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 Post subject: Re: andrewk
PostPosted: Mon Mar 19, 2007 7:09 pm 
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Good deal. Did you replace the filter?



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 Post subject: Re: andrewk
PostPosted: Mon Mar 19, 2007 7:50 pm 
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Not yet, but before I run it again I will. :wink:


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 Post subject: Re: andrewk
PostPosted: Tue Apr 03, 2007 11:57 am 
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ttt... I updated my "chain cutting systems" article on page 2.



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 Post subject: Re: andrewk
PostPosted: Tue Apr 03, 2007 12:23 pm 
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always a good read.


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 Post subject: Re: andrewk
PostPosted: Tue Apr 03, 2007 11:50 pm 
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thanks for the encouragement. I did another installment, got sprockets done... now I need to finish it up. Lots to write about on the subject.



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PostPosted: Wed Apr 04, 2007 4:37 am 
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Keep it coming.



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 Post subject: Re: andrewk
PostPosted: Sun Apr 08, 2007 1:11 am 
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Article on Chain Saw Cutting Systems, is done!



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PostPosted: Fri Aug 31, 2007 7:29 pm 
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Well, its another summer here and gone, and time for things to slow down a bit. I thought I could go over some more theory, and will make it through some ignition and later carburetion theories when I get time to type. Some of these theories will apply to beyond OPE, and should be beneficial.

If there is anything that you would like to see covered, or discussed, input is welcomed.

If interested, check in for updates shortly.

I also stickied this, mainly for my ease of reference-

Andrew



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PostPosted: Fri Aug 31, 2007 8:09 pm 
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Ignition Principles of Operation-

Most small engines are equipped with a magneto ignition system to create spark for combustion to take place. A magneto is capable of creating in excess of 20000 Volts of electricity at the spark plug electrode tip, without any outside supply of electricity, such as a battery. In this article, we will cover what types of magneto ignition there are, as well as how they actually work, and the science behind it.

Here is an example of different magnetos-

Image

There are two types of magneto ignition, one that uses points and condenser, and solid state. Breaker points are essentially obsolete at this point, as most manufacturers have been using solid-state ignition for the past 25 years or so.

The biggest reason for the elimination of points is that points begin to wear and deteriorate as soon as they are put into service. They require constant maintenance and adjustment. Over the years, many manufacturers produced kits that eliminated the points, and turned the ignition into a solid-state setup. The most recognizable name for most is the Briggs Magnetron kits that were very popular, and still are for aficionados of older equipment.

Here is an example of an external mount solid state kit. It is not the Magnetron kit, of which I could not find a picture.

Image

The points and condenser act as a switch to cause the ignition coil to send the spark through the spark plug wire to the the spark plug. This can still be seen in an older car distributor.

Solid-state electronic components are what we use today. They replace the mechanical action of the points with an electronic version of the same thing, called a transistor.

Solid-state magnetos consist of few parts, which is the beauty of them. They have the circuit board, windings, an armature, and they are sealed with epoxy to protect them from the elements and vibration.

Now that we have discussed the different types of ignition systems, we should discuss the components that make it work.

The first is the flywheel. The flywheel will have a magnet embedded in it, and there is usually only one. Most of the time, you see two pieces of metal, but the magnet is U-shaped, and it has a north and south pole, which is essential for the magneto to work properly. On a side note, the flywheel is also responsible for cooling in a small engine. They have wings on them that intake air from the outside and displace it underneath the shrouding and on to the cylinder. It is for this reason that keeping mice nests out from under the shrouding is important.

Here is an example of a flywheel-

Image

Here we need to dive into some basic science, in order to fully understand how these systems work.

The first thing to talk about here is magnets. I am sure most of us here have used, or played with magnets. Magnets have a magnetic field. Magnets also have north and south poles, just like Earth, which is also a magnet.

The Earth's magnetic field is what makes a compass work, and what causes the "Northern Lights" at the North Pole. (The Northern Lights are also known as Aurora Borealis (Astronomy is also a hobby of mine))

You may remember from Physics class about magnetism. A magnetic field consists of what are called "lines of flux". Maybe you remember what every teacher does with iron filings, to demonstrate the lines of flux- but here is a drawing-

Image

The lines of flux are invisible, but the iron filings prove they exist. These lines are 3-dimensional and surround the magnet.

These lines of flux will interact with any conductor they come near. A conductor is anything that will transmit electricity.

When a magnet is moved near a conductor, an electrical current is produced in said conductor. This is called electro-magnetic conduction. The amount of current produced is directly proportional to the strength of the magnet and the speed it is moving.

When a magnet moves on a conductor, the electrical current produced is pushing back against the magnet. This happens because the electrical current produced is of opposite polarity of the magnet used to generate it. (See the Law of the Conservation of Energy, and Newton's third law) This interaction is known as eddy currents, which will be important to know later in this article.

