Capacitance and metal transfer

Old Henry

Old Henry

Well-known member
Thought you might be interested in the effect of capacitance in our condensers on the pitting and "****" on our points. In trouble shooting rough running of my engine I just removed the condenser which is an Echlin ECH FA54 from NAPA and had seemed to be working fine but was the easiest possible problem to check so I did. I tested its capacitance and it was .3149 mF. (Meter shows 314.9 nF, which is the same as .3149 mF, in case you're wondering.)

IMG_3716.jpg


I then removed the points to check them and found that the "opening" points were pitted on the point arm and a corresponding "***" on the base as shown. (These points were new 9,000 miles ago.)

Burnedcontactpoints_zps8bd20b23.jpg


Of course, the "closing" points were not affected at all since there is no arcing when closing, just when opening. They're still as good as new.

Normalcontactpoints_zps77479120.jpg


Just in case you all might be interested in why this metal transfer occured and how to prevent it. Here's the answer. (From here: http://www.farmallcub.com/phpBB2/viewtopic.php?f=11&t=38576)

"The more or less capacitance your condenser has will reflect on the condition of your points or how long the points will last.

A condenser with to much storage or capacitance will cause a build up (metal transfer) on the mounting side of the points while a condenser with not enough storage or capacitance will cause a build up (metal transfer) on the arm side of the points. Sometimes the right sized condenser will end up in your ignition system and no transfer will occur.

This is why you have to file a used set of points (eliminate the metal transfer) before you can gap them with a feeler gauge. You do not have to file points if you use a dwell meter. The dwell meter takes into account the metal build up, because it looks at the points electrical measurement rather than the mechanical measurement.

The condenser capacity is measured in microfarads. A microfarad is 1/10 of 1/1,000,000 of a farad (.0000001 farad)There are specialized testers to do this measurement. The typical condenser will have between .2 to .3 microfarads. The variation in condenser capacity can vary widely, (most condensers fall somewhere around .25 microfarad).This is why some contact points last longer than others. It is not the points fault but is the condensers fault instead.

Look for the metal transfer. If there is none consider not replacing the condenser as it is matched to your particular ignition system. If there is metal transfer replace the condenser as you have nothing to lose in the process."

So, my arm contact point was pitted and the corresponding metal transferred to the base contact point as a "***" because the capacitance of my condenser was too high. The one I replaced it with was very close to .250 mF so should not effect the new points in the same way the old consenser did.

Bottom line: If your points ain't got no ***, don't change the condenser - you got a good one.

Just thought you might like to know. :cool:
 
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Henry,

Good information!!! On our tester the .30 mfds dont show the arc that we see with the ,25 mfd units. Be interesting to see these in another 9000 moles.
Question, was the info from the farmall site a "positive ground" vehicle ??
 
Good point (no pun intended) Bubba. Those old Farmall Cubs were positive ground; am I correct in thinking the metal deposit will be opposite on a negative ground system?
 
Good info but a couple of minor corrections...a microfarad is 1 millionth of a farad thus .000001 of a farad. The digital multimeter shown is set for reading capacitance and in the pix it reads in nanofarads, a nanofarad is 1 billionth of a farad thus .000000001 of a farad. To convert nanofarads to microfarads divide by 1000 as correctly stated, or more easily just move decimal 3 to the left.
 
A person needs to find a tester that will measure for leak down. It's necessary to know the leak rate and the capacity to know if it is a good one.

The science of the late 19th century stumbled along with trial and error testing but they finally figured it out that inductor coils and capacitors will work outside of an AC circuit if the DC power is pulsating and creating a half wave AC current flow. The charge and release capability was initially what they were looking for to make the inductor coil work more in tune with half wave AC. They also discovered that the energy transfer was speeded up enough, with the capacitor in the circuit, to keep the circuit breaker points from arcing too much. Killed two birds with one stone!

Now if they could make a reliable capacitor that would last at least 8 to 10k miles in the 21st century, we would be cooking with gas.
 
