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Author Topic: Electric Rule Question  (Read 2227 times)

Online Brett Buck

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Electric Rule Question
« on: January 16, 2014, 12:31:17 AM »
Does anyone know why we are specifying (section 2) a maximum no-load voltage of 42 volts? That's in the ballpark of a safety threshold of sort, but does anyone know the history of that one?  "28" (nominal, usually spec'd to 22 to 34) volts has been a standard avionics voltage forever, for safety reasons, and our more recent satellites run at 70 to save weight, but I am not sure I have ever heard 42.

   I am attempting to do a rules change to better integrate the various bits of the rule book, and that will be a Paragraph 2 change, but I keep getting hung up on unrelated strange things. It kind of looks like a copy-and-paste from FAI, but I would interested in the opinions here.

   BTW, all you guys flying gas turbines, be sure yours is below 7 lb, 11, ounces of thrust!

    Brett
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Offline Tim Wescott

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Re: Electric Rule Question
« Reply #1 on: January 16, 2014, 12:41:30 AM »
Someone may have been following the automotive industry: http://en.wikipedia.org/wiki/42-volt_electrical_system.

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Offline Mike Anderson

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Re: Electric Rule Question
« Reply #2 on: January 16, 2014, 08:07:24 AM »
Apparently pulled from the AMA "Electric" rules -  back when these were first set down, there were two classes of electric power Control Line "Speed" defined - Cl 1 is 8.4 volt max, Cl 2 is 42 volt max.  Battery packs were NiCads and charging at the field was quite common - the most that you could charge from a 12 volt source at the field was a 7 cell (8.4 volt) pack.  Astro-flite and probably some others had a reasonably priced charger capable of charging 35 cells at about 5 amps, which made for a 20 minute charge (35 cells is 42.0 volts).  It's likely that 42 volts was chosen around the equipment that was commonly available, and in order to eliminate high-tech/experimental batteries and home-built/expensive charging systems.  At any rate, it appears that the Stunt limit was pulled from the old "Electric" rules.  So fire up your 11-1/2 cell LiPo charger and get soldering.

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Offline Kim Doherty

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Re: Electric Rule Question
« Reply #3 on: January 16, 2014, 09:34:27 AM »
For our application it is quite simply a lethality issue.

"For vehicles to continue to meet growing customer needs, electrical power must be increased," says Dennis Wiese, program executive for 42-volt architecture at General Motors Corp. (Detroit). "As it is, wires and semiconductor switches get unmanageably big. It takes a high voltage to get them back down to size."

The industrywide standard of 42-volts was selected several years ago by an automaker consortium led by the Massachusetts Institute of Technology (MIT, Cambridge, MA).

Tom Keim, principal research engineer and director of the consortium says 42 volts is the threshold—anything higher presents safety concerns. Because 50 volts can stop a human heart, anything higher than that requires special safety systems to prevent contact with wiring. In addition, any voltage above 60 needs more heavily insulated wires and connectors that would add weight.

From an article by Austin Weber , June 1, 2002


Kim.
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Offline Tim Wescott

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Re: Electric Rule Question
« Reply #4 on: January 16, 2014, 09:44:58 AM »
Quote from: Kim Doherty on January 16, 2014, 09:34:27 AM
Because 50 volts can stop a human heart, anything higher than that requires special safety systems to prevent contact with wiring.

Can.  Doesn't always.  I've grabbed onto 120V while working on electrical stuff, and I haven'tn'tn'tn'tn'tn't suffered any ill effects to speak of.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Mark Scarborough

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Re: Electric Rule Question
« Reply #5 on: January 16, 2014, 12:01:06 PM »
Quote from: Tim Wescott on January 16, 2014, 09:44:58 AM
Can.  Doesn't always.  I've grabbed onto 120V while working on electrical stuff, and I haven'tn'tn'tn'tn'tn't suffered any ill effects to speak of.
Tim, thats YOUR opinion, probably best not to ask the opiniion of those who know you however
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Offline RC Storick

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Re: Electric Rule Question
« Reply #6 on: January 16, 2014, 11:03:02 PM »
Pretty soon the rule book will be able to fly with all these changes and revisions. They say when the paper work out weighs the airplane its done.

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Offline RC Storick

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Re: Electric Rule Question
« Reply #7 on: January 16, 2014, 11:06:09 PM »
Quote from: Kim Doherty on January 16, 2014, 09:34:27 AM

 Because 50 volts can stop a human heart, anything higher than that requires special safety systems to prevent contact with wiring. In addition, any voltage above 60 needs more heavily insulated wires and connectors that would add weight.

