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Thread: Starter solenoid questions

  1. #1

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    Starter solenoid questions

    Pulled the solenoids out of the J4 - the master works just like a normal solenoid, but the starter solenoid is, well, different.

    It has two small pins, and only the left one appears to be connected to anything. (It of course has the two large terminals for the contactor) The left pin shows maybe 5 ohms to the metal case. The right hand one shows infinite to all other pins. Neither is hooked to the input.

    It looks like the start switch has to feed 12 volts to the left pin to engage the contacts, and the case gets tied to ground. If that is so, can I use the master solenoid as the starter solenoid, thus just providing a momentary ground to the coil (like most start solenoids)?

    Or should I just get B&C to send me a bulletproof three terminal solenoid?

  2. #2
    windy's Avatar
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    I know first hand that if you try to use a starter solenoid (designed for intermittent duty) in place of the master solenoid(continuous duty), the plane can catch on fire...in flight.


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  3. #3
    Gordon Misch's Avatar
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    Gordon Misch's Avatar
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    The above is automotive, but is like on my -12. The "I" terminal is ignored. I can send you a photo tomorrow if it would help. It's a NAPA starter solenoid, and yes, my IA knows that.
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    Gordon Misch's Avatar
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    Quote Originally Posted by windy View Post
    I know first hand that if you try to use a starter solenoid (designed for intermittent duty) in place of the master solenoid(continuous duty), the plane can catch on fire...in flight.
    C'mon Windy, the story! Please??
    Gordon

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    wireweinie's Avatar
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    Quote Originally Posted by bob turner View Post
    Pulled the solenoids out of the J4 - the master works just like a normal solenoid, but the starter solenoid is, well, different.

    It has two small pins, and only the left one appears to be connected to anything. (It of course has the two large terminals for the contactor) The left pin shows maybe 5 ohms to the metal case. The right hand one shows infinite to all other pins. Neither is hooked to the input.

    It looks like the start switch has to feed 12 volts to the left pin to engage the contacts, and the case gets tied to ground. If that is so, can I use the master solenoid as the starter solenoid, thus just providing a momentary ground to the coil (like most start solenoids)?

    Or should I just get B&C to send me a bulletproof three terminal solenoid?
    Your starter relay is an automotive one. If you replace it, you have a choice of two styles of aviation grade relays. If you use the the style with one small terminal, just connect the wire from the start switch. if you use the style with two small terminals, connect one to the wire from the start switch and jumper the other to ground.

    As Windy says, if you use the wrong relay, bad 'stuff' happens. A start relay will be marked 'intermittent' or 'int.' and a master relay will be marked 'continuous' or 'cont.' on the label. And either relay can be found with one OR two small terminals, so they can look the same but differ in internal connections.

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    As said here DO NOT USE START SOLENOID IN PLACE OF BATTERY SOLENOID, but last resort you can use a continuous duty master in place of start solenoid if it is high enough amperage, just don't do it the other way around, the intermittent duty start solenoid can break open or closed I guess and either cause an in fire or just open and you lose all power, both bad in flight.

  8. #8
    windy's Avatar
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    Quote Originally Posted by Gordon Misch View Post
    C'mon Windy, the story! Please??
    The jackasses at the shop that did the upgrade on my -12 to an O-320 engine, along with replacing the generator with an alternator, installed a master solenoid that they picked up off the hangar floor.

    After 10 hrs of engine break-in, I was merrily flying over the mountains east of Ogden on my way to a fly-in, when I started smelling smoke. Hoping the smoke was outside, I opened the window to sniff. The open window drew the smoke forward from the battery box area & filled the cockpit, practically suffocating me. If I’d have had a parachute, the -12 would have been on its own.

    Not knowing exactly where the smoke was coming from and trying not to panic, I dove toward the ground as fast as possible, which was the only thing I could remember from pilot training about putting out fires. I spotted a dirt road & a field next to each other and opted for the road at the last minute, since there were a bunch of rocks on the field. It turned out that the road was very short and curvy, but I got landed and stopped without hitting anything. There I was, in the middle of nowhere, with no cell phone signal, on top of a mountain at 8,500 msl, after a fire in the cockpit.

    I jumped out of that plane and ran like as if I was being chased by a bear. When I turned around after my escape, I expected the plane to be engulfed in flames, but no, it just sat there. I got brave enough to tiptoe over and open the cowling, expecting to see a charred new engine, but no, the engine was still shiny new.