This electro-magnetic induction was discovered by Micheal Faraday (who is probably known better from the SI unit of capacitance, the Farad...) and another important discovery that lies within his theory is that if a copper coil of wire is exposed to a changing magnetic field, that is, the field changes from north to south or vice versa, an electric current is induced in the wire. An experiment some might remember from high school is the alnico magnet in the varnish coated copper wire tube, with a galvanometer hooked to the wire. My high school physics teacher showed us this, but he was an old teacher, and I don't know what technology has brought to the classroom in the past 5 years, or if other schools were the same as mine.

Lets summarize briefly so that we can apply what information is presented here to magneto ignition systems.

Magnets have invisible magnetic fields, known as magnetic lines of flux. (High school Physics)

When a magnet moves by a conductor, the lines of flux interact with the conductor, and this interaction induces electricity. (Faraday)

This shows us how magnetism and electricity can interact. Before we can apply these theories totally, however, we must first discuss a bit about magneto construction.

Most magnetos are similar in construction. A steel or soft iron core, usually U-shaped is make of thin stampings, laminated together, called the armature. They [the laminations] are slightly insulated from each other by a thin coating of oxide. This is where eddy currents come into play. If the core were solid, it would have strong eddy currents that would cause heat and make the coil less efficient than with the laminations. The eddy currents are reduced by using laminations that are slightly insulated from one another.

Here is an example of the laminations. This is actually a coil from a Continental aircraft engine, but the construction is the same.
Image

And a magneto off of a small engine-

Image

This laminated core transfers the magnetic lines of flux through the windings without actually being magnetized itself.

Wrapped around the core are two windings of wire, called a primary, and a secondary winding. The primary is the low voltage side of the coil. It usually has about 200 turns of coated copper wire wound tightly around the armature. One end is grounded, and the other end is connected to the solid state controller, or the breaker points.

The secondary winding has as many as 20000 turns of a very fine wire, and is wrapped around the primary. It is the high voltage side. One end is grounded, and the other is connected to the spark plug wire.

Now that we know how this coil is constructed, we can further discuss the operation.

The Magneto mounts close to the flywheel. There is an air gap between the legs of the armature and the flywheel. This is to ensure that there is a transition of polarity, which is essential if you remember Faraday's theory discussed earlier. As the flywheel spins past the armature, the magnetic flux lines travel up the legs of the armature. Because both the primary and secondary windings are wrapped around legs of the armature, an electric current is induced by the lines of flux cutting through the windings. As the flywheel magnet moves by the legs of the armature, the polarity of the magnetic field changes direction.

The current builds until either the points open or the solid-state switch, usually a transistor opens the circuit and the circuit is no longer complete. Current can't flow if the circuit is not closed.

When the circuit is opened, the concentrated magnetic field in the windings collapses, and this process creates high voltage, 15-20,000 Volts, depending upon the design, and this current is able to jump the spark plug gap under up to 150 PSI of compression, to ground, to complete the circuit.

The secondary windings are wrapped around the primary, so that when the magnetic field is building, reversing, and collapsing, a step-up in voltage occurs in the secondary windings.

By using a laminated armature, a primary and a secondary winding, the magnetic lines of flux can be directed and amplified to ultimately give us up to a 20,000 volt spark. This is happening on every revolution of the flywheel, so at 12000RPM, it would be happening 200 times a second.

Now that we have a firm foundation on how the ignition event happens, we can look further into the subject.

It is worth mentioning that magneto ignition is not the only type of ignition used on small engines. There are a good number that also use a traditional battery ignition, with an automotive style coil and condenser. They also use points to collapse the field, or there are some that use a capacitor to discharge, or collapse the field. The operation is the same, but like someone said, there is more than one way to skin a cat.

Here is an example of different battery ignition coils-

Image

As well as a pic with it installed on an engine-

Image

Now that we know how the ignition event happens, we can now talk about when it needs to happen. This is called timing, and will be the subject of the next article.

As always, if you have any questions, please feel free to ask.

Andrew


Last edited by andrewk on Sun Dec 16, 2007 9:03 pm, edited 3 times in total.


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PostPosted: Sun Sep 02, 2007 3:14 pm 
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Article updated- 9/2/07



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PostPosted: Sun Sep 02, 2007 5:59 pm 
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Ignition advance is a very misunderstood subject. I'm looking forward to it.

Norm



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 Post subject: Re: andrewk
PostPosted: Sat Dec 22, 2007 9:40 pm 
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Article on snowblowers (pg1) updated 12/22/07.

Article on Igntion systems finished 12/21/07.

Still composing ignition advance article to be posted in a new installment. Sorry to keep y'all waiting.

Andrew



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PostPosted: Tue Jan 08, 2008 2:02 am 
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Hi all-

Below is my most recent learning experience. A valuable lesson was re-learned here.

Had a Honda Genset come into the shop last week, customer complained that it was "blowing breakers" when the 220V compressor they had for their race trailer was hooked up. Said they were also running lights off the 110, but the 220 was the one blowing.

I look it over, and notice that there is a receptacle broken, but it is still insulated from all other contacts. It is also a 110 plug, so I eliminated it from the equation, but ended up replacing it for the customer anyway. The rest of my visual analysis went smooth- I didn't see anything visually wrong.

