testing capacitor?

[old-9]

It has been a long time since my electronics classes. Trying to get good spark on my 41 9-N, front mount. You know how hard it is to R&R the dist. I think the capacitor is the problem just want to rule it out. As always thank you for your help. joe

 

[old]

Not often a condenser as they are called in a distributor goes bad but now days common to have a new one be bad right out of the box. You can sort of test one with a VOM but the test is not 100% sure to get you a good reading and know for sure it is good

 

[Janicholson]

An ohm meter(if old battery powered analog type) will show a few ohms then drift back to zero. If digital probably nothing. Either way it is not being tested well, just kinda. They live in a circuit that can have 250 or more volts into and out of it as the coil discharges through its wires to the plugs. A real capacitor checker is an expensive tool that is not worth the ownership for those like us that dont need it but twice a lifetime. The ohm meter showing infinite resistance says it is not shorted (at very small voltages but not working voltage). Aan ohm meter reading of full conductivity is a definite bad condenser. Jim

 

[JMOR]

(quoted from post at 19:03:31 11/30/22) It has been a long time since my electronics classes. Trying to get good spark on my 41 9-N, front mount. You know how hard it is to R&R the dist. I think the capacitor is the problem just want to rule it out. As always thank you for your help. joe

ou do remove the distributor from tractor to work on distributor don't you? For the highest percentage of people (those without the equipment, knowledge, skills to perform such cap tests) it is standard procedure to simply substitute another cap.

 

[504]

I don't remember what we charged them with, but we did and then sorted them to the workbench. If they jumped a spark then were fine. I have seen one bad condenser in my life and one IH Scout that did not have one at all.

 

[Geo-TH,In]

I've been in electronics for a long time.
I'm not convinced there is a good capacitor tester.
I keep my old used condensers(capacitor) in a drawer.
The best test is a simple substitution test.
Install the old good condenser and see if it helps the spark.
When points open the condenser is subjected to a much higher voltage than the test instrument provides.

 

[old-9]

George, the early Fords,9,2,8Ns, the Distributors are mounted on the front of engine. Like between the fan and engine right behind the generator. Lots of fun to R&R for someone our age, so I want to get it right the next time. Although I have been getting faster at the R&R. joe

 

[Geo-TH,In]

Joe,
Have you changed the points and condenser on the 225 slant 6?
I would remove plugs, get the engine timing mark lined up with TDC.
I then mark the position of the rotor and pull the distributor.
Install point and condenser, install distributor.
I had a way to statically time the engine. It was close enough to start the engine then use a timing light.
Changing points and condenser was an annual event just before winter.
I can't say that I ever had a bad condenser.
If you take one apart, they are nothing but foil separated by an insulator. If I recall the insulator, the dielectric, was paper or cardboard.
Not much to go wrong as long as moisture doesn't get inside.
In the early days of radios, they rolled their own capacitors using aluminum foil and paper, then dipped them in wax to keep the moisture out.

 

[grandpa Love]

Make life easy on yourself and take the 2 bolts out of the distributor and work on it on a table. Swap the condenser, easy and cheap. Get a good one from Napa

 

[CKain(MI)]

a capacitor/condensor is a little like a battery. will hold a charge for a short bit. When you put an ohm-meter on it, you will get a good needle deflection, then it will drift back to low. Then reverse the leads and touch again, once more it should deflect quick and way ovver, then slowly drift back towards zero. That would be a good capacitor. If it's open interanlly(defective) there will be no deflection. If the meter just shows a low and constant reading, its shorted.
If the capacitor is open, the engine will still work fine. The points will go back quickly!

 

[JMOR]

(quoted from post at 12:16:52 12/01/22) a capacitor/condensor is a little like a battery. will hold a charge for a short bit. When you put an ohm-meter on it, you will get a good needle deflection, then it will drift back to low. Then reverse the leads and touch again, once more it should deflect quick and way ovver, then slowly drift back towards zero. That would be a good capacitor. If it's open interanlly(defective) there will be no deflection. If the meter just shows a low and constant reading, its shorted.
If the capacitor is open, the engine will still work fine. The points will go back quickly!

orry, my friend....that is not always true. The spark is much weaker w/o a condenser & sometimes they will not have a strong enough spark to run. I have verified , as you can see & hear.

https://i.imgur.com/m84PvvB.mp4
with audio:

https://i.imgur.com/5RG9078.mp4


This post was edited by JMOR on 12/05/2022 at 02:46 pm.

 

[Jim in LA]

I had a Sprague Tel-Ohmike capacitor analyzer once, it was a very good piece of test equipment. Very good leakage test and had the electronic eye indicator. They sell for quite a premium on Ebay now.

 

[Janicholson]

though a some what usable test, the voltage from a digital meter is not sufficient to do that (high impedance) the analog meter will do what you have indicated, but it will not provide the 200+ peak Voltage that can bridge a failed dielectric film. Jim

 

[JMOR]

(quoted from post at 19:07:01 12/01/22) though a some what usable test, the voltage from a digital meter is not sufficient to do that (high impedance) the analog meter will do what you have indicated, but it will not provide the 200+ peak Voltage that can bridge a failed dielectric film. Jim

ot much eqmt needed to determine cap value, shorted, open and exposure to 170 volts peak voltage. May not be perfect, but a pretty thorough test

 

[docmirror]

The voltage across any auto condenser never goes higher than 18V. Best not to apply 120VAC to it.

My experience with an ohm meter is that when the leads are first touched to the condenser, the inrush voltage used to measure the resistance(from the meter) excites the dielectric and shows a low resistance at first, and then the resistance slowly rises to > 20M ohms within about 15 seconds.

 

[JMOR]

(quoted from post at 19:52:55 12/01/22) The voltage across any auto condenser never goes higher than 18V. Best not to apply 120VAC to it.

My experience with an ohm meter is that when the leads are first touched to the condenser, the inrush voltage used to measure the resistance(from the meter) excites the dielectric and shows a low resistance at first, and then the resistance slowly rises to > 20M ohms within about 15 seconds.

ery obviously, you know absolutely nothing about such ignition systems, so to prevent exposing your further ignorance, you need to remain silent.

 

[JMOR]

(quoted from post at 00:23:13 12/02/22)

(quoted from post at 19:52:55 12/01/22) The voltage across any auto condenser never goes higher than 18V. Best not to apply 120VAC to it.

My experience with an ohm meter is that when the leads are first touched to the condenser, the inrush voltage used to measure the resistance(from the meter) excites the dielectric and shows a low resistance at first, and then the resistance slowly rises to > 20M ohms within about 15 seconds.

ery obviously, you know absolutely nothing about such ignition systems, so to prevent exposing your further ignorance, you need to remain silent.

K, I was a little harsh last night, so I'll try this: Virtually all ignition coils of those days were 100 to 1 turns ratio, so when the points open and field collapses, the 20,000 volts of spark voltage 'transforms to the primary as 20,000/100 = 200 volts. Not just theory, but easily observable on an oscilloscope. Need more proof, hold your finger on the primary while engine running. Probably should skip the latter if you have a pacemaker.
At points opening (left):

full cycle: