Bad News... Good News... Bad News


Staff member
Lifetime Gold Member
Feb 26, 2004
Bloomington, MN
I put my battery trickle charger on my Camaro a couple of days ago so it would be ready to go for this weekend.

Bad news... Nothing but a click, click, click, click from the solenoid this morning. :(

The 3 year battery is only 3-1/2 years old so I wasn't too surprised it had died but I had noticed that the battery always drained down if it was left sitting for more than a week.
A quartz clock should run for a LONG time without draining the battery and that should be the only draw occurring.

Good news... I got a new, 72 month 800 cold cranking amp battery for only $130. (Fleet Farm) :D

The Camaro cranked to life very quickly with the new battery so I decided it was time to do some trouble shooting.

The Volt gauge ALWAYS sat at 14V when the car was running and the battery never seemed to get a full charge.
(It should drop down after running a bit, shouldn't it?)

It made me suspect that the alternator might be the cause.

I conducted a "ripple test" with my muti-meter as follows:
  • Set the multimeter to a low setting on the VAC (alternating current) voltage scale.
  • Turn on your engine.
  • Gently touch your voltmeter's probes to the battery terminals.
  • The voltmeter should read 0 AC. Any other reading indicates a bad diode.
It did NOT read zero.
It was actually around the middle on the 50VAC setting!

Bad News... Looks like there are bad diodes in the guts of the alternator.

I know I can rebuild the thing but I may have a Lifetime warranty on it.

But... Do you think I can find the darned receipt for it. :(


Staff member
Lifetime Gold Member
Feb 26, 2004
Bloomington, MN
I'm totally befuddled.

Just to be sure the test was valid, I repeated the "ripple test" on my 2015 Impala (which never drains the battery) and got the exact same results. :screwup:

With this comparative information, I don't think there is anything wrong with the Camaro alternator.

There was no real drain on the Camaro with it idling and no lights or accessories "On" so maybe the alternator wasn't actually engaged yet.
But the Impala's headlights were on so the alternator should have been charging.

I'm going to repeat the test with all accessories "ON" to put the electrical system under a load and make sure the alternator is charging the battery.
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Staff member
Lifetime Gold Member
Feb 26, 2004
Bloomington, MN
Test repeated…
Car idling, headlights on, fan on high, stereo on…

Same result with the multi-meter.

The VAC setting is confusing to me as there’s no numbers on the scale.

How do you read the VAC scale on this old non-digital multi-meter?
(Previously, I've only used it to measure resistance and 12 DC tests.)


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Knuckle Dragger

Mayor of Simpleton
Staff member
Lifetime Gold Member
Nov 2, 2002
Waddell AZ
I know they teach the AC voltage test to check diodes but I've found most alternators will fail the test. I'm guessing the switching isn't as quick as the guy that came up with the test thinks it is. If you have bad diodes it generally isn't a charging issue, it and electronics weird behavior issue.

The tried and true system loading with a carbon pile while still installed in the vehicle is still the standard for me. Watch that Impala when comparing anything. It is ECM controled and will run at 13V sometimes depending on what the ECM is trying to do with it at the time. All the rule of thumb charging rules go out the window with the new stuff.


Veteran Member
Oct 3, 2013
SK, Canada
FWIW, and quite "unscientific" back in the day my experience was that when an otherwise good battery wouldn't seem to "completely" charge up, the alternator had at least one defective diode. Granted, that's well over 40 years ago but I thought I'd just toss it out there.


