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Re: L-IVP Battery Cooling
Hi Colin-
Your earlier post indicated that you were not going to protect against starter
loads so that leaves the rest of the electrical system.
I may be missing something but I don't
understand how a fuse between the cable and the power buss(es) would
provide protection. Given the variable nature of the loads, particularly the
inrush current each time the hydraulic pump starts up or a landing light is
turned on, how would you size it? It would have to be sufficient to handle
every device operating at once plus some additional capacity to prevent the
fuse blowing inadvertantly.
I generally operate with a number of
circuits turned off. For example, I don't use cockpit, nav and landing
lights during the day. (The landing lights are retracted except at low
speed). I don't use pitot heat VFR. Under those conditions would there be enough
additional sustained current from a given short, particularly one
of the small gauge wires that are most numerous, to cause the fuse to blow?
I agree that an electrical fire is something to be avoided. I think the liberal
use of heat shrink and careful mechanical installation are a good defense. I
cover the shanks of battery and other uninsulated terminal lugs with heat shrink
to reduce exposure.
Incidentally, the stuck PTT switch I
experienced was due to the switch terminals getting pushed together and
shorting out. The avionics shop hadn't put heat shrink on each terminal, just
over the whole assembly. I covered each one on the
replacement. It seems to me that the odds of a loose wire shorting against
the cables would be enhanced by the ANL fuse and holder. It
would require two extra terminal lugs, also the holder's terminal
posts and the exposed areas of the fuse itself are vulnerable. A solid cable
would have continuous insulation.
Speaking of Nuckolls, a quick glance at his
diagrams shows no fuses on any battery leads.
One difficulty I thought of with remote
battery installation is with a pressurized model. Those cables would have
to penetrate the firewall and I'm not sure what a good method might be for
sealing them. That would be one advantage of the firewall mounted battery.
-Bill Wade
----- Original Message -----
Sent: Wednesday, November 04, 2009 5:39
PM
Subject: [LML] Re: L-IVP Battery
Cooling
The Bob Nuckolls wisdom on this is that some
voltage drop is okay for a starting system.
I'm only repeating that not endorsing
it.
(Caveat, if you have a full feathering prop and
would like to air restart after feathering, it takes 20-30 seconds of
vigorous
cranking under nasty cold conditions to get it
out of feather. Voltage, and cold cranking amps helpful
here)
That doesn't worry me nearly so much as high
current unprotected wires in the cockpit, at least when not in starting
mode.
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