Wiring a relay for headlight and have questions.

[Wingedwheel]

Hey guys, I'm putting the finishing touches on my bobber wiring and I need some help figuring something out. I went with a small battery (12v 1.3AH)

and it starts the bike just fine. What I'm looking to do is incorporate a relay so that the lights will only come on when the bike is running. that way I can use a two position toggle for high and low beams but don't have to worry about remembering to turn the light off when I'm starting the bike. Could someone enlighten me (hehe get it?) as to the best way to accomplish this? The original system was a '72 and I'm running stock components. I used a TC bros chopper wiring harness for the ignition basics and those are all wired in I just need to wire my lighting and not sure about the best way to go about it. Thanks for any help in advance.

 

[TwoManyXS1Bs]

... What I'm looking to do is incorporate a relay so that the lights will only come on when the bike is running. that way I can use a two position toggle for high and low beams but don't have to worry about remembering to turn the light off when I'm starting the bike. Could someone enlighten me (hehe get it?) as to the best way to accomplish this? The original system was a '72 and I'm running stock components...

Sounds like you need a custom gadget/circuit, one that taps into one (or all three) of the stator wires, reads the output voltage, and after a preset delay, energizes your headlight/lighting relay. Easily done with a diode (or diode trio), but the delay part adds complications.

 

[retiredgentleman]

My 1978 XS650SE uses something called a Safety Relay. Headlight turns on only after the alternator starts to produce voltage. Why are you trying to re-invent something that Yamaha has used for many decades?

 

[XSLeo]

Yes, as RG said, Why reinvent the wheel, just use a later safety relay with the headlight function in it. Then just wire it as you would a stock harness.
72 had e-start so it should have the yellow wire coming up from the stator. Look at any later wiring diagram to see which wires to use for the headlight. Should be easy, power in/power out.
In your pic you show the stock mechanical regulator, I assume you are still using the stock rectifier, I might consider swapping them for a solid state versions. Will get better charging.
Leo

 

[Wingedwheel]

I'm not trying to re-invent guys, just looking for suggestions. I know the later models used the safety relay but wasn't sure where to hook it up, probably should have looked at the later diagram . Yea Leo I considered going with the combined reg/rec but I wanted to see how many stock parts I could still incorporate and make improvements as I went along. If you look at the pic you can see the rectifier mounted below the regulator and as long as it's working and not giving me problems I figured I'd use them for now and spend $ on other things I needed. There are two other bikes in my garage and they demand equal attention lol. I will say I figured if anyone answered my question it would be you, RG or 2M. looks like I went 3-3 . Now where did I put that lottery ticket............

 

[5twins]

I'm not sure how long that old reg and rec will continue to work being enclosed like that. They get hot and need cooling air, especially the rectifier. The old mechanical regulator does work but it's output is very inconsistent. It's voltage demands from the charging system are constantly bouncing up and down, even at higher RPMs. This works the stator and, in particular, the rotor harder than need be. As you're probably aware, burnt out rotors are a pretty common problem on these bikes. In my opinion, that spastic mechanical regulator contributes to the problem.

 

[XSLeo]

You might be able to use a lighting relay, The 4 prong should work. They turn on a circuit when tripped.
Terminals are numbered. 85 and 86 trip the relay, yellow wire to one, ground the other.
power in on 30, power out on 87A to dimmer switch.
I have collected a lot of the 5 terminal relays from cars in the salvage yard. If thrown in with a bunch of other parts they come practically free.
I think I paid like $12 for half a dozen relays a dozen lug nuts, some long battery cable and some other stuff.
Leo

 

[Wingedwheel]

Actually 5T they are mounted in a box I made with no bottom and a mesh cover so they should get plenty of air flow, hopefully it works out but I was also looking at another thread about how to put your own set together that works better than the stock components. Leo I was thinking about a 5 pin relay. When the yellow wire was mentioned earlier that's the one I was targeting for my trip voltage. I'm assuming that one isn't energized until the alternator starts putting out after the bike is started? I've been looking into how all this would work together and it was also nice to learn how the relay's handle the load so it doesn't go to the switch or wiring. Getting a pretty good plan together.

 

[TwoManyXS1Bs]

Relays have a 'pull in' voltage, and a 'release' voltage. For example, a 12v relay may 'pull in' (switch on) at 9 volts, then 'release' at 6 volts. If you can't get that amount of rectified voltage on the yellow wire, may need to look into a 6 volt relay, and/or pursue the other options of tapping into the white wires...

 

[Wingedwheel]

Ahhh the mystery deepens, thanks 2M Perhaps I need to check my voltages with the bike running before I proceed.

 

[retiredgentleman]

Typical voltage on the yellow wire at 1200 rpm is about 14 volts AC (not DC)

 

[TwoManyXS1Bs]

Dug out some automotive accessory relays of the type I believe XSleo is referencing.
My older relay is somewhat smaller, and has a coil resistance of 70 ohms.
My newer relays are somewhat larger, and have a coil resistance of 80 ohms.

Rigged up a test, where I could apply activation voltage slowly, and record the pull-in and release voltages.

The older/smaller relay pulls-in at 7.5 volts.
The newer/larger relays pull-in at 5.3 volts.

The older/smaller relay releases at 5.0 volts.
The newer/larger relays release at 3.7 volts.

I hope these are within the range of the yellow wire's output...

 

[XSLeo]

The yellow wire has the about the same voltage as the white wires. The white wires are thee sets of windings with one end of each set coming together. where the windings come together is where the yellow wire hooks in. So if one end of a winding has about 10 volts the other end should too.
I may have checked the voltage on the yellow wire once long ago, but I don't recall what it was.
Leo

 

[Wingedwheel]

Thanks 2M the fact that you took the time to do that test is amazing and really appreciated. A few columns up RG stated that the voltage on the yellow wire is AC. I'd read something about that somewhere but I'm wondering if it's going to be a problem if I tap into it there?

 

[TwoManyXS1Bs]

These relays work best on DC current. Adding a diode from the yellow wire to the relay's energizer coil is the way I'd go. Like a common 1N400x series diode, with the polarity band pointing toward the relay's coil. Other side of the coil would go to ground.

The OEM relay may (?) have an internal, unseen, diode in it, giving the impression that it doesn't use one. Dunno, someone would have to test for that.

 

[Wingedwheel]

So your saying to do this? If the voltage from the yellow wire is AC I'm assuming the diode keeps the relay from getting confused so to speak? I'm also guessing it should be wired like this.

 

[TwoManyXS1Bs]

I was thinking more like this:


Edit: Added 100uF electrolytic capacitor. Up to 220uF is okay.

 

[Wingedwheel]

OK that makes sense, thank you.

 

[mrtwowheel]

Check out Honda switches and wiring diagrams. Honda uses a cutoff switch in the starter button to turn off the light when the starter button is pushed, no relay. Never thought this out for the XS's but it may be possible.

Edit....There is a small Radio Shack switch that works in this manner that fits well into a switch housing. Starting procedure on these Hondas.....turn key, light comes on, push the starter, light goes off, get that thing started quickly or turn the key off, no problem, no relay.

Scott

 

[Wingedwheel]

Appreciate the input Scott but it's kick only. I'm also looking for a compact housing with light controls and horn only, no turn signals.