On my way home from town I set the cruise and the truck started bucking and jerking on cruise control. Cancel cruise control throttles fine, Set cruise again bucking and jerking. So I pull over unplug the field lead and drive home. No issues at all. Pull out my Fluke DVM and measure at the BATT terminal of the alternator and was getting 0.244 not a typo... So of to the part store again to get another alternator under warranty.

Edited June 6, 20168 yr by Mopar1973Man

Didn't you just replace this recently? 

I wonder why it burned up the diodes so fast.

Unknown why but it failed the NAPA test stand. The new one pasted. So I can say that bad alternator diodes can do some really weird things like bucking and jerking with fly by wire cruise control.

Probably the best thing to do is once you get a rebuilt is just order Larry B's diode bridge and install right away. But I've never taken apart an alternator except a simple one on my JD tractor. I have no idea whats involved if brushes fall out or what making tough to do.

Just a screw driver... LarryB's diodes are expensive I can keep rolling alternators over on warranty for less. I'm thinking of getting of ahold of National Alternators and getting a high output diode pack and go from there.

35 minutes ago, Mopar1973Man said:

I can keep rolling alternators over on warranty for less. 

You're going to need to install a quick release for an E-Z 4 minute RNR.

Only took me 5 minutes to yank it out. But took over 3 hours to get to town get the alternator and return home with the new one...

 

I want to mention something about test the number I typically suggest are after the batteries are fully charged and everything is warmed up with all accessories turned OFF. Why? Because like what I playing with accessories and test it can change the AC voltage number greatly depending on how big of load you have turn on at the time. So say for example low or weak batteries, headlights on and blower motor on will produce a higher number. So like when I detected the AC noise issue I pulled over pulled the field lead and drove home. So when I test at home it was invalid high number because I've already discharged the batteries driving home with the A/C on yet. So when I hooked it up and test I was getting extremely high number because the load of the alternator charging the batteries. Now when NAPA test it the number is even higher because the ripple test is done under full load which is worse case possible. So like I had them test the new one and it tested out at 1.1 AC volts for ripple test. So when I got home and hooked it all up I was getting at the start .6xx AC volts. So I tiddy up and hauled out and charged everything up and came back after 10 miles and tested again .025 to .029 at idle no accessories. 

Also the reason why the at rest value... Because there is way too many things for loads that people might use on their trucks. Like turning on the headlights I've got another 200w worth of bulbs burning compared to a stock truck so if we all use the same thing which will produce a more even number and less false positives.

Edited June 7, 20168 yr by Mopar1973Man

I'm elctrically challenged and possibly mildly retarded, do you have a video of exactly what your doing and how your testing the alternator? 

Get a good RMS multimeter and set it to ac on the scale .000 v.   Then while the truck is running just connect the multimeter to the battery lead coming from the alternator and a ground and read how much AC noise is in your DC system.

 

 

Mike,

 

we really should break out an article for testing for AC noise. 

Edited June 7, 20168 yr by Me78569

I think a lot of people get nervous when testing anything related to the electrical system and a DVM just complicates things even more.  A simple video in would go a long way for some people and allow them to see how simple it is to test for AC noise.  I've worked electronics on F16s for a lot of years and a lot of people can't wrap their minds around the electrical world but they can be geniuses in others. 

agree'd we need to have a video for it.  

Mike made a video long ago. It doesn't show the whole process, but most of it.

I couldn't find it.  

 

I will have to dig.  

found it

 

 

Thanks tyler!

Yessir. Thanks @Mopar1973Man for the vid!

That video is skewed being it was done from the batteries not the alternator. You DVM has to be of good quality and have a setting for 2V or less. If the smallest scale is 200v it will not work.

 

Make sure all loads are off and the batteries are charged up before testing.

 

0.010 to 0.030 is a good alternator

 

0.050 marginal (Some folks have reported weird things at this level)

 

0.100 Fail. The alternator is producing too much and TQ converter locking issues typically occur.

 

This is the best one to explain the process and what is going on.

 

Now you understand why I said to unplug the alternator and go for a drive if the alternator noise is an issues it should be gone now and the noise issue should be gone as soon as you unplug the field lead like in the video. 

Edited June 7, 20168 yr by Mopar1973Man

Just now, Mopar1973Man said:

That video is skewed being it was done from the batteries not the alternator.

 

 Delete and re-make!

Updated video... Other videos are deleted now as well so this is the only video in my library for AC noise testing now!

 

 

Edited June 7, 20168 yr by Mopar1973Man

6 hours ago, Mopar1973Man said:

Updated video... Other videos are deleted now as well so this is the only video in my library for AC noise testing now!

 

 

Perfect! The only thing I didn't hear in the video was the acceptable level of AC noise. 

Great, I finally figured out on my own by piecing all these things together and NOW you guys wanna compile and make this into an article!

 

The nerve! 

 

 

 

Jk of course! 

 

Glad ad this is finally happening! 

When I get some more free time I'll do just a "Alternator AC Noise" article.