H4 Headlights
01-20-2006, 03:16 PM
#31
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Over-drawing the circuit isn't necessarily an issue of sudden catastrophic failure. Over-drawing the stock circuit can take out the switch contacts on the light switches and relays. (don't ask how I know!!) It can also overheat the wire insulation, causing it to become brittle and fall off, which isn't a good thing on a moving light application.
01-20-2006, 03:24 PM
#32
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Kinda late joining this discussion, but I've got a write-up of my swap to H5's, including photos of how the connectors differ on an H4.
http://www.928oc.org/928oc_michigan/headlight.html
http://www.928oc.org/928oc_michigan/headlight.html
01-20-2006, 03:34 PM
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Originally Posted by BrianG
Over-drawing the circuit isn't necessarily an issue of sudden catastrophic failure. Over-drawing the stock circuit can take out the switch contacts on the light switches and relays. (don't ask how I know!!) It can also overheat the wire insulation, causing it to become brittle and fall off, which isn't a good thing on a moving light application.
4 year of 100/80W has not done any of this on my 89. You indicate you had a problem - was it with higher wattage than that?
01-20-2006, 03:48 PM
#34
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Originally Posted by Bill Ball
The plug that is on early cars that have sealed beam headlights, like yours, is the same as the H4 plug - so, no splice needed.
I am not sure if the buckets on sealed beam headlights units with the chrome trim ring even have the tab. On the later car the headlight assembly has a little tab or prong-like protrusion on the lower part of the lamp, at the 5 and 7 o'clock positions. On the bucket's leading edge there is a hole that mates to the prong. This keeps the lower edge of the bucket from flapping in the wind and rubbing the fender. If you go with 7" H4's then this is not an issue. If you go with 8" and remove the chrome trim ring, I'm not sure if you need to do anything to prevent the bucket edge from flapping. I had to extend the tab/prong due to the change in headlamp assembly position. When the tab and bucket did not engage, the paint wore off the lower edge of the bucket. Others have done this on early cars. Maybe they can comment.
I am not sure if the buckets on sealed beam headlights units with the chrome trim ring even have the tab. On the later car the headlight assembly has a little tab or prong-like protrusion on the lower part of the lamp, at the 5 and 7 o'clock positions. On the bucket's leading edge there is a hole that mates to the prong. This keeps the lower edge of the bucket from flapping in the wind and rubbing the fender. If you go with 7" H4's then this is not an issue. If you go with 8" and remove the chrome trim ring, I'm not sure if you need to do anything to prevent the bucket edge from flapping. I had to extend the tab/prong due to the change in headlamp assembly position. When the tab and bucket did not engage, the paint wore off the lower edge of the bucket. Others have done this on early cars. Maybe they can comment.
Originally Posted by Big Dave
Kinda late joining this discussion, but I've got a write-up of my swap to H5's, including photos of how the connectors differ on an H4.
http://www.928oc.org/928oc_michigan/headlight.html
http://www.928oc.org/928oc_michigan/headlight.html
I did notice the other day, though, there is some minor "rubbing" on the front edge of the fender where the light recesses.
It appears the bottom of the light housing is rubbing on the top of the fender (inner portion of the circle). Can housing be adjusted/raised? or is there something else that needs to be adjusted to get the housing "off" the fender. - I've done no adjustments that could cause this rubbing, so I'm guessing something's worn out or come loose; I don't see what it could be. Thanks.David
01-20-2006, 04:14 PM
#35
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Originally Posted by Bill Ball
Hey Brian:
4 year of 100/80W has not done any of this on my 89. You indicate you had a problem - was it with higher wattage than that?
4 year of 100/80W has not done any of this on my 89. You indicate you had a problem - was it with higher wattage than that?
No, but it was a different vehicle. It was an older chev 1/2 ton, and using 100W high beams eventually burnt out the contact point in the headlight switch.
It took years, though.I just have the philosophy that, if you are going to exceed design limits, you should bolster the system. Of course there are over-stress margins designed into every system, but who knows how much??
01-20-2006, 04:24 PM
#36
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Bill,
OK techie time - 100W headlamps are spec'd for power @ ~12.8v,
but since they get ~13.5v when the car is running its actually a higher consumption typically when on - actually about 110W due to power proportional to ~V^(1.6) for bulbs.
