Testing condensers

[Meco3hp]

Hello,
Can somebody explain to me how to test a condenser? I've done a search but can't find any solid info on the subject. I'm wanting to test condensers in FBM, & B&S mags and such. I have a good multi meter, and a good buddy of mine has a real nice Graham coil tester. Any help on the matter?

Thanks
Richard

 

[Ed Stoller]

Re: testing condensers

I do a functional check on capacitors , or condensers if you like , using a simple analog volt meter, the old kind with a meter that has a needle. Basically, set the meter to the olms setting and measure the resistence. For a good capacitor, the needle should jump towards zero then move towards infinity as you make contact with it. Then switch the meter leads and do it again. This time the needle should jump about twice as far. The first time you are putting a charge of 1.5 volts on the capacitor. When you reverse the leads, you are reversing the charge so the needle will jump further. One end of the capacitor must be disconected from the circuit. If the meter has some selection, choose a high resistence range.

If the needle stops at a resistence value other than infinity, it is leaking the charge and is bad.

Ed Stoller

 

[Gary Pflum]

Re: testing condensers

Hi,
If you have a buddy that has a cond. tester (his sounds like mine) use it to verify if the cond. is bad or may be the cause of a problem. If the cond. is old, get rid of it and put in a new one. If it is good and old, get rid of it. On odd shaped conds. or unavailible conds, remove the insides of the housing and put in a capacitor. Insulate one wire and solder the other to the housing for ground. seal the capacitor inside the housing with silicone. I have used this for over 20 years on magnetos and they are still working.

 

[Chuck Parcher (Ks.)]

Re: testing condensers

The proper way to test condensers/ capacitors is with a capacitance meter. You can type in the words capacitance meter in either YAHOO, or GOOGLE, and several companies that make and sell them should show up.
A capacitance meter measures mfd micro ferads. The mfd's are the ability to store energy until it is released. Simply having a condensor that is'nt shorted out is not enough.... To high of a capacitance will cause one side of your points to pit, and the other side to peak up whereas the points don't get a good flat contact. to low of a capacitance causes the same effect in the opposite serfaces. You can buy condensors of specific mfd capacitance for the application needed. For instance a Maytag 92 uses a condenser of about .20mfd's the solid state capacitors work also, but there has been some discussion as to them holding up under vibration, and heat. I know they work well in some applications. If you can't afford a capacitance meter, most automotive electric shops will have one, and some parts stores. probably not the chain auto stores. Now I'll probably have 87 experts tell me I am wrong, but that's my story and I'm sticking to it. I does matter what the mfd capacitance for what application is or is required. other wise you will just burn up the points ....pitting, peaking etc.

CHUCK
p.s. I bought a good capacitance meter from a company off of the internet for about $50.00 plus s&h and I use it all the time. It was well worth the money.
chuck

 

[BWegher]

Re: testing condensers

Rarely, a condenser passes the value test and not work. There is also a leak test. Since new condensers are so cheap, its hard to justify not replacing old ones. The only perfect test for a condenser is to put it in service and see if it works.

 

[Chuck Parcher (Ks.)]

Re: testing condensers

Just because it works, does not mean that it has the proper capacitance for the application, and work properly. I have some condensors that are as low as.08 mfd's, and some older ones that go way up into the .70 to .80 mfd. range. They make them to store energy at a certain rating for a reason.....
CHUCK

 

[Harry]

Re: testing condensers

After thirty five years of electronic work in the field of broadcast radio and television, I guess I'll have to put my .02 in here. I've seen my share of open, shorted and leaky capacitors in my lifetime and one that blew up like a fire cracker while at work.

While writing the "magneto Page", I added this little tidbit in the summary page: After rebuilding a Ford 2N to the point that nothing should go wrong, one day while mowing the field the tractor lost power. It would start and sort of run, but its get up and go had gone and went. I was suspecting everything that I had done, like setting valve tappet clearance, carburetor, fuel line, coil, etc. It turned out to be the capacitor across the points in the distributor and it was a brand new one! It was obviously cheaply made, so newer is not necessarily better. I put the old capacitor back in and everything was back to working again!

http://www.old-engine.com/magneto.htm

Having checked hundreds of capacitors, I have no need for a precision capacitance meter. The old Radio Shack multi-meter on the high scale will check any of them for me as Ed Stoller pointed out above. Too many of us have gone through the throw-away mentality of 1960's auto repair when the condensor got thrown out with the points. It was a quick way for the mechanic to make a couple of extra bucks and "save" the customer from a return visit.

