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Old 4 Weeks Ago   #1
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Flickering lights

Lately I noticed that all the lights inside and outside the car (headlamps, DRL, overhead lights, etc.) are flickering in sync like in the Supernatural TV series. What's going on?
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Old 4 Weeks Ago   #2
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Quote Originally Posted by Geolith View Post
Lately I noticed that all the lights inside and outside the car (headlamps, DRL, overhead lights, etc.) are flickering in sync like in the Supernatural TV series. What's going on?
Unregulated voltage?

Get the alternator checked.. should be 14v maximum output..

Do check the basic battery and earth connections too.
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Old 4 Weeks Ago   #3
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Re: Flickering lights

The flickering happens only when the engine is idle, so maybe the alternator is failing? No idea how to check it though.
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Quote Originally Posted by Geolith View Post
The flickering happens only when the engine is idle, so maybe the alternator is failing? No idea how to check it though.
A basic volt meter costs less than 2 beers..

Set to Volts DC .. and the probes on the 2 x battery terminal posts
it should show 12 /13 with engine OFF

@14 Volts with dngine running
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Old 4 Weeks Ago   #5
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Re: Flickering lights

Aren't the built-in voltage gauge readings enough for the assessment? If I'm reading it correctly, the gauge shows 16V at idle and 12V with engine off. Admittedly, it's not the most precise gauge in the world, but still...
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Re: Flickering lights

Looks like 16 and 14 to me..

Had no idea this feature existed..

But probably time to check the earth connections..

You are still using the factory lighting.. no weird upgrades??
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Old 4 Weeks Ago   #7
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Re: Flickering lights

On face value your alternator voltages look normal.

First of all I'll apologise for the rest of the post as many will know exactly what I'm talking about but there will be many who may benefit from some more tech info.

If your lights do not flicker when running off battery and the engine stopped then this is a clue.

As you know unlike a dynamo (which produce DC) and alternator produces AC voltages varying from -nV to 0V to +nV. This AC voltage is rectified into DC. This DC voltage will vary from 0V to +nV to 0V to nV .........

This is a high ripple voltage which has to be smoothed to produce a more steady voltage. Now in power supplies used in the home this is done using a capacitor(s). These store charge and help to smooth out the voltage waveform. In the car the alternator / PSU has no such capacitors. Instead the vehicle battery operates as the capacitor.

Now I'm suspecting that your battery battery when being supplied with energy from the alternator is showing/having a high ripple voltage. e.g. +10V to +14V to 10V.

Now this could be a battery issue or an alternator issue.

If we take a typical old style incandescent light bulb (or even halogen) then at household mains frequency of 50Hz you will not see any flicker. However at 25Hz (depending on the bulb) then you might detect flicker.

Now as you say that the flicker disappears as the engine RPM is increased then the rate at which the alternator goes from 0V to +nV to 0V to +nV increases so the ripple voltage increases and thus the time between battery top up vs battery drain decreases and also the shorter the period the less the battery is drained between top up pulses.

If the alternator is the source of the high ripple then this indicates that one or more of the diodes in the alternator have failed. This means the battery is seeing 0V to +nV to 0V to 0V to +nV ..... i.e. the alternator is only topping up the battery at a 50% duty cycle.

If the battery is the source of the problem this would be because one (or more) of the internal cells have or are going high resistance.

An oscilloscope would pin point the problem as one could see the waveform from the alternator.

Another by far less definitve way is to use a digital voltmeter and set the voltage range to AC and not DC. In the AC setting then it will block DC voltage measure the varying AC/ripple voltage. However this will just give you a value of say 2V AC but this on its own is not enough unless you have made the measurement before or can compare to another 500X at the same idle speed.

Now if you are lucky and have a digital volt meter that will also measure frequency then you may find that the frequency of the ripple voltage at idle on your car is at 25Hz (say) but on another 500X is 50Hz. This would confirm a diode failure in the alternator.

Hope this all makes sense?
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Old 4 Weeks Ago   #8
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Re: Flickering lights

Quote Originally Posted by varesecrazy View Post
You are still using the factory lighting.. no weird upgrades??
No, everything is stock.

Quote Originally Posted by s130 View Post

Hope this all makes sense?
More or less, but it still sounds rather complicated to me, so I'll let the service guys handle it. I've booked a check-up by the end of the next week. Thanks for the info!
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Re: Flickering lights

How fast are the lights flickering and is it a steady pattern or random. A failled diode is likely to give a faster rate than the 25Hz suggested by S130 (depending on design details) but even 25Hz is a pretty fast rate and would not be noticable on a filament lamp (I know this for sure because I've used half wave rectified mains, which gives 25Hz, to "dim" bulbs). If the flckering is random it's likely to be worn or stuck brushes or a bad connection.

