Backyard Charging Tests failed

[kensousa]

I've been driving this truck for a year with no issues.
Suddenly while driving to work, my headlights are getting dimmer by the mile.
Get to work and battery is dead.
Since I have no tools at the office, I throw a new battery in her and drive it home.

With the truck not running, fluke meter shows 12.6 volts across the battery so I think that's normal.
With the truck running, I'm only getting 12.5 volts instead of what I think is supposed to be closer to 14 volts.

So now I assume the alternator is toast. However, I was taught that if you put a wrench behind the boss at the center of the rear of the alternator (while running) and the boss is magnetized, that the alternator is working.

I get A LOT of magnetism with this test, yet I cannot get over 12.5 volts at the battery while running.

Am I off base with these tests and/or is there another test that I can do to help identify the culprit?

Picture shows the back of my alternator to help identify.

thanks

[Andy4639]

Look for the voltage regulator on drivers side of core support. It's what regulats the voltage in a stock truck. If the alternator hasn't been changed out for a late model one.

[Longhorn 70]

Take the alternator off and have Azone or Orealy check it. I had a similar problem while on a long drive.

I grounded the field terminal of the alternator to drive to get a regulator. I had a 50/50 chance of picking the right terminal and put a test light from ground to the F terminal. I guess I lucked out. Once grounded, it was charging the battery with everything it had. I had to pull over every 10 miles or so and disconnect because I could smell the battery in the cab.....ewwww.

Have it tested and see what they say.

The one in the pic isn't an internal regulator model. The internal regs have a small tab you can ground to test the unit.

[cdowns]

i'd take the handel of a screwdriver and give the little squar regulator pictured and give it a few firm wacks to see if that solved your charging problem


it does not matter if you use a metric screwdriver either

[dolphstanley]

pull your positive battery cable off while it is running and if the engine dies the alt is bad

[Ironangel]

Originally Posted by dolphstanley

pull your positive battery cable off while it is running and if the engine dies the alt is bad

"True Dat"

[Ironangel]

Originally Posted by cdowns

i'd take the handel of a screwdriver and give the little squar regulator pictured and give it a few firm wacks to see if that solved your charging problem


it does not matter if you use a metric screwdriver either

"Tru Dat Too"

[SCHRUMGMC]

Never seen one of them things before

[alsriv2]

Originally Posted by cdowns

i'd take the handel of a screwdriver and give the little squar regulator pictured and give it a few firm wacks to see if that solved your charging problem


it does not matter if you use a metric screwdriver either

Gotta love them thar' metric altenators!

[GASoline71]

Classic sign of a failing voltage regulator. New one is about 15 bucks at the local parts store, and EZPZ to replace. Look down by the drivers side headlight for the little black box.

Unless you had a later model alternator in the truck that is internally regulated... the alternator probably isn't bad. I think the internally regulated alternators didn't show up in GM vehicles until around 1974.

Even my 1971 El Camino I used to have, had an external voltage regulator.

Gary

[Scott>72-GMC]

I would check the voltage reg I spent lots of time and money on alternators and batteries had the same problem as you barely made it to work lights dimmed and battery died as I pulled in couldn't figure it out neither did the multiple auto parts stores and Walmart finally traced the wires back to this box and did some research and that's what it was a 20$ part LMC has it listed for also if you have an internal regulator on ur alternator u can bypass this
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[Scott>72-GMC]

http://67-72chevytrucks.com/vboard/s...d.php?t=119379
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[Scott>72-GMC]

Posted via Mobile Device
Posted via Mobile Device
You can also get a bypass wire connector for the newer alternators
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[kensousa]

Originally Posted by kensousa

I've been driving this truck for a year with no issues.
Suddenly while driving to work, my headlights are getting dimmer by the mile.
Get to work and battery is dead.
Since I have no tools at the office, I throw a new battery in her and drive it home.

With the truck not running, fluke meter shows 12.6 volts across the battery so I think that's normal.
With the truck running, I'm only getting 12.5 volts instead of what I think is supposed to be closer to 14 volts.

So now I assume the alternator is toast. However, I was taught that if you put a wrench behind the boss at the center of the rear of the alternator (while running) and the boss is magnetized, that the alternator is working.

