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Re: L-IVP Battery Cooling
Bill said, I may be missing
something but I don't understand how a fuse between the cable and the power
buss(es) would provide protection.
In a rear mount installation, it would be hard to
protect the long wires during starter operation. However, assuming a front
mounted power grid,
you could limit the amount of current the long
wires see in flight by inserting a fuse between the long wires and e.g. the
battery bus bar that
feeds the airplane in flight.
My goal was simply to protect the installed
wire. My strategy was fairly simple:
1) for each bus
figure out what max continuous load is
2) size the main feed wire based on a continuous
rating of that load
3) size the anl on that bus to blow at the
current for which that wire is rated for the 2-minute limit
So for example, if you wanted 70A capacity on your
main bus you would pick at least a #8 wire.
The #8 wire has a 2-minute rating of 90A. A
40A ANL will blow after about 30 secs at about 90A but will run forever at
70A.
A 40A anl will also tolerate about 130A for 5 secs,
enough to get your hydr pump started.
The anl's are mostly mounted on the side of the
battery box, easily inspectable and away from passenger activity.
One test for reasonableness is "What is the
probability of this happening?"
Another test, and I think a more meaningful one is
"What is the worst damage that could occur if this thing does
happen?"
I had a friend fill a new T210 with smoke because
of a misbehaving battery in the back. IMC. He had to shut down
all electrics. Fortunately for him, all the relays opened and his AI was
vacuum driven.
I had my own Nissan Stanza fry its entire wire
harness and burn a hole through the fender. Nothing stopped it until
we ripped the terminal off the battery. That was a serious amount of
smoke!
I'm sure both of these designs passed rigorous
design reviews and in both cases what actually happened was a low probability
event.
The problem with low probability events is that
when they are happening to you, they are 100% happening to you.
Colyn
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