Tip - Alternator Battery Problems

I thought I would share this with others in the hope that they didn't end up spending alot more money than needed to cure what seemed to be an alternator problem.
I recently bought a 1993 Chev Lumina Sedan with the 3.1 Liter V6. I got it real cheap because it had been in a minor accident with only cosmetic damage to the front bumper and some plastic parts. The owner also said it needed a new alternator and possibly a new battery, then went on to describe how you could boost it to get it going but the engine would die after about 10 minutes and the battery would be too low to restart it. He then demonstrated and the car died at about 8 mninutes after removing the cables.
So, I bought the car and towed it home.
The battery was a pain in the butt to get to, but I managed to get one clamp of my booster cable on the positive terminal and one on the engine block and got the car started again, so that I could test the output of the alternator. Result only showed a repid decrease in the battery voltage, so I figured the previous owner was right and that the alternator was the culprit.
Next day I finally disassembled all the junk in the way of getting at the battery and found that even after a 12 hour charge the previous night, it had dropped in voltage from about 12.79 volts earlier that morning when I took the charger off, down to 12.02 volts. I suspected that even if I could start the car at that voltage, the battery might not have enough power left to energize the magnetic field in the alternator in order to generate power. (The battery was a "Sure Start" 650 Amp, 465 Cold Cranking Amp's.) So, I replaced the battery with one I knew was good out of my old car, (Crappy Tire, 800 Amp, 650 Cold Cranking Amps), and checked the voltage before starting the engine. Pre-startup voltage was 12.62 volts. With engine running was 14.52 volts. After running for about 5 minutes, then shutting off the engine, voltage was 12.85 . Looks like the alternator works.
I have to swap plates etc with my old car before I can take it for a serious test drive, but I'm reasonably certain it will continue to charge properly. If not, I'll repost to let people know.
D.BC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

Hi D...
Thanks for sharing that; what you virtually 100% surely have is a battery with one shorted cell. A thing that used to be very rare, but seems to be happening more and more these days.
Take care.
Ken
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

WTF?! I'm going to make that my new signature. ;)
--
Steve

"the battery might not have enough power left to energize the magnetic field
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Steve Mackie wrote:

Hi...
Only if you're real real old, like me :)
Gotta go back to about the 50's and replace the word alternator with generator :)
Take care.
Ken
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Steve Mackie wrote:

Oh, at first I thought you were going to use the brand name of the battery "Sure Start", for your sig.
D.BC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

MAke sure the battery isn't drawing down with the key off. That could possibly be due to a bad diode in the alternator, which will allow proper charging (until another diode goes) but will cause a key off current draw that will make the battery go flat in only a couple days.
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Nate Nagel wrote: <------------ snip ----------------->

I ran the car again today at idle for about 10 minutes and had these results:
Pre-startup voltage: .................. 12.65 Running voltage: ...................... 14.32 + or - approx. 0.12 volts Voltage after shutting off ignition: .. 13.32
I'll take the car for a long drive in a couple of days, after I get into town to do the insurance thing and get plates for it. I did try recharging the battery that was in the car to start and it did seem to take a good charge (12.74 volts), but after only 6 hours, it was down to 12.03 volts again. I don't have a proper battery electrolite tester, just my trusty pocket digital multimeter.
D.BC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

Eh, that sounds like the battery then. it should hold at least 12.5 volts indefinitely with nothing connected to it. enjoy the car...
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.