So my first step in diagnosis was to try to replicate the failure. We don't have much 220 stuff in the shop, only a welder and our compressor. I plugged the compressor in, started the generator, and then turned on the compressor. Sure enough, it blew the breaker.

I replicated this failure 3 times, trying to 'jiggle' the plug, trying different plug-ins, to no avail. My next thought was to test these plugs to see if they are grounding out where they shouldn't be.

About 5 minutes spent with my multimeter proved that the circuits were intact. However, it still tripped the breaker. Frustrated, I pull the panel off the side and open it up to see if there could be something wrong inside. I found nothing.

I double checked the compressor motor plate to make sure that it didn't draw too much current for the system (30A), and it didn't. I called the customer to verify the same with theirs, and it checked out ok.

At this point, I had spent more time on the job than it was probably worth, and was starting to lose my cool a bit. So I put it off to the side for the weekend so I could come back at it with a cool head.

So today I went back reluctantly to the machine, and I fixed it in about 45 seconds. I took one look at the thing and realized what my problem was. On the control panel, where the 240 V plugs are located, there is a switch, and above it, it says <-120v (Switch) 240V->. Guess what position that darn switch was in?? I didn't even notice the freaking thing. Since it was separate from the 120 plugs, I never considered that the 240 plugs could be used for 120 as well. I flipped that switch, plugged the compressor in, fired it all up, and it ran like it should. I almost cried. :)

When voltage is low on an electric motor, amp draw goes up proportionally. In this case, it was enough to trip the breaker, causing the reported problem.

This is yet another reminder to keep "peace of mind" when working, and explore all options before making hasty decisions. If I would have checked voltage output, I would have found the problem and realized my previous mistake. As it sits now, I can't justify really charging the customer anything but our minimum bench fee, which is $30.76 after tax. That doesn't cover 1/2 of my time into it-

Funny thing is, I never noticed the compressor running at half speed like it must have been before the breaker tripped.

You learn something everyday.

Regards,
Andrew



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PostPosted: Sun Feb 03, 2008 12:34 am 
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Alright- Time for another lesson- This time in assumptions.

My boss (the owner of the company I work for) had tuned up a guy's chainsaw after he brought it in complaining of a high idle. (When the idle is high on a saw, the chain never stops spinning, as the centrifugal clutch is still kicking in.) It came back right away, complaining of the same problem. The boss went through it again, and looked it over, and didn't find anything wrong. So he put a set of diaphragms in the carburetor, tested it, and it worked fine. So we sent it on it's way.

Two weeks later, the customer returns with the saw, and the saw is exhibiting the same conditions. This time the ticket goes to me, since I sort of specialize in 2-cycle repair, and because the boss was at his wits end. So I print out the previous service tickets, and observe that the saw has a new carburetor kit, new fuel filter, air filter, and spark plug, all installed within the last month.

I started this one out right- First things first were compression and ignition checks, to ensure the basics were there. The saw passed with flying colors. I went to inspect the fuel line, and found a crack in it that the boss had missed. I replaced the fuel line, and the saw worked great. My first mistake was not running the saw first to replicate the condition. The saw then acted up. The saw responded well to carburetor adjustment, and I sent it out, noting we had missed the fuel line the first time.

Customer brings the unit back 3 days later, and its doing the same thing. I scratch my head, and go directly into the carburetor. I find a small piece of dirt in the needle assembly, so I clean the carburetor, test it, and send it out the door, only to have it come back 2 hours later and the customer is mad as hell. I jumped to the conclusion that since it was fuel delivery, it must be a bad check valve in the carburetor, so I order the carburetor.

The carburetor comes in today, and I anxiously install it, and put it on the ground and start it up. The saw sings like new. I dialed in the carburetor, picked it up off the ground, and it idled up and wouldn't come down. I richened the idle mixture way up, and it settled down, but it had a bad rich stumble when you gave it throttle. I set it back down, and it flooded out. I re-set the carburetor, and replicated the result. I tore the saw back down, and found the culprit the entire time- A torn intake boot.

When we test chainsaws, we set them on the ground and run them so it is easy to dial in the carburetor. We then give them a couple quick revs and a short high speed run off the ground to ensure the settings are correct. The problem in this case is that when the saw was on the floor, the intake boot sealed against itself. When it was picked up, the weight of the saw sagging on the AV mounts was enough to open it up, causing the condition.

My biggest mistake was assuming that the boss had checked over the saw throughly. Since I assumed he did, we made a mistake that I could have stopped the first time had I started over and not gone from where he left off. Granted, intake boots hardly ever fail, and when they do, it is not usually like that. That is the weirdest intake boot failure I have seen, but I still should not have assumed it was checked out before.

As it sits now, we have time invested and parts invested that were not necessary. We can sell the part to someone else, but we are out the time. Luckily when I explained this to the customer, he understood, and was happy that we finally found the problem.

While you may not repair outdoor power equipment for a living, this is a valuable lesson in proper diagnostics. Never assume anything.

Andrew



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