I guess they have never grabbed a coil wire with 40,000 volts. Or shocked by a DC welder.It ain't voltage its amprage that kills. However both of those tickle a little.
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Online Brett Buck

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Re: Electric Rule Question
« Reply #8 on: January 17, 2014, 01:45:25 AM »
Quote from: Kim Doherty on January 16, 2014, 09:34:27 AM
Tom Keim, principal research engineer and director of the consortium says 42 volts is the threshold—anything higher presents safety concerns. Because 50 volts can stop a human heart, anything higher than that requires special safety systems to prevent contact with wiring. In addition, any voltage above 60 needs more heavily insulated wires and connectors that would add weight.

   I figured it was a safety issue. I am not inclined to dispute the point one way or the other, it doesn't seem to be inhibiting anything.

   We run higher voltages to save weight, not to add it!  Copper is lighter than Kynar.

     Brett
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Online Brett Buck

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Re: Electric Rule Question
« Reply #9 on: January 17, 2014, 01:48:16 AM »
Quote from: Robert  Storick on January 16, 2014, 11:03:02 PM
Pretty soon the rule book will be able to fly with all these changes and revisions. They say when the paper work out weighs the airplane its done.



I think we passed that point long ago. I am working on a change that has the potential to significantly reduce the volume of the rules. I may not make it for this cycle but I would rather get it righter than faster. Nothing revolutionary, but a lot of cleanup.

    Brett
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Offline Trostle

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Re: Electric Rule Question
« Reply #10 on: January 17, 2014, 02:12:27 PM »
Quote from: Brett Buck on January 16, 2014, 12:31:17 AM
Does anyone know why we are specifying (section 2) a maximum no-load voltage of 42 volts?
    Brett

When we changed the power plant rules for our AMA CLPA event to follow the FAI rules, we pretty much adopted the FAI standard from their F2B rulebook.  This is when we adopted the 15 cc limit with no adjustment for 4-stroke engines and the FAI wording that allows for electrics.  From the FAI F2B rulebook:

"Electric power shall be limited to a maximum no load voltage of 42 volts."

I do not think we should change our rules that would in any way restrict the use of electrics any more than what the FAI rules already do.

Keith
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Offline Avaiojet

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Re: Electric Rule Question
« Reply #11 on: January 17, 2014, 03:16:11 PM »
The hobby shop I hung out in, the owner, Ted, had an issue with guys sitting on the counter.

He took a 12V car battery and a coil and rigged the counter top with two copper wires.

Ted had an on/off switch under the counter.

Yes, ouch! Guys would fly off the counter.



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Online Brett Buck

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Re: Electric Rule Question
« Reply #12 on: January 17, 2014, 06:01:07 PM »
Quote from: Trostle on January 17, 2014, 02:12:27 PM
When we changed the power plant rules for our AMA CLPA event to follow the FAI rules, we pretty much adopted the FAI standard from their F2B rulebook.  This is when we adopted the 15 cc limit with no adjustment for 4-stroke engines and the FAI wording that allows for electrics.  From the FAI F2B rulebook:

"Electric power shall be limited to a maximum no load voltage of 42 volts."

I do not think we should change our rules that would in any way restrict the use of electrics any more than what the FAI rules already do.

Keith

    I am not suggesting we do, I merely wanted to know the backstory. If anything, I would remove the voltage limit entirely. Getting hooked up to 43 volts is a very minor safety concern compared to flipping engines capable of 2 HP with razor blade props with our fingers, or reaching around it to take the battery off, and we aren't banning that.

     Brett
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Offline phil c

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Re: Electric Rule Question
« Reply #13 on: January 17, 2014, 08:59:20 PM »
the whole point is that based on testing and experience something less that 50 volts can't force enough current into the body to kill you.  42 volts is adequate for anything we are flying, including RC, something like 4500 watts.  That oughta be enough, except maybe for a 787  :>)-
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Offline Dean Pappas

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Re: Electric Rule Question
« Reply #14 on: January 20, 2014, 08:16:43 PM »
Hi Brett,
The 42V is a copy of the R/C rule, no doubt. That rule started with FAI and an arguably out of context copy of the IEC 30 V RMS or 42V peak that is used to define "non-mains" safe low voltage.
Above that, things like screw terminal blocks have to have an insulating cover and be safe (untouchable) with a 6mm dia. "baby finger" probe.
The RC FAI rule book no longer reads 42.0V but something silly like 42.99. I will go check, so please expect an edit to this post.

take care,
  Dean
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