It's your meter, no question about it. If you look at the face and don't find "True RMS" anywhere on it then it is useless for this measurement. Measuring AC voltage without the car running is also telling you the meter is no good for this measurement.

I can understand buying a cheaper meter. As long as you don't go too cheap, they will work just fine for most typical hobbyist applications. But they do have their limits. If you go really, really cheap, they can actually become a safety hazard. You could do something wrong and have it blow up in your hands. As a minimum, I tend to recommend at least buying an auto ranging meter to anyone that asks.

Here is a decent explanation of the alternator output. About 1/3 down the page are waveforms.

http://www.bcae1.com/charging.htm

The unrectified output waveforms are a nice AC voltage. The cheap meters which are not RMS rated can measure these waveforms since they are purposely built assuming that is the waveform being measured. You can see the waveforms are a nice sinewave that is symmetrical around 0V.

The rectified output waveform is the output of the alternator. Cheap meters can't handle that waveform. It is not a sinewave nor is it symmetric around 0V and that means cheap meters which are not RMS rated can't handle it.

To also note, that rectified output waveform without any filtering should measure at 4% RMS voltage of the DC voltage. So, with 14V DC output, the alternator could measure up to about 0.6V AC RMS. Remember, this is with no filtering and the battery does do some filtering.

The YouTube video says 0.1V AC voltage maximum, but that was measuring directly at the battery. The alternator post will read higher than at the battery. You would also typically read a lower AC voltage with no electrical load on the car and a higher AC voltage when the electrical system is heavily loaded.

 

Yah I understand, just wanted to wait for a few more replies. True RMS No way I got two bad alts and my truck alt is also bad, dist is prob broke. So I need to buy a decent meter $$$ and have my dist repaired $$$


Weird part is if I move the meter with the leads in the air it gets a 30 Vac reading close to the dist, while running. That's what makes me think RF/EMI nose interfering with my digital/programmable distributor. No solid core wires or any of that bs I've been thru a lot of this and that checking and testing.

 

I wouldn't pay any attention to readings you get if the metter isn't connected to anything. Especially if it's close to the distributor

 

I've been trying to track down a high rpm tach flutter, no its not the ground that's low rpm flutter. Car is well grounded!

 

tach filter installed and working?

btw, if you reverse the leads on the non RMS meter on AC you probably get zero right? another test to verify it is the meter...

 

You don't need another meter. Turn on the headlights and turn the heater fan to high. The alternator wouldn't keep producing 14V DC with a bad diode.

I've seen good meters read significant AC voltage with the leads near a wire with AC on it. It's not a big deal and doesn't really mean anything. Even with so called suppression wires, some amount of leakage will happen when you're sending such a large voltage pulse down the wires.

 

I was talking to another guy to see if he thought it would be the tach filter and he thinks it's an electric motor(alt). I think it test the same, but I'll double check soon as the car is back together.

 

Can't took the leaky bent shaft chinna water pump off last night. I did some shopping and ordered a Extech True RMS meter also.


edit: No blower motor, e-pumps or e-fans.

 

The Extech should work well for you. Did you go autoranging too?