REFLECTOR: How to protect the battery bus

Douglas Holub doug.holub at tx.rr.com
Sat Feb 17 01:18:03 CST 2007


I'm planning on putting a 200 amp shunt right at the battery + terminal (24 volt system.) I've been reading that the big wire going from the battery to the starter isn't protected in certified aircraft, and there's not much metal in our airplanes to which it could possibly short, but I just feel better knowing that it would be virtually impossible for the battery to ever be able to discharge itself to ground (maybe after a crash?), which could easily get something hot enough to catch fire. 

Doug Holub

  ----- Original Message ----- 
  From: Keith Hallsten 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Friday, February 16, 2007 9:40 PM
  Subject: Re: REFLECTOR: How to protect the battery bus


  Hiroo,

   

  Why is there a shunt in the starting circuit?  Starting will take several HUNDRED amps, and there's no need to measure them.  A shunt that will work at that range won't have much precision for normal electrical system currents.  What are you really trying to measure?  If you put a shunt in the alternator "B" lead you will measure what current the alternator is producing, which seems useful to me.

   

  Keith Hallsten

   

   


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  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Hiroo Umeno
  Sent: Friday, February 16, 2007 11:56 AM
  To: reflector at tvbf.org
  Subject: REFLECTOR: How to protect the battery bus

   

  Last weekend, I cranked the fickle Franklin one too many times.

   

  (Yes, I am still trying to find out why it simply will not run.  Long story.)

   

  On the third cranking, the voltage on the battery must have dropped sufficiently that the starter motor stopped turning the prop.  I probably left my thumb on the starter button a tad longer than I should have.

   

  The shunt blew and the whole electrical system went (except the backup battery system that ran the instruments (glad to know THAT works well).

   

  That got me thinking.  Shouldn't there be a CB or something protecting the starter line?  I've heard that the starter line is the only line that should NOT have a CB on.  Yet I've managed to fry the shunt.

   

  Any thoughts?

   

  Hiroo



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