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Narvas, H4's, what about fuses?
A year ago I've installed H4's w/ the "stock" 60/55 bulbs. I used 12 gauge wiring throughout, bypassing any pre-existing stuff. Basically, I wired it up from scratch, 4 relays but only two fuses from the battery. (I know I should have used 4 for a completely bulletproof system but I have one for driver side high/low and one for passenger high/low)
If or when they blow, it is really easy to diagnose. I used 5 amp fuses when I first started but those blew out as soon as I hit the high beams. Since then I've put in 10 amp fuses and they have held up for over a year, which tells me they were adequate. Now I've switched to Narva's, along w/ the excellent high temp sockets. The bulbs are 130/100's and the driver side fuse has blown twice already. I'm not really content w/ just replacing them w/o knowing WHY they blew out. Is it as simple as not having a big enough fuse? Would a 15 or even 20 amp fuse be more appropriate for these high power bulbs? When I started out w/ H4's and had 5 amp fuses, they both blew out together which meant they were way off the mark. If only one side keeps blowing out, does it mean the fuse is not matched to the system or is it something else? Can't tell why the other side wouldn't blow out either. Any ideas? 
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01-06-2005, 07:17 AM
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Join Date: Aug 2002
Location: Galivants Ferry, SC
Posts: 10,550
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Ideas? Yes.....basic physics:
Watt/Volts=Amps 60W/12V = 5 amps "running" current. For various reasons, you fuse with a slightly higher rating to accommodate inrush current and other variables, usually over size by 25-30% = 6.5 amps. Note that Porsche stock size is 8 amp fuses. Quick and dirty just ratio this for the higher wattage: 130W/12V = 10.8 A......next "up typical rating is 15 amp ( ATO blade style fuse) or 16A "suppository" style Porsche fuses...... Wil
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Wil Ferch 85 Carrera ( gone, but not forgotten ) |
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01-06-2005, 07:47 AM
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Awesome. That's the exact formula I was trying to figure out. Thanks Wil.
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01-06-2005, 07:59 AM
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Join Date: Aug 2002
Location: Galivants Ferry, SC
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Simple physics....but next time anyone is in doubt over what kinds of formulas to use...there are always places like this on the web:
http://www.simetric.co.uk/si_watts.htm Wil
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Wil Ferch 85 Carrera ( gone, but not forgotten ) |
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01-06-2005, 08:08 AM
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Join Date: May 2001
Location: Peoples Republic of Long Beach, NY
Posts: 21,140
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routine is that load should be 70% of fuse rating. I usually go larger.
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Ronin LB '77 911s 2.7 PMO E 8.5 SSI Monty MSD JPI w x6 |
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01-06-2005, 09:57 AM
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