R2800 Coil specs?

Discussion in 'Engines' started by Daddio, Jul 14, 2009.

  1. Daddio

    Daddio New Member

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    Does anyone know the primary and secondary coil resistance for a Pratt Whitney R2800-CB3 low-tension ignition system? I'm seeing some variation in different cylinders' coils on , and I don't know if it's OK or if somebody was simply desparate enough for parts to use whatever would make fire.
    (This engine will not be flying, so reliability is not immensely critical. Expensive yes. Life-threatening no. I do want to make it right.)
    Thanks,
     
  2. Cutman

    Cutman New Member

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    Daddio,
    I've got a few manuals on hand and I'll try to get you a figure. Looking at the Service School Manual you are talking about American Bosch and Scintilla systems, correct?

    I envy you the opportunity to work on R-2800's, they sure seem like fascinating beasts to me.

    Get info for you shortly.

    John "Cutman" Steele




     
  3. Daddio

    Daddio New Member

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    I have a R-2800-CB Double Wasp Maintenance Manual, reissued March, 1957, part no. 166498.
    I've been through it about six times looking for some ohms. Nothing yet.
     
  4. danjama

    danjama Member

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    Doesn't resistance depend on the length of the coil?
     
  5. Cutman

    Cutman New Member

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    Daddio,
    I'm looking at a CB manual dated August1950. Nothing specific seems to be listed.

    However, I'm remembering my basic electricity. Shouldn't resistance between the primary ground and the Primary + be zero, as would the leads of the secondary? Not open, but 0 ohms. The coils are wraps of wire, therefore with very little inherent resistance. It's the relationship between the number of turns in each that defines the current/voltage output.

    Somebody else validate my theory please. Your mileage may vary.

    Cutter


     
  6. Cutman

    Cutman New Member

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    Daddio,
    Now I'm looking thru my Overhaul manual for A B series engines, and the only reference I see to a resistance is in the Magneto Test Procedure on pg. 1427 (manual part no 49656, dated July 1942). It says "COIL-Before installing the coils in the magneto, check the resistance of the secondary winding with the No. 11-1274 Ohmmeter. The reading must be from 5000 - 7000 ohms."

    That seems to reference the internal coil of the magneto NOT the primary or secondary resistance of the transforming coils ON EACH CYLINDER that I assume you are interested in.

    Any Help?

    Good luck, Cutter



     
  7. Daddio

    Daddio New Member

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    That is talking abot a coil IN the magneto? My R2800 uses the low tension system with one coil on every cylinder. I imagine the transformer would be nearly the same, but if it uses slightly different gauge wire, the resistance would be different also.
    I just finished measuring all my coils.
    They ranged from 7.5 k-ohms to 8.5 k-ohms measuring from the high tension lead to ground.
     
  8. engguy

    engguy Member

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    Sounds like a nice job you have, well thats if it pays good. You said your 2800 is it yours? I wish we had an outfit here that did that sort of thing. Used to years ago at Boeing field, I don't think theirs was a CB though.
    Are the coils different part numbers? Is that a primary coil resistance figure?
     
  9. Daddio

    Daddio New Member

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    The coil specs I reported were the secondary windings. The 1 or 2 primary coils I checked, if I remember right, were in the range of 3 - 5 ohms. I didn't check all of 'em; I didn't have those connectors off and didn't want to pull them just for the data.
     
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