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bob88
Joined: 24 Feb 2013
Posts: 99
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 Posted: Fri Sep 26, 2014 11:39 am Post subject: Circuit protection for long battery wire |
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It seems there should be a current limiter to protect the long P27 wire from battery to starter relay up front. What size fuse should be used? The starter draws the most, up to 300 amps but I don't see fuses in this range.
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john.maccallum(at)bigpond
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| Posted: Fri Sep 26, 2014 5:13 pm Post subject: Circuit protection for long battery wire |
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Yes I thought about that as well. You would indeed need a big Fuse to take
care of the stall current of the starter motor.
I decided in the end the to not do that and I just double insulated the 2 Ga
Tezel Battery Cable with Nylon Conduit.
If the Battery or starter Solenoids go to ground then I guess I will just
destroy the battery (hopefully lots of smoke but not much fire).
I think the stall current of the Starter is 170 amps so somewhere around 180
amps should be ok. You can get ANL and AML fuses and lots of other
Types in those sort of fuse ratings.
Cheers
John MacCallum
VH-DUU
RV 10 # 41016
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Kelly McMullen
Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ
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| Posted: Fri Sep 26, 2014 7:05 pm Post subject: Circuit protection for long battery wire |
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There is zero need to fuse that wire. No certified plane with the battery in the rear has any circuit protection between the master relay at the battery and the starter relay.
If that wire ever shorts, it will burn enough metal to eliminate the short, faster than an ANL would open the circuit. Bob Nuckolls, host of the AeroElectric forum and long time industry electrical guru does not recommend an circuit protection on that wire beyond what the master relay provides. The only line you might want ANL on is the power lead from the alternator. Easy to find in the 60-100 amp range.
Kelly
On Fri, Sep 26, 2014 at 12:39 PM, bob88 <marty.crooks(at)comcast.net (marty.crooks(at)comcast.net)> wrote:
[quote]--> RV10-List message posted by: "bob88" <marty.crooks(at)comcast.net (marty.crooks(at)comcast.net)>
It seems there should be a current limiter to protect the long P27 wire from battery to starter relay up front. What size fuse should be used? The starter draws the most, up to 300 amps but I don't see fuses in this range.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=431149#431149
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Kelly McMullen
A&P/IA, EAA Tech Counselor
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stein(at)steinair.com
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| Posted: Sat Sep 27, 2014 8:27 am Post subject: Circuit protection for long battery wire |
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Kelly is spot on…and to that point there will be a LOT (dozens to hundreds) of wires in your airplane that aren’t each individually protected with their own fuse/breaker – both big and small. You design circuits such that you can remove power (or a breaker/fuse is able to) and eliminate problems, but it is impossible to physically protect each and every single wire with its own protection device so you follow the best practices and design around the 99th percentile, not the 1th percentile (while keeping the 1th percentile in mind).
Just my 2 cents as usual.
Cheers,
Stein
From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of Kelly McMullen
Sent: Friday, September 26, 2014 10:05 PM
To: rv10-list(at)matronics.com
Subject: Re: Circuit protection for long battery wire
There is zero need to fuse that wire. No certified plane with the battery in the rear has any circuit protection between the master relay at the battery and the starter relay.
If that wire ever shorts, it will burn enough metal to eliminate the short, faster than an ANL would open the circuit. Bob Nuckolls, host of the AeroElectric forum and long time industry electrical guru does not recommend an circuit protection on that wire beyond what the master relay provides. The only line you might want ANL on is the power lead from the alternator. Easy to find in the 60-100 amp range.
Kelly
On Fri, Sep 26, 2014 at 12:39 PM, bob88 <marty.crooks(at)comcast.net (marty.crooks(at)comcast.net)> wrote:
--> RV10-List message posted by: "bob88" <marty.crooks(at)comcast.net (marty.crooks(at)comcast.net)>
It seems there should be a current limiter to protect the long P27 wire from battery to starter relay up front. What size fuse should be used? The starter draws the most, up to 300 amps but I don't see fuses in this range.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=431149#431149
===========
target="_blank">http://www.matronics.com/Navigator?RV10-List
===========
">http://forums.matronics.com
===========
le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
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