Battery charger causes false readings

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Battery charger causes false readings

Postby volrem » Tue May 31, 2016 1:52 pm

Hi

I was playing with my NVH kit to get it know better. Measured one car at idle and noticed quite high vibration (54 mg) at 50Hz.

It was strange and first thing that popped in my mind was 220V electricity frequency.

Oh yeah. I didn't disconnect battery charger when I started the car. Stupid me.

But bigger question is can some other electrical "thing" from car itself cause false readings?

Both caputers attached. With and without charger. I measured with laptop on battery power. As soon as I disconnected battery charger (from car) this vibration was gone.

What do you think?
Attachments
395BAO idle.pddata
With battery charger
(223.58 KiB) Downloaded 33 times
395BAO idle wo charger.pddata
Without charger
(86.44 KiB) Downloaded 28 times
volrem
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Re: Battery charger causes false readings

Postby Steve Smith » Thu Jun 16, 2016 12:35 pm

Hello Volrem and thank you for the post, sorry for my late reply

Interesting capture and topic for sure.
Given we are around 50 Hz in this case, you have been able to prove the battery charger as the source of your noise, but how was the noise evident via PicoScope?

One possibility is via the OBD/USB lead used to obtain engine and road speed as this would be connected to battery power/ground and so through to the noisy charger.

Given your test leads are "floating" (BNC leads to the 3 output NVH interface) then your laptop ground would be subjected to the identical noisy ground, as would PicoScope connected via USB.

There is no connection to ground via the accelerometer as the internal sensing device is insulated from the magnetic base

To confirm this "ground" source of noise, if you were to ground the rear of your scope away from the vehicle (4425 and 4225 only) should the noise vanish, then it was certainly "ground based" noise

Alternatively the noise could be present as a result of EMI (Electromagnetic Interference) from the battery charger. Grounding the rear of the scope would have little effect here.

Whilst PicoScope and the test leads are well screened to avoid the pick up of noise, the same cannot be said for vehicle wiring, overhead lighting, lift motors, welders and overhead power cables!

The location of the scope, test leads and 3 output interface in relation to the source of this interference (battery charger) all have the potential to pick up this noise.

Could you confirm the scope was connected via the Pico Blue USB cable and not a USB extension lead?

I guess the message here is forewarned means forearmed.
You quickly identified 50 Hz as the same frequency as mains voltage, so when obtaining such test results, be sure to check your vehicle set-up.

This should not be an issue when road-testing!

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