Alternator Noise

On Tue, 07 Dec 2004 00:52:03 GMT, (John_F) wrote:

Well lets say you are a hot shot mechanic and disconnect the hot side
of the battery first with your handy dandy metallic wrench. Some
sweet young thing walks by and distracts you for an instant and the
wrench handle contacts the battery box or some other part of the
airframe. There will be a big flash as a couple of thousand amps
flows in the wrench handle. A hole will appear in the aluminum
airframe or battery box where the wrench contacted it . This is bad
but what happens next is worse. The flash is next to a battery vent
cap and the O2 and H2 gas inside the battery ignite and blow the top
off of the battery spraying battery acid in your eyes and all over
the airplane.
Need I say more?
John


Thanks for the explanation. I was confused and thought you meant to
disconnect the ground from the alternator before the field. I do
understand to disconnect the battery negative first and reconnect it
last for the reasons you've given. I've been that 'hot shot' before
and startled the hell out of me! Luckily nothing serious happened,
just a little black spot on the battery box.

If I may indulge you, when disconnecting/reconnecting the terminals at
the alternator, is there any particular order, or precautions one
should take?

TIA.
z

zatatime writes:


Thanks for the explanation. I was confused and thought you meant to
disconnect the ground from the alternator before the field. I do
understand to disconnect the battery negative first and reconnect it
last for the reasons you've given. I've been that 'hot shot' before
and startled the hell out of me! Luckily nothing serious happened,
just a little black spot on the battery box.

Fortunately, typical GA starting batteries have limited current
capacity; something like http://www.trceng.com/services/coe.htm
will turn a 12" Crescent wrench bright orange before you can say
"Oh s&*8"


If I may indulge you, when disconnecting/reconnecting the terminals at
the alternator, is there any particular order, or precautions one
should take?


With the battery ground off; the order does not matter. What DOES matter
is getting each wire back to the correct spot. You may wish to tag them,
take a picture, and then remove them.

The biggest way to have grief is grounds. The case of the alternator
may have a grounding wire. (I'd hope so, but...) The VR will be on
the firewall and typically should be grounded via its mounting bolts.
But corroded/dirty ground connections are more common than ants at
a picnic. Shine things up bright before reassembling. Be sure there
are star lockwashers to bite into the joining surfaces.

It's also possible there are insulating washers/spaces behind certain
bolts. Don't lose them or mix up where they go.
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