Headlight relay Q

[greywolf]

I've never head of anybody blowing a 20A fuse in that situation. The rule of thumb is fuse to allow a 20% over margin of safety for a continuous circuit. The flash to pass switch is only supposed to be used for momentary activation though so it still meets the criteria.

[alibx11]

Hate to drag this thread out but would it not be safer to use the multiples 230w /14v  = 16a as when the bike is running it's charging at 14v+

But as Greywolf says it's not designed for continuous  use so 110w or 120w is the normal running load.

If the 20 amp proves too light I'll try a 25a then 30a etc to get lowest safe rating.

If the relays burn out or cause trouble I can always just reconnect the existing headlight sockets as they're just cable tied to the fairing frame and are still active.

Thanks for the comments blokes.

[greywolf]

You don't want to go more than 20A as an overload can overheat the wire. That's what the fuse is there to prevent. If you go to a bigger fuse, you'd also need heavier wire. 20A will do fine.

[Hondaman]

You don't want to go more than 20A as an overload can overheat the wire. That's what the fuse is there to prevent. If you go to a bigger fuse, you'd also need heavier wire. 20A will do fine.

It shouldn't be a problem as it came with a 40a fuse originally.

[Hondaman]

Oh, I've just purchased one from ebay/china that comes with 2 fuses so I'll let you know how it goes

[greywolf]

It shouldn't be a problem as it came with a 40a fuse originally.

Hopefully not, but I don't have complete confidence in a company that uses the wiring scheme indicated and uses a 40A fuse on a device that doesn't use half that.

[Rich:-)]

Just about to do this mod to mine and came across this thread but there is an error in the current calculations for fuse value shown that I wanted to highlight.

230w / 12v nom = >19a
230w / 13v =  >17a
230w /14v  = 16a
This is not how it works as the wattage is not fixed, it's function of the the current & resistance.
 
The claimed wattage of a bulb is stated for a set voltage (12.8 volts I've read), as the voltage at the bulbs increases so does the current and thus the wattage. The resistance is more or less fixed when the filament reaches operating temperature (it does change slightly though).

Therefore at 12.8 volts a 55 watt bulb should be taking approx 4.3 amps and thus has a resistance of 2.98 ohms.
With a loom improvement allowing 13.5 volts on the bulb terminals the current would then be 4.5 amps and the wattage would be 61.16 watts.

Sorry to be a "know it all" but I'm an electronics engineer so thought I'd share.

[greywolf]

Then you would know a fuse is about protecting the wire, not the load. As long as the fuse will blow before allowing the wire to overheat yet allow at least a 20% margin over draw to prevent unnecessary fuse deaths, it's a good choice.

The thing about adding headlight relays is it is common for both high and low beam relays to get the power from a single fused wire instead of the stock two fuses. The flash to pass switch adds the high beam to the low beam load. Nit pickers like to run a power wire from each relay through a 15A fuse on each wire. A single 20A fuse on the typical one power wire setup seems to work fine though as long as the flash to pass switch is only used as a momentary switch. I prefer the 2 wire setup though as a blown fuse or relay gone bad on a dark night would allow a flick of a switch to be able to see again.

[Rich:-)]

Yeh, I'm planning a 2 fuse system but see no issue with a 1 fuse system. I don't even use the 'flash to pass' button on a bike as most drivers in the UK don't understand want it means when you flash at them. I reckon they think you are challenging them, or maybe telling them off and are thus more likely to start behaving aggressively.

As for the purpose of fuses..., yes I've argued long and hard with people over their actual purpose. Some believe it's to protect the equipment but it's not, as you rightly stated, it's to protect the wiring and ultimately prevent a fire.

[greywolf]

My big issue with a one fuse system is a blown fuse on a moonless night away from city lights and traffic forces you to get off the road without being able to see anything. A two fuse system lets you select the other beam.

[Rich:-)]

Yeh, electrically speaking there is no problem with a 1 fuse system but there is a safety reason why the manufacturers use 2 separate fused circuits. It also means you can fuse lower, which I like.

[joderest]

Going back to the start of this thread, there have been a few tails of generator over heating on the forum since fitting my headlight switch, and I now do not run with dip beam off, as do not want to cook the generator.
I bow to GW's knowledge on things electrickery.

[Rich:-)]

You are correct in not running with headlights off.
The system of regulation used on these bike means all unused power is dumped back into the stator which is then turned to heat. I'd rather have 110 watts of mainly heat radiating out of the front of my bike rather than going into the stator.

Only switch off the lights if you're actually using the power elsewhere - lots of ancillary for example.