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Author Topic: Can I use this current to power my Arduino  (Read 941 times)
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I've got dirty power from the primary side of a small engine coil. I attached a 5v led with built in resistor to the primary side of the coil and ground. The led lights up and blinks with the pulse of the ignition.

On the scope I get a very quick 200 - 400 volt spike every time the coil fires. I'm new to using a scope and I'm very skeptical of my scope data. My next move was to use an opto isolator so Arduino can count the spikes. Works fine. The current goes from the primary coil wire to the + input side of the opto. The - input side of the opto is grounded back to the motor.

After the current runs through the opto isolator, can I run it into a capacitor and then a  voltage regulator to power Arduino? If so what size capacitor should I use and how should that circuit be constructed?

Thanks!

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Do the pulses only go positive or do they also go negative?
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Positive only.

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After the current runs through the opto isolator, can I run it into a capacitor and then a  voltage regulator to power Arduino? If so what size capacitor should I use and how should that circuit be constructed?

Current doesn't pass through an opto-isolator, only light from the emitter goes to the base of transistor. So you wish to power your arduino board by the power emitted by the internal LED in the opto-isolator? This idea is kind of a insult to electronics fundementals.  smiley-grin

Lefty


« Last Edit: July 26, 2011, 02:08:14 pm by retrolefty » Logged

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Lefty,

I'd like use the current produced by the primary side of the coil for two things.

1. A trigger to count RPMs (working).
2. Can I use a capacitor to clean up the current and power the Arduino?

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Lefty,

I'd like use the current produced by the primary side of the coil for two things.

1. A trigger to count RPMs (working).
2. Can I use a capacitor to clean up the current and power the Arduino?



I would have to see the schematic drawing of the complete primary circuit of the coil. As there has to be a voltage source powering the primary I won't say you can't do what you wish, but I'm reluctant to say more without much more detail.

Lefty

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"current produced by the primary side of the coil "
That doesn't make sense. You inject a current pulse into the primary side, the secondary outputs a higher voltage, lower current pulse to fire the spark plug. The coil is just a transformer.
There is not much current going into the primary side; you can see it's pulses; and if can see those individual pulses on an LED then it is not high enough frequency for you to be able to rectify into a meaningful DC current.

Is there a battery anywhere along the line, like to spin the motor over when it starts? Or does it create its own spark from you spinning it manually with a starter rope or something?
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There is no battery, it fires when spun with a starter rope as you suggested.

Thanks!
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Just guessing that the small engine has a magnet mounted on the rotor and every turn it comes close to an inductor coil it induces voltage spikes on the coil to fire the pistons. Could that be right for small engines like lawn mowers? I speak of engines but I have no practical experiences though.
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Just guessing that the small engine has a magnet mounted on the rotor and every turn it comes close to an inductor coil it induces voltage spikes on the coil to fire the pistons. Could that be right for small engines like lawn mowers? I speak of engines but I have no practical experiences though.

Yes, they use a small 'magneto'. There could possibly be enough energy to allow rectifying/filtering and then regulating to power a arduino. But one really doesn't know if there is enough reverse power avalible from the magneto and if the voltage 'spikes' might be too high for a regulator input, possibly a zener clamp might also be required. Could be an interesting experiment, but probably not something a novice at electronics would be able to sort out.

Lefty
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The coil (magneto) on an air-cooled engine puts out about 10Kv to spark the plug. Your meter just isn't fast enough to catch that peak.

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Maybe the way to do this is to add some sort of battery and charging circuit, have the engine charge the battery and have the Arduino just pull its power from the battery. Hopefully that would smooth things out.
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Maybe the way to do this is to add some sort of battery and charging circuit, have the engine charge the battery and have the Arduino just pull its power from the battery. Hopefully that would smooth things out.

Sounds much better than dealing with high voltage spikes. Plus, you may mess up the engine firing sequence by tapping too much from the magneto (now that rings a bell). I should write this down. Liudr made one comment about cars that was actually remotely correct. I really know next to nothing when it comes to cars.  smiley-red
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Just guessing that the small engine has a magnet mounted on the rotor and every turn it comes close to an inductor coil it induces voltage spikes on the coil to fire the pistons. Could that be right for small engines like lawn mowers? I speak of engines but I have no practical experiences though.

Correct. But in your car, it does not use a magnet, it using a ignition coil, the primary is a pulsing ( on/off) from the 12 V to produce a high voltage spike. Think just like an Nicolas Telsa Coil.

It look like remout is trying to "harnest" power from the high voltage <--the wire going to the spark plug. Yes ?

I am afraid it is not going to work. I agree with CrossRoads here. The moment you put a load at the secondary, it will not have enough power generated. You have to understand, the high voltage is connect to a spark plug <--- is an OPEN circuit. The spark is produce when the voltage is high enought to conduct ( die-electric of air ) between  the two piece of metal of the plug.  A bit like a capacitor when you apply a high voltage ( over the voltage capacity ) and the result is "POOF". The capacitor started conducting.

Therefore harnesting power from a lawn mower spark plug will not work.
   




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The spark is produce when the voltage is high enought to conduct ( die-electric of air ) between  the two piece of metal of the plug.  A bit like a capacitor when you apply a high voltage ( over the voltage capacity ) and the result is "POOF". The capacitor started conducting.

That's not quite how it works; you can find a correct explanation here. A modern mower ignition is still the same principle as a system using battery ignition.

It would be interesting to put a small load on the secondary to see how much power could be pulled off before the spark stops firing. Of course the proper course of action would be to equip your engine with a charging circuit -- assuming the flywheel has the necessary magnets -- or find one that has one.
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