I get A LOT of magnetism with this test, yet I cannot get over 12.5 volts at the battery while running.

Am I off base with these tests and/or is there another test that I can do to help identify the culprit?

Picture shows the back of my alternator to help identify.

thanks

Update:
I tried smacking the voltage regulator with one of them metric screwdrivers mentioned here..... No luck.
So I bought a new voltage regulator and installed it tonight and the symptoms are the same.
Am I correct in stating that a battery that is being charged correctly by the charging system will read somewhere north of 14 volts?
If so, then I'm still stumped.

Based on the magnetizing symptom, the alternator seems to be alternatin'
And with a new voltage regulator, I would think that all is well, but it's not.

Anybody have any other ideas of where to look next?

thanks

[71Sixer]

I believe there is a fusible link on the wire that runs from the voltage regulator to the battery. It could be blown. Check continuity from the voltage regulator to the battery + terminal (disconnect the battery terminals first). Below is the wiring diagram link. You could also check voltage at the regulator, and you are correct, the voltage across the battery should be about 14Vdc when charging.

http://farm4.static.flickr.com/3645/...c2a8064d_o.jpg

[Andy4639]

With the truck at idle it maybe just above 12.5 volts. Give it some gas and hold it around 2000RPM and see what it reads. It should be close to the 14 volts then!

[Steeveedee]

A couple of observations-

Charging voltage must be a minimum of 13.5 Volts as measured at the battery to ensure that it will be charged. You aren't getting that, so it's going to continue to get discharged, as will the new battery.

Removing a battery cable while the engine is running runs the risk of popping a diode...thus proving that the alternator is bad, (at least, now). Don't do this, unless you have money to spare. If it didn't pop a diode when you tried it, go buy some LOTTO tix, you got some luck on your side.

The alternator generates alternating current, rectified by diodes. It is not magnetized in any way. That's why, if the battery is dead, you can't push start a car with an alternator, unless you feed the field with some potential, which can be as little as 1.5 volts from a "D" cell.

[Andy4639]

You need a volt meter to check the condition of the battery. A fully charged 12 volt battery should read 12.73 with nothing hooked to it. This is at 100% charge after sitting for at least 6 hrs off the charger and no drain on it.
Ok to charge a battery that is being used it has to put more in than coming out, so the vehicle works on 12 volts min. so you need at least 13 to 14 volts going back into the battery. perferably 14 volts.
The chart is what we use in the golf cart world to check batteries with and it's a standard of the industry.
A digital volt meter is your best friend when it comes to checking batteries.

[Longhorn 70]

There is a little brown wire on the junction block near the battery
there are 2 fuses in that line
for the meter
IF you are charging by measuring the voltage at the alternator but not on the gauge, check them.

[468BIGBLOCK]

Originally Posted by dolphstanley

pull your positive battery cable off while it is running and if the engine dies the alt is bad

and my neighbor did this and it caused a voltage spike and fried his radio and speakers. it did $400.00 worth of damage to his car.

[71Sixer]

Originally Posted by 468BIGBLOCK

and my neighbor did this and it caused a voltage spike and fried his radio and speakers. it did $400.00 worth of damage to his car.

Agreed - the battery acts like a capacitor for the electrical system and buffers the voltage spikes created by the alternator. There are other methods for troubleshooting the issue.

[ole dollor]

the alt. in the pic is an external reg.type alt. look for a fuse up around the front right side and another one around the battery area, it takes a real short fuse and the holder is just a small round plug in....you can pull it apart and the fuse will be a short glass type fuse...most of the time they are either blown or just broke all to pieces. might also check the fuses at the fuse box also. they get rusty and make a bad connection....

[kensousa]

Update:
New battery
New external regulator
New alternator (matched to the external regulator)
Two new inline fuses. One at battery, One on drivers side

12.4 volts at battery at idle and at high rpm

12.01 volts at alternator at idle . 12.05 volts at alternator at high rpm

Any other thoughts guys? This one is killing me. ....

[Andy4639]

The only thing I can think of is a bad spot in the wiring some where, where is the question though.
If your only getting 12.04 and 12.05 no matter what the engine RPM is then something isn't letting the juice flow and with all new components I would suggest start looking into the wiring.

[KEL]

borrow another meter ?