any time the current draw on a stock circuit is upped significantly ........
relay baby, relay.

----- Original Message -----
From: "Rocket J Squirrel" <camping.elliott@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, September 29, 2009 5:58 PM
Subject: Re: No High Beams

>I don't dispute your knowledge and experience.
>
> Let's see how closely VW cut things.
>
> 97.58 (Bentleys) shows the brake light switches fed by a single 18 gauge
> wire through a 8A fuse (S8). 18 gauge wire is rated to carry 13 amps,
> continuous, in free air, forever, if it has insulation rated for 60C.
> There are insulations rated for higher-temperature operation, and the wire
> can be run up to 18A or more with better insulation. But I don't know what
> kind of insulation is used in the Vanagon, so I'll use this rating, the
> most conservative I could find.
>
> The two brake lights on the Vanagon are 21W, so they each draw 1.8A,
> steady-state, although the turn-on surge of a tungsten filament can exceed
> the steady-state value by 5 to 10 times because a cold filament has lower
> DC resistance than a hot one.
>
> So the initial turn-on current of the two bulbs together can be anywhere
> between 18 to 36 amperes, but that surge will be brief - somewhere in the
> tens to hundreds of milliseconds. Less than a second, anyway.
>
> Clearly the steady-state current draw of the two bulbs (3.6A) is well
> below the 13A current rating of the wire and the 8A fuse. The fuse can
> handle the brief turn-on surge.
>
> When I doubled the load by adding a pair of 21W trailer lights, the fuse
> blew the moment I stepped on the brakes for the light test. Maybe because
> the steady-state current (7.2W) exceeded the 8A rating of the fuse --
> that's darn close (anyone know the tolerances on these cheap fuses?). More
> likely, doubling the inrush current to somewhere in the range of 36 to 72
> amperes popped the fuse.
>
> But doubling the brake light loading doesn't exceed the current carrying
> capacity of the wire. "Noxious smoke and fumes" are not likely to result
> from passing 7.2A through wiring rated to 13A @ 60C insulation. The inrush
> current of the bulbs is too brief to heat a length of wire 12 or more feet
> long by more than a few degrees. It certainly won't "glow like a lightbulb
> filament" even if I was passing 16A through it steady-state due to a
> wiring fault. It would get darn warm and eventually the insulation would
> fail somewhere.
>
> Going from 3.6A to 7.2A in wiring very conservatively rated for 13A is
> safe enough for me, especially since I only drive with the trailer a few
> times a year. I reckon the engine will give out before the wiring will.
>
> BUT -- Mike B. is right: DO NOT try this at home. Just because I jump off
> a bridge doesn't mean you should. I do not need a phone call from your
> widow's lawyer. Never modify any wiring or electrical accessories on your
> van unless you know what you are doing and are willing to accept the risks
> of a miscalculation.
>
> --
> Mike "Rocket J Squirrel" Elliott
> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
> 74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
> Bend, OR
> KG6RCR
>
>
>
> On 9/29/2009 5:16 PM Mike wrote:
>
>> You should NEVER swap up to the next size fuse, when any type of circuit
>> fault causes the correct size fuse to keep blowing.
>>   The fuse rating is engineered to blow at nearly the maximum
>> current-carrying capacity of the wire.  If you add a greater load to an
>> existing circuit, and that causes the original size fuse to blow, that
>> means that the wiring is pulling more amps than the wire size is able to
>> safely handle.  If you proceed to install the next-size-larger fuse, you
>> now have created a fire hazard that could cause a total loss of your
>> treasured vehicle.  When a wire draws too much current, it gets hot,
>> melts insulation, the copper can even glow like lightbulb filament along
>> its entire length!  Not good!  At this point the wire becomes the
>> weakest link and 'blows' instead of the fuse!  Ii's also capable of
>> filling the vehicle with noxious smoke and fumes.  Do you want to keep
>> your family in this vehicle?  I can't recommend it.
