What is acceptable ripple voltage for E53 4.4i V8 water cool alternator?
 

I am trouble shooting for Trans. Failsafe Prog. Alternator ripple testing from autozone read 56mV and technician told me it was too high. Does anyone for sure knowing what is acceptable range?

May be someone with watercool alternator can go to the autozone to establish a baseline and share the result here.

Thanks.

I will look what that number means as there are standards for all the out puts
What was the highest amp out put measured?
Voltage?
Diodes failed, is that what they are claiming?

Test
Bad diodes are a common cause of alternator failure. The diodes are part of the rectifier assembly that converts the alternator's AC output to DC. The alternator's charging output flows through six diodes in the rectifier assembly before it goes to the battery and electrical system.* To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale. * With the engine running, touch the meter probes to the battery terminals. Any amount of AC voltage would indicate a bad diode, so you'll need to replace the alternator.
More details
Best Answer: One or more diodes in the alternator have failed. You can measure this yourself if you have a digital voltmeter - place the voltmeter across the battery with the engine running. The AC volts should be well under 0.1 volt, and I bet yours reads more than 0.5 volts AC. An oscilloscope gives and even better picture, but the meter tells the story. When I worked in aviation I saw dozens of those, and I have seen maybe half a dozen in cars. Recharging batteries by running the engine is a common cause.

Bad diodes reduce alternator output 33%, 67%, or 100%, depending on how many go bad, and the ripple can drive electronics crazy. If you have a bad diode and remove the battery lead for an old-fashioned alternator test the ripple can reach most of a hundred volts and ruin thousands of dollars worth of computers, controllers, sound system and security system components.

What is acceptable ripple voltage for E53 4.4i V8 water cool alternator?
 

+1. Yikes that's a big ripple. The diodes are part of the vReg. I would replace the VR and bet that would fix the issue. If you can get a slip ring kit to replace them at the same time better yet.


Update: 53 mv is only 0.053 v I misread as 0.53 at first. 1/20th of a volt shouldn't be causing problems but that is certainly an average. If it's 0.02 most of the time with a spike of 0.3v occasionally the machine will spit out "too high ripple" even if the average is reasonable.

I'll take a reading on my car and report what I find.

Ok I just measured my vBat at the cig lighter.

250msec average was about 70mV but 1mSec spikes were -350 and +400 mV. So on an oscope there will be a tiny sliver of voltage spike of about 1/3v probably each time the current switches which diode is allowing forward bias.

Now I really want to figure out which oscope app/hardware to get for my iPhone.

Thank you all for the responses.

When car is running idle with no other accessory is on, the alternator measured 14.5v which is good. My one year old battery reading is good at terminals under the trunk but reading is not good (failed) under the front hood at auxiliary battery posts. May be this is normal or may be battery voltage drops too much from battery to the front. I have no starting problem at all.

Most online reading said that ripple voltage should under 50mv but can go high up to 100mv depend on the car. So I do not know the ripple that I got 55mv is too high or is acceptable. The car throw "Trans Failsafe Prog" from time to time and seems to be slipping between 2nd to 3rd gear. But it will disappear if you restart the car. My 01 X5 V8 only has 120K. I love the car but it will be disappointed say the least that tranny failed at 120K.

Thanks,
ala2000

Disassemble, Clean and re-tighten the jump + post under the hood. Also check and clean the grounds and positive wiring connections to the starter and the alt. Then retest. The jump point gets most of the failed issues. Also, check the grounds points near the battery for poor connections.

Look up Volt drop testing for a quick measurement of how to test these points.

Examples
https://www.aa1car.com/library/voltage_drop_testing.htm
https://www.youtube.com/watch?v=qPpHRuddhh4

I highly doubt a ripple is yours problem but an actual drop in voltage eg dips to 12v when coming to a stop, that's the kind of thing that will give you failsafe mode. Use something to monitor voltage real-time and see if you get drops below 13v.

I turn on the cluster testing mode with test 9, I will be able to see voltage while I am driving. idle time=13.5v driving without headlights on=13.8-13.9v.

Here is how to for turn on the cluster test mode
https://www.ifixit.com/Guide/How+to+...k+feature/7617

Thanks,
ala2000