ac to dc

forgotmyname

A standard brake light bulb wont flash anymore than the current headlight bulb.

If it flashes add a capacitor simple, just choose the smallest possible so the brake light does not stay on after you release the brakes.

You really do seem to be making a mountain out of a molehill with this.

twhitehousescat

do electrolitic capacitors work on AC ?


I did consider using pure AC , however 2 things stopped me ,

Capacitor :

my readings where

"A capacitor is two conductors (usually plates) separated by an insulator. The more surface area, and the closer together they are, the higher the capacitance. Electrolytic capacitors have a thin film rolled up in the can. This film is covered in a thin oxide layer, and the thinness of this layer is what gives electrolytic capacitors their high capacitance relative to their size.

This oxide layer is created by the chemistry of the materials in the capacitor, and the polarity of the voltage applied to each side of the film. A voltage applied in the correct direction builds and maintains the oxide layer. If the polarity is reversed, the oxide layer dissolves.

If the oxide layer dissolves, you no longer have an insulator between the two plates of the capacitor. Instead of two plates separated by an insulator, you have two plates separated by a conductor. Instead of a device that blocks DC, you have a device that conducts it. Basically, you have a wire in a can."


AC car/bike LED bulbs

although the ones above state that they can be used on AC , I contacted classic dynamo and Reg , probably the largest supplier of LED bulbs for older bikes

AC = NO , as in you may get one day out of them before they fail .

hence the reason for a simple ac to dc circit

A_Nice_Englishman

twhitehousescat wrote: »

AC car/bike LED bulbs

although the ones above state that they can be used on AC , I contacted classic dynamo and Reg , probably the largest supplier of LED bulbs for older bikes

AC = NO , as in you may get one day out of them before they fail .

hence the reason for a simple ac to dc circit

The LEDs bulbs incorporate 'a simple ac to dc circuit', presumably designed by an experienced electronics engineer. I'd expect it to work better and last longer than a home made circuit. I'd prefer to trust my life to a commercial product too. If you're using the bike on the road you'll have to declare your mods to your insurer and I doubt if they'll be impressed.

To be honest, if it was me I'd forget about LEDs and just use a normal incandescent lamp.

twhitehousescat

A_Nice_Englishman wrote: »

The LEDs bulbs incorporate 'a simple ac to dc circuit', presumably designed by an experienced electronics engineer. I'd expect it to work better and last longer than a home made circuit. I'd prefer to trust my life to a commercial product too. If you're using the bike on the road you'll have to declare your mods to your insurer and I doubt if they'll be impressed.

To be honest, if it was me I'd forget about LEDs and just use a normal incandescent lamp.

the coil is not capable of suplying an extra 21 w to feed a stop bulb , the model destined for the USA market had a much larger coil and a battery with a simple rectifier

the one for the netherlands , used a 5w h/light bulb , yes 5w! a 3 watt tail bulb and a 5 w stop bulb (no battery )

Heedtheadvice

Spam? Given the advertising......


refers to post that was after the OP's post on

• 9th Jun 19, 10:34 PM
• and immediately prior to this one.
• Reported and it has been deleted by admin

that

The problem is to get 6v, you need about 6v+2v, the 2v to power a linear voltage regulator. On top of this you will need at least 4 diodes for a bridge rectifier, two caps and 7006 (voltage regulator IC. and with 6vac (about 8v peak) you are very close, using shottkey diodes in a bridge that is

A buck converter would be more efficient, which is a switch mode psu.

Either way think you have little to play with. I would be more inclined to leave it as it is... as I am lazy.

Alt a push, would try a 4 diode bridge rectifier, capacitor, and rewire all the leds and attach it to a constant current source circuit. Probably the best option if you know electronics, and can get the parts.

Apparently a filament light bulb is about 5% efficient.

This ebay circuit apparently from 6v-30 but a 4-30 one would have been better (if there is one), not sure if I would purchase this https://www.ebay.co.uk/itm/DC-800ma-Constant-Current-LED-Drive-Driver-Power-Supply-12V-Car-battery-10W-C50/221771855009

These look more promising https://www.ebay.co.uk/itm/MP2307-Adjustable-Mini360-DC-DC-Converter-Step-Down-Buck-Voltage-Regulator-UK/231914348146

The trick is to get it working with a flashing rear light (probably illegal). For a brief moment and LED can be overdiven and produce a really bright light. Make to on/off period too long and it burns out.

Am think about bicycle lights too, but they (mostly) flash?

