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12-28-2017, 07:58 AM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
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Quote:
Originally Posted by Tomcat RV4
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
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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.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
Last edited by Mel : 12-28-2017 at 08:25 AM.
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12-28-2017, 09:33 AM
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Join Date: Jan 2015
Location: uk
Posts: 57
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Quote:
Originally Posted by Mel
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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And of course some careless person may short out the terminals with spanner. 
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12-28-2017, 09:54 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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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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12-28-2017, 10:02 AM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
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Quote:
Originally Posted by rv7charlie
But I'd have to disagree with the comment about AC vs DC & muscle contraction. Ask anyone who's been Tased.
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A little research will show that a taser IS (for all practical purposes) AC. Typically they alternate at about 19 pulses per second.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
Last edited by Mel : 12-28-2017 at 11:19 AM.
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12-28-2017, 10:20 AM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by Mel
A little research will show that a taser IS AC. Typically they alternate at about 19 pulses per second.
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And, until current flow stabilizes, for a fraction of a second DC acts like AC.

__________________
Galin
CP-ASEL-AMEL-IR
FCC Radiotelephone (PG) with Radar Endorsement
2020 Donation made
www.PuertoRicoFlyer.com
Last edited by GalinHdz : 12-28-2017 at 10:26 AM.
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12-28-2017, 10:34 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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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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12-28-2017, 10:42 AM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by rv7charlie
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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.

__________________
Galin
CP-ASEL-AMEL-IR
FCC Radiotelephone (PG) with Radar Endorsement
2020 Donation made
www.PuertoRicoFlyer.com
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12-28-2017, 11:08 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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