    In the meantime, a friend who had also been flying along to the fly-in in his supercub, landed (in the field, past all the rocks) to see what the delay was all about. I’ll spare all the details, but suffice it to say that by the time we both took off, a Bobcat and a D6 loader both ended up stuck in a mud hole in the process of dragging my -12 over to the field, since the curvy dirt road was too short for takeoff. Had to hand prop the -12, since there was no electrical.

    After getting back to the shop that did the work, it was discovered that the (intermittent duty) master solenoid had been fried, burnt the positive cable to the battery, melted the battery, burnt the wooden spacer block above the battery in the battery box, and charred the fuselage stringer in that area. I was lucky.
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  9. #9
    wireweinie's Avatar
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    The coil of the start relay is a lower resistance than the master relay coil. This allows a greater current flow when activated, which, in turn, creates greater magnetism. That means that the movement of the slug, inside the relay, is more violent than that of the master relay. This is a design feature that helps with the slag that builds up on the contacts when using the starter motor. This is the same reason that the factory installed start relays were 6 volt.

    The higher current flow in the coil, also produces more heat. Not a problem for momentary use but after 2 to 3 minutes, the relay case will be to hot to touch and you can smell it.

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  10. #10

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    Thanks. No chance that I will use a starter solenoid for a master. You all covered that last year, and Wendy's story of course clinched that.

    And Gordon's drawing is what I needed.

    When I was testing this thing yesterday I failed to ground the case. My only heartburn with using it is rather than a ground wire through the starter button I need 12 volts. Not really a big deal, I guess.

  11. #11

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    Quote Originally Posted by wireweinie View Post
    The coil of the start relay is a lower resistance than the master relay coil. This allows a greater current flow when activated, which, in turn, creates greater magnetism. That means that the movement of the slug, inside the relay, is more violent than that of the master relay. This is a design feature that helps with the slag that builds up on the contacts when using the starter motor. This is the same reason that the factory installed start relays were 6 volt.

    The higher current flow in the coil, also produces more heat. Not a problem for momentary use but after 2 to 3 minutes, the relay case will be to hot to touch and you can smell it.

    Web
    Straying a bit, but same topic, my '57 C-310 has the original starter relays, 1940ish type WWII era, they are working still but thought I would replace them, until finding out what Cessna wants for the current replacement relay.. drumroll... almost 2000 dollars each. Thats not happening, so I got out my original 1957 parts catalog and found the original part number of the Leach relay and found a couple new old stock on ebay for 15 bucks. The starter relays and battery master relay all use the same part number, it is a Leach 200 amp continuous duty relay. Both my starters have the original Leach but the battery relay has been replaced by the newer Cessna replacement, its the one to the right of the stacked starter relays.

    Turns out only one of the new old stock Leach relays I got on ebay is the correct 7220-24 part number, the other one is new old stock but it is 7220-3-24 and it looks like the 7220-24 cant tell them apart from looking at them except for the -3 in the part number. I looked up the specs of the two numbers and the correct one is 200 amps INDUCTIVE while the -3 is 200 amps RESISTIVE.

    Both coils are 132 ohms, and I see no other difference between the two, only the inductive vs resistive 200 amps rating. I havent taken them apart yet to see what is different inside.

    Any idea what the difference is?
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    Eddie Foy's Avatar
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    Hot bad for a Jarhead!

    Quote Originally Posted by wireweinie View Post
    The coil of the start relay is a lower resistance than the master relay coil. This allows a greater current flow when activated, which, in turn, creates greater magnetism. That means that the movement of the slug, inside the relay, is more violent than that of the master relay. This is a design feature that helps with the slag that builds up on the contacts when using the starter motor. This is the same reason that the factory installed start relays were 6 volt.

    The higher current flow in the coil, also produces more heat. Not a problem for momentary use but after 2 to 3 minutes, the relay case will be to hot to touch and you can smell it.

    Web
    "Put out my hand and touched the face of God!"

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    Windy's story in post #8 is much better when she tells it in person, while acting out various scenes and conversations. It's what I call a three-beer story.

    Thanks. cubscout
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    wireweinie's Avatar
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    Quote Originally Posted by Eddie Foy View Post
    Hot bad for a Jarhead!
    Thanks Sir!

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  15. #15

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    The one big thing I learned about electricity is that it moves faster than I do...... learned that many times, the hard way....
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  16. #16
    Steve Pierce's Avatar
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    Original 1982 Piper master solenoid. Slightly modified battery shelf and battery install.
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    Steve Pierce

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  17. #17

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    Cole hersee is an major supplier of vintage aircraft solenoids.

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