2005 Dodge Grand Caravan 3.3 - Testing alternator with basic tools - Also some fancy tools! - PART1

Repair done in Part 2:
• 2005 Dodge Grand Carav...
2005 Dodge Grand Caravan 3.3L towed in. I opened the hood and found the negative terminal off. When I installed the terminal it arced like a welder! The customer doesn't do any work on their vehicle so not many things that can cause that kind of current discharge. Most likely being a faulty diode pack in the alternator causing a dead short. Alternator is right there so opted for the low tech approach.
I removed the main battery cable from the alternator then reinstalled the negative terminal. This time no major arcing! No further testing required! Needs a new alternator. End of story!
Except it was the end of the day and I felt like doing more! This alternator was incredibly noisy. Even with the main power cable off. After just a short amount of time running it got over 300*F. Right after shutting it off I checked resistance from the main power post to the case of the alternator. I got 0.8ohm. My leads are 0.2ohm so that's like half an ohm of resistance! I started filming a minute after that and it was up to 1.8ohms but that's still VERY BAD. This would be going through the diodes so it should be millions of ohms. This is what the new one tested as.
Thankfully on these Caravans the alternator is very easy to change!
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[@mychicksrthick]

My alternator is showing 5 holmz is that bad?

[@Stavros1977]

Hi i have this same van. 2005 3.3 V6 and my battery light is on. Alternator is fairly new. Do u think the battery is bad? Battery is 3 years old and it's rebuilt. Thx

[@eurbanautotech]

@Stavros1977 Hi. The alternator is what turns that light on. Sometimes it can be other things preventing the alternator from doing its job but it's usually the alternator. Rebuilt alternators are a coin toss. Sometimes they'll last a long time. Sometimes they'll fail in 6 months. What can also fail is the circuitry inside the alternator that's responsible for turning on the dash light. This would cause them to turn the light on even though everything's working just fine.
A bad battery can cause an alternator to fail but if it starts your car without a boost then it's unlikely to be a battery issue.
Ultimately the charging voltage would need to be checked. Both in DC volts and AC volts. Start the vehicle and turn on a bunch of electrical loads. Blower on hi (with air conditioning off), rear defrost on, hi beams on, etc. Charging DC voltage should be above 13.3V and holding steady. A bad alternator may initially show a good charging voltage then slowly drop below 13V. You'd also want to see less than 50mV ( 0.050V ) AC. Anything over 100mV ( 0.100V) is a bad alternator.
Alternatively what you could do is hook another car up to yours with booster cables. Keep the other car off and start yours. If the battery light stays off then that would indicate you have a problem with your battery or your terminals. If it's still on then start the other vehicle. If your battery light now goes out then you know you have a bad alternator in your car.

[@Stavros1977]

@@eurbanautotech Thank you very much for your detailed reply. I like last paragraphs explanation as I will try this. Also if it is my alternator which I suspect, what brand of alternators do you recommend? Thx