Probably the smart thing to do, a-yup.

--
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 9:32 PM Scott Daniel - Turbovans wrote:

> 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
>>>      >>
>>>      >>
>
>