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5Vdc from 48Vdc - Options?

No. Electrolysis is the corrosion mechanism and the electrical potential of each element is what makes the difference rather than its material. For any metal/non-metal compound the non-metal will form at the cathode and the metal will form at the anode. However, there is nothing to stop the newly formed non-metal recombining with the electrode.

Consider the common case for cars at least - road salt disolved in water with a steel electrode (the chassis). If the chassis is positively charged you get sodium forming on the chassis, which will react with the water and ultimately be washed away. If OTOH the chassis is negatively charged you get chlorine formation, which is free to combine with the iron in the steel. This forms ferric chloride solution, a.k.a. PCB etchant. That of course is a particular nasty but many other substances can have similar effects. The problem is that you are forming potentially very reactive non-metals on the negative lead. On the positive lead you are forming metals that are not going to attack the electrode itself.

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Andrew Smallshaw
andrews@sdf.lonestar.org
Reply to
Andrew Smallshaw
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Now that makes sense. It isn't somethign I had ever looked into: ot was just a gut feeling suggestion. I figured it would take a long time for electroysis to have any noticeable effect on something as substantial as a car chassis given the small currents involved.

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Andrew Smallshaw
andrews@sdf.lonestar.org
Reply to
Andrew Smallshaw

ion

There is something very significantly wrong with this discussion. This is not about the car chassis being "charged" either positively or negatively. The only issue is the current flowing in the electrical paths. If you have a potential across a connection, then you will see the sort of electrolysis you are describing. But it will be at the point of contact between the two metals.

Talking about things being "positively charged" has no meaning in this context. A potential has to be in relation to some other point. Connecting the positive or negative lead of the battery does not make the chassis of the car "positive" or "negative" with respect to anything other than the other terminal of the battery!

Are there any references that discuss this sort of electrolysis? If what you are saying is true, then ocean ships could be protected from corrosion just by connecting the positive terminal of a battery to the hull! Instead they bolt great hunks of light metal (magnesium IIRC) to the hull *below* the water line to allow a complete circuit to form. The electrolysis then removes the sacrificial metal and leaves the hull relatively unscathed.

Rick

Reply to
rickman

Why does this make sense? If the center electrode emits electrons, how does that change anything with the breakdown potential of the vapors in the engine? What is the mechanism? If the polarity is reversed, why wouldn't the electrons emitted by the ground leg do the same thing?

I just don't get how in this case current flowing in one direction is different from current flowing in the other.

Rick

Reply to
rickman

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Because the centre electrode gets hotter than the outer ground electrodes and so is more likely to have electron emission.

kevin

Reply to
kevin93

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I don't think the issue is related to electron emission. At least not as a first order effect. The voltage is what causes ionization of the vapor in the area of the spark plug. I don't think the creation of free electrons is important to this. But I couldn't swear to it.

Besides, if I am not mistaken, the voltage on the center spark plug electrode is not negative in a positive ground system. The spark voltage is from the collapse of the magnetic field in the coil. With a negative battery voltage that builds the field in the coil, the collapsing field makes the spark wire positive. Do I have this correct?

Rick

Reply to
rickman

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No. It depends on the windings of the coil. It won't be an autotransformer, because the primary current is so much higher than the HV secondary current, and thus the primary is wound with large wire, the secondary with small wire.

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 [mail]: Chuck F (cbfalconer at maineline dot net) 
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Reply to
CBFalconer

Unless one is driving a car with a Kettering ignition system or similar. Okay, that was a few years back. But the single coil was in fact an autotransformer (ignition coil), if I recall correctly.

Jon

Reply to
Jon Kirwan

Interesting idea, but I don't think the term refers to the mechanical construction of a coil. I believe it refers to the electrical connections of the coil.

While reading up on this, I found something interesting. When a car uses one coil for two spark plugs, they don't need a distributor. If the two plugs were connected in parallel one would fire at a lower voltage than the other. So instead of a parallel connection, it would seem they use a series connection. The coil is actually two coils on the same core or one coil with both ends brought out. The article I read seemed to be saying that one coil is connected across the two plugs so the same current runs through both. It got a bit bizarre indicating that the plugs should be replaced in the same cylinder they were removed from to maintain a "favorable direction of electron flow". I'm not sure what that even means.

Rick

Reply to
rickman

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I have some doubts. Consider that a reasonable 4 cycle engine will have the two cylinders in opposition, meaning in phase. One will be on compression, awaiting a spark, and the other will be on exhaust. So the atmosphere around the plugs is quite different. If the one on exhaust takes more volts to arc, it just wont (if connected in parallel). I'm not saying this happens, but it might.

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 [mail]: Chuck F (cbfalconer at maineline dot net) 
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Reply to
CBFalconer

I don't know how to reply to that. You are speculating about what might be the case. But it is clear that no matter what happens with the mixture, if the plugs are in series they will both fire. Once I thought about it a bit, I realized that this is the only practical way to use a single coil for two cylinder.

What happens if one plug fouls? With a parallel connection it would cause two cylinders to misfire and the engine would run *very* roughly. In fact, it could cause a problem with both plugs fouling as a result of the un-ignited fuel.

Rick

Reply to
rickman

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They won't, and can't, be in series. One side of the plug is automatically 'grounded' by the threads. Thus they have to be in parallel.

--
 [mail]: Chuck F (cbfalconer at maineline dot net) 
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Reply to
CBFalconer

Eh? Not if the transformer secondary is either floating or grounded to the bodywork at a centre tap. All that happens is that one plug centre is at +50kV or whatever, and the other one is at -50kV, relative to the bodywork.

Nobby

Reply to
Nobby Anderson

Sure they can. The secondary is not grounded anywhere within the transformer, unlike a single-ended ignition coil.

Reply to
Jim Stewart

The ground has nothing to do with a series vs. parallel connection. Of course the secondary of the coil has to be floating.

Rick

Reply to
rickman

I guess we can debate this all day (or night). The site I found that mentioned this was a bit dubious talking about "maintaining a favorable direction of electron flow". So I would not really consider this a reliable reference. Does anyone actually know the details of how this is done?

Personally, I have no doubt that they wire the coil with the opposing plugs in series. It solves a number of possible problems with spark failures.

Rick

Reply to
rickman

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Wiring the plugs in series is(was) commonly done on 4-stroke 4 cylinder motorcycles. This allows the use of 2 coils instead of 4 as adding a distributor is mechanically relatively complex. The cylinders connected to single coil run 360deg out of phase.

Reply to
Rocky

Nothing to do with the coil. Look at a plug. It has a single hot lead (fed from the distributor or equivalent) and the other end, which is the thread, screwed into the head. So two plugs have, at most, three independent terminals, assuming the heads are not insulated from each other. Please describe the 'series' wiring of those.

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 [mail]: Chuck F (cbfalconer at maineline dot net) 
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Reply to
CBFalconer

360deg out of phase ? You've come full circle. :-) 
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Reply to
ArarghMail903NOSPAM

Connect one end of the coil to the hot lead of one plug and the other end of the coil to the hot lead of the other plug. The common ground is the connection between the two plugs.

There is no connection required between the coil secondary and the common ground.

Rick

Reply to
rickman

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