Old Henry said:
Thought you might be interested in the effect of capacitance in our condensers on the pitting and "****" on our points. In trouble shooting rough running of my engine I just removed the condenser which is an Echlin ECH FA54 from NAPA and had seemed to be working fine but was the easiest possible problem to check so I did. I tested its capacitance and it was .3149 mF.

IMG_3716.jpg


I then removed the points to check them and found that the "opening" points were pitted on the point arm and a corresponding "***" on the base as shown. (These points were new 9,000 miles ago.)

IMG_3722.jpg


Of course, the "closing" points were not affected at all since there is no arcing when closing, just when opening. They're still as good as new.

IMG_3728.jpg


Just in case you all might be interested in why this metal transfer occured and how to prevent it. Here's the answer. (From here: http://www.farmallcub.com/phpBB2/viewtopic.php?f=11&t=38576)

"The more or less capacitance your condenser has will reflect on the condition of your points or how long the points will last.

A condenser with to much storage or capacitance will cause a build up (metal transfer) on the mounting side of the points while a condenser with not enough storage or capacitance will cause a build up (metal transfer) on the arm side of the points. Sometimes the right sized condenser will end up in your ignition system and no transfer will occur.

This is why you have to file a used set of points (eliminate the metal transfer) before you can gap them with a feeler gauge. You do not have to file points if you use a dwell meter. The dwell meter takes into account the metal build up, because it looks at the points electrical measurement rather than the mechanical measurement.

The condenser capacity is measured in microfarads. A microfarad is 1/10 of 1/1,000,000 of a farad (.0000001 farad)There are specialized testers to do this measurement. The typical condenser will have between .2 to .3 microfarads. The variation in condenser capacity can vary widely, (most condensers fall somewhere around .25 microfarad).This is why some contact points last longer than others. It is not the points fault but is the condensers fault instead.

Look for the metal transfer. If there is none consider not replacing the condenser as it is matched to your particular ignition system. If there is metal transfer replace the condenser as you have nothing to lose in the process."

So, my arm contact point was pitted and the corresponding metal transferred to the base contact point as a "***" because the capacitance of my condenser was too high. The one I replaced it with was very close to .250 mF so should not effect the new points in the same way the old consenser did.

Just thought you might like to know. :cool:
Click to expand...

I think excess oil on the contacts made this issue even worse. Both pics show burnt oil .
 
Looks like he's stretching it at 9,000 mi.on those points.I would have changed those things he calls points long ago.Goes for the plugs also.Sounds like he's being penny wise and dollar foolish. OMO. ken ct.
 
Good info Henry .I think Henry Ford was looking for a lot more miles on his diver distributor's at 3,5 to 4 volt system .more like 50.000.
 
Considering the fact that most people didn't put more tha 5k a year on their cars. Changing pointa every 2-3 years was just gemeral maintainence
 
ken ct said:
Looks like he's stretching it at 9,000 mi.on those points.I would have changed those things he calls points long ago.Goes for the plugs also.Sounds like he's being penny wise and dollar foolish. OMO. ken ct.
Click to expand...

I change the points every 10,000 miles as Ford recommends. That frequency has always worked for me. How often do you replace your points and plugs. ken ct?

What capacitance condenser do you use? How does it affect your points' life?
 
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denson1932 said:
Good info but a couple of minor corrections...a microfarad is 1 millionth of a farad thus .000001 of a farad. The digital multimeter shown is set for reading capacitance and in the pix it reads in nanofarads, a nanofarad is 1 billionth of a farad thus .000000001 of a farad. To convert nanofarads to microfarads divide by 1000 as correctly stated, or more easily just move decimal 3 to the left.
Click to expand...

My meter was set for automatic scaling so it automatically converted the .3149 microfarads to 314.9 nanofarads for the display. They are both the same quantity. Kind of like saying 4 quarts or 1 gallon. Both are correctly describing the same quantity. I used the term microfarads in my discussion as that is the term most are familiar with even though the meter shows the same quantity in nanofarads (three decimal places to the right as denson1932 said). I wouldn't call his comment a correction as much as a clarification - reconciling my description with the illustration that were both really talking about and illustrating the same thing. ;)
 
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