foglights

[coolcoupe]

Anyone know what amperage fuse you need for foglights and backup lights.I'm adding both of them and to put proper ones in.

[supereal]

Originally Posted by coolcoupe

Anyone know what amperage fuse you need for foglights and backup lights.I'm adding both of them and to put proper ones in.

Determine the wattage of each lamp. Multiply that figure by the number of lamps. Then divide that amount by the voltage of the vehicle, and the answer is the current draw. Fuses should be at least 10-15 percent higher. The formula is P (power in watts) is the product of I (current in amps) times E (voltage). I have never been convinced that fog lamps are necessary for anything except decoration, particularly if the output of the generator will be insufficient to operate the entire load.

[coolcoupe]

I don't know the wattage of this lamps. Is there a role of thumb or is there a standard fuse to use?

[supereal]

You can cross reference with a chart to show wattage with lamp number. Most good parts vendors can do that.

[Pete]

Originally Posted by coolcoupe

I don't know the wattage of this lamps. Is there a role of thumb or is there a standard fuse to use?

There is no rule of thumb. It is an exact science.
You will need to either know the bulb number so you can look up the info or hook it up on the bench with an ammeter in the circuit. Once you determine the current draw you can select a fuse 15% more than that number.

It is not likely you will be using the backup and fog lights at the same time so the stock generator should be ok.

[Old Henry]

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It is not necessarily the size of the bulb that determines the size of the fuse. It's the size of the wire going to the bulbs. You're not trying to protect the bulbs with fuses, you're protecting the wire if it shorts to ground from burning up. Here's a chart that shows how many amps a certain gauge of wire will carry over a certain distance at 12 volts that might help. http://www.offroaders.com/tech/12-vo...gauge-amps.htm On that chart, 14 gauge wire is big enough with 12 volts to carry 15 amps up to 20 feet. That is a pretty stock size of wire in most vehicles. So, a 15 amp fuse or smaller is adequate for that example. As is noted on the chart, wire 2 gauge sizes bigger is needed for 6 volts to push the same current through the wire as 12 volts does. So, if you have a 6 volt system, in the above example, you'd need 12 gauge wire to carry 15 amps 20 feet. Note that you use the same size of fuse - 15 amp or smaller - with 14 gauge wire and 12 volts as you use with 12 gauge wire and 6 volts.

You, of course, have to know the gauge of your wire. 12 volt systems use smaller gauges than 6 volt systems.

The amperage load on the wire from all of the light bulbs that it's powering needs to be calculated to be sure you have a big enough wire to supply all of the bulbs. Here is a calculator to determine amps from known volts and ohms resistance (which you can determine for any bulb with an ohm meter.) http://www.rapidtables.com/calc/elec...calculator.htm Some examples: I just tested the resistance on the brake light filament of the halogen bulb I use to have in the car. It was .5 ohms. I put that into the calculator with 6 volts and got 12 amps. So, two of those combined is 24 amps just to power those filaments. Looking up on the other chart, for 6 volts to push 24 amps 20 feet would need 10 gauge wire (the 12 on the chart for 12 volt plus two for my 6 volt.) That's why I used 9 gauge explained below, just to be sure. Probably overkill, 10 gauge would do. In comparison, the tail light filament in the halogen bulb has 5.5 ohms resistance. That's only 1 amp draw.

I put some 6 volt halogen bulbs in my tail lights to get them brighter but the brake light filament would hardly light up. I calculated the load of those bulbs and figured I needed 9 gauge wire to power them. I ran such from the starter solenoid through a 25 amp circuit breaker and relay activated by the brake light switch to power them. Then I learned about the Sacramento Vintage Ford super bright bulbs that work even better than the halogens and replaced the halogens with them.

If you calculate the size of fuse based on the draw of the bulbs, and the draw of the bulbs is too much for the wire, the fuse will be too big for the wire, the light would not fully light, and the fuse would never blow to protect it.

After all of the above, Pete has got it right (and a much more succinct answer). Use a fuse a bit bigger than the total draw on the circuit, provided that you know the wire is big enough to carry the draw.

[Pete]

"It is not the size of the bulb that determines the size of the fuse. It's the size of the wire going to the bulbs."

