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  #1  
Old 12-24-2013, 12:04 AM
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Question about light wattage.

When you change the bulb wattage of one of your lights, do you need to add a higher amp fuse? I had 55 watt H3 bulbs, but I was at autozone and saw 100 watt H3 bulbs. I purchased the 100 watt bulbs, but now I'm wondering if I should increase the fuse which is a regular 8 amp to a 15 or 25 amp. Anyone? Oh and of anyone wants to know, the bulb is behind a fresnel projector lens so its really not much brighter than a standard halogen bulb

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Old 12-24-2013, 01:55 AM
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i think it should be the other way around. you're not trying to protect the
bulb, but the wiring. if the draw of the appliance is higher than the system
was designed for, the safeguard is to have the fuse blow BEFORE the
wiring is damaged. i would never advise increasing the fuse rating but
maintaining it as is....or in extreme instances, go lower (blow earlier).
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Old 12-24-2013, 02:39 AM
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Thanks for the insight
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Old 12-24-2013, 06:37 AM
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If the stock fuse and wiring won't handle the higher wattage, you can rewire it to use a relay. The relay circuit must be wired and fused to handle the wattage you'll be running. Guides regarding wire gauge in relation to length and amperage should be around if you search the internet.
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Old 12-26-2013, 01:41 AM
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I added the relays, but the stock fuse kept blowing. I upgraded the fuse to a 16a vs the 8a and itr seems fine now. I did fuse the 2 relays at the #30 pin with a 25a & 30a fuse.
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Old 12-26-2013, 06:32 AM
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Ismalley, I recommend using the replacement headlight lamp specified in your Owner's Manual. Increasing the fuse amperage rating is asking for trouble. A fire may start under the hood due to under-sized wiring.
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  #7  
Old 12-26-2013, 08:56 AM
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If you use a relays you need a coil supressor (Diode or Resitor).
Good (expensive) relays have a build in coil suppressor usually a Diode, cheap ones don't.

If you open a switch in a 12 volt relays system the relay coil generates up to 1500 Volt, extremely bad for the car electronics. If the fuse blows it just tries to protect the electronics in your car. Replacing it with a lager fuse means something else will blow up, usually something much more expensive. It may take a while but it will happen.

The simplest form is a diode parallel to the coil (with the bar on the Plus side) That way the current passes trough the diode and not back into the system. This diode needs to be large enough to handle the current.

As for the light fuses, never use a fuse larger than needed, 12 volt, 100Watt = 8,3 Amp.
The fuse needs to be a little larger, the current trough a lamp is higher before it warms up.
If you want to calculate the maximum current check the lamp resistance, if cold it has the lowest resistance (Voltage= Current x Resistance).


Rob
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Old 12-26-2013, 12:23 PM
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I used Mercedes relays....but I have never been wrong listening or taking advice from the forum, so I think I will just go remove the lights and use the regular ones. I just got my transmission replaced this month, I want to enjoy my reverse and normal shifting without having a fire under the hood of my car. Thanks everyone.
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Old 12-26-2013, 02:26 PM
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Which fuse is blowing? If the headlights are wired through relays, how is it the headlight fuse is blowing?

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Old 12-26-2013, 04:03 PM
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Quote:
Originally Posted by sixto View Post
Which fuse is blowing? If the headlights are wired through relays, how is it the headlight fuse is blowing?

Sixto
87 300D
Check google "relais parallel diode " for the answer to that.

Rob
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  #11  
Old 12-26-2013, 08:21 PM
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The Mercedes ice cube relays I've popped open have a diode. Does this mean the OP's relay doesn't have diodes or the diodes are bad?

Sixto
87 300D
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  #12  
Old 12-26-2013, 08:50 PM
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As another mentioned, use a relay to isolate the higher amperage circuit from the lower amperage circuit. A bigger fuse is begging for a fire. Although, once you create the new circuit, you need to put the bigger fuse in that circuit. Otherwise it would be an isolated and unprotected circuit.

Get a cheap relay, some leds, and a power supply to play around with. Cheapest power suppliee are the ones sold for rc car racing chargers. Protek. Mine can do 20 amps.
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  #13  
Old 12-27-2013, 03:25 AM
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Problem solved. Relays are still intact, I swapped the lights around and now everything is fine. I was connecting the low beam and the 100w on the same power supply wire. didn't figure it out till later when I went to go disconnect them

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