So, I had my alternator checked at a local auto parts store and these were the results. The guy told me that my alternator would last about 2 days then it would most likely leave me stranded. I am wondering if based on these results, is he right or was he just trying to push me into making the sale? I really don't have $150 to spend on an alternator plus labor charge.

 

That does seem like a lot of ripple, although I've never seen the output of an alternator on an oscilloscope before. I would definitely think that your electrical system is not appreciating the almost half a volt of AC you are feeding it.

According to this, it should be able four times lower (90mV). I think one of your diodes may be open.

 

I recently changed my alternator. I manage to get it at a junk yard for $80. The change was pretty simple i would say, but you do have to be able to know a little mechanic.. but otherwise time consumin thats all

 

Your altenator output looks fine, loaded and unloaded! The ocillscope readings look good....what made you check your altenator by the way?

 

well, last week I started my car and both the brake and battery light on my dash came on. I searched on the org and posted a thread and everyone said it was the alternator. I also went to two different Advance Auto stores and they both told me that the alternator had a "ripple" and it was going bad. One guy even said it would last about 2 days then break down. This is why I replaced it with a brand new alternator and now I'm having electrical issues. Nothing works inside: radio, windows, AC, windshield wipers, horn, NOTHING! Any ideas why???

 

I think you are crazy. That much ripple is unacceptable in any DC power supply I've ever seen. The three phase design specifically meant to reduce ripple. I'm going to go out during my break and read how much AC my alternator is making.

EDIT - My ripple is 20mV AC under load. So I would say 411mV is too high (About 20x too high!).

 

the output wave is suppose to look like a picket fence and when you start missing the tops here and there is a def altenator.... no biggie....good call!

 

There is just a lot of misinformation around on the internet, and electronics is a topic that is not understood very well to begin with. I don't know how many people have told me not to touch the positive and negative terminals of a 12 volt lead acid battery at the same time. I usually don't get worried until working with 70+ volts. Hell, telephones run at 48 volts. You can't feel that unless you put the conductors in your mouth. (When I was a kid, i used to use my teeth to strip insulation. Something about being young and stupid).

Anyway, I do agree that there will always be ripple in the output, but the scale of it is what's important. All generators produce AC, that's just the nature of them. However, if you have a DC circuit, that AC need to be rectified, and while some ripple will invariably make it through, minimizing it is very important. Sensible vaules are below 100mV.

 

check this thread: http://forums.maxima.org/4th-generat...placement.html

it might be something related to your situation.

 

How about you check the fuses and make sure none are blown. If you replaced the alternator I hope that you had the battery disconnected. Seems as if you could have shorted out some wiring during the installation. Also make sure that all wiring connections to the alternator are tight.