Veteran Member
Aug 1, 1999
I'm thinking those diodes are not set up as a full wave bridge, just a rough DC current that's filtered by the battery resistance? With everything off might put a small 12 bulb in series with the + battery cable, if it stays lit start unplugging fuses until you find the circuit that's drawing current, then trace that around to find the culprit.

rocket dawg

Veteran Member
May 5, 2015
Grand Rapids Mi
If you bought your alternator at Auto Zone, you don't need a receipt. Just the phone number you used when you purchased it. I just replaced a 22 year old alt at AZ and I had to think what my phone number was back then. The Autozone I used could not test my alternator so the just handed me a new one. If you have an aftermarket stereo, they pull more juice than you might suspect. Your quartz clock really doesn't use much at all. I have to charge my battery every 2 weeks with this newer CD-media player, same in our 2004 GMC Envoy that sits most its life at our cabin. Before the stereo change, I could let the car sit most of the winter and charge it once maybe twice. We bought a week long timer for the GMC and charge it twice a week for an hour or two with a Battery Tender brand charger. The price of batteries is high while the quality has diminished. I have a NAPA battery in it now, it replaced a 14 year old Interstate battery. I highly doubt I'll get anywhere near 7 years out of the napa battery.


Staff member
Lifetime Gold Member
Feb 26, 2004
Bloomington, MN
I'm pretty sure I got the alternator from NAPA because they didn't have one in stock at my local AZ that day.

Yes, it's an aftermarket stereo but I've never actually measured the draw from it.

By the specs, I've got a much better battery now and a very generous NastyZ member sent me a 100 AMP PowerMaster alternator that he didn't need.

Thank You, Coadster32!!!

I've been considering adding a pusher fan in front of my A/C condenser because the factory fan doesn't seem to pull enough air at idle or stop/go traffic to keep the A/C output at the proper temp.

This alternator will easily keep up with the extra power draw of a small, additional fan.
(My plan is to wire the fan through a relay triggered by the A/C compressor circuit when the compressor is running.)

I'll need to run a heavier gauge wire for the alternator, when I add the fan.
That's all still in the planning stage.

Jim Streib[email protected]/albums
Apr 6, 2004
Saint Louis, MO USA
In 35+ years of installing car audio, I only did one AC ripple test and it was using an oscilloscope. We had a vehicle with alternator whine and tried all kinds of things and then saw the ripple with the scope. I cannot remember the amount of ripple but I checked another car that was there and it had a lot less. I then shut off the cars engine that had the alternator whine and took jumper cables to the other car that had less ripple and had it running and then original cars whine went away. Told the customer to get another alternator and all was fine after that. I do not know if possibly the customer had other issues that he did no tell me about like the battery going dead over night or what.

I do voltage checks on my 68 Nova fairly often and I like to see at least 1V over what the nominal voltage is in the battery after sitting a few days. When I measured it last, the day before Easter prepping for a show, the battery measured 12.37V and then I started the car and it was on high idle with the choke being on and then the battery voltage went up to 14.60V and then after I blipped the throttle to get it to a low normal idle I then reached in and turned on the parking lights and the low beam headlights and then the voltage across the battery read 14.30V

I then turned the headlights and parking lights back off and the voltage then read 14.97V

I then turned on just the parking lights and the voltage dropped to 13.88V

I then turned the parking lights off and the voltage went to 14.84V

I then shut the car off and the battery with the surface charge went to 13.00V and then after time kept dropping and dropping and then settled at around 12.79 and I stopped my testing for that day.

A few weeks later I checked the battery after the Easter show and it was sitting for almost 3 weeks unstarted and NOT on a charger (but I do have a Pioneer underseat radio that draws 0.01A for it's memory) and the battery voltage was at 12.34V

Prior to Easter it was at 12.37V and then 3 weeks later after a drive and no trickle charger connected to it, the voltage was at 12.34V

More info is I'm working with an 8.5 year old battery, an original 37A alternator and an original mechanical external regulator.

My system has been fine and while I did have a concern about getting a backup solid state regulator I opted for another correctly date coded original.

If you have 0.02A or less draw with things shut off, then you should be fine between running the car to bring the voltage back up every few weeks.

If while driving down the road and your voltage is at let's say 14.2V and it keeps getting lower and lower the longer you drive it with the same accessories still on, then the alternator is not large enough.

My battery voltage sometimes has gotten to a maximum high or right around 15.2V or so but I have to think it is due to the ambient temperature that my tests are being run at and after the car has been started after sitting a while. It doesn't stay at that high of a voltage for too long though so I am not overly concerned.


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