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Date: Sat, 10 Sep 2005 21:26:22 -0700 (PDT)
From: Michael LaFleur <mike.lafleur@sbcglobal.net>
Subject: Re: [FlyRotary] Re: Overvoltage control (help Ed A)
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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In the case of a load dump, where the battery is
disconnected for a charging circuit, you will see more
than 100 volts.

The alternator, being low impedance will cause large
positive transients. Simultabeously, the collapsing
field will cause negative field decay transients.
These can and will be in excess of 100 volts. All
charging systems should have protection for this.
Don't you?

--- Jim Sower <canarder@frontiernet.net> wrote:

> 
> 
> Finn Lassen wrote:
> 
> > I think the +100 volts statement relates to no
> battery load.  Have you 
> > /anyone actually /seen/ that happen?  I guess if
> the electrical system 
> > was designed so that a contactor could disconnect
> the battery from the 
> > load circuits and the load circuits (avionics)
> still be connected to 
> > the alternator you would have a situation where
> you could wave your 
> > avionics goodbye.
> > Perhaps.  But that wouldn't be very clever. 
> Anyone who designed his 
> > system to protect his avionics from a Battery over
> voltage and ignored 
> > the Alternator deserves whatever happens.
> > Let's say on top of that that one (or all) of the
> three retifiers 
> > shorted out too, you'd have 100 volts A/C into
> your avionics. Not a 
> > pretty picture. (I've seen Zener diodes short out
> regularily due to 
> > overload/voltage; rectifier diodes usually fail
> open - but not 
> > always).   We're stretching a bit here aren't we? 
> Back to the 100 V 
> > that we've already agreed can't happen, shorted
> diodes causing AC 
> > (which I'm not at all sure can happen), all three
> rectifiers (that's 
> > all SIX diodes shorting at the same time (none of
> them failing open 
> > which is more common), zener failing, etc.  If a
> diode fails every 
> > 1000 hrs, the whole bank failing would happen
> every 1000^6 hours.  
> > That's a one with TWENTY ONE zeros behind it.
> 
> I think I can live with that ... Jim S.
> 
> >
> > Finn
> >
> > Jim Sower wrote:
> >
> >> <... the alternator is capable of producing over
> 100 volts ...>
> >> I don't think so ...
> >> ...
> >> Bottom line, with the regulator failed (or
> bypassed) to send full B+ 
> >> voltage to the field, the charging voltage never
> exceed 18V in my 
> >> experience.
> >
> >
> >
> >
> > -- 
> > Homepage:  http://www.flyrotary.com/
> > Archive and UnSub:  
> http://mail.lancaironline.net/lists/flyrotary/
> >
> >
>