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/
   

     

--
Homepage:  http://www.flyrotary.com/
Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/