>>
>> Mike B. (licensed FAA aircraft mechanic, and licensed electrician in 2
>> states)
>>
>>     ----- Original Message -----
>>     *From:* Al Knoll <mailto:anasasi@GMAIL.COM>
>>     *To:* vanagon@GERRY.VANAGON.COM <mailto:vanagon@GERRY.VANAGON.COM>
>>     *Sent:* Tuesday, September 29, 2009 7:09 PM
>>     *Subject:* Re: No High Beams
>>
>>     Actually, Rocket J. you can discern the wire size to the brake lights
>> by
>>     gazing at the current track in the bently. With that in mind you can
>>     estimate the current carrying capacity, then see if the total draw
>>     exceeds
>>     the reasonable capacity of the wire.  If it does't then just fuse to
>> the
>>     next higher value.  If it does exceed the RCOFTW by some you might
>>     have to
>>     run a second circuit.   Works for all accessories of course.
>>
>>     Pensionerd.
>>
>>     On Tue, Sep 29, 2009 at 7:20 AM, Rocket J Squirrel <
>>     camping.elliott@gmail.com <mailto:camping.elliott@gmail.com>> wrote:
>>
>>      > Along those lines, I instantly blew the fuse for the brake light
>>     circuit
>>      > when I connected up my little trailer and tested the lighting. Not
>> a
>>      > miswiring, just the additional load of the trailer's two little
>> brake
>>      > lamps was sufficient to pop the fuse. VW must rate the fuses
>>     pretty close
>>      > to the expected load current so even a non-shorting fault is
>>     sufficient to
>>      > open the fuse. Had to swap up to the next-sized fuse there.
>>      >
>>      > --
>>      > Mike "Rocket J Squirrel" Elliott
>>      > 84 Westfalia: Mellow Yellow ("The Electrical Banana")
>>      > 74 Westrailia: (Ladybug Trailer company, San Juan Capistrano,
>> Calif.)
>>      > Bend, OR
>>      > KG6RCR
>>      >
>>      >
>>      >
>>      >  On 9/29/2009 4:15 AM Frank Condelli wrote:
>>      >
>>      > In a message dated 28/09/2009 3:14:30 P.M. Eastern Daylight Time,
>>      >> LISTSERV@GERRY.VANAGON.COM <mailto:LISTSERV@GERRY.VANAGON.COM>
>>     writes:
>>      >>
>>      >>        If you were to read my _Headlamp Relay Upgrade_
>>      >> (http://frankcondelli.com/hdltrela.htm)   webpage.  It
>>     specifically says
>>      >> that it is necessary
>>      >> to change the 10 amp  fuses to 15 amp when installing the higher
>>     wattage
>>      >> bulbs.
>>      >>
>>      >>
>>      >>
>>      >>   Mark Drillock got it, right on the  button.  Both fuses 9 and
>>     10 were
>>      >>>>>>>
>>      >>>>>> blown.
>>      >> I guess those little 10 amp  fuses don't like the bigger lamps I
>>     have in
>>      >> both
>>      >> units.  And since I  drive at night very seldom they could have
>>     been out
>>      >> for
>>      >> some  time.<<<<<<<<
>>      >>
>>      >>
>>      >>
>>      >>
>>      >>
>>      >> Cheers,
>>      >>
>>      >> Frank  Condelli
>>      >> Almonte, Ontario, Canada
>>      >> '87 Westy & Lionel Trains (_Collection for sale_
>>      >> (http://frankcondelli.com/trainsal.htm) )
>>      >> _Frank Condelli &  Associates_
>>     (http://frankcondelli.com/busindex.html)
>>      >>  -
>>      >> Vanagon/Vanagon Westfalia Service in the Ottawa Valley
>>      >> _Vanagon Stainless Steel Exhaust  Systems_
>>      >> (http://frankcondelli.com/exhaust.htm)
>>      >> _BusFusion_ (http://www.busfusion.com/)  a VW Camper  camping
>> event,
>>      >> Almonte, ON, June 11 ~ 14,  2009
>>      >>
>>      >>