Lighting resistor

[johnny248]

What does the 5w lighting resistor actually do? Manual says if your cluster lights burn out often, check this resistor. Just wondering what it is doing with the lighting.

[kuromi]

Hi Johnny,
The ballast resistors bleed electrical current from the regulator/ rectifier to ground on the lighting circuits.
This reduces the amount of current passing through the lights. If the resistors are missing or not working, all the current is dumped through the lights causing them to blow/ burn out.
It's like if you're blowing up a balloon, the resistor would be like a hole in the balloon leaking air and stopping the balloon from popping if you tried blowing it up too much.

[johnny248]

OK, that is what kind of what I was thinking, but wouldn't that only be in a situation where the headlamp circuit is open, or the headlamp was removed?

[kuromi]

Just been looking at a wiring diagram and see what you mean - I don't think my previous post is accurate
Just had a look through my manuals. The haynes motorcycle electrical techbook shows the resistor used as a headlight stand-in when the head lamp is off and is disconnected when the head lamp is on.
My melody manual shows the cluster lights on the same part of the circuit as the headlamp in parallel so that in this case the load resistor would stand-in for the headlight, speedo light, tail lamp.

I'm wondering if on different scooters the resistor only fills in for the headlight and not the other lights, e.g. if you had side lights on but not your headlight?

Going to have look online at some wiring diagrams to put my puzzled brain at ease.

[johnny248]

My elite manual shows that resistor on the same circuit as the headlamp and the cluster lights, which I think is designed to protect the cluster lights in case the headlamp is burnt out, or somehow not turned on.

I don't plan on using the headlamp through the factory wiring and was trying to determine if I need to increase that resistor to say 15w or 25w ?

[kuromi]

This is what's printed in the Melody manual, couldn't find a diagram online of the Elite.
Not sure how you'd remove the headlight and keep the rest. I guess you'd stick in a resistor that matched the ohm value/ resistance of the head lamp with a power rating similar to the other resistor where the headlamp would be.
Not sure how that would affect other parts of the circuit though or where you'd stick another lamp.

Honda Melody charging/ lighting circuit diagram

image.jpg (139.86 KiB) Viewed 6906 times

[johnny248]

Everything still works with the headlamp unplugged, its just that it could possibly burn out the cluster lights fromnwhat I can see.

[johnny248]

Everything still works with the headlamp unplugged, its just that it could possibly burn out the cluster lights fromnwhat I can see.

Elite is a little different.

[kuromi]

Wasn't expecting a diagram like that!
Does that mean you have the lights on all the time? Can't see any switches in there.
It looks like the resistor limits current through the bystarter, maybe balancing it against the resistance of the meter lights and headlights/ dipped beams so that the lights get enough power and not too much goes through the bystarter.
If you ditched the headlight bulb, it'd be like closing a lane on the freeway - the traffic flow in the other lanes would increase and pop your bulbs/ knacker your bystarter. That's why good earth connections are essential as a bad earth increases resistance - like debris on the freeway to carry on the analogy.
I reckon if you measured the resistance across the headlight bulb that would give you the value of resistor to use in place of the bulb. Then find a resistor with the same wattage rating, which from the diagram would be 25W minimum for your '94 Elite.

[johnny248]

The headlamp is always on. There is a switch for high/low. Currently I have the switch rewired as an on/off , which triggers a relay to switch power directly from the battery to the headlamp. I have 15w and 25w 6.7ohm resistors. Id like to throw the 15w in there and hope that is enough. I could use the 25w to match the bulb, but that's another 10w of power I am turning to heat.

[johnny248]

Where are my electrical guru's? lol Since I am eliminating the headlamp from the circuit, should I replace that 5w resistor with a 25w resistor to keep the electrical load the same as it would be with the headlamp still installed?

[kuromi]

Looks like the electrical gurus are away on holiday.
Oh well, I'll take a stab then...
The power ratings on resistors refer to the max. power they can handle and not what they'll draw. This is to do with how much heat they are capable of dissipating, not how much they do.
So for a 12v system, the maximum current is:
25W / 12volt = 2.1amp max
5W / 12volt = 0.4amp max

If you use the 5W resistor, any current over 0.4amp will overload and burnout your resistor and there's probably a fire risk too.
The 25W resistor should be able to handle the power.
It might be worth sticking it somewhere windy mounted on a heat sink to help it radiate heat.

I'll take a look at the power ratings on my Melody's lighting resistor when I get home tonight to compare values, I don't want to be responsible for blowing your lights.

[johnny248]

I was thinking I could simply wire in the a 25w 6.8ohm resistor in place of the headlamp. That will simulate the load of the headlamp bulb, and I believe protect the other bulbs. I'm not sure, but I have a feeling that the regulator works off the load it is seeing, and by altering that, it changes the output voltage of the regulator?

[Trafficjamz]

I was thinking I could simply wire in the a 25w 6.8ohm resistor in place of the headlamp. That will simulate the load of the headlamp bulb, and I believe protect the other bulbs. I'm not sure, but I have a feeling that the regulator works off the load it is seeing, and by altering that, it changes the output voltage of the regulator?

The headlamp circuit is AC and has nothing to do with the other lights.

The resistor in that circuit is for the bystarter only.

Why are you running the headlamp on the dc side? Your charging system will not be able to keep up.

[johnny248]

I didn't know the headlamp was on AC ? I didn't even know a 12v light bulb work on AC.

The diagram shows the headlamp, bystarter, and meter lights running on the same circuit, so they are all on AC?

And the brake lamps and turn signals are on battery DC voltage.

After looking at the manual again, it does in deed say when checking the headlamp measure on AC 12.1v - 13.6v

Ive never experienced a lighting system that isn't on a 12V DC system.

The battery and DC charging system can't keep up with a 25w bulb if it was running directly off of the battery?

The way it is currently setup is:




I have not had any problems with this as far as battery or charging goes. It runs at ~14v and the charging system has seemed to do fine as far as keeping the battery charged. The only issue I came across was the two 194 meter lights burning out, which I was assuming is from over powering of the regulator since it does not have a headlamp wired into the original headlamp harness. My thought was to insert a resistor in place of the original headlamp to keep the regulated side working properly and not burn out my meter bulbs?