Robert G8RPI.
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Old 4 Weeks Ago   #10
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Re: Flickering lights

Perception of flicker (in humans) is dependent on frequency, depth/amplitude of low to high values, the average overall steady state luminance and direct vs peripheral vision angle.

The depth/amplitude is a factor determined by the type of light. Incandescent filament bulbs have a fairly low brightness amplitude. However it is there and depending on the other factors mentioned can be perceived by some more sensitive people.

I just mention this because I have extensive past experience of this back in 1987 where I was a member of a small team of engineers and human factors experts working on this exact problem of flicker in VDUs and proposing an alternative standards method to actually measure the flicker of any given device and then overlay their flicker waveform frequency components (derived from Fast Fourier Transform) over a set of perception curves as measured by formal human factors test studies of hundred of people.

VDUs of the 80s had screen refresh rates of 50Hz / 60Hz and depending on the phosphor persistence (long or short) could flicker like mad at frequencies below these and would lead to nausea, eye strain, headaches etc.

Regarding if a diode loss would cause a problem or not does depend on alternator design. For a simple four diode bridge rectifier then loss of one half of the bridge would double the ripple voltage and therefore potentially double the likelihood of flickering perception.

Back to the problem in question. An oscilloscope would quickly show all both voltage and frequency variations going on and by some simple test methods help track the problem down.
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Quote Originally Posted by Geolith View Post
No, everything is stock.



More or less, but it still sounds rather complicated to me, so I'll let the service guys handle it. I've booked a check-up by the end of the next week. Thanks for the info!
Tell us if they flicker..

1. Flicker Differently
2.do NOT flicker

When the engine is OFF : not runnning
So power is purely from 12v engine starter battery.

Thanks to those with a better understanding for their great explanations and suggestions
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Re: Flickering lights

Quote Originally Posted by varesecrazy View Post
Tell us if they flicker..

1. Flicker Differently
2.do NOT flicker

When the engine is OFF : not runnning
So power is purely from 12v engine starter battery.
When the engine is OFF the lights do NOT flicker at all.
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Re: Flickering lights

Quote Originally Posted by g8rpi View Post
How fast are the lights flickering and is it a steady pattern or random. A failled diode is likely to give a faster rate than the 25Hz suggested by S130 (depending on design details) but even 25Hz is a pretty fast rate and would not be noticable on a filament lamp (I know this for sure because I've used half wave rectified mains, which gives 25Hz, to "dim" bulbs). If the flckering is random it's likely to be worn or stuck brushes or a bad connection.
All I can say is that it's definitely random. Here's the video I made showing the headlights flickering. Maybe it will give you some idea.

https://mega.nz/#!C6RwwSZS!_e7H8-kot...kdqV6I_PXA91mE
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Re: Flickering lights

Now that video helps a great deal.

That is not flicker (flicker is normally defined as repeated regular higher frequency modulation).

What you have videoed is some form of modulation effect caused by something possibly cutting in and out that is possibly loading and unloading the vehicles 12V system OR the alternator is dropping in and out causing the battery voltage to drop from 14V to 12V and the pack to 14V. A poor electrical joint from the alternator that is heating and cooling could cause this as could an internal alternator joint issue.

As you say it affects many of the vehicles lights then an analogue volt meter (read traditional moving coil needle) is ideally suited to measuring the battery voltage. As the lights modulate you will hopefully see the meter needle move in synchronisation with ups and downs of the lights. A digital volt meter (DVM) is not ideal for this as it is a sampling device with period display updates so it is not really possible to get an accurate conclusion/feedback.

Shame you are not located near me (Southampton) as this is an interesting problem that I've never seen before so would have ideally like to investigate with you.
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Last edited by s130; 4 Weeks Ago at 19:56.
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Old 4 Weeks Ago   #15
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Quote Originally Posted by s130 View Post
Now that video helps a great deal.

That is not flicker (flicker is normally defined as repeated regular higher frequency modulation).

What you have videoed is some form of modulation effect caused by something possibly cutting in and out that is possibly loading and unloading the vehicles 12V system OR the alternator is dropping in and out causing the battery voltage to drop from 14V to 12V and the pack to 14V. A poor electrical joint from the alternator that is heating and cooling could cause this .

Shame you are not located near me (Southampton) as this is an interesting problem that I've never seen before so would have ideally like to investigate with you.
Excellent

Thanks.

Local? Probably only a couple of days BY BOAT..
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