Secondary side? I thought we were discussing the source on the other side and how to prevent the abrupt stop in current flow from the source.
The diode there does work like you said.

Well, as for this, I suggest you check out "snubbers". IMO, connecting a cap across a relay/switch/mosfet is considered a better than connecting it across the source.

Because if it is across the relay, it has to charge from ground to the source voltage level. But, if it is across the source, it has to charge from the source voltage level to the spike voltage level. In the first case, time needed is more, hence current flows for a longer duration after the switch is opened. If we want the the current to flow for the same time in the second case too, a much larger cap is needed. So, your method will work too, but it needs a much larger cap than in my method.

I do not doubt your knowledge buddy! The doubt was not on PWM circuit but on how to prevent the "inductive kick". As you say let us stop right here. Else, people will doubt which forum they are on!

I do know that much! Yeah, there will be no arcing in a MOSFET, but it can heat up and get damaged.

Consider this, the stator is a large inductor, the primary capacitor is also large enough to buffer some energy. Now the PWM frequency is in the KHz or MHz range. Thus the stator capacitor combo doesn't even see the switching. There will be no inductive kick, since the capacitor is going to absorb the current with just a small voltage rise. The stator will just supply the average current draw through the switch and secondary inductor. (The instantaneous on current on the switch can be a lot higher than the primary current, it will be equal to the secondary current draw.)

So the primary voltage will rise to the point where it matches the induced amount of energy determined by the RPM. So if in that case the voltage on the primary capacitor does rise too high, you could have a small shunt resistor switched on to dump just enough energy to keep the voltage from rising high enough to cause issues with the voltage rating of the stator/capacitor, if needed.

l guess I must not have been expressing myself correctly on this one. It's a pretty complex dynamic system that cannot be understood just by looking at the steady state, because of the presence of inductors and capacitors. (Nasty combination if you have to do the math.)

Anyway, now i'll really get out of it, before they tell us to go to an electronics forum and ban us.

Maybe more relevant is a schematic and discussion of the shunt regulator? That should be useful and more relevant.

Ok. your last post was pretty clear! Maybe it will work that way.

Here is the circuit diagram. Any suggestions are welcome.

^^ Do you have an explanation on how it works? From what I can see it shorts the coil of the stator when the voltage rises above a certain preset point by driving the thryristors into conduction. Am I right?

Yes you are correct. It shunts the stator coil when the voltage rises above a certain limit.

Alright, so on to the mods you've done to the stator. I'm guessing rewound the coil with thicker wire and perhaps some more turns to keep the voltage up when the load is higher? If so, does all that fit into a standard stator armature without any modifications? And how does it affect the engine at idle speed, I would imagine it will load the engine more.

There are 2 separate coils in the original stator - one for the battery and one for the lighting, apart from the ignition coil. This lighting coil is grounded and hence we can not directly use a rectifier without suffering from 50% loss. So, if I have to unground that coil I may as well rewind it. The lighting coil was 64 feet long and wound around 4 poles. Wire used was 21 AWG. The battery coil was around 48 feet long and wound around 3 poles. The wire used was 24 AWG. I used 20 AWG wire around all the 7 poles. Length of wire I could wound was approx 70 feet.

About the engine load, I do not feel any difference at all. Anyways 100W=0.13hp, to put things into perspective.

At 2.5k rpm and above, my coil maintains 13.8V with a 60W bulb switched ON. So, I guess, it can handle a 100/90 set up. What do you say?

I am aware of the W vs HP comparison, that's why I asked about idle RPM the engine produces the least amount of power there. But I suppose that can easily be compensated by the idle adjustment. (A heavier loaded stator will cause some greater amount of rotation resistance.) Take for example a car, if you switch on the headlights while idling you can actually hear a slight difference. So the question actually is did you have to set the idle higher to compensate for the extra load? (I kinda know the answer, the extra bit of load is almost insignificant, but it's always good to clarify. Perhaps this all this discussion will be useful to someone.)

As for the 100/90 setup, one way to find out: "Try it." Chances are that it'll pull it along quite nicely.
For me, I bought a bike that runs on full DC anyway. The only interesting bit for me could be to upgrade a few bits after a year or two. (Stuff like HIDs and maybe a more sophisticated regulator.)

Nope, I haven't touched the Idle Screw for a long time! And about the car, come to think of it, I did actually notice it, but never linked the 2 topics together!


Yeah I will try it out in a few days.

That is nice. Which bike do you have?

And one thing - I have set the regulator to 13.8V. Over the internet, I have found various values ranging from 13.8V to 14.6V. What is your take? I certainly do not need a premature battery change!

I own a 220DTSi, which is quite brilliant as far as stock lighting goes.

And battery charging voltage, it depends on the battery and how much you ride (long distance or not), but probably in the 14V range. Check Lead-acid battery - Wikipedia, the free encyclopedia.
Yea, I do like wikipedia. I doesn't always have correct info, but mostly it's good for these things. As such I don't think you'll face many issues, just that you may end up with a discharged battery. If possible check on a stock bike/regulator, add your own thoughts and adjust accordingly.

My P150 showed 13.8V. Another P180 UG3 showed 14.2V. And let us not talk of other manufacturers! The Bajaj service manual shows 14-15V as the permissible range. Apache FI manual shows permissible range as 13-15V! Hence was the confusion. I think I will stick to 13.8V only! BTW, do you know what your bike shows?

I don't know the voltage for my bike, generally don't tinker much with these things. Even though I have the interest. To me this discussion is as much about learning as it is about sharing what I know about batteries (chemistry) and electronics. I'm still a rookie biker and gearhead. My fields are actually chemistry and software engineering, and I have interests in engine technology, bikes and all that.

Great Thread!

Looking forward to the know more about Abhijeet's Project

My 2 Paise:
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I have CBZ Classic 1999 Model, which came with a 5A Regulator and couldn't do more that 35w bulb up front.
All CBZ owner will know how pathetic CBZ's headlight was. Anyways, tried fitting lots of headlight combinations but nothing worked out, as the current gets distributed.

After few years when i was in Mysore in 2005, read on xBhp and heard from various mechanics that i need to increases the number of turns on the motor. Which i was not willing to, as i dint had time to do it myself and couldn't trust anyone else.

So what i did was, just removed the factory fitted Rectifier, check for the voltage and current generated, fitted Pulsar's 7 Amp Rectifier along with a bigger 7 Amp Battery. And now i am using a 65w Philips bulb upfront with a switch to put it on Rectifier or directly on the motor output, and trust me guys having a 65w Philips inside a projection lamp is a killer

I forgot to snap some pictures when i went home last month, will share them when i go next time.

Point is, i was able to support higher wattage headlamps without going thru the trouble. And that pulsar 7A Rectifier dint cost much either.

But in case i need to put 2 65w Bulbs; which i initially planned to; i would definitely need something on the lines of Abhijeet's project.

Great Thead! Keep up the good work :-)

That is interesting. But, your headlight was originally running on AC and not through the battery. So, after your regulator mod, you ran it completely from the battery? What happened to the AC from the stator coil? You used it somewhere?

HI ALL
Although most stuff spoken here is way above my understanding of electronics.
I am planning on converting my headlight to dc on my discover 125.
here is my plan.
The battery is due for replacement,so planning on buying a bigger battery probably 7 ah .And to increase charging rate by re routing the power going to the headlight to the battery to boost the rate of charge .