Date: Sun, 6 May 2007 22:11:31 -0500
Reply-To: Matt Roberds <mattroberds@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Roberds <mattroberds@COX.NET>
Subject: Re: Help identifying part (image provided)
In-Reply-To: <c4e7c5f90705060839i29f575b7qb26e5f370a2c9893@mail.gmail.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
On Sun, 6 May 2007, neil wrote:
> Is there a specific type of electrical tape that will withstand heat
> generated in engine compartment?
Yeah, it's called "heat shrink". :)
Seriously, you can usually get electrical tape to stick pretty well.
One tip is to buy the name brand stuff, not the "500 rolls for $1" at
Harbor Fright. IMHO the "cheap good stuff" is 3M "Tartan 1710" and the
"good good stuff" is 3M "33+".
Another tip is to _cut_ the tape with a sharp knife or scissors, instead
of trying to tear it or pull it apart. When you tear it or pull it, the
plastic backing gets stretched out, and the adhesive on that last 1/2"-1"
(12-25 mm) of tape seems to not work very well... the end will stick down
at first but soon it will come loose and unravel. The end of the tape
shouldn't be under tension when you stick it down - just wrap it around
the wire.
Yet another tip is to make sure the wire or whatever you're sticking the
tape to is reasonably clean. It doesn't have to be ready for surgery,
but the tape will NOT stick to oil, grease, or thick dust. Sometimes a
wipe with a rag is all it takes; sometimes you need to squirt a little
brake cleaner onto the rag first before wiping. Along these lines, try
to minimize the amount of fingerprints on the sticky side of the tape -
they aren't as bad as engine oil but they will make the tape stick a
little less.
While we're in the electrical department, there are different kinds of
heat shrink as well. Polyolefin heat shrink is the good stuff and can
almost always be recognized by its matte finish; this is what most
places sell. PVC heat shrink is the cheap stuff (it doesn't work) and
usually has a shiny finish. The leading offender in passing off PVC as
"heat shrink" is Radio Shack.
Most hardware stores sell small packages of heat shrink, usually 4"
(100 mm) pieces in various sizes. A package like this is good to throw
in your tool box for fixing a few wires occasionally. If you have a big
heat-shrink project coming up, it's a lot cheaper to buy it in 4'
(1.2 m) sticks, either online, or at a local electrical or electronics
distributor - *NOT* Radio Shack!
The heat shrink you find most often is "2 to 1" - if it's 1/4" (6 mm)
before shrinking, it will be 1/8" (3 mm) after shrinking. This is
almost always enough, but if you need to get the heat shrink over a
really big connector or something, you can get "3 to 1" heat shrink -
1/4" before shrinking will be 1.3/16" (2 mm) after. You can also get
heat shrink with thicker walls for big stuff like battery cables. Black
heat shrink is available in every size and type; red heat shrink is
available in most sizes and types; you can also get clear, white, and
various other colors if you want them.
It's worth getting an "official" heat gun to do heat shrink with. A
hair dryer isn't hot enough. If you don't do much shrinking, the $10
plastic heat gun from Harbor Fright is fine. If you do a lot of
shrinking, get the $50 metal-cased kind that looks like a hair dryer on
steroids. In an emergency, you can sometimes get heat shrink to shrink
with the heat of a soldering gun, especially the 100 W or more "pistol"
kind. In a dire emergency you can do it with a cigarette lighter or
candle, but there's a fine line between "hot enough to shrink" and
"tubing or wire insulation on fire".
> Also, I used #14 wire to extend #20 (?) gauge that connects to side
> marker light lamp bases.
There is no 20 AWG wire in a Vanagon. There is also no 18, 16, 14, 12,
10, 8, 6, 4, 2, or 0 AWG. It's all metric. :) Metric wire sizes are
just the cross section of the wire in square millimeters; some common
sizes on VWs are 0.5, 0.8, 1.0, 1.5, and 2.5 mm^2. Because Ohm's Law
knows no borders, the actual sizes of the wires used for different tasks
end up being pretty much the same, no matter what it says on the rack at
the store. The side marker light wire will always be thinner than the
headlight wire, which will always be thinner than the alternator output
wire, which will always be thinner than the starter cable.
The main thing when replacing wire is to always use at least the same
thickness, or thicker. Repair 18 AWG with 18 AWG, or 16, or 14, etc...
repair 1.0 mm^2 with 1.0 mm^2, or 1.5, or 2.5, etc. There are lots of
charts floating around that give comparisons between AWG and metric
sizes; http://www.tvss.net/train/gen-wire.htm is short and sweet -
always go _down_ the chart. If Bentley says 0.75 mm^2, use 16 AWG
or thicker. If Bentley says 4 mm^2, use 10 AWG or thicker.
> I know the light will draw what it draws, but is the use of larger
> gauge wire going to cause any problems?
Practically, no.
It does make your van weigh a little more. Also, it will, theoretically,
increase the voltage to your sidemarker lamps a little, which will make
them brighter, but will also make them burn out sooner. The small
lifetime difference will be totally swamped out by other factors,
though. :)
If you get into really insane gauge differences, like splicing a piece
of 24 AWG wire to a piece of 8 AWG wire, it starts to be hard to make a
good splice, mechanically. The thick wire is stiff and the thin wire
flexes and sometimes it breaks after bouncing around on the car for
awhile. (There are fusing considerations too.)
Try to use "automotive" copper wire on your van if at all possible. It
is stranded, and usually stranded more finely than "house" wiring, so it
will be more flexible. Solid copper wire (single strand) will eventually
work-harden and break from the vibration. In a pinch, use what you have,
but swap it out for the right stuff when you're able. But don't use
aluminum wire unless you're trying to get that extra 0.05 mph out of
your van for the Formula One qualifying laps.
Most automotive wire from the FLAPS has PVC insulation, which is good to
about 85 C or 185 F. If you dig around, you can get wire with "cross
linked" insulation, like "SXL" or "GXL". This is usually good to about
125 C or 255 F. The PVC stuff does most every job, but the cross-linked
stuff is nice if you have a big wiring project and/or want to spend the
money.
If you're making battery cables for some reason, consider using welding
cable instead of "official" battery cable. Welding cable is almost
always more finely stranded than battery cable, so it's more flexible,
and the insulation is usually rated for higher temperatures as well.
Matt Roberds
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