Thread: Battery or Alternator bad?

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one wire alternators are great.....


for forklifts & tractors. A 3 wire setup gives you a better system. The alternator charges when it starts spinning, not waiting until you "wing" the motor. Also, with a 3 wire, the regulator gets a voltage sense signal, and actually knows (about) what to charge, as opposed to the one wire, which charges at a predetermined rate.

Take your test meter & check the alternator, once you have the alt spinning enough to charge. It should be 13.8-14.2 volts. If so it's operating. Next step would be to have the unit checked at your local parts store. If they have a good test unit, it should be able to tell you if you have a bad diode.

While you're at it, have 'em load test the battery as well.

Originally Posted by fitzwell

Take your test meter & check the alternator, once you have the alt spinning enough to charge. It should be 13.8-14.2 volts.

How do I check the alternator? At the battery like mentioned above? or can I put my voltmeter direct to the alternator some how?

Whew!
What the other guys are saying:
1. Take your volt meter and measure the battery voltage with the engine OFF. Put the + lead on the positive battery terminal and the - lead on the negative terminal. Write down the voltage reading.
2. Start the engine and rev it slightly to get the alternator going (one wire alternators take rpm to start). Let the engine go back to idle. On the back of the alternator is a big terminal lug...the one you touched to make a spark and start this in the first place. Put your + voltmeter lead on this and the - voltmeter lead on the battery negative OR any other ground....like the intake manifold. Read the voltage. Write it down
3. Compare the two readings. When you charge a battery, the charging voltage must be greater than the battery voltage....battery voltage is roughly 12 VDC and the charging voltage out of the alternator should be in the 13.8 to 14 ish range. If the alternator is not putting out more than 12 volts, suspect the alternator.
4. Another way to test the alternator (poor man's test) is to start the engine, rev it to get the alternator started, and then disconnect the battery. If the engine runs on the alternator, then the alternator is putting out some energy...maybe not enough but if the alternator is completely dead, the engine will not run.

Originally Posted by robot

Whew!
What the other guys are saying:
1. Take your volt meter and measure the battery voltage with the engine OFF. Put the + lead on the positive battery terminal and the - lead on the negative terminal. Write down the voltage reading.
2. Start the engine and rev it slightly to get the alternator going (one wire alternators take rpm to start). Let the engine go back to idle. On the back of the alternator is a big terminal lug...the one you touched to make a spark and start this in the first place. Put your + voltmeter lead on this and the - voltmeter lead on the battery negative OR any other ground....like the intake manifold. Read the voltage. Write it down
3. Compare the two readings. When you charge a battery, the charging voltage must be greater than the battery voltage....battery voltage is roughly 12 VDC and the charging voltage out of the alternator should be in the 13.8 to 14 ish range. If the alternator is not putting out more than 12 volts, suspect the alternator.
4. Another way to test the alternator (poor man's test) is to start the engine, rev it to get the alternator started, and then disconnect the battery. If the engine runs on the alternator, then the alternator is putting out some energy...maybe not enough but if the alternator is completely dead, the engine will not run.

spot on.....until # 4.

DO NOT disconnect the battery cable while the engine is running & reconnect it. The resulting voltage spike can (and will) kill anything electronic sensative in the vehicle. That was a test that kinda worked in the 40's-early 60's.

the other poor man test is take a small screwdriver, and carefully place it near the rear bearing, while the unit is spinning. If there is a magnetic field that pulls the blade in, the unit is charging, although it's kinda hard to tell how much.

one last test would be to check the ground side of the system. Check voltage across the battery & write that # down. Now,place the + probe on the positive post, the ground probe to the point where your ground cable attaches & check that. More than about 1/10 of a volt difference, you need to check the ground side of the system.


and, as always,

just my .02

Bucks, do you have a battery charger? If the alternator is good, charge the battery and see if it keeps it's charge. Sounds like , if it isn't the alternator(which is the most likely suspect, given the spark) that maybe you have a drain in your system related to the electric fan hookup, or any other new wiring. If you take the battery to Autozone with the alternator, you can kill two birds, with one stone, so to speak!

AutoZone Just schooled me I guess..........

I was at home, jumped the car. Removed cables and let it idle. Removed the Negative battery cable and the car did not skip a beat. Ran just fine.

Took the battery to Autozone to have them test it. Told him what I did. He said "no make no difference at all!" Unless I am running an old generator and NOT an alternator, my test I did means nothing. He hooked it up to see if he could get a read. Dead. He said the battery is only 3 months old so 95% sure it's not the battery."

I took a one wire alternator to Advance Discount one time to be tested and they didn't know how to hook it up to their machine. They had plugs for every other alternator setup, but not one wire. So, you might run into that.

If you have a dash voltmeter, simply turn on the key and note the voltage. If it reads 10.5 or more it should crank. If you get it started, bring the rpms up a little and the voltmeter should rise to almost 14 volts or thereabouts.

Don

Just called Auto Zone and got results- They charged the battery for 75 minutes and did a load test. All is well with the battery.

Guess I need to take my alternator in and see what it tests!

I've either misread your post, or somethings not making sense. Even if the battery is discharged enough to not turn over the engine, and, the cells are all ok. You should still get a 12 volt reading, if it's sealed battery your pretty well done. If it has caps, you can check from cell to cell and find the bad one, just to satisfy yourself and know it's the battery or not. The alt, is it a GM? If so, take a look at the rear case and look for a 'D' shaped hole. It will be about 5/16th to 3/8th across at the flat side of the 'D'. If you can look in the D hole, you should be able to see the backside of the voltage regulator. With a battery hooked up and everything ready to go, have the engine running at an idle. Using a small screwdriver or metal probe, ground the case at the 'D' hole and the back of the regulator. If the alt is working, you will get 16 to 16.6 volts on the gauge or meter. You will only need to do this for 2 or 3 seconds to make the test. What you are doing is, bypassing the regulator, and causing the alt to put out full voltage. If the test shows the 16 volts or so when the probe is applied, and then returns to the 13.6 to 14.4 volt range, you know then, that the alt is working, and the regulator is working. This leaves the battery as the faulty part. The part that makes me wonder is, you would get the solenode to click at first, but tested out of the car it was dead. An open circuit in the battery? Sniper

While I was speeding along with the two finger hunt and peck typing method I use, you said you received word that the battery is ok. As mentioned in a earlier post, it might be wise to check for a draw in the system. Take your meter and hook it up between the + cable and + post. Hook up the ground to the ground battery post. The meter should read around 2 or 3 volts, now take a test light, and touch it across the + cable end and the + battery post. The meter should drop off to 0, and the light shouldn't come on. If the light comes on and the meter reads a voltage, you have a draw. Leave the light and meter hooked up as is, and start pulling fuses one at a time, until the meter and the light go out. As soon as the light goes out stick the fuse back in, if it lights, you have found your circuit that the draw is on. Now it's a matter of finding what the cause is. Sniper

Originally Posted by bucs012

How do I check the alternator? At the battery like mentioned above? or can I put my voltmeter direct to the alternator some how?

Basically if the volts are right you don't have to worry about amps or anything else. Test at the battery. Volts at rest on battery as mentioned, 12.6-12.8. Start the car and with everything turned on that uses electricity, you want to see 1 volt more than battery voltage with the engine off.
I know a lot of people love those one wire delcos but I would wire in a regulator to run an old style Ford alternator personally.