AC ripple test

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hal0persin
Newbie
Posts: 2
Joined: Tue Feb 20, 2018 1:22 am

AC ripple test

Post by hal0persin » Thu Feb 22, 2018 4:26 am

Guys I feel pretty dumb, I attempted to do a ripple test on a 2009 GMC sierra and the waveform has me stumped. I have never seen a waveform like this before but I think it is due to the ignition wires under the hood creating noise. Maybe if you guys take a look at the waveform you can enlighten me as to if I actually have a bad alternator or if I have not set the scope up correctly. I used the guided test in the software and connected to the b plus terminal of the alternator and a good ground. When I first started the capture it said channel over range until I changed the voltage scale to plus or minus five volts. Any and all help would be much appreciated.

Thanks, Zack
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ben.martins
Pico Staff Member
Pico Staff Member
Posts: 100
Joined: Tue May 16, 2017 1:02 pm

Re: AC ripple test

Post by ben.martins » Thu Feb 22, 2018 4:25 pm

Hi Zack,

Please do not feel dumb. We are all here to help and never be afraid to ask.

To me that does look like ignition noise as you say. Using the guided test is absolutely fine but might I suggest increasing the sample rate to 1MS across the screen instead of the 250kS that the preset loads. This will help capture further detail. The other suggestion is if possible can you connect directly to the battery positive and negative? This will hopefully remove the noise you are picking up at the moment as I believe the battery is on the left hand side of the bonnet as your looking into the engine bay. This means you can drap the cables outside of the engine bay and then you can stick the original scale of +-1V as the leads will be less likely to pick up ignition.

Apart from the noise though the waveform doesn't look too bad but if we can get another capture with the noise gone we would have a much clearer idea.

May I ask what is the problem with the vehicle?

Kind regards

Ben

hal0persin
Newbie
Posts: 2
Joined: Tue Feb 20, 2018 1:22 am

Re: AC ripple test

Post by hal0persin » Thu Feb 22, 2018 6:33 pm

I will retry my capture that way and see if the noise clears up. I am having an intermittent p0641 code for a 5 volt reference circuit. I checked the failure records and saw the reference voltage was at 1.1 volts when the code set but the sensors on that reference circuit read greater than 1.1 volts. This seemed odd because how could a sensor read a higher voltage than the reference voltage? so I took detailed notes on the codes and the data from the records and cleared the codes and sent the customer down to road in the hopes I could replicate the issue. Before I let the vehicle go I tried numerous times to induce the issue by matching the conditions in the failure record but couldn't replicate it. I then decided a battery and charging system test couldn't hurt because that is the heart of the electrical system. I had just started using the pico scope as a diagnostic tool and had heard excessive ripple could cause weird or erratic issues from today's modern vehicles because computers like ones and zeros not alternating current. This was a stab in the dark and also a learning experience in using the pico for this test. I am kind of stumped on this vehicle and that is why I went back to the basics first.
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