Thus the current will be about 8.15 A Vs your fuse @ 7.5A. Now ATC fuses have a bullt in tolerance + an uncertainly range for trip power dependant primarily on ambient temperature & manufacturing tolerances. Bottom line - you are on the edge @ 100W - though 80W is OK.
If you come to Phoenix in the summertime - leave before nightfall !
I would just swap to 10A fuses for the high beams - so they stay on under all conditions. Note that some bulbs are hopelessly optimistic about ratings. I run 55W/'100'W H4's - however in measurements (off the car) they are 55W/~85W actual ratings... many bulbs a have a wide tolerance range and also vary considerably from their specs - so who knows what you really have.... (measure them?)
The 1mm^2 core area of the headlight conductors is good for up to 10A rating (inc tolerance), but not much more.
With sufficient current you will damage the wires - but you'll also be wasting much of the power you want to use to illuminate the road in heating those wires.
At 130W you will be loosing almost 0.8V at the bulb to voltage drop from power loss in the wires - this will reduce the potential maximum brightness by approximately 18% since brightness is proportional to ~ V^(3.4).
Bulbs are actually quite challenging to understand, though all too easy to use...
Alan
OK techie time - 100W headlamps are spec'd for power @ ~12.8v,
but since they get ~13.5v when the car is running its actually a higher consumption typically when on - actually about 110W due to power proportional to ~V^(1.6) for bulbs.
Thus the current will be about 8.15 A Vs your fuse @ 7.5A. Now ATC fuses have a bullt in tolerance + an uncertainly range for trip power dependant primarily on ambient temperature & manufacturing tolerances. Bottom line - you are on the edge @ 100W - though 80W is OK.
If you come to Phoenix in the summertime - leave before nightfall !
I would just swap to 10A fuses for the high beams - so they stay on under all conditions. Note that some bulbs are hopelessly optimistic about ratings. I run 55W/'100'W H4's - however in measurements (off the car) they are 55W/~85W actual ratings... many bulbs a have a wide tolerance range and also vary considerably from their specs - so who knows what you really have.... (measure them?)
The 1mm^2 core area of the headlight conductors is good for up to 10A rating (inc tolerance), but not much more.
With sufficient current you will damage the wires - but you'll also be wasting much of the power you want to use to illuminate the road in heating those wires.
At 130W you will be loosing almost 0.8V at the bulb to voltage drop from power loss in the wires - this will reduce the potential maximum brightness by approximately 18% since brightness is proportional to ~ V^(3.4).
Bulbs are actually quite challenging to understand, though all too easy to use...
Alan
01-20-2006, 06:19 PM
#37
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I tired 80/50 H4 and they were quite dim. The 100/80 look normal brightness to me, certainly not HID level. Perhaps I got over-rated bulbs. Anyway, I've checked the wiring and can't see any change at all, nor any warmth when running. The high beams are only 25% over the original bulbs.
Hey Brian, wouldn't the switch be isolated from the bulb draw by the relay?
Hey Brian, wouldn't the switch be isolated from the bulb draw by the relay?
01-20-2006, 06:32 PM
#38
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Bill,
Yes in a 928 the switch only control the relay so carries the same load (minimal) whatever headlights you run. The headlight relay is quite capable of switching upto 20A. The headlight wiring is actually a weak point in the design - its actually quite poor to have 1^mm wiring for headlights and the wiring distance is quite long too. I suspect Porsche did this a safety mechanism - the resistance of the wires actually helps reduce startup current & limits upward power expansion to rediculous levels (I'd put 180W high beams in the rediculous category).
If the bulbs you have have in have worked fine for years you are probably still going tobe OK... Keep a few spare fuses handy though!
Alan
Yes in a 928 the switch only control the relay so carries the same load (minimal) whatever headlights you run. The headlight relay is quite capable of switching upto 20A. The headlight wiring is actually a weak point in the design - its actually quite poor to have 1^mm wiring for headlights and the wiring distance is quite long too. I suspect Porsche did this a safety mechanism - the resistance of the wires actually helps reduce startup current & limits upward power expansion to rediculous levels (I'd put 180W high beams in the rediculous category).
If the bulbs you have have in have worked fine for years you are probably still going tobe OK... Keep a few spare fuses handy though!
Alan
