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  #31  
Old 12-28-2017, 07:58 AM
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Mel Mel is offline
 
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Quote:
Originally Posted by Tomcat RV4 View Post
You are correct,auto starters stopped using separate solenoids in 50s, in auto conversion,
(Subby) ignition switch worked starter flawlessly with out separate solenoids.when was
last time you burned up starter in auto cause stayed engaged ? Tom
The main reason for using 2 separate solenoids on aircraft is to avoid having an "always hot" wire running to the starter. In automobiles the starter terminal is not readily accessible while working under the hood.
On aircraft, we are typically working in close proximity to the starter terminal on a regular basis.

Note that I didn't say what's right or wrong. It's just the reason it's been done that way for so many decades.

And on the discussion about "voltage/current" grabbing you. You are comparing DC to AC. When working with AC, it's the alternating current that tightens you muscles and won't let you turn loose. DC does not do this.
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Last edited by Mel : 12-28-2017 at 08:25 AM.
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  #32  
Old 12-28-2017, 09:33 AM
tomww tomww is offline
 
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Quote:
Originally Posted by Mel View Post
The main reason for using 2 separate solenoids on aircraft is to avoid having an "always hot" wire running to the starter. In automobiles the starter terminal is not readily accessible while working under the hood.
On aircraft, we are typically working in close proximity to the starter terminal on a regular basis.

Note that I didn't say what's right or wrong. It's just the reason it's been done that way for so many decades.

And on the discussion about "voltage/current" grabbing you. You are comparing DC to AC. When working with AC, it's the alternating current that tightens you muscles and won't let you turn loose. DC does not do this.

And of course some careless person may short out the terminals with spanner.
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  #33  
Old 12-28-2017, 09:54 AM
rv7charlie rv7charlie is offline
 
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In response to Mel's post, not only is there the inconvenience of burning a hole in a tool (or yourself) on that hot starter terminal, there's a much bigger danger in the case of a crash, where that wire will be hot and likely arcing to ground around hot fuel and oil. Much less risk with a starter contactor next to the battery, even if it's not routed through a master contactor.

But I'd have to disagree with the comment about AC vs DC & muscle contraction. Ask anyone who's been Tased.

https://en.wikipedia.org/wiki/Electrical_injury

It's really about Ohm's law; not AC vs DC.

http://www.brighthubengineering.com/...ck-comparison/

The 2nd link answers the question about how much current it takes, but it still depends on Ohm's law.
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  #34  
Old 12-28-2017, 10:02 AM
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Originally Posted by rv7charlie View Post

But I'd have to disagree with the comment about AC vs DC & muscle contraction. Ask anyone who's been Tased.
A little research will show that a taser IS (for all practical purposes) AC. Typically they alternate at about 19 pulses per second.
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Last edited by Mel : 12-28-2017 at 11:19 AM.
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  #35  
Old 12-28-2017, 10:20 AM
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Quote:
Originally Posted by Mel View Post
A little research will show that a taser IS AC. Typically they alternate at about 19 pulses per second.
And, until current flow stabilizes, for a fraction of a second DC acts like AC.



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Last edited by GalinHdz : 12-28-2017 at 10:26 AM.
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  #36  
Old 12-28-2017, 10:34 AM
rv7charlie rv7charlie is offline
 
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https://en.wikipedia.org/wiki/Electroshock_weapon

Pulsed DC is not the same as AC.

But hey, I think I remember being wrong before, so maybe I'm wrong now.

Regardless, DC *will* cause muscle contraction, and that's the real point.
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  #37  
Old 12-28-2017, 10:42 AM
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GalinHdz GalinHdz is offline
 
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Quote:
Originally Posted by rv7charlie View Post
https://en.wikipedia.org/wiki/Electroshock_weapon

Pulsed DC is not the same as AC.

But hey, I think I remember being wrong before, so maybe I'm wrong now.

Regardless, DC *will* cause muscle contraction, and that's the real point.
FWIW: AC is any "alternating current" so pulsed DC is actually a type of AC. What most people call AC, and what you are probably referring to, is actually Sinusoidal AC. Easy to confuse Sinusoidal AC with AC.

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  #38  
Old 12-28-2017, 11:08 AM
rv7charlie rv7charlie is offline
 
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https://www.google.com/search?q=alte...hrome&ie=UTF-8

Enjoy....
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