Merc-O-Tronic schooling please

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    bill-mcnamara

    Canada Member - 1 Year
    Replies: 204
    Topics: 49
    #193737

    I did a Capacity test on the condenser from the Sea King Midget, and found 0.23uf compared to 0.27uf from a couple of used condensers from a ’50’s JW I’d been working on.
    Seems ballpark to me.

    Also tried the Leakage & Short test, and found that the “newer” units moved into the green Leakage range but stayed there about 1/4 of the way into the green for 15 seconds or so.
    The capacitor from the Midget went into the green but then moved back left to the narrow black bar which indices a good condenser as stated in the text.
    The manual also states that if the needle stays in the green, the condenser is leaking or shorting and must be replaced.
    Seems that the older Midget condenser seems OK, but the later JW units were both faulty.
    Are these valid conclusions at this point?

    The manual then describes a third “Series Resistance Test”……….which is a bit confusing at this point, and I’m not sure what it would tell me anyway…..yet.

    Bill.

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    jeff-register

    US Member - 1 Year
    Replies: 1159
    Topics: 48
    #193740

    Bill,
    When testing caps I use a digital meter to get a “face value” The Merc O T gives load testing value. Now lets look at design date from the 50’s. What is drifting from “new” values with the MOT meter? What you are testing is the dielectrics of the cap. It was rated at a given value when new. Elapsed time of testing should be finite, reflection of run time. I don’t have my manual in front of me but all resistance test will look for flaky or open conditions. We had Vitals monitors in I.C.U. in the hospital that would go flaky because the sheets lint made semi conductors & changes values. A blow out with Med air fixed them. Contamination with the MOT & environment contaminates both. I would tap on the component while testing. & remember design is from the 50’s. How long has it been since the machine has been calibrated too? I tinker with electronics & any data on the MOT is very protected + manufactures of these have components “built to value” a run of say 10, 000 & then there’s no more to replace.
    A cap is rolled up foill, insulator (waxed paper) & foil encased. Easy to get shrinkage, deformation & leakage + failure intermittent values. Check at different temps ( ice pack & hair dryer) to evaluate, not too hot but mtr temps anyway.
    The vibrator which outputs Pulsed D.C. for coil testing has a frequency it pulses at to charge/ discharge the coil for testing to simulate points opening/ closing & the frequency should be around say 5000 refering to engine RPM & I’m sure an electro-mechanical devise is not stable. Looked in to it years ago & even a heavy duty switching like a darlington transistor was hard to find. The early auto radio has a vibrator to make a pulsed signal to input a small transformer (coil) to up the voltage, inverter to run the tubes in the reciever.
    Coils are transformers on induced from magnetic flux not an direct AC voltage not inclusive of early battery fed type outboards.
    P.S. I researched cays from Vishay man. & the rep advised voltage rating @ 800 or above for Mags.

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    bill-mcnamara

    Canada Member - 1 Year
    Replies: 204
    Topics: 49
    #193757

    Thanks so much Jeff for your extensive response.
    Unfortunately I feel like some of my chemistry students did by the end of one of my classes!
    Sorry, but my knowledge if electronics is less than minimal.
    Bill.

    frankr
    frankr

    US Member - 1 Year
    Replies: 4812
    Topics: 48
    #193761

    I have a Merc-O-Tronic manual, but don’t have a MOT instrument, so my knowledge is a bit limited. I also have some electronics training. Somebody said that education is what you have left after you forget everything you learned. But some generalities about condensers that you might find helpful:

    Capacity. Importance of correct values varies with the application. Very important in a TV tuner circuit. Far less important in an ignition circuit. I’d consider anything within 20% to be ok and it will run fine.

    Leakage: Compare to a leaky water bucket full of holes. Water leaking out of the holes is water lost. Electricity leaking through the “holes” in a condenser’s wax paper sheet is electricity (energy) lost. Lose too much energy and the spark produced becomes weaker. Having said that, wax paper/foil condensers are inherently lousy—they ALL leak. It’s a matter of how much you can tolerate. Experience has proven that the condensers we are working with can be pretty durn leaky and still run..

    Series resistance: Post mortem examination has shown me that the method used to connect the wire to the foil sheet varies among brands. A poor connection is almost like disconnecting it intermittently. Of condensers I’ve torn apart, OMC are pretty good on that score. Wico condensers I’ve torn apart are crap.

    Conclusion: We are far too unforgiving. A lot of them that we throw away will still run.

    Tubs
    Tubs

    US Member - 1 Year
    Replies: 2788
    Topics: 161
    #193762

    • This reply was modified 1 month, 3 weeks ago by TubsTubs.
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    bill-mcnamara

    Canada Member - 1 Year
    Replies: 204
    Topics: 49
    #193768

    Thanks Tubs, good tip on warming up the condenser and testing it again.
    Just for fun I tested 15 used condensers yesterday and found 7 of them faulty. They had been in storage out in a cold garage though.

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    bill-mcnamara

    Canada Member - 1 Year
    Replies: 204
    Topics: 49
    #193769

    Good practical advice Frank, thanks so much.
    Bill.

    frankr
    frankr

    US Member - 1 Year
    Replies: 4812
    Topics: 48
    #193771

    The MOT appears to be nothing but an Ohmmeter with the dial markings modified. The same test can be done with a common analog multimeter. On a high Oms scale the needle will jump up as the condenser charges, and return to near infinity when fully charged. How close it returns to infinity is indicative of leakage. One important thing to remember–this is a hands-off test. If you are touching the condenser and wire (or the test leads) you will get a false reading because you are also reading the leakage through your body. This is called getting a shock, if the voltage were high enough (it’s not).

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    kirkp

    US Member - 1 Year
    Replies: 104
    Topics: 7
    #194006

    Frank, regarding your statement “On a high Oms scale the needle will jump up as the condenser charges, and return to near infinity when fully charged. How close it returns to infinity is indicative of leakage.” So if it returns to infinity, is that high leakage or just the opposite where the farther away from infinity, the higher the leakage?
    Thanks
    Kirk

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