Ignition Condenser

[bjmullins]

I am looking for a 0.2 microfarad condenser. Does anyone know of any part number from any manufacture that is a 0.2 microfarad? It is for a 1946 Evinrude Lightfour and I know the original value because it is printed on the base of the condenser. However after looking at various places, Mallory Marine, Sirrea and auto parts stores, I have found that they are only listed by application, and never the capacitance value. I would prefer one with a seperate type mounting tab, as opposed to the soldered on type, but any kind could be modified. And of course the lead length is totally unimportant because it will all have to be rewired and spliced/soldered together.

Thanks.

 

[tashasdaddy]

Re: Ignition Condenser

welcome to iboats. hate to recommend another forum, these guys may know where you can get the parts "http://www.aomci.org/"

 

[Vic.S]

Re: Ignition Condenser

Just get any one from an auto parts store thats for a coil and points type ignition system that you can fit in. It will work OK.

 

[Silvertip]

Re: Ignition Condenser

Yes -- any auto parts store with a clerk that's older than 18 should be able to fix you up. Those condensers are pretty generic. You can also hit your local farm store and head for the tractor equipment section. They have tune up parts for most older points-ignition tractors. Those will work too.

 

[F_R]

Re: Ignition Condenser

Since you are going to have to jury-rig it in, head to your electronics store. Actually, I bought a bunch of these on-line for about 25 cents each. And they are way better than the paper/foil condensers sold for motors. I use them in the antiques all the time.

The general rule is that within +/- 10% is fine. Even 20% will do. This one is .22 or .02 over....that's 10%. Don't worry about the voltage rating as long as it's over about 50V.

 

[Chris1956]

Re: Ignition Condenser

The old Ford condensers were .25 microfarads. I would think these will work. I am not sure of the capacitence of the old lawnmower condensers, however they will likely work as well.

BTW- I think the clerk will need to be 40+ years old to remember these!

 

[Texasmark]

Re: Ignition Condenser

The size depends upon the inductance of the ignition coil. If you control the amplitude and rate of rise of voltage on an opening switch (points) in an inductive circuit, you will eliminate or significantly reduce arc over which erodes the contacts and eventually makes replacement necessary.

So in that respect you can't get too large.

However, the condenser (capacitor) has to give back that stored energy before the next opening so you can't get too big, especially with multi cylinder engines operating at high rpm's.

I recall numbers in the .015 to .02 microfarad region.

Mark

 

[Texasmark]

Re: Ignition Condenser

Scuse me...... 0.15 to 0.20 microfarads.

 

[Silvertip]

Re: Ignition Condenser

I wouldn't use the capacitor shown in the picture as there is no simple way to handle vibration since those leads are not flexible. Electrically it will certainly work but in the case of an outboard, I feel vibration will get to that style capacitor.

 

[F_R]

Re: Ignition Condenser

A small gob of silicon will keep it from dancing around in there.

 

[tmcalavy]

Re: Ignition Condenser

Engine Blade & Prop in Milwaukee probably has them, or a close/workable substitute.

 

[F_R]

Re: Ignition Condenser

With all due honor and respect, I don't subscribe to the theory that you can't go too big. The pulse that charges the capacitor only lasts for a limited time. A too-big capacitor would not charge up to capacity in that limited time. The voltage at the capacitor rises as the capacitor charges. It would be like dumping a cup of water into a 5 gallon bucket.

After the charging pulse ends, the capacitor then discharges back through the coil, the discharge voltage being in series with the naturally occuring voltage in the coil. Being in series means an increase in voltage, resulting in a higher induced secondary voltage. But if the capacitor was only partially charged, the discharge voltage would be lower, resulting in less induced secondary voltage.

At least that's the way I understand it.

 

[Texasmark]

Re: Ignition Condenser

F_R,

Having thought about it, I agree with you.

The points close and the inductor loads up with energy per the relationship: Energy stored = 1/2 L(i squared). (L is inductance of the coil and i is the charging current at any given instant which increases over time.

When it's time to fire a plug, the points open and the inductor attempts to keep the current flowing by generating whatever voltage that is required to do that, theoretically to infinity with no physical limits, nor losses (which there are). Since one side of the coil is at 12v, the other end is what rises in voltage and that happens to be where the opening points are....so you have this arcover till the points get wide enough to exceed the voltage capability of the coil and the current stops.....course you now have a nice pit in your points from the arc.....and that's only one plug fired once.

