If you have a controllable circuit breaker or a switchable relay in series with the B-lead, you can control an over-voltage event. The Aeroelectric connection offered a 'crowbar' type protector for a while that would disconnect the B-lead automatically, and if memory serves, Bob Nuckolls now says that with an effective attention-getter to notify of over-voltage, the battery will easily damp the voltage to below damage-causing levels long enough to hit the B-lead disconnect. The only issue left is whether there is enough combustible material in the alternator itself to cause any real danger as it runs away, electrically isolated from the rest of the plane.

My personal opinion is that each person should carefully evaluate the relative risks of opening & modifying an inherently extremely reliable device, at their personal skill level. I spent about half my working life doing electronics service work and I'm pretty confident in my abilities in this area. My flying RV-4 (Lyc) has an unmodified '1-wire' alternator.

Charlie

Ed Anderson wrote:

Just curious, Todd. When you had your alternator run-a-way, did you have a battery or other load on the line. Yes and you are correct, just because the odds are 1 in 1000,000 does not mean your 1 couldn’t come up tomorrow. And I STILL DON”T use approved plastic fuel cans (or any other kind) – one refueling fire was enough {:>).

Thanks for providing that info to the list – now others can see alternator over voltage is a possibility with a car alternator and without the modification to the field coil circuit may be impossible to shut down – short of shutting down your engine.

But, if 60 years of experience is not worth anything regarding alternators – then what is experience worth regarding anything. Like just about everything else in this “hobby”, you are constantly assessing risk (or should be) and I decided the risk of modifying my alternator to eliminate the remote risk (base on my experience) of over voltage was higher than an over voltage condition. YMMV {:>)

Ed.

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW <http://members.cox.net/rogersda/rotary/configs.htm>

http://www.rotaryaviation.com/Rotorhead%20Truth.htm

------------------------------------------------------------------------

*From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *On Behalf Of *Todd Bartrim
*Sent:* Sunday, July 05, 2009 3:07 AM
*To:* Rotary motors in aircraft
*Subject:* [FlyRotary] Re: Modify Alternator for External Regulator

Yeah, that's what I said too Ed, then it happened to me when I was still early in my flight test (on the ground fortunatly).
However after years of carelessly pouring regular old auto fuel from plastic fuel cans, despite all the warnings, I've yet to have a problem. But I did hear of a guy that caught his plane on fire this way. ;)
So yeah, I'm sure it could happen. Hope it doesn't though. It would sure ruin my day.

Could it happen, undoubtedly, however, in 60 + years of driving automobiles, I have never, never had an alternator run wild – the ones that failed, just died. So if I can get by another 60 years {:>), then I’ll probably hang up my wings (or who knows perhaps get another pair {:>)



Ed

Todd
C-FSTB
RV9 Turbo13B



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