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Ignition Condenser - Does anyone really understand?

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Schwee
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Ignition Condenser - Does anyone really understand?

#1

Post by Schwee » Thu Apr 29, 2010 2:16 pm

I have an HD dual point, which also has two condensers. Is there any way to test the condensers?
OK, just replace them, but with what? Is there a car part number?
What's the difference / specifications other than size?
I'm not really sure what a condenser does. What's the difference among the variety of car condensers that would fit?
Is there any difference between 6-volt and 12-volt? How are condensers measured?

I know that most people just ignore them and replace them every year or two; I've had these for probably over ten years.
On a dual point, the condensers are on the bottom of the "distributor" (timer, actually), so I usually just deal with the points and skip the condensers, especially now that my local HD dealer doesn't stock classic parts and whatever I order online is probably from China.

Back to the 6-volt/12-volt issue. I converted my pan to 12-volt years ago, but I'm still running "6-volt" coils.
What condenser shoud I use?



hjans
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Re: Ignition Condenser - Does anyone really understand?

#2

Post by hjans » Thu Apr 29, 2010 3:28 pm

How the Ignition System Works
by Malcolm Holser
--------------------------------------------------------------------------------

The way the ignition works is this: You connect a coil to some electricity, and it builds up a magnetic field. You stop feeding the electricity, and the field collapses, inducing flow. The voltage, in this open circuit, builds rapidly toward infinity and eventually it must go somewhere, and arcs across whatever is handy.

Relays do this, and generate a back-spike when they are disengaged, arcing across the contacts of the controlling switch. Often, a "diode clamp" will be placed across the relay coil to prevent this. (always in electronics that cannot tolerate voltage spikes).

The ignition coil is really two coils intertwined, with the leads to one going to the spark plug, and the leads to the other going to the points. Your points close, and a magnetic field builds up. They must stay closed long enough (they DWELL closed for a bit!) to energize the field. They open, and the field collapses. The inductance of the collaspsing field does not care which of the two intermingled coils created it -- it dumps into both, but because of the way they are wound, it mostly dumps into the spark-plug side. Enough gets into the points-side, though, that there will be a spark across them as well. The condensor is there to absorb this. Without a condensor, your ignition will work fine, but your points will very rapidly pit because of the arcing, and may weld themselves together. Alway replace the condensor with the points -- it is more common that a poor condensor has caused the points to fail than the points wearing on their own.

Electronic ignitions use big transistors to turn on and off the one side of the ignition coil and internally damp this feed-back voltage with big diodes, a far better solution, but not one available in the 1800's when Benz invented the spark-plug. Many newer ignitions augment the energizing current to the coil with a Capacitance-Discharge (a capacitor is charged and then quickly dumped to the coil). This allows the coil to charge quickly, and the "dwell" becomes less critical. A condensor and capacitor are the same thing, though, and this use may have led to thinking that the capacitor in a normal system boosts the spark voltage. It might, but the effect would be minimal.

Even though the points stay open for quite some time, the spark only occurs the instant they open. A little basic electrical theory:

The ignition coil is a step-up transformer. There's a 12V coil, wound around many, many, many fine turns of wire which are connected to the high voltage wire of the coil. Transformers work on a *changing* magnetic field. While the points are closed, the field is steady, so no voltage comes out of the coil. The instant the points are opened, the field created by the 12V current collapses suddenly, producing a high voltage in the fine windings, and a short, low-current, high voltage spark. No matter how long the points are open (or closed) the spark only lasts an instant. The reason the cap needs to be on right is because you want the spark to have to jump as small a gap as possible, so less voltage is lost crossing it.

Incidentally, the collapsing magnetic field also induces a current in the 12V windings. This would normally arc across the points, pitting them and shortening their life. This is why you have a condensor, to absorb this unwanted 'inductive kick.'

Schwee
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Re: Ignition Condenser - Does anyone really understand?

#3

Post by Schwee » Thu Apr 29, 2010 5:16 pm

Thanks for the science; very cool explanation.
Still, can any one answer my questions:
1. How are condensers measured/rated?
2. How are they tested?
3. What part number can I request at AutoZone?

hogboy52
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Re: Ignition Condenser - Does anyone really understand?

#4

Post by hogboy52 » Thu Apr 29, 2010 8:14 pm

Condensers are measured in micro-fahreds.
They can easily be tested with an ohm-meter. Place the leads on the base and terminal end of the condenser. The meter will go to zero end of the scale then smoothly climb to the other, infinity end of the scale (the battery inside the meter is charging the condenser). If you switch the leads the condenser will discharge then charge in the opposite direction. If the meter stays at zero the condenser is shorted. If it doesn't move it is open. If it stays in the middle of the scale, the condenser is leaky.
All regular points ignition systems are basically the same so whatever condenser will fit into the space should do fine.
I never replace a condenser if the points show only a small amount of pitting as there is a good chance a new one will be bad.
I have to wonder at running a six-volt coil at twelve volts. I would think the current through the points would be much higher than normal and cause the points to over-heat, but as it seams to be working OK, you can judge that for yourself.

...

Schwee
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Re: Ignition Condenser - Does anyone really understand?

#5

Post by Schwee » Thu Apr 29, 2010 9:47 pm

Thank you, gentlemen. Just what I needed. :D

panz4ever
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Re: Ignition Condenser - Does anyone really understand?

#6

Post by panz4ever » Fri Apr 30, 2010 1:13 am

K, understand about the condenser and what it does and the test is great to determine if they are good (or not). First time I have read/seen such a good explanation.

