Starter Issue... toasted contactors....

Discussion in 'Maintenance Bay' started by Piper_Six, Nov 21, 2021.

  1. Piper_Six

    Piper_Six Pre-Flight

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    1959 Bonqnza K35
    On my K-35 Bonanza, IO-470, has this TCM Energizer starter... always had difficulty starting, with a good battery and full charge, usually seemed to struggle to turn over, and finally after several tries would start. Noticing the cables were really old and tired looking, I replaced all the main cables with Bogart cables, and replaced the contactors last year.

    Of late, the starting seems to be sluggish and showed very same symptoms of difficult to turn a few blades, and eventually would start with the battery being drawn down significantly. (I notice on these difficult starts, the current draw would be in the 30 to 45 amps all the way into run up and finally come down before take off and settle down in flight to normal levels 1-2 Amps).

    This last week, on one of these very hard to start days, I think I got a bit frustrated and tried too many times, and this time, it went just CLICK and nothing... I tried a few times... but then looks like the starter has shorted to ground ! the hot side of both the contactors showed burnt signs - seems like they have arced to case... battery discharged significantly...

    Shut everything down and sure enough .. it looked charred...

    Have new starter on order, and replaced both contactors again...

    I did download the Sky-Tec troubleshooting guide and followed it, all the numbers seem fine (I did this with the starter disconnected)... right now the starter is showing a dead short.

    Question: With the starter disconnected, I do see a full bus voltage on that hot wire to ground when I crank (push button start) - that is normal I would think ... and the dead starter... showing a full short between the terminal to case... that is NOT normal.. am I on the right track ?

    Here are the pics of the charred contactors :(
     

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  2. Magman

    Magman Pre-takeoff checklist

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    The engine doesn’t have to spin really fast to start and will only take just so

    much abuse before a failure.

    I suggest having mag e-gap checked and possibly installing Slick Start.

    Otherwise you will have the same issue with your replacement Starter.
     
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  3. kmacht

    kmacht Pre-takeoff checklist

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    Sounds like it may be time to engage a competent mechanic on this one. Burning and arcing isn’t something to mess around with in an airplane based on some random suggestions on an Internet forum. It could be just a bad starter or it could be something more serious that caused the starter to go bad in the first place. You need a mechanic familiar with your engine and electrical system to find out before you just put another starter in there and hope it’s good enough.
     
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  4. flyingbrit

    flyingbrit Pre-takeoff checklist

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    A stationary starter has a very low resistance...typically less than 1/10 ohm. You cannot measure it properly with an ordinary ohmmeter. A specialized 4-wire meter would work, but I doubt that there are any published specs on what the normal reading is. Starters are ideally tested by measuring the current when free running and with locked rotor.

    Before condemning the starter I would remove it and measure at least the free running current. If it spins and draws <50A or so it is probably OK.
     
  5. Bell206

    Bell206 En-Route

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    To be blunt, no. Your very first post sentence had the original clue. Regardless I would have the entire start/charge electrical system properly checked especially the ground connections before throwing more parts at it.;)
    Sure. But without a load it is meaningless. One trick to check higher amp circuits is fabricate a test light with a landing light bulb or similar.
    FYI: you can fabricate equivelent cables at a cost much lower than Bogarts.
     
  6. Piper_Six

    Piper_Six Pre-Flight

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    That is good to know - so the extremely low resistance is what I am probably interpreting as a dead short. Yes, the mechanic plans to do the test on a bench.
     
  7. Piper_Six

    Piper_Six Pre-Flight

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    Yes - agree with you, am having the mechanic check it out thoroughly.
     
  8. Dan Thomas

    Dan Thomas Final Approach

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    Bad contactors have resulted in many, many AMUs spent on new batteries and starters. This sounds like an old, worn-out, oxidized contactor. Imagine a tiny internal resistance in those contacts of maybe .03 ohms. With a starter draw of normally 250 amps or more, this would get cut to maybe 200, but that causes a 6.5-volt drop across the contacts. 6.5 volts at 200 amps is 1300 watts, more than the heat output of a really good toaster concentrated in that tiny canister. It will get really hot. If there's arcing going on in there it gets much more fiery.

    We've talked about this many times here. Taking voltage drop readings across the master and starter contactors while the engine is cranked easily reveals what needs to be fixed, and does it economically and quickly.
     
  9. Piper_Six

    Piper_Six Pre-Flight

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    I agree Dan, that is why they were replaced just a year ago. The old ones were really really old.. I did cut one open and posted pictures on here... This time the contactors were still shiny new, just a year old... that's why the suspicion on the starter. Checking the mag e-gap, as suggested here, is also something we haven't looked at yet.
     
  10. Silvaire

    Silvaire En-Route

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    Bench test the starter but you also need to check the starter adapter. The Continental is a unique system and a new adapter is going to cost you some bucks. Also, it will only be warranted if it is installed with a new starter.
     
  11. Dan Thomas

    Dan Thomas Final Approach

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    Yeah, I missed that part about it being a new contactor. Still, I'd suspect contactor quality, or maybe the mechanic managed to turn the stud when he was connecting the cables. Mustn't do that. The stud has a square head on it, with the top side nice and flat for the solenoid disc to contact. Lots of area to carry the current. Rotating the stud puts a corner of it in contact with the disc, and that causes a bit of resistance that makes plenty of heat. It will tilt the disc enough to put the other stud into corner-contact, too.

    If the starter was shorted and burned the contactor, the master contactor should also be burned. Those two are in series and carry the same starter current.
     
  12. Piper_Six

    Piper_Six Pre-Flight

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    Yes, both the contactors showed signs of excess current and charring, just as you have described.
     
  13. Piper_Six

    Piper_Six Pre-Flight

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    Starter replaced - WOW ! What a difference ! Starts QUICK ! and with ease, blade turns so fast - have never seen it start so quickly or spin so fast before .... may be it needed the starter all along... the one that came out seemed stuck - would not turn by hand. Haven't done a bench test yet - it smells really bad like the windings are burned. Also cleaned all the connections and confirmed the ground connections.
     
  14. Dan Thomas

    Dan Thomas Final Approach

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    Sounds like a failed starter bearing. The starter's armature runs very close to the field pole shoes, and bearing wear can result in contact, adding terrific friction as the poles magnetically pull on the armature. The inductive reactance of the starter goes way down when it's stalled or nearly so, increasing the current flow considerably.
     
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  15. Gary Ward

    Gary Ward Pre-takeoff checklist

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    Thanks for the update/solution to your starting problem. So many times folks come looking for help online and get help but never come back to update the folks who tried to help.

    Happy Thanksgiving.
     
  16. Dan Thomas

    Dan Thomas Final Approach

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    In a former career I was the shop foreman in an air-brake remanufacturing shop. We had an 800 number for folks to call with troubleshooting help when they couldn't figure out what component in the system was at fault. I dealt with many mechanics that way. In 12 years I had ONE guy call back and thank me.
     
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  17. Piper_Six

    Piper_Six Pre-Flight

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    Totally agree, it is only common courtesy to return with how the issue was resolved. There is such a great deal of "learning" one can get from here. While we all do defer things to a qualified A&P, many times, in the time it takes to get with the shop and have it looked, this forum and this discussion helps immensely in learning from others who may have gone through similar things or are knowledgeable and willing to share. I, for one, greatly admire, respect and thank all the folks who chime in with very valuable thoughts/suggestions and ideas. Also enjoy the occasional blast of humor that is very enjoyable !
     
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