

Not all 10SI's are created equal. There were 10SI alternators with 37amp, 42amp, 55amp, 61amp, and 63amp ratings. All of them had an internal regulator/brush holder, and two slip-ring brushes.

The #1 Terminal, (Marked "1" on the case) is connected to the dash warning light.

During normal operation the lamp stays off. If the regulator is damaged, the #1 terminal provides ground, and the warning lamp will usually light.

The #2 Terminal, (Marked "2" on the case) excites the 10SI into operation and is connected to the battery positive.

You can check this alternator yourself. With the engine off, disconnect all wires (BAT wire will be hot so be careful removing and tape the end). Attach #2 alternator terminal to "BAT", then connect a load to the "BAT" terminal, like a spare headlight. Start the engine and see if the headlight shines. Here's the drawing:

If it shines, you may have a bad battery connection or a bad battery. Don't forget to check ground connections as these are equally important as Positive connections.

[padgett]

Thanks - the little printed test report has no load test indicated. Have verified that BAT voltage (11.9v) is on BAT and #2 and does not change when running.

Have alternator back out. Odd thing is that ALT light goes out when engine is running even though voltmeter shows no charge. Just took to AZ and their tester (SPC/OTC and possibly the same unit as at PB) also passed the tests. This time I listened as the unit spun up and I heard nothing that indicated that a load was applied.

Going to set up a test rig with battery, motor, and headlamp as suggested and will see what happens.

[Ronnie]

Be aware that the headlight will shine when connected to AC or DC current. Check the outputs of the alternator with a multimeter. If you get a voltage reading on the AC scale and erratic or no readings on the DC scale it would point to the diodes being bad.

[Guest simplyconnected]

Also, you should read a HEALTHY 13+ volts, not 12-. Alternators can't charge a 12V battery if they don't put out more than 12V.

[Guest Mike_s]

Many moons a go I saw a utube video of how to diagnose and rebuild\repair a GM alt. I don't know if it's still there, but thought it was worth mentioning

[Tinker]

Here is more than you ever wanted to know about Alternator Theory .

And here is the VIDEO about alternator repair. It is a two part video each about ten minutes or so.

This is not a Reatta alternator but it is 98% the same. The only things that he did not do was to check the rotor for internal grounding and he did not check the stator for grounds either. Of course, this alternator was fairly new too. So, maybe he felt he didn't have to.

[padgett]

Hokay: made a test rig with a 3/8 drill, 1" socket, Powermate, mess of jumpers, an 1157 bulb and socket, 6054 headlamp, and a HF DMM.

Could feel load come on and headlight was bright so alternator is good. Going to have to take a real close look at the wiring.

FYI you can spin an alternator with a hand drill and the countertourque is not real bad. Suspect if doing A Lot with a Real Load would rig a fixture for the drill press. Should just need two brackets.

Thanks for the all the fish.

[Guest simplyconnected]

And the VOLTAGE??? (This is the most important part, padgett.)

The idea is to put your alternator under load, and check voltage. You need to measure more than 13 volts under load.

You did a good check, and I like the idea of 'feeling countertorque.' The 6054 uses 65/35-watts (.09 horsepower on high beam).

If 746-watts = one hp, then 65/746=.087hp (just under a tenth).

[padgett]

Voltage went from 11.9 to 14.6 when spun. Not much of a load but enough that something should have happened. Now will have to check all of the wiring. Could have messed something up when was repairing the tachometer.

[Guest simplyconnected]

Install your alternator, start your car, turn your headlights (for a load), and check voltage on #2. Stick your meter prod into the connector, and the other prod on ground. This senses battery voltage and turns on the field every time your battery falls below 12v.

I will assume you have properly bonded grounds to the body as well as the engine.

Between your battery and your alternator, there isn't anything, really. The GEN light is optional, and as long as #2 is attached to BAT, it should charge when voltage falls. The tach has nothing to do with your charging system.

[padgett]

Agee, the tach has nothing to do with the charging circuit but removing the entire instument cluster to repair the tach does.

[Ronnie]

Have you actually tested across the battery terminals to see if the voltage goes up when the car is running. If not it could just be the voltage reading on the instrument panel not showing the correct voltage.

[padgett]

Yes, have lotsa $2.99 HF DMMs just for that purpose. If necessary can instrument multiple points. Battery voltage was not climbing before, is now.

Meanwhile it is healed. Put it back in car and now is working. Must have been a bad contact somewhere. When first spun with drill, nada occured then suddenly it loaded. Might have been something under one of the brushes. Alternative is that the waving of a new unit by it had an effect. Question is whether the healing is permanent or temporary so will take portapower along for a few days. Suspect finding another alternator at the PickandPay might be a good itea.

[Guest Mike_s]

"Alternative is that the waving of a new unit by it had an effect."

I've occasionaly used the "The ride softly but carry a big wrench" form of automotive relations, how the car can tell when I've left the tools at home is beyond me.

[padgett]

And the latest: when just tested in the garage, the serpentine belt shredded. Could this have been the problem all along ? We'll see what effect new belts have.

[Guest simplyconnected]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: padgett</div><div class="ubbcode-body">Question is whether the healing is permanent or temporary so will take portapower along for a few days.</div></div> Answer is directly commensurate upon your proximity to Indian burial grounds. This proportionally applies to all computer glitches, too.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tinker8r</div><div class="ubbcode-body">Here is the VIDEO about alternator repair. It is a two part video each about ten minutes or so.</div></div>

I watched both segments, and I urge you to follow these instructions. Apart from the video, I would use 400-grit sandpaper (or finer) on the slip rings. Brushes leave a fine coating of graphite (a natural lubricant), and you only want to polish dirt and oil (glaze) off the surface. I cringed when I saw the guy 'wrenching' sandpaper back and forth. Lightly polish while the pole pieces are spinning to keep it round.

[padgett]

Replaced belt and now everything is functioning properly on 10 mile test run. Glad it shredded in the garage.

[Guest simplyconnected]

I am too. How many miles are on this alternator? Have you ever checked the brushes?

[padgett]

Just bought the car - an '86 Fiero GT - for a very good price understanding that it needed some work & have been going through it for the last week or so. This was a surprise but suspect the belt was going all along. Unfortunately I just did not think of it.

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: padgett</div><div class="ubbcode-body">Just bought the car - an '86 Fiero GT - for a very good price understanding that it needed some work & have been going through it for the last week or so. This was a surprise but suspect the belt was going all along. Unfortunately I just did not think of it. </div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">On spare car, not a Reatta but a 10SI is a 10SI right ? Circuit looks the same.</div></div>

Now all you need is a good 3800 to go with that 10SI in your Fiero. I had an '88 Fiero Formula and that was always the swap I wanted to do. I think I made the best swap in the long run. I swapped the Fiero for a Reatta. I got the 3800 I wanted, more room, bright red paint, power steering and a much better ride!

[Booreatta]

My Fiero tossed the belt 2 years ago when the ac comp locked up car has been sitting since. Will restore this car some day in the future, they are really neet cars