nuckolls.bob(at)aeroelect
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 Posted: Fri Dec 26, 2008 7:29 am Post subject: Is this scheme valid to save weight, add fle |
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At 11:16 PM 12/25/2008, you wrote:
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Hi Bob Thx. for the reply
My mission is to electrically connect my aft battery to the upfront 914
supplying it sufficient amperage and voltage, while being able to fit
wires neatly under door sill/fuse seam and allow routing required to
connect to battery switch (tight bends).
Old style starter amp draw is stated at I think 60 amps, I have new style
that is a bit less.
If I can save some weight in the process that is a bonus.
Just a quick calculation of one #4 compared to two #8s for 5 meters of
wire would be a savings of a little over a half pound with two #8s.
The larger the diameter of wires, the harder it will be to route under
door sill and allow for door centering pin receptacle to help keep door
from bulging.
#4 Tefzel wire is .310" in diameter
#6 EPDM jacket 259 strand is .332" diameter (#4 406 strand .380")
#6 Chlorinated Polyethylene 660 strand is .370" diameter (#4 1045 strand
.420")
It's true I could lap solder #6 welding wire to #4 Tefzel, but my interior
cover/conduit for wires would need to be larger to accommodate, and the
laps would be in an already tight area. Butt soldering #4 Tefzel to #6
welding would approx. be the same diameter.
I am not sure of the weight of welding cable compared to Tefzel, but I
would think it heavier.
I have a Hobart TRT 250 TIG welder. The ground wire I suspect is EPDM
jacketed. It has cracks and splits and in general the jacketing is in bad
health. True it sees a lot of UV and for a TIG ground strap that is fine.
Are you be happy with using EPDM jacketed welding cable for the full run
to and from engine to aft battery knowing if it smokes, a dozen feet is in
the cockpit (aeroplane is fiberglass)? How about only 1 foot?
Same question with Chlorinated Polyethylene jacketed welding cable:
Are you be happy with using Chlorinated Polyethylene jacketed welding
cable for the full run to and from engine to aft battery knowing if it
smokes, a dozen feet is in the cockpit (aeroplane is fiberglass)? How
about only 1 foot?
Knowing I need flexibility for routing at battery switch, want the
smallest diameter that is feasible, be able to provide reasonable voltage
and cranking amps, not take unreasonable risks of breathing noxious fumes
if wires smoke, not have much risk that aging wire insulation will crack
and split and be the instigator of smoke and loss of electron flow and be
of a reasonable weight.
What would be your two favorite choices:
****#4 Tefzel with #6 EPDM jacketed butt soldered battery and battery
switch ends?
****#4 Tefzel with #6 Chlorinated Polyethylene jacketed butt soldered
battery and battery switch ends?
****All #4 EPDM jacketed wire?
****All #4 Chlorinated Polyethylene jacketed wire?
****Two paralleled #8 Tefzel wire that doesn't need twisting?
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To use terms like "reasonable weight" and "this wire
is heavier than that wire" without quantifying the overall
weight savings.
I think I'd run 4AWG welding cable throughout. The
delta-weights are trivial and the effort to run multiple
twisted, spliced, variable gage wires has a poor return
on investment and looks pretty chopped and hacked when
you're done.
I've never understood the thought process that suggests
smoke from one kind of insulation is preferable to smoke
form another kind of insulation. When you get the first
whiff of ANY smoke, all switches are OFF ASAP.
I can't speak to your experience with cracked insulation
on welding cable. The stuff I've been buying around here
for years looks like this:
http://aeroelectric.com/Pictures/Wire/4AWG_Welding_Cable_1.jpg
I'm not sure of the chemical makeup of the two layers
but it's a sure bet they're selected for robustness as
insulation on wires that lay on gravel roads and get
run over by dump-trucks. The fat wires in your airplane
are not subject to great abuse by liquids, mashing,
pulling, etc. They're easily observed during annual
inspection for degraded performance such as cracks.
The risks for using this stuff is exceedingly low, the
benefit for low cost, flexibility, and ease of installation
is significant. The idea that you're going to save a few
ounces at most on total installed weight may be
intellectually pleasing but probably won't produce
practical benefits later.
Bob . . .
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