Wrong.
The load in the circuit, in this case, bulbs, determines the load hence fuse size..
The wire has no effect as long as it is adaquate in size (gauge).
The wire draws no current.
The load determines the fuse size.
The fuse does protect all of the components in the circuit.

[quickchange34]

Pete you got it right!!

[Old Henry]

I have fog lamps on my car that I installed after a bout with fog when I wished I'd had them. I've never been in fog since. But, I use them all day on road trips on two lane roads as driving lamps for visibility better than the headlights. They look cooler to oncoming traffic that headlights too. They are as bright as headlights, just yellow.



Huh? Whadaya think?

I just tested the resistance of my combined fog lamps and got .5 ohms. On the amp calculator I previously referred to that's 12 amps and can be run (and are run) on 14 gauge wire. So, a 15 amp fuse would suffice (but I run mine off of the headlight circuit breakers with the same protection.)

(I know. More than anyone really wanted to know. But, I so like the feel of my fingers bouncing the my key board. So, there you have it.)

[Old Henry]

Originally Posted by Pete

"It is not the size of the bulb that determines the size of the fuse. It's the size of the wire going to the bulbs."

Wrong.
The load in the circuit, in this case, bulbs, determines the load hence fuse size..
The wire has no effect as long as it is adaquate in size (gauge).
The wire draws no current.
The load determines the fuse size.
The fuse does protect all of the components in the circuit.

If it's the load on the circuit that determines the fuse size required rather than the wire size, why is all 14 ga. house wiring protected by a 20 amp circuit breaker and all 12 ga. wiring protected by a 30 amp breaker when no load is even known? So, if you put a 30 amp load on a 14 ga. circuit in the house you should run that circuit through a 30 amp circuit breaker?

And, what is it about the components in a circuit that need protection and how does a fuse do that?

It's not that big of deal. Certainly not important enough to get egos involved. I just like to clarify the physics when appropriate. The advice is the same. If you know the load on a circuit in the car you can get by with a smaller fuse matching that load than what might be needed to protect the wire under its full load capability. But, if you don't know the load on the circuit (such as the cigar lighter circuit that could have varying loads plugged into it) better use a fuse to protect the wire under its full capability. For fog lamps like mine a 15 amp fuse is just right. I think that's all coolcoupe really wanted to know.

[Pete]

Originally Posted by Old Henry

If it's the load on the circuit that determines the fuse size required rather than the wire size, why is all 14 ga. house wiring protected by a 20 amp circuit breaker and all 12 ga. wiring protected by a 30 amp breaker when no load is even known?


The load does not want to be over an NEC standard for a given wire size. Remember what I said in my previous post, "the wire has to be appropiate for the design circuit load".

So, if you put a 30 amp load on a 14 ga. circuit in the house you should run that circuit through a 30 amp circuit breaker?

A person's home owner insurance would be void if you do that.

And, what is it about the components in a circuit that need protection and how does a fuse do that?

Switches, line voltage thermostats, relays, motor starters etc etc are all rated for a maximum current. You fuse or breaker them at what the NEC says to for that type of equipment.

It's not that big of deal. Certainly not important enough to get egos involved. I just like to clarify the physics when appropriate.

No egos involved. I was just correcting a statement you made. The 3 inch thick National Electrical Code book will answer all questions..

The advice is the same. If you know the load on a circuit in the car you can get by with a smaller fuse matching that load than what might be needed to protect the wire under its full load capability. But, if you don't know the load on the circuit (such as the cigar lighter circuit that could have varying loads plugged into it) better use a fuse to protect the wire under its full capability. For fog lamps like mine a 15 amp fuse is just right. I think that's all coolcoupe really wanted to know.

My fog lights draw 20 amps apiece (40 total at 14V).
I have a 50 amp breaker on the circuit. It is wired with #6 wire. #8 wire is rated at 40 amps but that would leave no saftey factor. The wire would run warm inducing voltage drop.

[koates]

Hi there, The important thing to know for a start is the system voltage, 6 or 12 volts. The next thing to know is the wattage of each bulb or sealed beam unit. Neither of these specs have been mentioned. When you provide this information we can work out the circuit current draw in amps and then recommend a fuse size. Very simple. Most period style fog lights (not modern) are approx. 35 watts each. Therefore a 6 volt system would draw approx. 12 amps. A 12 volt system would draw 6 amps. To keep things simple then a 20 amp fuse would do the trick easily. It will blow if there is a short circuit. Rocket science is not required here. Regards, Kevin.

