Alternator Ripple Test

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Alternator Ripple Test

Postby Mk1_Oz » Fri Oct 13, 2017 10:50 am

Long time reader, first time poster. Hi to all. New to diagnostics and a little out of my depth but getting there!

Due to a few electrical issues I decided to do an alternator ripple test to ensure my alternator is not putting any AC into the electrics of my race car.

I put the red probe on the +ve terminal on the alternator and the -ve to a good earth. The result is this graph;

Ripple Test.jpg



To me this looks rubbish. Am I right in thinking that my alternator has 1 or maybe 2 diodes failed? The sample waveform Pico provide does not have the large spikes.

What do you see?????
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Re: Alternator Ripple Test

Postby liviu2004 » Fri Oct 13, 2017 8:00 pm

Really bad. Looks like half of your diodes are not working.
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Re: Alternator Ripple Test

Postby Mk1_Oz » Sat Oct 14, 2017 3:00 am

This was done at idle speed with no load on.

How many diodes total would I have? Do all alternators have the same number?

I bought a new regulator this week "just in case". Looks like I need to put it in and repeat the test!
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Re: Alternator Ripple Test

Postby Mk1_Oz » Sat Oct 14, 2017 8:19 am

Whilst waiting for the admins to approve my last post I have been playing.

I replaced the regulator pack and retested with this being the result;

Ripple Test-New Reg2.jpg



Although it looks better it is still ugly. I can pick out repetitive peaks and troughs but I still have the major spikes and the sharp negative peaks indicated by the green arrow.

I then decided to measure the alternator current, with car lights on, using the 600amp probe and got this;

Ripple Test-New Reg Current Probe.jpg



I am not sure what to make of this. It appears to be clean and repetitive but the sharp peaks worry me. I was expecting a more rounded profile.

Can anybody with the necessary skills tell me what I am looking at please????? I am starting to think that I DO NOT have an alternator issue but I cannot explain the spikes I am getting in the voltage pictures. Maybe the diodes are now OK due to the regulator replacement but maybe one or more of the windings are faulty (new alternator required)??

As a final check, I decided to connect the scope to the fuse that feeds the Davies Craig controller (I guess I could have used any live wire in the system to get the same picture). This is what I got;

DC Controller1.jpg



To be honest this horrifies me. 16v peaks!!! I am not sure if these spikes relate to the AC spikes from the first picture but regardless, the controller would not be happy!

Although my scope is a great tool I am finding that I am constantly asking questions beyond my knowledge. I love to learn but currently I am constantly trying to catch up!!!!! Heeeelp.
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Re: Alternator Ripple Test

Postby liviu2004 » Sun Oct 15, 2017 10:35 am

16V voltage spike is nothing. Those are inductive loads being switched off.

Have a look here: topic17271.html
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Re: Alternator Ripple Test

Postby Mk1_Oz » Sun Oct 15, 2017 12:10 pm

Hi, thanks for your input.

The picture of the 16v spikes was taken at an idle of maybe no more than 900rpm. That means 7.5 ignition firings/second (900/2 per recolution/60). The picutre shows 5 spikes in around 2.64ms so many many many more events.

The electric water pump was not operating at the time nor any other motor so the only pulses should have been from the ignition.

I need to do some more investigation.......
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Re: Alternator Ripple Test

Postby Mk1_Oz » Thu Oct 19, 2017 7:30 am

I replaced the alternator and the ripple test looked great. Very few spikes and what were there were much smaller peak to peak. I tested the quality of the 12v feed (14.2v actually) and it was lovely and clean. Very happy.

Looks like those horrible peaks were not ingition related but something to do with the poor condition of the alternator.
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Re: Alternator Ripple Test

Postby RYM6746 » Thu Oct 26, 2017 9:53 pm

It wasn't the cleanest alternator waveform, but what we're the actual faults that you were trying to rectify?

You have to remember that the battery acts as a "cushion" and cleans alot of this noise up. I would be looking at the electronic device you suspect to be faulty and see if those spikes are actually making it all the way to the component and even if they do, does the component behave as expected with the alternator disconnected.
I personally wouldn't be putting an alternator in it until I could PROVE it was that causing the problem.
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Re: Alternator Ripple Test

Postby Tronic » Fri Oct 27, 2017 10:58 am

Hi Mk1_Oz

Could you please upload, if you still have them, any of these spiky captures you took? It would be very interesting to have a closer look at them.
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Re: Alternator Ripple Test

Postby Mk1_Oz » Fri Oct 27, 2017 11:18 am

Cannot locate them. They might be on the lads laptop - I will take a look when I can pry him off of it!
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