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Old 28th February 2019, 11:05   #1
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Default Why do 2-wheeler lights dim / brighten depending on accelerator input?

I apologize in advance for contributing to yet another thread with a "question mark" but I guess this should fly since this is a valid technical question.

I'm putting it here in the riding safe segment because I feel that the bike safety is overall, being affected by this longstanding issue - bikes and scooter headlamps dim to almost nothing when the revs are low, and irritatingly enough blast a high beam light when the revs are rising, affecting oncoming traffic and being extremely distracting at the same time in dark roads, as if there aren't enough reasons for bikes being a menace in Bangalore roads.

I'm quite well-versed in the technical aspects, off the top of my head its an alternator issue (alternator charging capacity/quality being too low) or it could be a bad grounding.

Question is, what can be done to eliminate this problem, or are other motorists not bothered by this issue at all? I feel this is a severe quality issue and simulate high/low beam switching which can be very disorienting and misleading in dark areas.
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Old 28th February 2019, 11:56   #2
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

If the headlights are routed through the battery, there would not be such dimming issues.
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Old 28th February 2019, 12:08   #3
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

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Originally Posted by starter View Post
If the headlights are routed through the battery, there would not be such dimming issues.
So what is stopping the manufacturers from doing that? My bike knowledge is not great as I hate 2 wheelers, so you may have to be more detailed.
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Old 28th February 2019, 12:36   #4
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

The lights of two wheelers with AC current (that depends on accelerator input) absolutely suck, and in my opinion, have no reason except that life is cheap in India. When a biker reduces speed because of some obstacle/animal etc, that's the time he needs most illumination, and the bike reduces the light output because of the sudden low revs.

The solution is to make it a DC bike by connecting headlight directly to battery (any two wheeler electrician can do this). Now you have to hope that the battery is getting sufficiently charged by the alternator, but it removes the problem of light depending on accelerator input.

Or, upgrade to better motorcycle with DC lighting. Life is worth more than the cost of upgrading motorcycle.
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Old 28th February 2019, 12:41   #5
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

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Originally Posted by dark.knight View Post
.
Re: Why do bike/scooter lights dim/brighten depending on acceleration input?
Well, the idle voltage and voltage at high rpms vary from 12.xx to 14.xx. Hence you get better current at higher rpms.
Quote:
Question is, what can be done to eliminate this problem, or are other motorists not bothered by this issue at all?
Well, most halogen bulbs do respond similarly to voltage change. So, what you can do is maybe switch to LED's.
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Old 28th February 2019, 12:50   #6
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

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Originally Posted by dark.knight View Post
So what is stopping the manufacturers from doing that? My bike knowledge is not great as I hate 2 wheelers, so you may have to be more detailed.
I think the reason behind this is that the vehicle will need a bigger battery and they have to hike the prices to compensate and they have to keep their prices competitive. So, they do not offer this feature in lower segment models.

One more reason as per my limited experience is that the HL Bulbs dont last longer on fluctuating ( Alternating) current which translates into profit for the companies (their labour charges for replacement are appx 70% of cost of the bulb). OEM bulb of same wattage retails at half price than these ASC guys charge. So its a win-win condition for both the ASC and the Company.

Many middle segment two wheelers have battery powered headlamps but that is offerred more due to segment standards than for the sake of the customers.

Last edited by Ry_der : 28th February 2019 at 12:51.
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Old 28th February 2019, 15:22   #7
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Default re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

Many conventional bikes with low powered batteries run headlamps with the electrical output of Alternator. When you accelerate, the beam of headlight brightens up and when u decelerate the beam of headlight becomes dim, this happens because power produced by engine is less than necessary to glow the halogen bulb at its full capacity.
In this case the headlamp uses fuel as primary energy source.

Some of the modern bikes having high powered battery rating such as 14Ah uses direct electric output from battery. In this case the brightness of the beam remains constant, and the bulb glows at its full capacity. Even when the engine is not running, headlamps can be switched ON.
And the alternator charges the battery while headlamp is using energy from battery (when engine runs).

And in both the cases fuel is used to power the headlamp directly or indirectly.

Source
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Old 1st March 2019, 07:59   #8
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Default Re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

Used to be the case in the Padminis & Ambassadors with dynamos too . You could clearly see the headlights & even instrument cluster lights brighten up as you revved.
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Old 1st March 2019, 10:02   #9
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Default Re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

Oddly enough, I still see this ocurring in my Zen (Carburetted, 1999) and my relative's Alto (2nd gen). It used to happen with both the 55/60 kit as well as the 90/100 kit(with relays), and the effect is seen in the instrument cluster as well.

As BHPians have already pointed out, it's due to the alternator. But is it an issue that can be rectified in my cars? Not sure yet. Hoping for some answers that suit a car.
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Old 1st March 2019, 12:23   #10
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Default Re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

This is what a regular DC(Ignition, Lighting, the works!) powered motorcycles stator looks like;

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As you can see there are 18 Poles solely to generate current.

