What should the fuse rating be?

[Guest KitCarson]

On electrical issues I can usually trace wires and get things to working, but need some advice. My bike has a 60 watt sealed headlight. It is served by a 15 amp fuse because I just looked. Tomorrow I am going to install a fancy set of driving spotlights and each spotlight is 50 watts.....for a total draw of 100 watts .....maybe not a draw? Just output? If the factory set up with a 60 watt rating is served by a 15 amp fuse,,,,,what size fuse should I install for the driving lights? Instead of hooking into the low beam headlight wire I am going to run a single wire from the battery to the running light power wire(it will be grounded to the frame) So how many amps does a 100 watt out put on a single wire really draw? If using power or watt formula....it is only pulling 9 amps? So really would not hurt to tie into the low beam wire?? This is why high power driving lights can be wired into the existing wires like a dealer does? and still run off a 15 amp fuse?

[Redneck]

I run a 20 amp fuse on a completely independent circuit that way if you have a short in your headlight circuit you still have lights. it really depends on wire size as long as the fuse blows before it burns the wires its fine.

[Guest KitCarson]

I run a 20 amp fuse on a completely independent circuit that way if you have a short in your headlight circuit you still have lights. it really depends on wire size as long as the fuse blows before it burns the wires its fine.

Thanks Mike......I will buy a 20 amp fuse and fuse holder.....did not think it would be real large........just need a little moral support!! Thanks

[SaltyDawg]

Running 100 watts will only require 8.3 amps so a 15 amp fuse will be fine but I would suggest running that through a relay and not hard wired to your lights and then to ground.

 

To figure amperage divide the total watts by the voltage in this case 100 watts by 12Vdc and you get 8.3 amps you always want to go 30% above that to allow for the initial surge when the lights come on.

 

I personally wouldn't run a 20 amp fuse on that circuit because if a wire shorts it might actually weld itself to the frame where the short is before blowing the fuse. Running a 20 amp fuse would require more than 240 watts to blow it. Bad things can happen before that fuse blows. Just my 2 Cents worth.

 

In looking at your question "This is why high power driving lights can be wired into the existing wires like a dealer does? and still run off a 15 amp fuse?" They are using the headlight circuit to toggle a relay which will then allow 12vdc from a different source to turn the lights on. The relay will draw minimal amps. If you were to wire into that circuit then you will be putting 13.3 amps on a 15 amp fuse and it will blow, maybe not right away but it will blow in the near future. In doing so you will lose all lights and that's a bad thing at night. Run the new lights completely independent of the headlight circuit. That way if one then goes out you still have lights.

 

One thing to remember, your headlight is not the only thing on that fuse if you are talking about a RSV. The front parking lights, the dash and some of the indicator lights are also on that circuit. Not sure if the turn signals are I would have to look in the manual and I don't have that with me. So that 15 amp fuse is covering more than just 60 watts.

[Squeeze]

Hi,

 

only Thing i have to add on SaltyDawg's Statement is ...

 

these Fuses blow on somehow tripple the designed Current. A 20 Amp Fuse goes out at 55 to 60 Amps. This is for a single, sudden Shortcut.

 

If you run constantly too much Draw, the Wire inside the Fuse will melt a bit anytime this occurs. And while melting, this Wire will allow less and less Overdraw. The Overdraw is normal and can not be avoided, so the Fuse will blow. This happens, according to Murphy, in the Situation were you will need the Circuit urgently.

[Guest KitCarson]

Thanks all: I will use a 15amp fuse......had fully intended to run straight from the battery in any event.......so just as Mike pointed out.....if all the rest of them burn out at night......you still have your running lights to get home with, I for one am not stopping at night to drop allen screws in the grass!! Will pick up a relay and double stick tape that to something also.......I was just curious about what the dealers do........granted the standard running lights are less wattage than these football field flood lights I am using, but still to me seemed to be border line as far as amp draw on one fuse....what several of you have said.....just confirms my suspicions......I did remotely remember all that stuff.......E over I x R.....P over E and I forgot that part:rotfl::rotfl:Thanks again. Kit

[Squidley]

Kit,

Just remember to run it through a relay, thats the only way I run any added electrical components.

[Guest KitCarson]

A couple of you knew I was installing the Baron Ultimate light bar kit on my bike.....do not know where that thread went.......so thought I would drop a note in this one. I got my wiring done.......fuse at the battery and relay velcro'ed inside the fairing......ready to go.......but hey as touted by the folks who sell this kit....beware!!! It does not fit the 2007 Venture.......nope!! . So if any of you were planning on buying it........your choice but will require some fabrication to make it work........it is designed to slip over the existing light bar after you cut off the ends where the existing signal lights are secured......thing is they forgot about the fork deflectors which are mounted exactly on the end of the light bar.......hum......It is a nice light set up.....but having had time to think....will require some heavy walled stainless steel tube, turn the end down to slip inside the light bar......and either silver solder it in or run a bolt through it........after cutting the weld that holds the existing ends in........Just though I would put that in the mix........yep the web site says it will fit.........customer service says that it will fit........Kit knows better!!

the fork deflectors sit right on the end of the light bar........still they keep telling me to cut them off.....um hum..........so it is off to the machine shop

Going to keep the lights as they will melt ashphalt!!! 100 watts of halogen!! Hard to explain things to sales people.......sure is!! Anyways they are not a bolt on kit............