Re: what is a relay?

Posted by txblu on November 15, 2004 at 06:11:09 from (199.46.199.233):

In Reply to: Re: what is a relay? posted by StuBC on November 14, 2004 at 17:46:11:

The purpose of a "fuse" is to "fuse" in case of a circuit short or other "current" overload. If it weren't for a fuse, the conductors would overheat and melt insulation which would allow wiring to short to other wiring and you could easily wind up with a fire.

The fuse is usually rated for 1.5 times the normal current.....if you need 10 amps to run 2 headlights, put in a 15 amp fuse and size the wiring accordingly which is 14 awg (good rule of thumb). IF your headlights are 35watt and you have 2, and a 6 volt system, you are right at (tad over) 10 amperes [if wired in parallel...one side of each to the fused wire (via light switch) and other side of each to chassis ground]. 12 volt system is half that (if you are using 12v lamps). You could still wire up with 14 awg and use the 15 amp fuse however.......you're protecting the wire (usually), not the thing using the power; however it does get protected also.

Now you could send a 12v wire to 2ea 6 volt 35 watt lights and wire the lights in series across the 12v input (12v hot....from the 15A fuse) to one light then other side of that light to input of the second light (not ground) and the output of that second light to ground). In that case the 14 awg wire would still be correct.

You can get fast blow and slow blow fuses. Slow blow fuses are designed to hold on higher than normal current (overload) for a few seconds.....like when a motor starts.

Even though a lamp usually has about 1/10 the normal resistance when cold, and hence a 10x inrush of normal current, it is very short in duration and in a tractor, a normal blow fuse usually is adequate.

And that's the rest of the story (Paul Harvey)

Ask another question.

This is fun.

Mark

Follow Ups:

• Re: what is a relay? StuBC 07:08:10 11/15/04 (4)
  • Re: what is a relay? buickanddeere 18:15:37 11/15/04 (1)
    • Re: what is a relay? txblu 09:17:55 11/16/04 (0)
  • Re: what is a relay? txblu 12:03:15 11/15/04 (0)
  • Re: what is a relay? RAB 09:47:24 11/15/04 (0)

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