In comparison, this is what a commuter motorcycles stator looks like;

Why do 2-wheeler lights dim / brighten depending on accelerator input?-ctstator.jpg

This is what a commuter motorcycles stator looks like, and among the 4 poles you see one is the Primary Ignition Coil which is present as unlike the DC Ignition system, power to fire is drawn from the stator, then you have 3 poles remaining, which are again split between charging the battery and powering the headlight.

So with an individual coil for powering the headlight you can presume why the headlight is much affected by the RPM.

Now the questions:

Why not tap 12v DC to power the Headlight?:

This is not hard at all, simply tap an ignition switch controlled 12v source.

But back-up a bit and you'll see me mention that there are only few poles to power the battery, which would mean that even if you tap 12v DC into the headlight it won't make a difference after the first couple of minutes of riding at lower RPM's as not only would your headlight start to flicker but your remaining electricals would start to under-perform as well.

Why not use a bigger battery?

Again, since there are limited poles to charge the battery and the RR unit is also not equipped to charge a bigger battery, the charge vs drain rate would not be in your favor and you'll only be able to use uninterrupted lighting for a marginally longer time before the headlights start to flicker and your remaining electricals start to under-perform. After all its not about the size of the battery, but the efficiency of the charging system that makes the difference, for reference the ZMA being a full DC motorcycle comes only with a 5Ah battery from 2011, the 18 Pole stator shown at the beginning is of the same motorcycle.

Why not use LED lighting?

LED's do not work well on AC current, and it is just a matter of time before they blow out.

You could tap 12v DC as mentioned before and run the LED, which is what most users do, but I'm not a fan because in the event that the LED blows when you're riding in the middle of the night in no-man's land you'd be forced to stop and be at the mercy of god knows what, and the worst part is you won't see it coming, like literally!

So should I live with crappy lighting?

Not exactly, the bulbs that come on commuter motorcycles are usually the extinct BA20D types of 35/35 rating, simply scrap it and go for a HS1/H4 conversion, a better output bulb like the Osram Rallye 45/40 and then raise your RPM until there are no more flickers, as on most commuter motorcycles the ASS sets idle way too low to prevent low FE customer complaints.

And you end up with this;

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The motorcycle on the Left is brand new and bone stock and has the High Beam firing, the motorcycle on the right is mine with the above mentioned changes, handle is turned a bit offset to avoid glare, Oh! And by the way its on Low Beam.

Cheers and Ride Safe,
A.P.

Last edited by ashwinprakas : 1st March 2019 at 12:49.
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Old 1st March 2019, 12:56   #11
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Default Re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

Quote:
Originally Posted by dark.knight View Post
Question is, what can be done to eliminate this problem, or are other motorists not bothered by this issue at all?
Sharing my experience with my Rx...

I've RDD 100/90 kit (which is extinct now) & use 60/55 bulb with the supplied rectifier. It will be hard to believe the light is not on battery. Even during idling the bulb should be 90-95% in full efficient. A slight more throttle its 100% bright

I had the same thought as why manufacturers don't do this; simple answer - cost.

Then why not route to battery; like Ashwin said, more coil winding to charge the battery - cost

Then why not bigger battery - again cost

LED? - Yes, kind of good solution as the consumption is less & gives more output. Ofcourse the worst parts being, they're extremely dangerous during rains & fog Weather conditions. Some of the high black pitch roads absorb all the white light & there by getting ineffective

But the manufacturers have to start thinking about moving away from 35/35 & start to adopt 60/55 which is the only way forward I see. And on a mass scale, I don't think it can cost more than Rs 750 per vehicle on exshowroom.
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Old 30th March 2019, 10:53   #12
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Default Re: Why do 2-wheeler lights dim / brighten depending on accelerator input?

Quote:
Originally Posted by ashwinprakas View Post
Why not tap 12v DC to power the Headlight?:

This is not hard at all, simply tap an ignition switch controlled 12v source.

But back-up a bit and you'll see me mention that there are only few poles to power the battery, which would mean that even if you tap 12v DC into the headlight it won't make a difference after the first couple of minutes of riding at lower RPM's as not only would your headlight start to flicker but your remaining electricals would start to under-perform as well.
I'm not very well versed with 2 wheeler electricals, but this seems to be the case with my Vespa. I believe the headlights are routed through the battery, since they come on with just the ignition at ON, without the engine running.
However, this does not mean that I don't get flickering lights. In fact, the backlight of the console and taillight also flicker.
There's another problem that Ashwin mentioned. My running on the scooter is low, so whenever I try to start the motor in the morning, the electric starter just doesn't do the job 7/10 times. Guess the entire electrical system starts underperforming after a while.
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