Check out one of our featured threads: http://www.smokstak.com/forum/showthread.php?t=7389

 

[Ralph Leonard]

Re: testing condensers

All of you folks that don't have electric backgrounds, listen up.

Ed and Harry are right on testing method and replacing with cheap (possibly poorer guality) capacitors.

Also, Chuck's take on capacitor value should be considered. Preventing points from burning is not its primary purpose. It is a side benifit. The coil alone has undesirable characteristics that causes a weak spark. The capacitor has opposite characteristics that cancel those of the coil. The value of the capacitor is selected to match the coil and should be adhered to as closely as possible. And yes, I know I'm going to regret this LOL

 

[Harry]

Re: testing condensers

Speaking of regret:

After I wrote the following on the stationary-engine maillist,
It makes sense to have a capacitor across the contacts to reduce erosion on the surfaces. It also may well goose up the voltage a bit too. I will be experimenting on this because I now have three engines in need of a buzz coil.

From: Ron
Subject: Re: BUZZ Coils
Harry,
I don't think I have heard this expression in relation to capacitors before. I always thought the capacitor served as a storage area for electrons which would then surge across the primary coil at the opening or closing of the ignition points, causing a stronger magnetic pulse in the soft iron core which, in turn, creates a flow of electrons at higher voltage to emerge from the secondary winding. By God, you are right! Goosing up the voltage is just what it does. Such a terse yet artistic descriptive phrase! Thank you for your contribution to my electrical vocabulary.
Ron http://www.old-engine.com/mageml.htm

 

[Chuck Parcher (Ks.)]

Re: testing condensers

50 yrs. ago I can remember that when the points were changed in a car, the condenser was also automatically changed also. I asked several people why, including my Dad, and he said that's just the way it is. Since then I have asked several people what condensers, or capacitors do and usually got the same answer I DON"T KNOW EXACTLY. Well when an engine is running the electricity that is running through the points in the distributor will skip,or fluctuate. condensers, or capacitors are also used in sound system speakers to stabalize frequencies. The same thing happens to the juice from the coil running through the points. An analogy, or metaphore would be something like this......On a farm with a well, if there is only a pump between the well and the house, when you turn on a faucet you will get surges in your water pressure. the pump will be going on-off-on-off-on-off-on-off and so on. If you put a pressure tank with the pump, then a bladder in the tank will stablize the water pressure, and the surging will stop, and your pressure will remain somewhat constant. I know this sounds simplistic but I hope it explains the basic principle. If there was no need for a variance in the mfd capacitance then they would only need to make ONE condenser, or capacitor and it would take care of every application, but that just is not the case. So enough said from me............
CHUCK

 

[Ken Majeski]

Re: testing condensers

When the points open the flow of current stops causing the magnetic field in the coil to collaps. This induces the spark. When the capacitor (condensor) is added it will absorb a charge causing the field to collaps more and faster and will induce a hotter spark. Also as mentioned before it will supress arcing at the points. I've used to ohmeter method of testing many times.

A common trick in the old garages was to charge up a condensor and throw it to someone.... And when they catch it they get Zapped...

You Don't even want to hear some of the tricks we have rigged up for people in the past.... Probably end up in a quick Lawsuit today

 

[Mac Leod]

Re: testing condensers

Ken, I belive you are mistaken...we would like to here some of the tricks you have done...

Mac Leod

 

[J.B. Castagnos]

Re: testing condensers

When the points open, the current stops flowing and the field starts collapsing. You get a reverse emf, current flowing in the opposite direction. This is what causes the low tension coil to fire an ignitor, when the points of an ignitor open they draw an arc across them. A condensor absorbs this reverse current causing the field to collapse imediately, the spark jumps across the plug. Without the condensor the points would draw an arc, the field would collapse slowly, no spark at the plug and the points would burn. As mentioned the condensor has to be matched to the coil.

