Alternator AC Ripple - Ferrari 550

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Alternator AC Ripple - Ferrari 550

Postby FioranoCars » Thu May 14, 2015 2:55 pm

Hi All
We have a trace of a problem 550 that seems to eat a battery every year! ... and trying to figure out why ... and about the only thing left is the alternator.
The battery is replaced, the parasitic drain is under 50ma which for a Ferrari of this era is perfectly good. The Starter motor draw is good.

Taking a closer look at the alternator, it looks like there is excessive noise on the ripple and it's taking a good 2-2.5 seconds after starting (3.5-4.0 seconds after crank trigger) to output full voltage, luckily I have readings from this car in 2011 to compare (not the AC ripple sadly), and while it outputs good Amps (when loaded, it gives at idle up to 80amps) and voltage (14.4v) the noise on the ripple makes me wonder if something is breaking down. We often see limited noise, not per each cycle or a factor of 3, and that we put down to "random" factors ... ie it's not related to the alternator cycle of 3 phases, so have historically not thought too much of it.

Certainly for me the delay in the output of volts and amps (no, not the belt slipping!) gives rise to questions of the potential immanent failure of the alternator (it's unusual and not something we see on the hundreds of these tests we do, unless there is an issue - ie the alternator only being able to output 5amps and no more)

The enclosed file shows the car at idle although relatively cold, with no artificial loads during the first segment and then the introduction of 30-50amps via a carbon pile battery tester to load the alternator. The amps go off the window, but the focus is the A/C ripple rather than the actual amps (you can re-scale if you must to see them!).

Ferrari_550_1996_Petrol_20150514-0003.psdata
Alternator AC Ripple
(2.69 MiB) Downloaded 79 times


The questions are ...
1. Does this noise have significance - ie a failure of a diode or some other component?
2. Does the delayed output signify something that others have witnessed? If so what?! Is it a precursor to failure?

Many thanks
Richard
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Re: Alternator AC Ripple - Ferrari 550

Postby KimAndersen » Fri May 15, 2015 11:58 am

Hi Richard

When you measured the parasitic current drain on this car, how long did this test last ?

I had a similar problem regarding a Fiat once, where the battery couldn't hold charge and where the battery have been changed multiple times.

The only tools I had to diagnose this Fiat, was a DMM and a current clamp. I did not check for ripple voltage at the battery as I was focused on the parasitic current drain this car had.

One of the first thing I did to insure that it wasn't some accessory there were making the parasitic current draw and I concluded that there were no.

It's here the strange part of my diagnostic begins. With the current clamp around positive cable at the battery I see no amps readings. I then put DMM in series with positive cable,and now I get a reading at around 80 mA which seems alright.

Then I turn on the ignition key a couple of times and suddenly when I was observing the amps reading at the DMM it begins show a reading of around 8 amps. Then I do the same test again which just confirm the what I have seen.

The high amp readings are first present after 5 minutes. My focus are then on the alternator as this part are connected to power all the time. I put current clamp around positive cable at the alternator and repeats the test from above.

A new alternator corrected the parasitic current drain this Fiat had.

I am not saying its the same with your car but you should check this as well. :wink:


Regards
Kim
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Re: Alternator AC Ripple - Ferrari 550

Postby FioranoCars » Fri May 15, 2015 12:11 pm

thanks Kim

Yes, tested parasitic drain, over a 8minute window as standard, and over longer periods (40mins-4 hours).
There was an small issue with the old tracker (it did not work, was a major discovery!) but was adding about 50-80ma and lots of fluctuations, so this was changed recently. We do parasitic drain tests to all cars with any starting/battery issues, as otherwise we're missing a major factor in most failures.

The drain is now very good, and happy this is not an issue.

Here is a screen shot for those who want to see at a glance the issue, Battery volts in blue, amps in red (at battery) and ac ripple in green (at alt):
ac ripple.png


I'll upload the starting captures for everyone too, from 2011 and now, showing the delay in charging output.
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Re: Alternator AC Ripple - Ferrari 550

Postby FioranoCars » Fri May 15, 2015 12:20 pm

So here is the 2015 waveform, showing alternator output taking 3.5seconds to reach full volts
2015 capture starting.png


Battery in blue, amps in red (goes negative when alternator starts to output), pos volt drop to starter in green, neg drop in black) ... and yes we're looking at the high negative volt drop, probably the cut-off switch as engine strap looks fine, but we'll do a segmented volt drop on them all to prove the cause, as it could be internal to the braiding etc...

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Re: Alternator AC Ripple - Ferrari 550

Postby FioranoCars » Fri May 15, 2015 12:23 pm

Here is the 2011 capture:
2011 capture starting.png


Note the battery was probably less charged, hence the higher instant output from the alternator. The starter was replaced in 2013, unrelated to all this.

See the volt output almost instant climb to full volts once the engine caught.

So my question is this, does this new "slower" climb on it's own prove a problem with the alternator?



Many thanks
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Re: Alternator AC Ripple - Ferrari 550

Postby tode » Sun May 17, 2015 7:32 pm

I do not know the system, but if the charge of the alternator is managed by a control unit, the difference between the two acquisitions is caused by a logic of the ECU.
If as I think the alternator is classic, without control, the problem is he, who can not generate enough power.
The idea of ​​a battery discharge more to justify the higher charging current in acquiring older, it does not seem good, if the plants are the same the car that has the problem shows a longer starting with a higher energy dissipation, I tried to calculate a math channel watts dissipated:

power diss2.jpg
Signal of good car, with matematic channel of power used in engine start


power 1.jpg
Signal of no good car, with matematic channel of power used in engine start


In track taken long ago, the alternator fails to restore immediately the energy lost (unfortunately the clamp has not measured the peak negative current) also reporting the voltage value immediately to the standard value, while in the track where the crank is longer, the power loss is greater, but the alternator fails to restore the energy.
For confirmation of an alternator is not operating at 100% I think a test drive with many users entered and the measurement of battery voltage, it may be sufficient.
I would check the value in voltage excitement of the alternator (if classical system).
This is my idea.
Greetings
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