5ktq Headlight Wiring

[Ameer Antar]

what's wrong? I don't get it. I did say that there can be voltage drop in 
wires, esp. if they are long and skinny. You used a formula (I^2*R losses) 
which is the power in watts which is wasted as heat in the wire. Wattage 
does not equal temperature. Depending on how much heat dissipates from the 
material and how much surface area there is, more watts do NOT necessarily 
mean higher temp, since some material, such as copper conduct heat away 
much quicker than others.

Here are the formulas needed: R of a wire is equal to length/area times the 
material resistivity coefficient [which is 1.7e-8 ohm-meters for Cu]. so 
the shorter the length, the lower the resistance. The lower the R, the less 
power wasted [I^2*R]. In other words, a short thin wire can replace a long 
fat one. So a 3" length of the original wiring [18-20 ga.] will have much 
less resistance than the original ckt, and prolly even a 10' length of 14 
ga. wire.

I would encourage the use of 16-14 ga. wire [as in my conversion] for the 
rest of the system. It is commonly thought that current rating is based 
only on wire gage. It also is heavily dependent on length, as shown by the 
formula for resistance. That's why extra long extension cords can be 12ga. 
instead of 14ga. The 120A rating of the 12 ga wire doesn't mean anything 
w/o distance. In households 12ga. wire is used in 30-40A circuits, but 
nothing like 120A. That's b/c the rating is from a certain distance from 
the main line. Even those huge 000 gage wires in power lines can contribute 
to quite a voltage loss. They're so thick, but the distance is enormous. 
This is why there are many transformers on the line which increase line 
voltage and decrease current, cutting power losses. This is all basic power 
technology. Point is a thick wire doesn't necessarily mean more current, 
unless we talk about length.

No fire to worry about...

-ameer

>Sorry folks, this is just flat wrong--don't burn your car up.
>_Voltage drop_ depends on length, current capacity depends on
>YOUR allowable wire temperature (I^2*R losses). If you can stand
>really hot wire, then higher current is OK (at work we use some
>mil-spec TFE-jacketed wire that is rated at something like 120
>amps in a 12-gauge section--wow! We don't use it for the high
>capacity (it only carries 8 amps) but for the high temp (the
>heater it powers runs at 190 dC and is infrared)). If you don't
>want a fire, use big wire. If you want reasonable voltage at the
>output, use big wire.
>
>cu, James Marriott
>'87 4kq (alias "late-B2 90q"), 180k
>'89 200q (MC1, Procon10/no bag), 126k
>Boise, ID, USA     http://www.webpak.net/~marriott/