 

[CharlieBiler]

Re: testing condensers

I will agree that the multi-meter (ohm) used in the high range of resistance, then reversed, is a good test of a condenser's leakage. I also agree that one must know the proper capacitance of the suspect condenser.

Recently I went through a pile of condensers. P&D ignition condensers were coming around and were dying when they got warm. They would all pass the resistance-charge test, but were found to have almost double the capacitance of the book rating. They all were on continental power plant engines and similar tractors. Sombody in Mexico goofed.

I work in a television assembly plant and caps litter every bench and trash can. It is a very expensive electronic cap that will equal the life expectancy of a good wound can condenser. In my shop there is a section of capacitors of every type, size, value and range; that could not be hauled with a pickup truck. I would be in a very bad pinch to even think of using a semiconductor cap on an ignition system. None will take the heat or vibration for long.

While high input voltage makes the spark, and the coil is the booster of that voltage; I have always found that it takes the proper capacitance to give a long and 'hot' spark. The side benefit of long point life is a direct follower of a good balanced capacitance.

 

[KidDynamo]

Re: testing condensers

Good and interesting info ! A question arises, though.......How can I match condenser value to the coil without having to run for hundreds of hours to see how the points react? I'm concerned not with automotive-type coils but coils in magnetos.

I refurbished four 4 cylinder magnetos this weekend and all could perform with existing coils and condensers but if I had to replace a condenser, and they are all extinct, would I be limited to using a guessed at value or is there some testing I could do to determine the correct condenser value?

 

[Meco3hp]

Re: testing condensers

Hello,
Ok I kinda follow this stuff, but just barely. Below is a link to the multimeter I have now. What do I set on it to do a test like Harry spoke of in his post.

http://buy1.snapon.com/catalog/item...m_ID=16690&group_ID=1369&store=uk&dir=catalog

ok looking at the picture the green section at 11o'clock is OHM.
the white section at 1 o'clock is DCV.
the orange section straight at 3 o'clock is ACV.
the orange sections at 5 o'clock is ACA.
and the white section at 7 o'clock is DCA.
Any help for a clueless soul?

Thanks
Richard

 

[Elden DuRand]

Re: testing condensers

ACTUALLY -

The main purpose of the capacitor "condenser" in points and coil ignition system is to both slow the buildup and collapse of the field in the coil and to cause a "damped oscillation" to take place in the coil when the points open.

What happens is that when the points close (and short out the capacitor), a strong magnetic field very quickly builds-up in the primary circuit of the coil. Incidentally, a small and insignificant spark is produced when the points close, similar to the spark produced when they open when there is no capacitor in the circuit.

When the points open (and un-short the capacitor), the field in the coil collapses and the counter emf generated by the collapsing field charges the capacitor. The resistance to a changing voltage that is characteristic of a capacitor slows the collapse of the field and this slight slowing of the collapse contributes to a more effecient coupling of energy to the secondary (high voltage) winding of the coil.

The damped oscillation (otherwise known as a "ringing oscillation") is caused when the field pushes energy to the capacitor then, after the field has collapsed, the capacitor pushes energy back to the coil rebuilding the field somewhat. This happens several times until the energy dissipated by the high voltage sparks has used up all the primary energy that was dumped into the coil when the points were closed. Usually, about 4 or 5 cycles of charge/discharge occur before the energy poops-out and this all happens within about 1/1000th of a second so what you think is one nice hot spark is actually several less energetic sparks all occuring in a very short time.

Another way to describe a damped oscillation is to liken it to the striking of a bell. When struck, the bell vibrates at what is called it's "resonant frequency". This is the frequency at which the bell shape is happiest at vibrating at and, naturally, the bell rings much louder at this frequency than at any other. In the coil-capacitor circuit, the two components make an electrically resonant circuit so the coil "rings". When it rings, it does so very loudly, hence the big, fat spark when it's happily resonant.

