Why is it so hard to test a Condenser? (Was: Condensers for Johnson / OMC)

[legendre]

quote Mumbles:

Can you be more specific as to what year and model you are working on?

In this case, it’s the same-old troublesome 1947-48 Johnson TD20.

quote :

Vishay and Orange Drops are two capacitors which will substitute for the original tin can caps if you can’t find them.

I’d think the Illinois Capacitor MPW (or MWR) part 0.22uF @ 630V should be right-on for this application. Probably fits inside the old can, as well.

[chris-p]

As mumbles has stated, I too have subbed in capacitor (get one with high enough voltage) into the original can, or simply wire by itself. The part can still be found though, post a wanted ad in the webvertize.

I have a few Mercotronics and a Stevens tester. If you are going to be getting into outboards more, I would recommend you get one. They are invaluable. I buy them whenever I see one for sale. They put a load on the coils/condenser to test. I have found myself, regarding OMCS anyways, that the condensors with the red paper style tops fail about 50/50. The newer ones with the black rubber caps seem to have a better pass ratio.

Now to your question, the condenser can be tested with an analog style meter. If you have done a few, and know what you are looking for in the spike. Instead of typing it all out, read here.

http://www.pochefamily.org/outboard/Con … sting.html

[The Boat House]

quote legendre:

Quick question – what’s the part number (NAPA, etc) for the generic ignition condensers used in the older Johnson / OMC magnetos? And does NAPA still stock these items?

[legendre]

@Tubs

Hey, there you go! Interesting, it’s supplied as a generic tubular condenser with an application-specific mounting bracket.. makes sense, I suppose.

The basic AL869 part was apparently used in numerous Chrysler / Dodge / Plymouth and AMC / Jeep / IHC vehicles (plus many others as well) from the 1940s through the mid-70s when electronic ignitions became the norm (would have been around 1975 or so).

A little searching turned up a whole boatload of cross-reference parts, one particular source listed all of the following codes: DCC-32, AL-111/T, 14000, 71469C1, AL869, AT14684, G124, 2103, AL111SB, 6K6, AL1531, 409 and AL531. Be forewarned – I have not vetted this list – but so long as the value is ~0.22uF with sufficient voltage rating (400 AC) any should work..

In any event, they are widely available on eBay under several different part numbers, for around $5.00/ea inclusive of shipping. The AL-111T seems to be one of the most common types sold.

[dave-bernard]

mercury unit used to test coils condensors etc.

[vintin]

It’s not hard to test condensers (capacitors).

https://www.google.com/search?q=inexpen … 8&oe=utf-8

[jethrob]

I don’t have any trouble testing them. Just hook them up to my condesner tester. If the light flashes they are good. If you send it to me with a sase I’ll test it for ya and send it back.

[jnjvan]

If you really want to thoroughly test a condenser, you need to apply real world conditions. These include the voltage and current that they see in service, as well as heat and vibration. Merc-O Tronic testers, Stevens testers, and the old magic eye testers all are capable of testing at the correct voltages and (possibly) currents. The problem with bench testers is that they don’t include the heat and vibration part. I believe that heat is a primary contributor to parts like condensers and coils that test OK on the bench, and in a quick run in the barrel, but fail three miles from the launch ramp.

I work as an electrical engineer, designing electronic controls for commercial vehicles (i.e. trucks). The primary enemies of electronic components in harsh environments are heat, vibration, humidity, and deterioration due to aging. All of these are present in old outboards.

John Van

[vintin]

quote jnjvan:

If you really want to thoroughly test a condenser, you need to apply real world conditions. These include the voltage and current that they see in service, as well as heat and vibration. Merc-O Tronic testers, Stevens testers, and the old magic eye testers all are capable of testing at the correct voltages and (possibly) currents. The problem with bench testers is that they don’t include the heat and vibration part. I believe that heat is a primary contributor to parts like condensers and coils that test OK on the bench, and in a quick run in the barrel, but fail three miles from the launch ramp.

I work as an electrical engineer, designing electronic controls for commercial vehicles (i.e. trucks). The primary enemies of electronic components in harsh environments are heat, vibration, humidity, and deterioration due to aging. All of these are present in old outboards.

John Van

Hi John,

Once the condenser fails under real life conditions, are you suggesting that it may still test good on a bench tester?

My understanding is that once the dielectric is compromised, the cap is bad from then on and a bench tester would pick it up.

I don’t have a capacitor checker but I often test them for short or open with a volt meter and watch the resistance rise as they charge up, usually going to the infinite.

Any advice about bringing an old capacitor that has been sitting idle for decades back to spec by applying a very slowly increasing voltage giving the cap time to ‘reform’? I know it’s a technique used on long idled audio equipment and wonder how it might apply to the condensers we find in our old outboard motors. I’ve never found an open or shorted ignition cap in my limited experience with old outboard motors.

Thanks,

Dan

[dave-bernard]

I make my own from capacitors.

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