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Old 06-01-09, 02:51 PM   #21
xXBADGERXx
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Default Re: Why do my lights get brighter when I rev the engine?

Well after reading all of the above I had a similar thing with my Varadero , it would get brighter when on the throttle . It turned out I had a dodgy Rectifier , and to add insult to injury it was knackering the battery . I managed to remove the Rectifier (had a Ducati logo on it as well despite being a Honda bike) and replaced it with another one sourced from CJ Balls at the right price . Battery went on a maximiser for a day and it sorted the problem out for me . My old Rectifier started to smell like fish as well for some reason . Not saying this is your problem but could also be a nod in the right direction .
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Old 06-01-09, 03:11 PM   #22
embee
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Default Re: Why do my lights get brighter when I rev the engine?

Alternator output is highly non-linear with speed. These curves are for car type machines but the curves will be a similar shape for a bike one.



Typically you'll get little appreciable output power at low rpm. Power is the product of volts and amps. You can draw off power for lights etc but if it exceeds what the alternator can produce at that speed then the voltage will start to drop to the point where you are relying on the battery to supply the balance of the current draw, typically down at basic battery volts of around 12V.

When you rev the engine the alternator output picks up quickly to the point where it can deliver enough current for the load (lights etc) and also start to recharge the battery, at which the regulator will control the voltage in the right region for charging, somewhere around 14V.

lamp resistance increases with temperature so they are not linear either (power vs voltage) but basically as the voltage picks up the current increases and they get brighter.

You don't notice this effect so much on cars because a) the battery has a lot more capability to provide current to supplement alternator output, b) the alternator output is generally just about sufficient at idle to cope with basic demand (pulley ratio etc), c) usually the idle speed is increased slightly by the engine management when electrical demand is applied to avoid flat batteries in traffic. Bikes are a lot more basic.
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Last edited by embee; 06-01-09 at 03:15 PM.
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Old 06-01-09, 04:15 PM   #23
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Default Re: Why do my lights get brighter when I rev the engine?

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Originally Posted by Baph View Post
Current is actually a flow rate. Nothing more. Think about tidal currents etc. There's a reason they share the same descriptive name. With a tidal current, you have the same volume of water, moving at a different vector (direction and/or speed).

When the engine rev's higher, the alternator puts out a higher voltage, at a higher flow (current).

The regulator then ensures that this increased voltage is reduced to 12v (approx). The current generally isn't reduced by the regulator.

By upgrading bulbs (eg, Osram Nightbreakers as stated), the bulbs are designed to glow brighter. This is accomplished by drawing more current due to lowered resistance in the coil. If the alternator isn't putting out maximum current (for the bulbs) they will be dimmer than they can potentially be. When the current raises (by revving the engine), naturally the bulbs get brighter.

In my case, when I honk the horn, some of that flow (current) is diverted away from the bulbs to the horns. Thus making my bulbs dim. I also have uprated bulbs FWIW.

Further to this, my bulbs get brighter when I rev the engine (I'm talking only the first few thousand RPM, then it's constant). I have tested the rectifier, and alternator. Both are fine the last time I tested them (after approx a year running with this setup).
Sorry this is complete cobblers.
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Old 06-01-09, 04:20 PM   #24
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Default Re: Why do my lights get brighter when I rev the engine?

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Was that the only reason you replaced it? Was it expensive?

Thanks!
Yes, I couldn't afford to risk failing the MOT (and the way it was behaving was a fail within the 'letter of the law') as I needed the bike that week. It wasn't pricey, £20 for a second hand unit, IIRC.

Badger, PMSL @ your finding the Ducati component on your Honda. I know other companies often provide electrics, but buying a Honda and finding it had Ducati electronics on it?
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Old 06-01-09, 04:50 PM   #25
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Default Re: Why do my lights get brighter when I rev the engine?

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Originally Posted by shifter View Post
It's not a good thing. the regulator does exactly that, regulates the voltage. If your lights get brighter with the throttle then it's on its way out and will probably take the battery with it.
Oooooohhh! Hold on - that's a bit extreme. Without some further checking your diagnosis of doom is a bit early.