So, when everything is working right, the capacitor does several things, (1): The capacitor slows the first field collapse and build-up after the points open, causing a better energy transfer and a hotter spark, (2): The damped oscillation gives several of these hotter sparks and, (3) because the voltage rise uopn the opening of the points is slowed by the capacitor, the points can open faster than the voltage rises, keeping arcing to a minimum.

As a note, points will arc even with a capacitor across them if they are opened very slowly. That's why the cam ramp for point-and-coil ignition on slow engines must be very steep if they are to run well at low speeds.

Long winded, ain't I??

Y'all can go back to sleep now.........

Take care - Elden
http://home.cybertron.com/~edurand

 

[Ken Majeski]

Re: testing condensers

"The main purpose of the capacitor "condenser" in points and coil ignition system is to both slow the buildup and collapse of the field in the coil and to cause a "damped oscillation" to take place in the coil when the points open.

What happens is that when the points close (and short out the capacitor), a strong magnetic field very quickly builds-up in the primary circuit of the coil. Incidentally, a small and insignificant spark is produced when the points close, similar to the spark produced when they open when there is no capacitor in the circuit."

Well... How can the condensor slow the buildup of the magnetic field when the points close as when the points are closed it is out of the circuit????

Also if the slow collapse of the magnetic field creates a Stronger spark how come Low Tension mags don't make a Hotter spark when turned Slowly...????

 

[Elden DuRand]

Re: testing condensers

Well... How can the condensor slow the buildup of the magnetic field when the points close as when the points are closed it is out of the circuit????

Also if the slow collapse of the magnetic field creates a Stronger spark how come Low Tension mags don't make a Hotter spark when turned Slowly...????

Ken:

I must not have been clear in my explanation. You are right in that, when the points close, the capacitor is removed from the circuit. The battery voltage that was on the capacitor when the points were open (after the spark occurs) is shorted out.

When the points close, the field quickly builds-up because the points have put the battery voltage through the primary winding. As I explained, when the points close, there is a very weak spark due to the rapid buildup of the field.

After the points open, the rate of change of the field strength is controlled by the capacitor. When the coil and capacitor are in resonance, a strong coupling exists between the primary and secondary of the coil and you get several strong sparks before the oscillation damps out.

Concerning your question about low tension magnetos; the faster you turn the magneto, the faster the magnetic lines of force are passed by the armature (reluctor in the case of Websters, etc). The faster the rate of change, the higher the induced voltage is.

Hope this clears it up.

Take care - Elden
http://home.cybertron.com/~edurand

 

[Ken Majeski]

Re: testing condensers

Ken:

I must not have been clear in my explanation. You are right in that, when the points close, the capacitor is removed from the circuit. The battery voltage that was on the capacitor when the points were open (after the spark occurs) is shorted out.

When the points close, the field quickly builds-up because the points have put the battery voltage through the primary winding. As I explained, when the points close, there is a very weak spark due to the rapid buildup of the field.

After the points open, the rate of change of the field strength is controlled by the capacitor. When the coil and capacitor are in resonance, a strong coupling exists between the primary and secondary of the coil and you get several strong sparks before the oscillation damps out.

Concerning your question about low tension magnetos; the faster you turn the magneto, the faster the magnetic lines of force are passed by the armature (reluctor in the case of Websters, etc). The faster the rate of change, the higher the induced voltage is.

Hope this clears it up.

Take care - Elden
http://home.cybertron.com/~edurand

Well.... I still says that when the points open and the capacitor charges causing the magnetic field to Rapidly collapse is what causes the main part of the spark Just the same as a coil winding (Armature) thats Rapidly passing through a magnetic field. True, the magnetic field will collapse if the circuit is opened but not near as fast as when the capacitor is in the circuit.

I do buy your Damped Oscillation theory but by the time that happens ignition has already taken place.

Remember years ago when Resistor plugs first came out and they said the Resistor filtered out the Harmfull end of the spark.... How could that matter as ignition had already taken place and it didn't matter anyhow... Probably just a selling point and it helped the Radio more than the Ignition...

This is what Makes Harry's Forum Fun.... And people can learn something besides...