>
>Does anyone know the wattage of the O.E. round headlights?
>
>I just installed square Sylvania's which draw 65 watts on hi-beam and 55 on
>low (each side) but I didn't install relays. If I recall correctly the O.E.
>headlight switch contains a circuit breaker which is designed to trip at 25
>amps.
>
The OEM wiring diagram shows the high beam to be 14 gauge on the '76 Palm Beach (all the diagrams I checked have 14 ga for
this circuit). Low beams are 16 gauge. For High beams, it's enough for 8-12 amps in the engine compartment. So, the upper
end of recommended curent says that you could safely drive 100-140 watts of headlight.
GM did put a 25 amp fuse in the head light circuit. However, 25 amps is more than twice the recommended current for the size
wire.
What we're concerned about here is:
1. voltage drop
2. heat in wires/switch
the voltage drop is current * ohms per foot * length
ohms per 1000 ft for 14 gauge is 2.53 = .00253
I'm estimating total loop for the headlights is around 20 ft (have to count the ground path as distance also). So, we get a
bigger voltage drop when we go to higher wattage lamps - which may actually reduce total light output as compared to OEM
lamps. The 55 watt lamps combine to give about a 0.5 volt drop. This drop reduces the luminous output of the lamps by about
10% from their full rated output. (As a rule of thumb, each 1% drop in volatage decreases luminousity by 3%)
A 65 watt lamp drops the voltage by .55 volts (3.9%), so the lamp actually puts out about 88% of the design luminousity.
Moving from 14 gauge to 10 gauge wire reduces the voltage drop by a factor of 3, and using relays will drop the length by a
factor of 2. So, even for the stock OEM headlights, a move to relays should give about 10% more light.
Heat in the wires and switch is no problem when using the OEM setup - providing all connections are clean and tight. Dirty
or corroded connections can create quite a lot of heat in a small space. Providing that the circuit is clean, the 25 amp
fuse should be adequate to protect against wire meltdown, but running 65 watt lamps plus driving lights is too much current
in my opinion (and exceeds current recommendations).
Henry
Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (408) 462-5199 / full service marketing
fax: (408) 462-5198
http://www.henry-davis.com
