Abnormal voltage spikes

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Joined: Sun Feb 08, 2015 9:03 pm

Abnormal voltage spikes

Post by heady2010 » Sat Feb 28, 2015 8:11 pm

high spike.jpg
Hi, when i'm measuring signals i keep getting very high voltage spikes when the car is running (see image of battery voltage) i'm guessing it might be from ignition system? I am making sure the cables aren't running near the coils and i've also got a second channel going to earth which brings this voltage spike down a bit. Is there anything that can be done about this?

Steve Smith
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Joined: Sun Aug 25, 2013 7:22 am

Re: Abnormal voltage spikes

Post by Steve Smith » Tue Mar 03, 2015 10:05 am

Hello and thank you for the post, would it be possible to post the psdata file here so I can look at the spike in detail?

You are right that during engine run conditions we have an enormous amount of noise present within the engine bay (mainly from ignition and injection events)

The noise will vary from vehicle to vehicle but is characteristic in all vehicles.

The PicoScope has the ability to capture all events about an engine bay as a result of its high sample count and rate which is invaluable when looking for those intermittent problems.

This however will also reveal spikes such as those seen in your capture that may or may not be of relevance. It is nice to see all the noise present in your engine bay as there will be times when the noise is relevant to the diagnosis.

Of course, the skill is with identifying what is relevant and what is purely noise.

We can take precautions to reduce noise as you have mentioned by:

Ensuring test leads are not running alongside consumers such as igniter, HT leads, and injectors.

Ensure the scope is grounded to a good vehicle chassis ground.

Ensure only the Pico blue USB cable is used to connect your scope to the PC, avoid USB extension leads.

Remove external battery chargers from vehicles under test (unless required for battery support)

Be aware of environmental conditions that can effect your capture such as noisy mains power supplies (ground), fluorescent lighting, and overhead power cables.

Incorporated into the hardware and software are features to combat noise such as low pass filters (all scopes) and bandwidth limiters (4425-4225)

I hope this helps, take care.......Steve

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