Electrical oddity question

JHZR2 · Feb 24, 2007

Hi,

My BMW is a 91 E30 3-series model. Came with sealed beam 5.75" headlights.

I plan to upgrade the relays/wiring when it gets warmer - but since I had the lights and it was nice today, I figured Id install them anyway.

I didnt use high voltage bulbs - just standard 60/55 for the lo-beam circuit and 55w hi-beams, just like the selaed beam light ratings that were in there before.

Recently, before I did this install, I had put in new fuses, all the correct amperages, as some of the OE ones looked kind of old and lousy (the fuse box is underhood, not in the car). I put new 7.5A fuses in for the hi-beam circuits... all was well, and it worked like a champ.

All I did was install the new lights. lo beams work great. Hi beams work great on the right side, but blow the 7.5A fuse every time. All the wiring is tight, I put dielectric grease on each connection, and everything was perfect at the same wattage bulbs in sealed beam form, not 20 minutes before.

Any idea what gives?

I did a test, and put in a 20A fuse in place of the 7.5A one. I waqs just going to be checking everything, so figured that all woudl be well, if I sensed the fuse getting hot, Id kill the lights. The lights worked very stable, without issue, for somewhere between 30 seconds and a minute, before I killed them because I sensed no wrong. The fuse stayed cool, and showed no sign of thermal distress.

So, any ideas? Im not comfortable with using a 20A fuse, but I would consider a 10 or perhaps even a 15A fuse in there as a stopgap solution. How terrible would this be?

Is there any sort of test that I can do to see what is wrong? An ohmmeter between the hot and ground on the lighting harnesses? Can I check the circuits at the fusebox to get an understanding of overall circuit resistance???

Also, given that there are already relays for the lighting circuits as OEM install, what would I want to do as an upgrade? Higher-rated relays? Would I perhaps only need to decrease gauge/increase wire diameter?

Any insight would be most apprecated.

Thanks,

JMH

Kestas · Feb 24, 2007

Just a thought... I'm guessing there's some startup phenomenon that the old style headlamps didn't have... meaning your circuit may have a current spike during startup. Though the 7.5A fuse may handle steady state conditions, it may not be able to handle startup before the filament warmps up.

JHZR2 · Feb 24, 2007

Got it... so perhaps a 10A fuse would be able to handle it and still be barely less safe (30W difference in throughput) than the 7.5.

Do I dare run my fluke ammeter through there? might I be better off trying to measure some analog, like voltage drop vs. voltage at the battery, then measure overall circuit resistance to get effective amperage? I ask this because my multimeter is a fluke 179 true RMS, and only has a 10A fuse.

Thanks,

JMH

427Z06 · Feb 24, 2007

Quote:

Just a thought... I'm guessing there's some startup phenomenon that the old style headlamps didn't have... meaning your circuit may have a current spike during startup. Though the 7.5A fuse may handle steady state conditions, it may not be able to handle startup before the filament warmps up.

This sounds like it to me. There are transients even with something as simple as a light bulb. If the new bulbs take longer to heat up the element to the operating temperature, the current draw will be greater during this period. A "Slow Blow" fuse might do the trick, but I don't think they make those in blades. You could measure the current to be sure, but I don't think a 10 amp would cause a problem.

427Z06 · Feb 24, 2007

Quote:

Also, given that there are already relays for the lighting circuits as OEM install, what would I want to do as an upgrade? Higher-rated relays? Would I perhaps only need to decrease gauge/increase wire diameter?

There was an automotive lighting website that went into great detail on this, not sure if it's still around. But in short, you'll have to replace much of the wiring and relays with stouter stuff. You'd also have to check if there is any diagnostics that run off of something like voltage/voltage drops that signals a light on the dashboard, etc.

Gary Allan · Feb 24, 2007

Quote:

Hi beams work great on the right side, but blow the 7.5A fuse every time.

I keep reading this ..(right side) ...yet it's not confirmed that the fuse blowing only handles the right side in all of your information ..hence my confusion.

If it only happened on the right side with the mere changing of bulbs ..I would swap bulbs and see if the condition occurs on the left.

If so, I'd ''''can the bulb

..or am I having a text challenged episode (totally possible)

.

JHZR2 · Feb 24, 2007

yes, I wasnt clear - the hi-beam circuit has two fuses, one for left, one for right. Im assuming that the 7.5A fuse for each side (which = 90W) is ONLY for the high beam bulb - this is an old fashioned system where the lo-beam bulb is dual filiment and burns at 55W (vice 60W) when the hi-beam is selected... and that is too much wattage.

Anyway, so there is a fuse for each side, and the one side stays A-OK, the other burns out each time.

Can I check the resistance of each side via a multimeter and through, say, the fusebox connection?

Thanks,

JMH

JHZR2 · Feb 24, 2007

well, I went to advance auto when I was outrunning errands and got some 10A fuses. Worked perfect - lights turned on without issue, and stayed on.

Maybe in hot weather, itll change, but given that I know that operating they use under 10A, I can likely get away with just putting in a 15A if absolutely required - but likely Ill not need to do that, so I hope...

Anyway, all seems OK... If my lighting system already has relays, is the only upgrade that I have to do install bigger wires, or do I need to set it up so that the relays get power NOT through the fuse box???

Thanks,

JMH

NYEngineer · Feb 24, 2007

Check out danielsternlighting.com. Excellent site and Daniel Stern is very helpful.

