Random AC spikes from alternator?

JHZR2

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I’m trying to diagnose some issues with torque converter lockup on my Ram. They are known for having EMI issues from a number of different causes.

I rewired my batteries, and have gone through all grounds.

I wanted to test the AC ripple from my alternator. With my cheap multimeter on AC, I put leads between the alternator 12V out terminal, and ground.

I generally got 0v, or the noise of the meter. The meter did not discern a frequency for this AC, which was strange.

Occassionally, the meter would jump to 3-4V. Then immediately disappear. This was a tiny fraction of a second at most.

I had autozone test the alternator, and they clam it has passed all testing.

So my question is, if there’s a sporadic 3-4V spike, what would this be an indicator of? I don’t know that it’s real... but if it is, that could be the cause of some issues I’ve been having.

My cheap battery tester says that there’s 22mV of ripple, but again, a cheap multimeter shows effectively nothing. There must be some level of ripple, so why didn’t the meter measure it? And that cheap tester might not sample fast enough, or see a 3-4V impulse.

If some part of an alternator diode pack is going bad, what kind of AC voltage shoukd one expect?

thanks!
 
AFAIK Over 1.5v AC constant between alt + and bat terminal - is enough to condemn the diode trio, make sure you turn on the lights, r defroster or heater and run it for a min before doing the test to turn excite the alternator. Get a reading at idle then raise the rpm to about 1500, there should be no noticeable change in the ripple.
Spikes are usually caused by issues in the windings or diodes.

It is best to use a scope to check the ripple.
 
Yeah definitely not seeing thst. AZ didn’t either.

Thinking it’s a false reading from my multimeter, though these trucks are emi interference prone. Definitely not an elevated, sustained AC voltage.

Thanks!
 
Cheap multimeters are useful. There is a reason why most technicians and engineers use use a fluke or other quality meter, and have a good needle vom. The spike you saw was most likely when something switched, ac fan, .rear window defogger, outside mirror heater,, seat, steering wheel heater, etc. A good battery should have absorbed most that spike. Get it tested and check grounds.
 
What may help (it certainly will not harm) is to add a few ground straps. While you have the crimpers get some tin covered braided ground strapping and some connectors and add one under the hood and one to the transmission using a bolt mounting it to the engine and then to the frame.
I had a VW that had terrible radio reception despite having a new OE amplified antenna and full OE cable with both the OE radio and the replacement.
Adding a 1" strap to the rear hatch to body, hood to body, 2" engine to frame, 2" trans to frame cured it 100% perfect reception so adding them can make a big difference.

I see quite a few of them missing from previous hack work or missing due to rotting away.
 
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