Couple of things remain unclear to me though.

A condenser is a condenser is a condenser right (taking out the OEM Delco vs China comparison)? No difference if the system is 6 or 12. Same part used in both.

What about the dual 6 volt coils in a 12 volt system? Only reason I am asking is that is what i would like to do for my 56 rat project. Have a complete dual point set up with OEM condensers and points and a set of OEM flywheels with the dual marks for it. Would like to run it/use them just because.

hogboy52
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Re: Ignition Condenser - Does anyone really understand?

#7

Post by hogboy52 » Fri Apr 30, 2010 3:15 am

..
Checking Volkswagen 6v. years and 12v. years the part numbers are the same. Also the same part is used for the alternator condenser and the gas tank sending unit condenser! Since HD used Chevrolet points I think they also used the Chevy condenser. The early VW also appears to be physically the same.

A six volt coil is 1.5 ohms and a 12 volt coil is 3 ohms. Running the 6v. coil at 12v. would double the current. If the coil didn't burn out, it and the points would still be running at much higher temperatures. I would just use a modern 12v. coil. The "single fire" coils are dual point coils.

..

hjans
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Re: Ignition Condenser - Does anyone really understand?

#8

Post by hjans » Fri Apr 30, 2010 9:35 am

again a short explanation on condensors or, the right name : capacitor

http://sound.westhost.com/beginners.htm#6_0 ( scroll down to capacitors chapter 6)

basically :
a capacitor is not a capacitor
specs differ on capacity-polarity-size-voltage
there are monopolar and bipolar cap's
size matters and depends on the capacity ( amount of farads) and maximum voltage

to prevent lots a sh#t : change it any time you change the points
the low price cannot be a reason not to.

Hans

Schwee
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Re: Ignition Condenser - Does anyone really understand?

#9

Post by Schwee » Fri Apr 30, 2010 2:06 pm

hogboy52 wrote:Condensers are measured in micro-fahreds.
They can easily be tested with an ohm-meter. Place the leads on the base and terminal end of the condenser. The meter will go to zero end of the scale then smoothly climb to the other, infinity end of the scale (the battery inside the meter is charging the condenser). If you switch the leads the condenser will discharge then charge in the opposite direction. If the meter stays at zero the condenser is shorted. If it doesn't move it is open. If it stays in the middle of the scale, the condenser is leaky.
...
hogboy, I love your test idea, but it didn't work for me. I have two ohm meters and four condensers (two of them new) and they all tested the same: zero/zilch. No movement of the needle on my RadioShack VOM and my digital ohm meter indicates complete open on all condensers. What am I doing wrong? :|

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Re: Ignition Condenser - Does anyone really understand?

#10

Post by awander » Fri Apr 30, 2010 4:10 pm

I am into old tractors, and when converting to 12V from teh original 6V, it is common practice to just insert a power resistor inseries with teh 6V coil. his prevents the coil primary winding from burning out when the higher voltage is applied to it. The resistor is called a ballast resistor.

Replacement 12V coils, supposedly, are the same as a 6V coil, but incorporate an internal ballast resistor. I haven't opened one up to check, so I can;t vouch for this.

If you wanted to use a ballast resistor in series with each of the 6V coils, you would need to use a 1.5 ohm power resistor(assuming that the ohm readings given in the previous post are correct. The power dissipated in this resistor would be 24 watts. Any resistor you find in a 1.5ohm value, designed for 6V-to-12V conversion use, should be capable of this.

hjans
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Re: Ignition Condenser - Does anyone really understand?

#11

Post by hjans » Fri Apr 30, 2010 5:46 pm

some more sites to visit on this matter
the capacity of a voltmeter to measure cap's depends on the internal resistance ( or the internal impedance).
Some justt won't do the job, digital ones often give problems.
Read the comments down here

http://wiki.answers.com/Q/How_do_you_te ... multimeter

http://www.electronics-radio.com/articl ... rement.php

http://www.angelfire.com/electronic/fun ... _caps.html (!!!!! my tip !!)

Hans

hogboy52
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Re: Ignition Condenser - Does anyone really understand?

#12

Post by hogboy52 » Sat May 01, 2010 3:36 am

Well, OK, the test doesn't work for me either. For years I had a cheap Radio Shack analog meter in my tool box that served all my automotive needs. The meter innards was simply a battery, a diode, and a series of resisters. It finally quit and I bought a digital type. I've had no need to do any ignition tests since except last year a friend had a '76 pickup that wouldn't run and I did a simple points closed, points open continuity test on his distributer and the meter swung about in the usual manner, but I was using his cheep old analog meter.

Schwee
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Re: Ignition Condenser - Does anyone really understand?

#13

Post by Schwee » Wed May 12, 2010 2:08 pm

After reading all of this stuff, I still don't know how to test my Panhead condensers.
Guess I'm just a stupid old biker. :|

hjans
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Re: Ignition Condenser - Does anyone really understand?

#14

Post by hjans » Wed May 12, 2010 2:54 pm

Schwee wrote:After reading all of this stuff, I still don't know how to test my Panhead condensers.
Guess I'm just a stupid old biker. :|
You're not stupid, just not an electronics engineer......
Just replace it, cheapest and most sure way to deal with problems....

Hans

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Re: Ignition Condenser - Does anyone really understand?

#15

Post by john HD » Thu May 13, 2010 12:51 am

i know more about electricity than the average joe.

i still do it the way hans suggests. capacitors are tricky business unless you have quality analog test equipment.

i have such equipment and still find it easier just to change then test.

john

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