JHZR2 · Feb 24, 2007

absolutely... he is who I buy my ecode lights from

JMH

Trav · Feb 24, 2007

Do a voltage drop test on the + and - also be sure there is no stray strands from the high beam circuit touching.A 55w bulb only draws 4.58 amps so s 7.5 amp fuse is plenty unless the demand is higher.unless both filaments are drawing current from the low side then both 55w and 60w filaments will be drawing current.You then need 4.58 and 5.0 amps for that circuit therefor a 10 amp fuse will hold because only 9.58 amps are being drawn.The issue may lie in the bulb itself as was posted earlier,switch them and see if the same thing happens if not its the bulb otherwise take a closer look at the wiring especially between high and low beam circuits.

JHZR2 · Feb 24, 2007

well, after some more research at roadfly.org, it seems that it is necessary to use the 10A fuses...

I guess in the old fashioned 5.75" sealed beam systems, though the lo beams have a filiment that stays on when the hi-beams are on, it is not the same draw... the hi-beam filiment of an H4 bulb is 55W and the H1 hi-beam bulb is also 55W... 110W=9.1A. For the H5006/9001 sealed beam system, lo and high beams on the outer bulb are 35W, the hi-beam 5001 is 50W... this puts 85W on the circuit, which is roughly 7A, depending on if you divide by 12 or 12.8, which is apparently the voltage they use for some of these calculations.

So the sealed beams are a 35W making the difference...

10A works great, and is the accepted solution amongst other upgraders...

JMH

427Z06 · Feb 24, 2007

Quote:

Check out danielsternlighting.com. Excellent site and Daniel Stern is very helpful.

That's the website.

Tosh · Feb 25, 2007

Quote:

well, after some more research at roadfly.org, it seems that it is necessary to use the 10A fuses...

I guess in the old fashioned 5.75" sealed beam systems, though the lo beams have a filiment that stays on when the hi-beams are on, it is not the same draw... the hi-beam filiment of an H4 bulb is 55W and the H1 hi-beam bulb is also 55W... 110W=9.1A. For the H5006/9001 sealed beam system, lo and high beams on the outer bulb are 35W, the hi-beam 5001 is 50W... this puts 85W on the circuit, which is roughly 7A, depending on if you divide by 12 or 12.8, which is apparently the voltage they use for some of these calculations.

So the sealed beams are a 35W making the difference...

10A works great, and is the accepted solution amongst other upgraders...

JMH

Pleased to hear you've found the answer. Now that you're sure it draws less than 10A, you can put your Fluke in place of the fuse to measure the exact amperage drawn. Might be a good baseline reference for others, and to see problems/differences between L and R?

Gary Allan · Feb 25, 2007

I too am glad that you've resolved this in a satisfactory manner ..but the FIRST THING that I would have done with two allegedly identical installations with different results ... would have been to see if moving the bulbs resulted in the same anomaly ..and THEN I would have blamed the BULB.

Your left new bulb was happy as a clam with a 7.5A fuse ..if I read everything correctly (always in question).

This violates my sense of "sensible" reasoning and diagnosis. (not that this is necessarily sensible when compared to others

)

The_Jeff · Feb 25, 2007

My headlights have no fuse and in fact run on a thermal circuit breaker.

I'm happy this design as a minimum has one fuse for each side, but what happens when this blows in the middle of the night while driving on a deserted road?

Any idea what the stock fuse size is/was?

When you upgrade the relays and wiring base the fuse on the new wiring size, there'll be a chart of wire gauge vs amp capacity.

JHZR2 · Feb 25, 2007

Quote:

..but the FIRST THING that I would have done with two allegedly identical installations with different results ... would have been to see if moving the bulbs resulted in the same anomaly ..and THEN I would have blamed the BULB.

Gary,

anything Ive posted does not absolutely exclude me from doing this - in fact, by the time I posted this yesterday, it was too late/dark, and today we have snow and freezing rain.

I am glad that I figured out that 10A will work as a fuse, as a stop-gap solution, because Id be very worried about using 20A fuses in there, or loosing use of my lights...

I will be doing just what you asked when this snowstorm ends...

Thanks!

JMH

Gary Allan · Feb 25, 2007

Quote:

Quote:

..but the FIRST THING that I would have done with two allegedly identical installations with different results ... would have been to see if moving the bulbs resulted in the same anomaly ..and THEN I would have blamed the BULB.

Click to expand...

Gary,

anything Ive posted does not absolutely exclude me from doing this - in fact, by the time I posted this yesterday, it was too late/dark, and today we have snow and freezing rain.

I am glad that I figured out that 10A will work as a fuse, as a stop-gap solution, because Id be very worried about using 20A fuses in there, or loosing use of my lights...

I will be doing just what you asked when this snowstorm ends...

Thanks!

JMH

JMH, have you ever watched a tread just drift way off in left field ..and you're sorta sitting there ..almost jumping up and down at how apparent something is to you ..and it seems to "not exist" in the plane of rationale that you're viewing ..cascading down the topic ..you know that there are multiple people that are methodical and organized ..and yet ..the most apparent thing to you..the most fundamental action when you see something "unright"..seems to just sorta hang in some obscure corner while just about everything else is in explored thoroughly ..and you're somewhat pondering, "what am I missing

"

..well, this is just one of those times for me

(visions of Airplane, "That's funny. John never vomits at home

"- cue suspense music)

Electrical oddity question

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