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Thread: Gear-Driven Alternator Clearance Question

  1. #1

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    Gear-Driven Alternator Clearance Question

    Engine is ECI O-320 / O-340

    Will a B&C model SD-20 (20 amp) alternator fit between the accessory pad and the firewall? Using conical mount; Installed length of alternator is 6.0" from face of mounting flange to back-end of alternator.

    B&C doesn't know and I haven't found anyone with ECI who knows. We do know that the SD-20S (not the unit in question) has lateral interference problems... but not length problems.

    B&C has a sale going on during this February and I've got four days to buy.

  2. #2
    DW's Avatar
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    What does yours measure??

  3. #3
    16-bravo's Avatar
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    Fits, just fine, with about a 1/2" between the firewall, and the Field plug.

  4. #4

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    DW,

    I'm doing some planning for an experimental Super Cub, so I don't have an alternator now.

    Thanks

  5. #5
    DW's Avatar
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    I have my engine moved back 1" and mine measures 5 3/4"

  6. #6

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    I have one of these as well but have been delayed in the installation. Has anyone heard these units produce noise when operating? I would think someone on here has some experience with them.

    Thanx for any info

  7. #7

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    68D,

    What have you heard about noise? Electrical noise or mechanical noise?

    And, did you find out from someone who actually uses the SD-20?

    I think Ed Doyle uses one, I'll try to contact him and see what he knows.

    Thanks

  8. #8

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    I just spoke with Ed Doyle about the SD-20. He uses it on his Lycoming, and said he has no clearance problems with the firewall nor the tach cable. Further, he has no noise problems with it.

  9. #9

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    Jasper,

    Thank you very much for finding out some info about this. I think it was Crash on here who put one on a few years back (sorry I have not had the time to search it) who said he would not put one on again for noise issues but I cannot remember what kind of noise he was referring to. Am glad to hear you have someone who has one on that likes it.

    For your electrical loads, are you close to the limit with this alternator with regular landing lights? I was thinking I would have to put on LED landing lights in order for the electrical loads to fall below the 80% level.

    Thank again.

  10. #10

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    68D,

    I will be using LEDs.

    However, with a normal electrical load, using conventional lighting and operating at 1800 RPM (or lower), I'd be afraid something would go lacking.

    B&C has output charts for these units on their website which gives current produced at certain "alternator" RPMs. For Lycoming engines, the alternator RPM is "engine RPM multiplied by 1.3.

    B&C told me that an alternator RPM below the minimum one, given at the top of the chart, would produce significantly lower current. So... these things don't really begin producing much useable current until they spin-up into RPM ranges shown on the chart(s).

  11. #11

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    I seem to recall that the adapter that mounts the alternator to the vacuum pump location also geared down the alternator so its output is further limited. I seem to recall that the SD-20 was the the same basic unit as the L-40 but it ran at half the speed so thus half the output.

    I haven't looked at the numbers for awhile but will again this spring as I hope to get my engine back on my plane and use it this summer and fall.

    thanx again for all the info.

  12. #12
    Steve Pierce's Avatar
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    Just pulled the engine off Ed's airplane. Alternator has clearance but is tight. It has to come off to get to the tach cable.

    As far as noise goes, unless the alternator is defective that is an installation issue.

    Sent from my SM-N900V using SuperCub.Org mobile app
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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