Along comes the capacitor which is wired across the points, in series with the high voltage transformer's primary coil. It absorbs energy in the form: Energy stored = 1/2 C(V squared) (where C is the capacitance value of the condenser) and it charges to a predetermined voltage resonantly (sine wave), since we now have an LC circuit, as it fills with the energy that was stored in the coil. The capacitor (condenser) limits the rate of rise and height of the voltage across the points, keeping it lower than arc-over potential, so there is little damage to the points....some arcing does occur, but not much relatively speaking.

The resonant voltage across the capacitor also happens to be across the primary of the coil (since the cap bridges the points and as stated, is in series with the primary coil of the high voltage transformer, so by transformer induction, the secondary voltage rises across the plug gap until sufficient voltage exists to bridge the plug's gap and produce the arc.

So, as you said sir, if the resonant voltage swing is too low, the plug voltage will be too low and the plug may not fire at all or fire incorrectly.

Per the equation above, the larger the capacitor, the lower the voltage, so there IS after all, a practical limit to how big it can be.

I respectfully stand corrected on "it can't get too big". Thanks for your help in getting this info correct and I enjoyed dwelling back into things I have been trying to forget. Grin

Mark

 

[F_R]

Re: Ignition Condenser

Whew! That far exceeds my understanding. I'll have to be careful when challenging your statements. I did use my GI Bill Education Benefits to study TV repair. That was back when TV's still had vacuum tubes. But then along came the race to the moon and technology has so advanced since then that I am little more than a dummy. For me, some of my toughest lessons were the study of coils and capacitors. With a capacitor, current leads the voltage by 90 degrees, vectors, and all that stuff. But until you did absorb those basics, you were lost with the rest of the course. I never did go to work as a TV repairman. I realized that the TV man was the lowest paid guy in town, considering what he has to know.

 

[Texasmark]

Re: Ignition Condenser

Thanks sir. I understand what you say. I was 35 years old and an intern to a Pennysylvania Dutchman (smart-elic) with a Masters in math (of all things) before I fully understood (thought I did, at least could work with them) the physics of inductance and capacitance. The prior 17 years I was just lost in the dark.

Agree on the TV man. Did moonlighting when in the service so that I could afford a ................................................................boat. Har Har. True it is. Twas small and under powered, but it did what needed to be done.

Mark

 

[steve66]

Re: Ignition Condenser

Hi I read your thread with great interest.I am forever buying and replacing condensers in outboards especially omc's.Finding condenser for old outboards, especially villiers mag seagulls are almost impossible and extremely expensive and the lack of space under the flywheel means fitting a conventional condenser difficult.I have a couple of questions -
How do you wire a capacitor into the system ie it has two whiskers that are soldered into the circuit board and a omc condensor only has one wire two the points?
What would be the best size capacitor to use universally?
Thanks for the thread
Steve

 

[F_R]

Re: Ignition Condenser

On a stock outboard condenser, the case (mounting screw) is the second wire.. So, if using an axial lead capacitor, simply ground one lead and attach the other one to the points. As suggested earlier, it is advisable to secure it somehow aginst vibration. Silicon, wire tie, whatever. .22 mfd is a very popular size in the electronics field, and adaptable to many outboards. Don't use the electrolytic type of capacitors.

EDIT! Correcting the number to .22 mfd, NOT 2.2 mfd. What a difference a dot makes.

 

[Vic.S]

Re: Ignition Condenser

Finding condenser for old outboards, especially villiers mag seagulls are almost impossible

A good few years ago I must admit I found that the condenser for a UK Ford Escort fitted the old Villiers magnetos.

Are you aware of the fan base in the US and Oz as well as the UK for Seagulls. Do you know of the Saving old Seagulls website at "http://www.saving-old-seagulls.co.uk/" and the SOS forum at "http://www.saving-old-seagulls.co.uk/FORUM/index.php"

 

[steve66]

Re: Ignition Condenser

Thank you F_R for your reply.I will give it a try.Hi Vic yes i know about sos,i use the forum a lot thanks for your advice.Is the escort condensor a square one similar to the villiers.Im guessing the condenser will also be used in old Fiestas as they both share the crossflow engine.
Steve

 

[Vic.S]

Re: Ignition Condenser

Is the escort condensor a square one similar to the villiers

I dont remember. It was well over 20 years ago. It may have been for a rearwheel drive Escort, before the days of the Fiesta. I just looked at what was on offer and picked one that I thought would fit. That's what I was advised to do by an old motor cycle repair shop.

It's still in there and OK but I have not looked at it again since the day I fitted it.

Villiers engine on an old lawnmower BTW but basically the same magneto as the Seagulls