Simple LED head and tail-light circuit

tipetu

tipetu

New Member
Hi, first post here on this forum! Got my china 80cc engine mounted on the bike yesterday and I`ve already made a little nice rectifier circuit for the 6-9Vac coming from the white wire on the engine. The tiny alternator on the engine cant handle anywhere NEAR 3W, so I had to go with diodes! Anyone interested in it? I`ll post it later on together with pics and schematics + a video! I recon it would cost somewhere around 2$ to fabricate :P Stay tuned!
 
Here I connected a 12V AC transformer just to show the difference

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And this is the voltage in DC after the diode bridge rectifier and the cap

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As you can see the diode lights up just fine!

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Wrapped it up with electrical tape. It`s somewhat waterproof :P

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Here it is :

4diodesbridgerectifier.jpg


The bridge rectifier here is the key. Not even sure what kind of diodes I used. I salvaged an old wall wart. Your call..
 
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that cap is smoothing out the bumpy positive cycle the diodes create. The diodes cut out when the ac-voltage switches polarity and the cap is beeing charged when it`s positive and when the diodes cut, the cap discharges. That way the voltage is as stable as possible.

I`d say all diodes from 1N5400 to 1N5408 would do just fine. Keep in mind that we are talking about only 6-9Vac here, and 0.16W power consumption. So no worries! Just dont use zeners cause they are too damn small.
 
tipetu said:
Here it is :

4diodesbridgerectifier.jpg


The bridge rectifier here is the key. Not even sure what kind of diodes I used. I salvaged an old wall wart. Your call..
Click to expand...

I've actually been looking at doing this myself with a bridge rectifier. Unfortunately, I got the bridge rectifier and got stuck. Looking at your diagram, it seems incomplete. Is the 1 K-Ohm box there a resistor? Where does the LED(s) work into this diagram?

Oh, and what are the specs on the diode(s) you are using?
 
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Hello, yes the 1K ohm is the resistor. And you would connect the led`s at the respective + and - at the right hand in the pic. If I were you I`d wait just a little while cause I`m gonna improve it a littlebit! I`ve ordered some ned parts and will be making a new schematics in near future!
Feel free to ask if you have any questions.
 
Mine's even simpler.

Get a 3W 3AAA (4.5V) unregulated LED flashlight and solder a wire to the (-) side of the LED and a wire to the (+). Solder the (+) wire to the white wire coming out of the engine and ground the (-) wire to the part of the bike frame directly in contact with the engine. That's it.

After all, an LED is just diodes (a rectifier) anyway. I use 3W LED named Energizer Element (from Sam's Club a few years back) and it's very bright. Only draws 250mA, so it's nowhere near the 3W maximum of the magneto. Don't waste time with making circuits when you don't need to.

The LED pulses very slightly at idle, but completely smooths out and brightens with engine speed.
 
The schematic shown above is for use if you have access to both ends of the coil in the magneto.
But, in our engines, you only have access to the white wire, the other end of the coil in the magneto is grounded.
Therefore, a more accurate schematic is shown below:
1dioderectifier.jpg

Yes, since the LED is a diode, you really do not need the rectifier diode, but you still need the resistor for proper current limiting., and I would put the capacitor after the resistor.
 
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Well, that`s true. The other wire is grounded so I use the black and white wire. But again, this does not mean that you can ground the output DC to the LED`s cause then you`d be looping it with the AC-generator`s ground. Hard to describe...
 
I think I understand what you are saying... You want to keep the AC ground and the DC grounds separate, but once you have rectified the output of the magneto, then everything from that point is DC, and grounds can be shared.
 
rohmell said:
I think I understand what you are saying... You want to keep the AC ground and the DC grounds separate, but once you have rectified the output of the magneto, then everything from that point is DC, and grounds can be shared.
Click to expand...

That`s what I thought too, but it shorted and didnt work?
 
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