ac to dc

twhitehousescat

Heedtheadvice wrote: »

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

my first (origional post)

"coil rewound and is capable of 6v at tickover rising to about 12v at full revs ALTERNATING CURRANT , a RG 6/12 ac regulator has been fitted , this as much the same as a zenner diode would be on a DC circuit, and basically "clamps" the voltage at a max of 6v AC

I now have a steady 6v ac , that does not increase with revs"

forgotmyname

You can get AC LED's though.... They are usually polarity sensitive when on DC. But you can get some that work either way around. The same bulbs will often work on AC also.

Its OK having 6V or 12V for that matter but if its 100ma max output then your not going to get many lights.....So how many amps can you get from your system now?

Whats that zener rate for before it glows brighter than the lights for that split second?

Heedtheadvice

^^^ Yes you did post that info about the generator output and the regulator.
I miss the point you make though, perhaps you could clarify?
My suggestion is based upon the 'constant' 6v ac resulting from the regulator output.

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

@that.

Of course there are much smaller physically sized capacitors (electrolytics) but they do not have the same rugged characteristics. Not sure if rugged lower voltage ones are generally available though the whole circuit could be enclosed in a box and potted to make it withstand the environment better, whether the OP could accept that.....probably yes but the ones I indicated come ready with spade terminals for easy construction.


Your point about the use of a battery, I agree with. A gel lead acid battery could be a great addition. It would increase the overall size of the unit and would be maybe more complex to provide electronically. As you have pointed out (and I mentioned earlier too) there are ways to achieve it. A schottky diode bridge could possibly produce enough dc charging voltage for a 6v type but woukd need a bit more consideration or the dc/dc convertors you mention.

maleman

If you want to keep it simple, just use a couple of bright LED's back to back plus a suitable series resistor. The value of resistor depends on LED characteristics, but trial and error works. Start high and reduce resistor value. I use them as a back light on my bicycle the AC generator putting out a totally unregulated supply that used to always blow bulbs. No flicker at any speed and been working for 20 odd years. Also very cheap

twhitehousescat

is there such a thing as an AC smoothing capacitor ? , a unit with 2 wires that will go across the load (steady voltage) and reduce the pulses caused by the simplistic magnet / coil generator ?

if so , what do you call this , and a link from farnell would be great , working voltage 6v ac

Heedtheadvice

is there such a thing as an AC smoothing capacitor

, well sort of but your terminology suggests it is for smoothing out AC......



I suspect what you are meaning by the 'pulses' are the two halves of the AC waveform, that is the positive half and the negative half of the cycle as would be output from your generator?


In that case No! The capacitor connected across the generated voltage would conduct and probably short circuit the generator output.....for a time!!


The smoothing capacitors you refer to are for rectified AC i.e. the resulting varying DC voltage - with the superimposed ripple from the AC source as would be produced by a diode or diodes in various configurations (such as the bridge rectifier as described earlier). Have a look at the diagrams at https://www.dummies.com/programming/electronics/diy-projects/how-rectifier-circuits-work-in-electronics/
Your generator produces a voltage equivalent to the AC voltage (depicted as a voltage against time sinewave) on the LHS and the 'lumpy' voltage across the + and - terminals "Output" on the RHS of the diagrams is the DC with lots of ripple on it i.e the AC rectified by the diode(s). The smoothing capacitor in this case would be connected between + and - to reduce or remove that ripple to make the DC voltage smooth and be approx. or approach Vmax. [ that is as the circuit I described in a previous post]


That capacitor I referred to in that earlier post (the CA05820) is being used exactly for that purpose - even though it is manufactured as a motor start/run capacitor. The physical nature of it makes it good for use in the vibrating nature of a moped!


You can get identically electrically rated capacitors (capacitance) in lower voltage ratings and a 16 or 25v rating would be suitable...but they are not strong physically and are generally designed for PCB mounting as part of a power supply or battery charger etc.! (Others are available but not as common)


If you really want one p.m. me and I'll send you one ( and a diode) for free to experiment with on your moped but I do not advise you use it as a final solution on your moped without extra physical support!!!

forgotmyname

twhitehousescat wrote: »

is there such a thing as an ac smoothing capacitor ? , a unit with 2 wires that will go across the load (steady voltage) and reduce the pulses caused by the simplistic magnet / coil generator ?

If so , what do you call this , and a link from farnell would be great , working voltage 6v ac

yes..............

But the main question you wont answer is whats the output capacity of your generator? And what losses have you got in regulating that output down to 6v?

From the figures others have posted, it maybe a case of you put the lights on and there wont be enough power to provide a spark.

You have your regulator, you have a rectifier? if not fit one and then add as many bulbs as you want until the engine wont run. Flickers add a cap or 20.

Heedtheadvice

Well, twhitehousecat, you said your brain was fading, what about the rest of you ? Are you taking up any of the suggestions?

that

twhitehousescat wrote: »

I now have a steady 6v ac , that does not increase with revs"

ok, so why not one shottkey and a normal diode to isolate that circuit a bit, loose .3+.7v (possibly have to play around a bit) and put a cap across the output. Personally would choose 220uf to 1000uf, but without knowing how smooth it will make it and how much drain the led circuit is, it is a guess, and should to stop the pulse dc, ending up with usb charging voltage - 5v. put on a battery powered cycle lamp

To be honest, I would have chosen 12v rather than 6v.

twhitehousescat

just to close this thread

I found a company that could supply 2 x bulbs , led type @ 6v and capable of accepting AC

I am using those along with a rg6 ac regulator , there is very slight "pulsing" at a low tickover , quickly disappears when riding

due to the low currant being used the lights have same brightness at tickover as they do at full revs




as I mentioned previously , on those bikes its a balancing act , if one bulb blows , the other glows very brightly , then fails , it was getting hard to locate the bulbs and they were becoming expensive

the upgrade to led cost about £35 for the ac regulator and £15 for the leds

if I sell the bike , they will be removed and used on next project