[V8COOPMAN]

Originally Posted by Pete

"It is not the size of the bulb that determines the size of the fuse. It's the size of the wire going to the bulbs."

Wrong.
The load in the circuit, in this case, bulbs, determines the load hence fuse size..
The wire has no effect as long as it is adaquate in size (gauge).
The wire draws no current.
The load determines the fuse size.
The fuse does protect all of the components in the circuit.

Pete.......Your reasoning here is about as tainted as the guy who believes that the MOST important aspect of determining the "correct" camshaft is by it's lopey idle.

The LOAD on a circuit (bulbs, in this case) determines the NECESSARY WIRE GAUGE to adequately and safely carry the current load of the bulbs.

The FUSE is then sized to protect the WIRING which has been adequately sized to carry that specific current load that the bulbs draw.

IF the wires in any circuit have been properly sized to safely carry the current for the INTENDED load (bulbs, in this case), then someone that doesn't understand the reason for fuses or circuit breakers would ALMOST think......"why do we need a $1 fuse to protect a 29 cent bulb?" Well, that fuse is there to protect (at the very least) that one wire way up there under your dash if the insulation rubs through and the bare wire touches any grounded, metal object. The sudden UNLIMITED rush of current through that wire will smoke the insulation immediately, and if that wire is bundled with many others in a harness, you'll smoke the whole harness PRONTO!

Fuses are designed to protect WIRE! Who gives a rats ass about protecting a bulb, or a $20 fan motor? DD

[Pete]

Originally Posted by V8COOPMAN

Pete.......Your reasoning here is about as tainted as the guy who believes that the MOST important aspect of determining the "correct" camshaft is by it's lopey idle.

The LOAD on a circuit (bulbs, in this case) determines the NECESSARY WIRE GAUGE to adequately and safely carry the current load of the bulbs.

The FUSE is then sized to protect the WIRING which has been adequately sized to carry that specific current load that the bulbs draw.

IF the wires in any circuit have been properly sized to safely carry the current for the INTENDED load (bulbs, in this case), then someone that doesn't understand the reason for fuses or circuit breakers would ALMOST think......"why do we need a $1 fuse to protect a 29 cent bulb?" Well, that fuse is there to protect (at the very least) that one wire way up there under your dash if the insulation rubs through and the bare wire touches any grounded, metal object. The sudden UNLIMITED rush of current through that wire will smoke the insulation immediately, and if that wire is bundled with many others in a harness, you'll smoke the whole harness PRONTO!

Fuses are designed to protect WIRE! Who gives a rats ass about protecting a bulb, or a $20 fan motor? DD

You better go back and read my post again.
TRY TO COMPREHEND WHAT WAS SAID THIS TIME.

[coolcoupe]

According to my fiquring, my foglights read 30 watts each times 2 lights gives me 60 watts.The chart says that 60 watts/6 volts=10 amps. I have about 15' of wire to run.I fiqure I could use a 12 to15 amp fuse,yes/no ?
Thanks for all the feed back!!

[Old Henry]

Originally Posted by coolcoupe

According to my fiquring, my foglights read 30 watts each times 2 lights gives me 60 watts.The chart says that 60 watts/6 volts=10 amps. I have about 15' of wire to run.I fiqure I could use a 12 to15 amp fuse,yes/no ?
Thanks for all the feed back!!

As I said before, a 15 amp fuse will protect 14 ga. wire which is probably what you have. (It'll protect any size larger than that too. So, it's a good size to use. It will protect the wire without being blown by the load.)

[coolcoupe]

Hi Guys, I did what you's said to do and when I threw the switches on everything lit up as they should !!!! I even hook up the backup light thru a switch and linkage bracket on the steering column so it just on comes on with tranny is in reverse !!! I hate wiring but got it done neat and properly Thanks Guys

[Marv]

If you get caught in fog and do not have fog lights put on your sunglasses if you have them with you. Some states they are illegal at night but they do improve your vision in fog a good bit.

[FireEngineMike]

The important thing is that CoolCoupe installed his lights and everything works.