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nuckolls.bob(at)cox.net
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 Posted: Thu Mar 20, 2008 5:22 pm Post subject: Plane Power Alternator Failure (brand new) |
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At 01:00 PM 3/20/2008 -0700, you wrote:
| Quote: |
<rv-9a-online(at)telus.net>
A friend had a Plane Power alternator fail after his first flight.
Apparently, he left the Master "on" (in ALT position) for 30-40 minutes
while he was working on the plane, and after that he noticed that his ALT
Field enable fuse was blown. It happened to a replacement fuse as well.
I checked the wiring right to the alternator-- no fault with it unplugged.
I can't measure any shorts to ground on the Alternator pins.
My theory is the the internal voltage regulator overheated and failed short.
My theory is that it would overheat because there was no airflow and was
providing maximum field current for a long time.
Has anyone else experienced this or have an alternate diagnosis?
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It's a plausible theory. The only schematics for regulators
I've been able to study take a sample of the AC from the
alternator's stator windings and won't turn the field on unless
there is a detected motion of the rotor. But I don't know that
all regulators do that . . . in particular, those used in
Plane Power's products. A phone call to them should reinforce
or wash out your hypothesis. They've been courteous and quite
forthcoming with useful information when I've had occasion
to communicate with them.
If the regulator doesn't shut down during engine-off
ops, then it full-fields the alternator. I wouldn't
expect this to overheat the regulator . . . but it
might have cooked insulation in the field windings
and cause a short there.
This is one of several reasons why the Z-figures are
configured to allow pilot/mechanic control of field
excitation both in flight and on the ground. Separate
but interlocked Battery and Alternator switches configured
to emulate the infamous split-rocker switch.
Give PlanePower a call and let us know what they have
to say.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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Tim Olson
Joined: 25 Jan 2007
Posts: 2875
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| Posted: Sun Mar 23, 2008 6:09 am Post subject: Plane Power Alternator Failure (brand new) |
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Are you sure it's a 40A unit? I thought Plane Power only
made 60A and 70A units. (and, a 50A continental model)
Could it be either a larger unit than you think, or
a different brand?
Tim Olson - RV-10 N104CD - Flying
do not archive
Ken wrote:
| Quote: |
gmcjetpilot(at)yahoo.com wrote:
> Gentlemen all, you are gussing.
>
> Call PP & send it back. Get the real reason. PP does modify the
> regulator & therefore he's the source of creditable facts. I can say
> a stock ND should not get hot with BAT/ALT on, but I stand to
> be corrected. I never tried it. However............
>
> For a regular internally regulated ND alternator, if it uses more than
> 50 millivolts, with the engine shut down you have voltage regulator or
> diode issue. Internally regulated alternators do not have a FIELD
> WIRE of course.
>
>
> >From: Ken <klehman(at)albedo.net <mailto:klehman(at)albedo.net>>
> >Subject: Re: Plane Power Alternator Failure (brand
> new)
> >Would not surprise me Vern. My wee ND IR alternator draws a couple of
> >amps and heats up quite noticeably with the engine off and the IGN
> >terminal (and B+ lead) connected to the battery. Fortunately the OV
> >relay lets me disconnect it by opening the alternator control switch.
> >Ken
>
> Ken is it possible you are reading more than the alternator? Master
> contactor?
>
No
It was purchased new about 5 years ago and it always did this. Of course
in a car the Ign terminal would not be powered with the key in the off
or accessory position. Newer models might sense rotation before they
power the field. But apparently this 40 amp unit that often is found on
small industrial equipment is not that sophisticated.
Ken
ps. I assume you meant to type 50 milliamps above. I've never seen
anything near that high (yet) but standby parasitic current "leakage" is
getting ridiculous on cars these days.
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