Date: Thu, 4 Dec 2008 22:41:46 -0600
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: Headlight Upgrade
In-Reply-To: <1983.192.168.0.115.1228442659.squirrel@hasenwerk.homeip.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Another factor that comes into play related to resistance is heat. The
best example of this is an actual case that got my attention because it
affected what I was doing. The application was not vehicular, but the
effects were the same.
I had an electric kiln for pottery operations and I needed to string
some wire for it. The kiln was rated at like 10,500 watts, 240 volts, 50
amps. I used a #8 cable rated for under ground use, and in that
application it had worked great. The temperature of the cable remained
the same no matter the weather. But when I installed it I laid it out on
the surface and treated it like a big extension cord. It worked fine
that way all through winter into spring, but one day in spring the
weather was really hot. The cable was laying on concrete and as the sun
passed over head, the shadows moved and left the cable exposed to the
light on that concrete. The kiln was firing, and every thing was moving
right along when I heard the breaker pop. I went and checked it. Then
reset the breaker. The power was back on the kiln for about 10 seconds
and the breaker popped. Hmmmm, I thought! What's going on? I doubled
checked the kiln for faults and found none. I unplugged the cable, and
re-plugged it, then turned on the breaker. For the next little bit it
ran fine - then POP! In a few moments it occured to me to feel of the
cable laying there in the sun. It was hot. Then it dawned on me.
Earlier when I strung the cable out for the day, it was cooler, and the
cable was not hot. Now, laying out in the sun on the hot pavement that
cable had gotten hot from solarization, and given that the wire size was
marginal for that big a load - it was OK when cool, but not when it was
hot. Given the size of the wire, the increasing resistance induced by
the heat of the sun was just enough to raise the amperage requirement to
the point it heated up the breaker and caused it to trip. Later, in
early evening after it had cooled down considerably, I reset the breaker
and finished the firing, because as the sun went down and things cooled
off, the induced resistance dropped the electrical load and allowed the
kiln to continue to operate. I found it really interesting that the
whole setup was so close to the limits of the electrical load, that heat
from the sun could trigger an increase in the resistance sufficient to
trip the breaker. I got a cable with larger wires soon after, and had no
more trouble. So, even though this was AC, it still speaks to the need
to have wiring of adequate size so resistance is lower. A little
oversize on the wire rarely hurts.
Regards,
John Rodgers
88 GL Driver.
David Marshall wrote:
> In short the more current you have the more voltage you will loose due to
> resistance in the wires. Install fat wires with fat bulbs and you're
> set with brighter lights.
>
> In long we can use Ohm's law:
>
> V = I x R
> P = I x V
>
> Where:
> V - volts
> I
> - current
> R - resistance
> P - watts
>
> So your 100W bulb
> (really 200W as two lights) is rated 200W @ 13.8V so current is:
>
> 200W = I x 13.8V
> Current is 14.5 amps
>
> Wire has
> resistance as is a part of the equation. The larger the wire the
> less resistance to current flow. So say for example 18 gauge wire
> from the battery thru the fuse panel and what have you to the lights is
> 0.01 ohms (not correct but good for the example) and the installing a 10
> gauge (fatter wire) wire from the alternator to the lights is 0.001
> ohms
>
> The formula for power loss is PowerLoss = Current^2 x
> Resistance
>
> Those lights need 14.5 amps, squared is 210.25 so
>
> 210.25 x .01 for the 18 gauge = 2.1 Volt loss
> 210.25 x .001
> for the 10 gauge = 0.21 Volt loss
>
> David Marshall
> VW
> Adventure Driver and BMW Adventure Rider
>
> http://www.hasenwerk.ca
>
> On Thu, December 4, 2008 17:01,
> Jonathan Poole wrote:
>
>> I know that many on the list
>>
> have made these improvements but I thought
>
>> someone may still be
>>
> interested in the improvement and specifically the
>
>> voltage
>>
> increase at the headlights that I achieved through the use of
>
> Frank
>
>> Condelli's relay kit and by running a 10 gauge power
>>
> supply from the
>
>> starter
>> to run the headlights.
>>
>> Before the above listed changes I was getting about 11.9
>>
> volts at the
>
>> headlights with the engine idling. After the
>>
> changes I get about 13.1
>
>> volts
>> at the headlight with
>>
> the motor idling.
>
>> This upgrade plus putting in the
>>
> 100/80 watt bulbs and aiming all 4 of my
>
>> headlights (south
>>
> african grill setup) has resulted in a dramatic
>
>> improvement of
>>
> night driving visibility. I had a shop aim my headlights
>
>> last
>>
> year but they did a very poor job and the lights were way off.
>
>
>
>> Before these changes driving under low beams only was a strain
>>
> due to poor
>
>> aiming and dim lights. It wasn't as bad as my old
>>
> 6v beetle used to be
>
>> but
>> in some situations I think it
>>
> could be considered dangerous or at least
>
>> annoying. Another
>>
> benefit of this modification is that my batteries
>
>> (house
>> and starting) maintain a higher voltage since the headlights pull
>>
> from the
>
>> alternator instead of the batteries. There is still a
>>
> drop when the
>
>> lights
>> are on but it is lower.
>>
>>
>
>
>> relay kit and bulbs:
>>
>>
> http://frankcondelli.com/hdltrela.htm
>
>> aiming
>>
> guide:
>
>> http://www.danielsternlighting.com/tech/aim/aim.html
>>
>> I picked up 25' feet (more than is actually needed) of
>>
> stranded 10 guage
>
>> wire at the local Lowe's and misc crimp on
>>
> connectors at the local auto
>
>> parts store. I ran the wire
>>
> without dropping the gas tank. Getting the
>
>> wire over the gas
>>
> tank involved sticking a coat hanger over the top of the
>
>> tank
>>
> space and then taping the wire to the hanger and pulling the wire
>
>> through to the other side of the tank.
>>
>>
>> Jonathan Poole
>> '83 AC Westy
>>
>>
>>
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