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Roscoe

Starter issue

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Sorry Biggles, I have to disagree. Battery isolator switches have been mandatory installations on race & rally cars for yonks. Their primary role is to isolate the battery in an incident and prevent fires. You have the same arcing within the solenoid but it is contained within the body of the solenoid just as the arcing would be contained within the body of the isolating switch. BUT you've gotta spend the dollars and get the right design. Frank (post#20) is right though and any stuck solenoid problem should be apparent immediately on starting and would be a " no go" event.

Sorry Gandalph but I have to disagree with you . I'm not denying that isolators are mandatory in racing cars , but they are not designed for breaking a fault current . Solenoid contacts are electrically operated , operate in milliseconds and are equipped to deal with high currents flows . Being enclosed ,or sealed and devoid of oxygen , they are also unlikely to support combustion . Breaking a fault current with an isolator is a slow manual affair . A bit like pulling the plug on a toaster without switching off first . Good luck ! .... Bob

 

 

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Not having the isolator in the situation described is just as likely to cause a fire as a faulty isolator.

 

A shorted solenoid and continuous ly running starter is highly likely to cause overheated wiring and an electrical fire.

 

A well routed isolator away from fuel lines is imho likely to be safer than overheated wiring in the engine bay.

 

 

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If the starter solenoid is jammed with the motor drawing full load current, or near to FLC , opening the manual isolator will draw an arc and , if in close proximity to flammable material , will cause a fire ...... Bob

I see. My isolator is mounted above the battery, which is behind the firewall. Nothing to burn.

 

 

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Sorry Gandalph but I have to disagree with you . I'm not denying that isolators are mandatory in racing cars , but they are not designed for breaking a fault current . Solenoid contacts are electrically operated , operate in milliseconds and are equipped to deal with high currents flows . Being enclosed ,or sealed and devoid of oxygen , they are also unlikely to support combustion . Breaking a fault current with an isolator is a slow manual affair . A bit like pulling the plug on a toaster without switching off first . Good luck ! .... Bob

The FIA kill switches are designed to do just that. How about 200 millisecond operation time, 2500 amp surge current capacity, rated for installation in hazardous situations?. There are also solid state versions that seem promising but I'll need to do more research before I stick my neck out for them.

 

 

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With an engine in front of you the pilot should be aware of "unusual" operation of the starter, but the warning light would weigh virtually nothing.

 

Any electrical system worthy of the name in an aircraft should be capable of isolating both the battery and the alternator in flight, in case of inflight electrical problems. It's also a good idea to turn off fuel and electrics before a crash landing

 

Some types of circuit breakers can be used as switches. Aircraft in hangars should really have the battery disconnected when not in use also. Nev.

 

 

  • Agree 3

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The FIA kill switches are designed to do just that. How about 200 millisecond operation time, 2500 amp surge current capacity, rated for installation in hazardous situations?. There are also solid state versions that seem promising but I'll need to do more research before I stick my neck out for them.

Of course there are many types of isolators ranging from $5 as jetjr says , to many hundreds of dollars for the more sophisticated ones , which may also be electrically operated and contain inbuilt electrical protection but are basically the same thing ,however I believe that here we are talking about those manually operated , and in the lower price range . High current carrying leads should be no longer than necessary , well restrained and maintained along with clean and tight connections . Introducing longer leads into the cabin just to mount a cheap switch seems to be counterproductive , as well as introducing another potential point of failure which as pilots we don't need . In the case of an engine fire ,which is the reason some give for fitting an isolator in the first place , it would be far better to follow the instructions in the POH for dealing with the fire .... ie. Increasing speed to Vne and look for a safe area to get the aircraft on the ground asap. Any in flight fire is more likely to be oil/fuel related rather than electrical , hence opening the isolator is likely to be a waste of time anyway . Opening the battery isolator would also cause loss of all instrumentation . Not a good idea when when your aircraft is at or near Vne , unless your glass panel or whatever has a reliable battery back-up . Some also seem to rely on these isolators for safety even when working on or around an engine . Would you replace a car engine drive belt , relying on some cheap device that may have faulty internals . The only safe isolation when working on any engine is to remove A lead from the battery, that way you can actually see the physical break and know you are safe . Don't trust cheap aftermarket parts . Your best insurance against that very rare occurrence of a jammed solenoid is to ensure that is clean and the cables are tightly secured . If in any doubt , replace it with one recommended by the aircraft manufacturer . Finally , if these isolators were considered a necessary safety item then wouldn't our regulator mandate their installation , maybe we should also ask why aircraft manufacturers do not fit them as standard equipment ...... Bob

 

 

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A fair bit of contentious stuff there, Bob. A agree about the longer leads into the cabin Avoid unprotected wires going through the firewall.. Nev

 

 

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