Hartstoc
Well Known Member
OK, this IS one of those questions that flies in the face of conventional wisdom, so answers like “we all do it and there are no problems” and “if it ain’t broke...” will immediately come to mind, but I have to ask.
Nearly all road vehicles have the battery wired directly to the starter solenoid, and most modern cars also have a plethora of built-in relays that power-up various sub-systems when the ignition switch is in various positions.
Nearly all RV’s instead have the intermittent starter solenoid wired in series with the continuous-duty master-bus solenoid, which in turn IS wired directly to the
Battery. Great idea, right? If the starter solenoid gets stuck you can kill the master! Is this a no-brainer or a bad idea?
I hope the url below will take you to an album with two images showing specs for the master and starter solenoids commomly used in our airplanes. As you will see, the following statements are true of the starter solenoid:
- It is twice as heavy as the master.
- Its coil draws 3amps vs just 1amp for the master.
- It is rated for 900 in-rush Amps vs. 150 for the master.
- It can handle several-hundred amp loads vs 80 amps max for the master.
That big fat wire conecting solenoid to starter is there for a reason- your starter DOES draw hundreds of amps from a well charged battery of appropriate size. The starter solenoid is heavy because it is designed to handle that for the time required to start the engine. Its coil draws higer amperage to insure that it slams the contactors together quickly and firmly to transfer all those amps with minimal arcing and resistance, and to overcome the force of a stronger return spring.
But what about that little guy feeding the master bus- what sort of experience is it having during engine start? True- it is in full contact mode already, so arcing should not be an issue, but those contactors and internal conductors are much smaller than those in the starter solenoid. Also, their face-contact pressures, powered by that little 1-amp coil, are far lower than those in the starter solenoid. Is the master solenoid acting as a resistor during starts? When you are cranking away during a problem hot-start with fuel injection, what sort of internal temperatures is the master solenoid seeing? Is it possible that micro-arcing is ocurring over portions of the contactor faces that are not in hard contact because of the huge current draw? Which of these contactors is really more likely to weld itself shut?
I don’t know if stuck starter solenoids Are really much of a threat. It could be that putting two of THEM in series would be a more proper way to prevent it but ouch, those suckers weight 24 oz each!
Sorry to say, I just have the questions and no answers, but I’m hoping some of you can provide those. One little test worth doing might be to temporarily make a SOLID connection(not with jumper cables!) to the starter solenoid, and observe any difference in cranking vigor. My guess is that any of you with larger, higher compression engines would see a significant improvement
https://images49.fotki.com/v1658/ph...5494CBE8862409EA11D8D7C-vi.png?solenoid-specs
Nearly all road vehicles have the battery wired directly to the starter solenoid, and most modern cars also have a plethora of built-in relays that power-up various sub-systems when the ignition switch is in various positions.
Nearly all RV’s instead have the intermittent starter solenoid wired in series with the continuous-duty master-bus solenoid, which in turn IS wired directly to the
Battery. Great idea, right? If the starter solenoid gets stuck you can kill the master! Is this a no-brainer or a bad idea?
I hope the url below will take you to an album with two images showing specs for the master and starter solenoids commomly used in our airplanes. As you will see, the following statements are true of the starter solenoid:
- It is twice as heavy as the master.
- Its coil draws 3amps vs just 1amp for the master.
- It is rated for 900 in-rush Amps vs. 150 for the master.
- It can handle several-hundred amp loads vs 80 amps max for the master.
That big fat wire conecting solenoid to starter is there for a reason- your starter DOES draw hundreds of amps from a well charged battery of appropriate size. The starter solenoid is heavy because it is designed to handle that for the time required to start the engine. Its coil draws higer amperage to insure that it slams the contactors together quickly and firmly to transfer all those amps with minimal arcing and resistance, and to overcome the force of a stronger return spring.
But what about that little guy feeding the master bus- what sort of experience is it having during engine start? True- it is in full contact mode already, so arcing should not be an issue, but those contactors and internal conductors are much smaller than those in the starter solenoid. Also, their face-contact pressures, powered by that little 1-amp coil, are far lower than those in the starter solenoid. Is the master solenoid acting as a resistor during starts? When you are cranking away during a problem hot-start with fuel injection, what sort of internal temperatures is the master solenoid seeing? Is it possible that micro-arcing is ocurring over portions of the contactor faces that are not in hard contact because of the huge current draw? Which of these contactors is really more likely to weld itself shut?
I don’t know if stuck starter solenoids Are really much of a threat. It could be that putting two of THEM in series would be a more proper way to prevent it but ouch, those suckers weight 24 oz each!
Sorry to say, I just have the questions and no answers, but I’m hoping some of you can provide those. One little test worth doing might be to temporarily make a SOLID connection(not with jumper cables!) to the starter solenoid, and observe any difference in cranking vigor. My guess is that any of you with larger, higher compression engines would see a significant improvement
https://images49.fotki.com/v1658/ph...5494CBE8862409EA11D8D7C-vi.png?solenoid-specs
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