Meeerrrk
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| posted on 15/3/09 at 09:04 PM |
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"pulsing" LED rear lights
i fitted some LED rear light units (side, brake, indicator)
everything appeared to be fine but my mrs was following me the other day and said they were flickering. at first i thought must be a dodgy earth, but
all wiring is fine.
The battery on the car was completely shot, wouldnt even take a charge from an optimate conditioner. Could only start it via jumping and even after a
50+ mile drive it still didnt have enough charge to start the car.
Could such a flat battery cause the led lamps to "flicker" or "pulse" with the engine running?
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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MakeEverything
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| posted on 15/3/09 at 09:06 PM |
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Yes.
The alternator puts out a DC waveform which is very square, which is what causes the "Flivker" effect. Particularly with LED's.
Bulbs might not notice as much, as they would dim and get brighter.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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Meeerrrk
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| posted on 15/3/09 at 09:09 PM |
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thats cool, thanks very much for the speedy, detailed response.
that'll learn me for not putting the battery on a conditioner over winter; its just a small bosch 8ah bike battery.
I'll get a replacement tomorrow.
thanks,
Mark
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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MakeEverything
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| posted on 15/3/09 at 09:19 PM |
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No probs Mark.
Ive always been told to get the best battery you can afford. I would put a heavy duty battery in to avoid early replacement!!
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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daviep
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| posted on 15/3/09 at 09:38 PM |
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quote:
Originally posted by MakeEverything
Yes.
The alternator puts out a DC waveform which is very square, which is what causes the "Flivker" effect. Particularly with LED's.
Bulbs might not notice as much, as they would dim and get brighter.
Sorry to hijack but can you explain this phenomenon to me in a bit more detail? I've always been under the impression there was no waveform from
a DC supply.
Cheers
Davie
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Ninehigh
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| posted on 15/3/09 at 10:14 PM |
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I'm guessing it's because the engine doesn't run perfectly smoothly and there's a small difference in rpm, plus the alternator
only produces electricity as whatever part turns passes the bushes. I suppose the real difference is negligable but I was told to fit a voltage
regulator before leds because the constant variation in voltage can blow them. Apparently they're very sensitive to things like that
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BenB
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| posted on 15/3/09 at 10:16 PM |
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I think what is being eluded to is the fact that the alternator puts out a dirty signal and it's normally the "capacitance" of the
battery which smooths out this slightly square signal into a nice smooth voltage. If you have a dead battery you don't get this smoothing.
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minitici
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| posted on 15/3/09 at 10:28 PM |
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Perhaps I have a peculiar persistence of vision - but I find all LED car lights a bit odd. They seem to 'dance' all over the place &
particularly when looking in the rear view mirror.
Is it just me?
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Meeerrrk
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| posted on 15/3/09 at 10:31 PM |
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i know exactly what you mean.
if you look straight at them; they seem fine. but when in your peripheral vision, they seem to act strange indeed. maybe they are magic and know when
your not looking at them and do funny things!!
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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minitici
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| posted on 15/3/09 at 10:37 PM |
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quote:
Originally posted by Meeerrrk
i know exactly what you mean.
if you look straight at them; they seem fine. but when in your peripheral vision, they seem to act strange indeed. maybe they are magic and know when
your not looking at them and do funny things!!
That must be it 
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prawnabie
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| posted on 15/3/09 at 11:16 PM |
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Ive always thought it was due to the alternator not running at the same speed throughout 1 revolution. You will get a number of "fast"
spots where the spark is occuring - newer cars combat this by a racheting pulley on the alternator?
Shaun
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davidwag
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| posted on 16/3/09 at 08:43 AM |
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Hi,
An alternator produces a three phase alternating current which is then rectified to produce a DC waveform, if you look at the waveform carefully with
a scope you can still see the pulses from each of the three phases on top of the DC. As has been said above the battery acts as a smoothing
capacitor.
David
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mangogrooveworkshop
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| posted on 16/3/09 at 10:03 AM |
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quote:
Originally posted by davidwag
Hi,
An alternator produces a three phase alternating current which is then rectified to produce a DC waveform, if you look at the waveform carefully with
a scope you can still see the pulses from each of the three phases on top of the DC. As has been said above the battery acts as a smoothing
capacitor.
David
http://en.wikipedia.org/wiki/Diode_bridge
yes the battery is a huge capacitor used to smooth the ripple
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Meeerrrk
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| posted on 16/3/09 at 07:10 PM |
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thanks for all the comments.
now, i replaced the battery on the car, starts and even runs much better
BUT the flashing led light was still present!
Now im thinking one of two things:
1) my side light circuit had only LEDs...led rear lights, LED number plate light, LED side lights. maybe the circuit doesnt have enough pull, the
lamps normally dim and brighten slightly (as said above) but with just leds there is no "dampening" there for fluctuation?
2) my rectifier is going tits up
any ideas on the above?
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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Meeerrrk
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| posted on 16/3/09 at 09:31 PM |
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doing some reading on regulator/rectifiers i wonder if ive cooked mine by running the car with such a flat battery, would that make sense?
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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David Jenkins
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| posted on 16/3/09 at 09:44 PM |
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The battery does act like a regulator (a bit) - not only does it smooth out the power, but it will 'absorb' high voltages (plain english
version!).