The alternator is on the end of the crankshaft, so when you rev the engine it turns faster, this induces a higher voltage in the windings, (a test of the alternator is to see how much voltage it produces; at 5000 rpm each phase should give about 70VAC), the current is regulated, to a nominal 12V, (actually up to 14.7 is acceptable), and rectified from AC to DC, by the regulator-rectifier, (you guessed that bit didn't you?).
At tickover the charging voltage may not rise the the level of the regulator limit, as such the electrical system will be powered by the battery - and importantly the voltage that it can supply, if that's less than the regulator limit revving the engine will cause the charge voltage to rise and the lights to get a bit brighter.
This very common, particualrly so if the battery is a bit low or not in the first flush of youth, unless you have a specific electrical problem, flat battery, overcharging, blowing bulbs etc, it's unlikely there is anything wrong.
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Old 06-01-09, 05:05 PM   #26
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Default Re: Why do my lights get brighter when I rev the engine?

I agree totaly, my statement was perhaps a bit sweeping. I did say later I'd test it on the meter. the figures you quote are spot on as well
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Old 06-01-09, 05:08 PM   #27
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Default Re: Why do my lights get brighter when I rev the engine?

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Originally Posted by ophic View Post
Sorry this is complete cobblers.
are going to try and explain why?

Quote:
Originally Posted by Sid Squid View Post
Oooooohhh! Hold on - that's a bit extreme. Without some further checking your diagnosis of doom is a bit early.

The alternator is on the end of the crankshaft, so when you rev the engine it turns faster, this induces a higher voltage in the windings, (a test of the alternator is to see how much voltage it produces; at 5000 rpm each phase should give about 70VAC), the current is regulated, to a nominal 12V, (actually up to 14.7 is acceptable), and rectified from AC to DC, by the regulator-rectifier, (you guessed that bit didn't you?).
At tickover the charging voltage may not rise the the level of the regulator limit, as such the electrical system will be powered by the battery - and importantly the voltage that it can supply, if that's less than the regulator limit revving the engine will cause the charge voltage to rise and the lights to get a bit brighter.
This very common, particualrly so if the battery is a bit low or not in the first flush of youth, unless you have a specific electrical problem, flat battery, overcharging, blowing bulbs etc, it's unlikely there is anything wrong.
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Old 06-01-09, 05:19 PM   #28
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Default Re: Why do my lights get brighter when I rev the engine?

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I agree totaly, my statement was perhaps a bit sweeping. I did say later I'd test it on the meter. the figures you quote are spot on as well
Of course they are - to sidetrack into the Top Gear Game thread with regards to The Squiddler.

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Old 06-01-09, 05:25 PM   #29
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Default Re: Why do my lights get brighter when I rev the engine?

I'd tend to go with sid's story.
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Old 06-01-09, 05:32 PM   #30
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Default Re: Why do my lights get brighter when I rev the engine?

Quote:
Originally Posted by chris8886 View Post
are going to try and explain why?
Thor already did, pretty much.

Quote:
Originally Posted by thor View Post
Current is the voltage divided by the resistance of the system. It's not a tap. Given that reving doesn't reduce the load on the electrical system, then it must be due to an extra voltage being produced by the alternator.
V=IR
voltage (in volts) = current (in amps) * resistance (in ohms)

To elaborate, unless R changes wildly (which it doesn't), V is proportional to I, in any part of the circuit.

So:

Quote:
Originally Posted by baph
When the engine rev's higher, the alternator puts out a higher voltage, at a higher flow (current).
that bit is correct. Higher voltage, higher current.

Quote:
Originally Posted by baph
The regulator then ensures that this increased voltage is reduced to 12v (approx). The current generally isn't reduced by the regulator.
that bit aint. Current in the circuit will change according to the change in voltage. The regulator regulates voltage and therefore it regulates current too.

Quote:
Originally Posted by baph
By upgrading bulbs (eg, Osram Nightbreakers as stated), the bulbs are designed to glow brighter. This is accomplished by drawing more current due to lowered resistance in the coil. If the alternator isn't putting out maximum current (for the bulbs) they will be dimmer than they can potentially be. When the current raises (by revving the engine), naturally the bulbs get brighter.
that aint right either. Osram Nightbreakers are rated the same as normal bulbs - 60W. Same voltage, therefore same current, same power dissipated, more light. They are more efficient.

Can we have another torque vs power thread now?
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