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GSP7

AC ripple Testing

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Can  I Test for AC ribble with my Fluke multi meter?

 

My local Alternator/ starter repair shop can check it again but I have to remove my alt. from my truck because he only does bench testing

 

He also said there will always be some slight AC ripple.  Is that true?

 

.

 

 

 

 

Edited by GSP7

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What's that ?

 

Mike had a video, "How to check a Dodge Ram Alternator for AC waveform"

 

but the video is disabled or errored

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I cant remember exactly how to do it.

 

You test DC volts and then turn the meter dial to AC and the numbers need to be a certain value or less?  Or some chit ? ?

 

 

.

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set the meter to ac with resolution to 0.000v ac.  measure power on the alternator charge lead to ground and see what value it reports.  I think anything over 0.03 is a fail on the diodes

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When I replaced mine last spring it was .05 so I had the parts house test it and confirmed. They tested the new one and it passed and they told me that anything over .01 was a failure on their tester. 

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From ME78's link, Mikes post


 

Quote

 

Normal output of the alternator is 13.5 to 14.5 volts DC but when flipped over to AC Volts it should never rise above 0.1 volts AC.

 

 

 

 

.01 or .10   ??? :think:

 

 

Edited by GSP7

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I thought .03 was the highest you would want so I am confused now.

Edited by dripley

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..03 sounds familiar. wasnt mike's truck .028 in his video?

 

 

 

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The article (above link) says .1 it's a fail.

 

Why can't we just move them diodes outside the alternator so we can just pop in a new bridge whenever the Trans goes hunting? Maybe bad questioning here, but a cool AC ripple gauge would  also be handy in the cab.

Edited by JAG1

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6 hours ago, JAG1 said:

The article (above link) says .1 it's a fail.

 

Why can't we just move them diodes outside the alternator so we can just pop in a new bridge whenever the Trans goes hunting? Maybe bad questioning here, but a cool AC ripple gauge would  also be handy in the cab.

 

Great ideas, quick change diodes:thumb1:

 

L8tr

D

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Originally I post 0.1 VAC would be a fail but under different circumstances, some people were getting issues below that number. So the 0.05 marginal number pops. Basically, if you can test and reach or pass the 0.05 (50 mv AC) I suggest having the alternator bench tested to verify if it bad or not. Because ever truck has different loads during the test and there is no way to accurately load the alternator from test to test so that why I suggest all load off hoping to even out the loads and get a test number we can all play by.

 

10 to 30 mV (0.01 to 0.03) is a normally good alternator.

50 mV (0.05) is getting marginal bench testing is advised. 

100 mV (0.1) is failing. Bench testing is still strongly advised to verify the alternator.

 

Once you fail both your test and then a bench test you can safely say the alternator diodes are done. Now the replaces are here on the site.

 

 

Edited by Mopar1973Man

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I think there is some problem with trusting the bench test guys, so knowing what a good DVM says while running in the truck is a better option and if you have to go that far to pull out the alternator for the test you may as well just change the diode Bridge and be done with it. The problem is if you change the bridge and the DVM says still too high of AC ripple then you have to remove again and change brushes and possible slip rings.

Even though changing the diode bridge is going to solve most problems, as I understand it, you have a little better stab if you replace the brushes too I suppose.

 

So where do you go for brushes?

Edited by JAG1

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The Alt/Starter motor shop guy that tested my alt.,months ago,actually tested the diodes pack its self. It had one bad diode

 

I just tested my rebuilt alt with new diode pack and brushes with my Fluke meter,,, Cold motor in the AM just fired up ,,, It is .029 - .03 ish

 

Good to go for my "new" ECM when it gets here

 

 

.

Edited by GSP7

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16 minutes ago, rogerash0 said:

Moparman will that denso replacement unit work on any alternator or ?

 

Design strictly for the Denso alternators on the Dodge Ram truck. I'm not sure of any other applications it might fit. 

  • Thanks 1

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02 dodge diesel, had alternator bench tested it showed that it passed. Battery volts 14.69 ripple volts .39 did it really pass noise level.

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Yes .05 or less is good according to Moparman.

 

Sorry about my comment you can't trust bench tests.... I don't really know thats true for sure. :rolleyes:

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Depends. 

 

Full load ripple is going to be much higher typically the local NAPA passright right around 1.0 volts AC at full load 136 Amps.

 

Idling engine and no load with DVM you want to be 50mV AC or less. 

 

Output voltage is meaningless. It the ripple voltage that is critical here. 

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Where should you take the AC voltage reading, at the battery terminals or the alternator + stud to case? On mine the measurements at the alternator are much higher than at the battery.

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