You can blow electrical stuff by running an engine without a battery... not sure what effect a knackered battery would have.
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Ninehigh
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| posted on 16/3/09 at 09:49 PM |
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quote:
Originally posted by David Jenkins
You can blow electrical stuff by running an engine without a battery... not sure what effect a knackered battery would have.
That's going to have to go in the "you learn something every day" list for today
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David Jenkins
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| posted on 16/3/09 at 09:56 PM |
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Glad to be of service!
Here's a naff american website - but it does explain what I was saying...
LINKY
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02GF74
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| posted on 16/3/09 at 11:06 PM |
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quote:
Originally posted by Meeerrrk
thanks for all the comments.
BUT the flashing led light was still present!
Now im thinking one of two things:
What exactly do you mean by flashing? Can you definitely see the LED go out? or does it pulsate i..e is on but gets brighter?
Also is the "flash"rate constant?
Does the flash rate change as you rev the engine?
Do they flash when engine is not running?
Dp all bulbs flash or just some?
Does flashing occur when headlamps are on?
1) my side light circuit had only LEDs...led rear lights, LED number plate light, LED side lights. maybe the circuit doesnt have enough pull, the
lamps normally dim and brighten slightly (as said above) but with just leds there is no "dampening" there for fluctuation?
Bulbs emit light by heating up a fairly large piece of metal; it takes time hence rapid power fluctuations will not be noticed. The
response time for a LED is very much less so you will see power fluctuations. The battery should supply more or less constant power. If the reulator
was not doing its job, you'd get voltage spikes that would very likley kill the LEDs.
2) my rectifier is going tits up
Do you have voltmeter to measure battery voltage when engine is running? Have you replaced alternator lamp with a LED bulb? If so, did
you fit a drop resistor to increase current draw?
any ideas on the above?
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Meeerrrk
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| posted on 17/3/09 at 06:54 PM |
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please see my reply below :
Q:What exactly do you mean by flashing? Can you definitely see the LED go out? or does it pulsate i..e is on but gets brighter?
A:they don’t go out, just get duller then brighter. It seems to be “in tune” with the fluctuation in engine idle speed (I guess its about 100rpm?)
Q:Also is the "flash"rate constant?
A: Answered in the above, with variaition in idle speed
Q: Does the flash rate change as you rev the engine?
A:When the engine is revved they seem to be ok but as the revs fall they seem to dim slightly
Q: Do they flash when engine is not running?
A:No, they are fine
Q: Dp all bulbs flash or just some?
A:Its just the led ones, but it is slightly visible as a dimming/brightening of the filament bulbs on the side light circuit (I’ve now fitted front
side lights and number plate lights as filament)
Q: Does flashing occur when headlamps are on?
A: No, it stops when the headlights are on, also stops when the rad fan kicks in (IE when more load is being demanded?!)
1) my side light circuit had only LEDs...led rear lights, LED number plate light, LED side lights. maybe the circuit doesnt have enough pull, the
lamps normally dim and brighten slightly (as said above) but with just leds there is no "dampening" there for fluctuation?
Q: Bulbs emit light by heating up a fairly large piece of metal; it takes time hence rapid power fluctuations will not be noticed. The response time
for a LED is very much less so you will see power fluctuations. The battery should supply more or less constant power. If the reulator was not doing
its job, you'd get voltage spikes that would very likley kill the LEDs.
A: I agree, but these LEDs are rated for 12v and 24v applications (10v-30v rated)
2) my rectifier is going tits up
Q: Do you have voltmeter to measure battery voltage when engine is running? Have you replaced alternator lamp with a LED bulb? If so, did you fit a
drop resistor to increase current draw?
A: I have checked voltage at the battery with the engine running, it fluctuates by about .75 volt which sounds too much. No I haven’t touched the
alternator lamp!
[Edited on 17/3/09 by Meeerrrk]
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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Meeerrrk
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| posted on 17/3/09 at 07:26 PM |
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tonight i have dug a little deeper. As standard the fireblade which my engine & electrics (wiring circuits) are out of had LED rear side/stop
lamps. The circuit for the brake light has a resistor in it, i have plugged this in but it doesnt seem to make any difference. But i then plugged a
resistor (the type for slowing flash rates down on led indicator applictions) across the side light line and it stopped the flashing. Problem being
the resistor got very hot very quickly!
So this says to me (im not electronics biased in the slightest!) that the circuit needs a bigger "pull" to stablise it? Which ties in with
the issue going away when the headlights are on or the fan kicks in
Is this a sign of the regulator/rectifier failing?
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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Ninehigh
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| posted on 18/3/09 at 10:37 AM |
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Sounds like standard electronics above my level of knowledge to me. Not sure what a rectifier does but I persume that it's supposed to stop the
flucuation in which case yeah it probably is, or it's unable to handle the speed of the fluctuation
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Meeerrrk
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| posted on 21/3/09 at 08:04 PM |
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changed the reg, and it wasnt the issue.
i did get to the bottom of it though, all sorted now
For Sale : 2008 Aries/Stuart Taylor Motorsport Locoblade (954 Blade)
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02GF74
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| posted on 22/3/09 at 10:38 PM |
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quote:
Originally posted by Meeerrrk
changed the reg, and it wasnt the issue.
i did get to the bottom of it though, all sorted now
and so what was it - bad earth?
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