Personally, I think you should have a battery backed up one, because once that engine no longer revs sufficient enough the light will die. Much easier to convert to usb voltage and use a bicycle one like here https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=rechageable+light+bike&_sacat=0

Heedtheadvice

So assuming your generator output is the same as the Netherlands model....???

the one for the netherlands , used a 5w h/light bulb , yes 5w! a 3 watt tail bulb and a 5 w stop bulb (no battery )

It can supply 13 watts.
That is approx 2 amps at 6v.


EDIT Added: Next assumption (I am unclear from what has been written!) the Led light will work of DC 6v !!


Further assumption the voltage you have measured ( 6v) is approximately 6v rms. The waveform and the voltmeter may make that untrue but for this purpose is probably accurate enough. (A bit of numerical rounding in this below that is insignificant)


That assume 6v rms will give you a peak ac voltage of 6*1.414 , say 8.5v.


A standard silicon rectifier diode would drop that to 8.5-0.7 (worst case) = 7.78v
two diodes as in a full wave bridge would drop that to 7.08v peak.
So more than satisfactory to supply 6v dc.
(assume a 5w led lamp - really bright!) then a 6A bridge rectifier would do nicely such as a Multicomp MP606G or similar. It can also be constructed from four diodes or four Schottky diodes for better performance but the max voltage rating of the led would need to be confirmed as capable first if using the latter!



Add a bit of smoothing with a capacitor approx current discharging capacitor at peak is about 1 amp. between generator ac cycle peaks

To do further calculations we need to know the frequency of the generator output at tick over (worst case scenario when there is longest time between the generator's ac waveform peaks. If that is know or can be supplied than it will improve circuit accuracy).
Next assumption: tick over is 500 r.pm. and one cycle generated per rev. gives approx 10Hz and for full wave rectifier 5mS between peaks. that is the time the capacitor need to hold charge. (actually less but give a big margin)

A 10uF capacitor will do that comfortably with excess to spare.
You need to consider also capacitor type. Widely available are motor start/run capacitors and I suggest one of those such as https://cpc.farnell.com/ducati/4-16-10-15-64/capacitor-10uf-450vac-tab/dp/CA05820
This type have good physical characteristics.


If no light that is to be powered is operating (i.e. not switched on) then the capacitor will hold significant voltage even after the generator stops. That should not be a problem at such a low voltage in terms of potential shock (it act in a similar manner to a battery by storing the voltage for a while) but can still (again like a battery) create a spark if discharged rapidly such as into a short circuit. It would be advisable, if that is seen as a risk, to connect a resistor in parallel with the capacitor, say 100ohms 1 watt rated, to discharge the capacitor in a controlled manner.



Conclusion:

A standard full wave bridge rectifier feeding a motor start capacitor is all that is needed.
Be aware that, not having a battery in circuit, no power is available for lights when the engine is stopped.

forgotmyname

A capacitor will only last a day??? Have you looked inside any power supply? there will be a ton of them with many running on the AC side.

And thats on 240v AC not just 12v.

When the oxide layer dissolves.... The standard life is around 10 years.... Although some cheapies may only last 5...

Fixed a few TV power supplies by recapping them.


youtube.com/watch?v=Z6BpyslpSN8

Jump to 1:42 and look at the diagram 400v between the live and neutral rails. A standard setup.

Just dont buy cheap parts like the first one he had that blew up. Cheap fake parts or putting a 200V cap on a 240V supply.



Dont buy cheap power supplies....

that

Heedtheadvice wrote: »

A standard full wave bridge rectifier feeding a motor start capacitor is all that is needed.
Be aware that, not having a battery in circuit, no power is available for lights when the engine is stopped.

Providing he does not stop, or coast down hill, and keeps it highly revved, you could be correct

That is physically a big capacitor. No 16-20v ones?

twhitehousescat

forgotmyname wrote: »

A capacitor will only last a day??? Have you looked inside any power supply? there will be a ton of them with many running on the AC side.

And thats on 240v AC not just 12v.

When the oxide layer dissolves.... The standard life is around 10 years.... Although some cheapies may only last 5...

Fixed a few TV power supplies by recapping them.


youtube.com/watch?v=Z6BpyslpSN8

Jump to 1:42 and look at the diagram 400v between the live and neutral rails. A standard setup.

Just dont buy cheap parts like the first one he had that blew up. Cheap fake parts or putting a 200V cap on a 240V supply.



Dont buy cheap power supplies....

NO , I stated that the LED bulbs that are advertised as being dc or AC , are not sutable for AC and will work but the AC will damage them and you will be lucky to get a single day out of them before they fail