Wiring question

Right now, I've only tested it as a working protoype on a breadboard, but it seems to work fine. As I said, I didn't have the Bosch relay so I used a generic Radio Shack 12v relay and emulated the Bosch relay.

Radio Shack sells little pre-made generic circuit boards. I usually use one of those then cut it down to size.

You may want to coat the board in silicone, but not too thick. The transistor does not need a heat sink, it's only used for a split second. However D2 gets used continuously. It will see about 1/4 amp and will dissipate about 1/4 watt. That's well within spec, but the spec assumes open-air operation, so try not to coat D2 too heavily. R1 will be used anytime the bike is in neutral, so like D2, it should not be heavily coated either. D1 is only used for a split second.

The current for the headlight only goes through the relay contacts, so this circuit should handle about 30 amps of headlight power. The headlight power still needs to go through the stock wiring in the ignition switch, so it is important to make sure the ignition switch and fuse holder isn't losing voltage. You should be tapping into the blue headlight wire after the 10A headlight fuse. You splice this circuit into that wire. The fuse side of the blue wire feeds 12v to this circuit, then the hi/lo-switch side of the blue wire connects to the output of this circuit.

The circuit needs about 10v to activate, however, once activated, it only needs about 5v to stay active.

www.geocities.com/loudgpz/GPZheadlightTrigger.html

Post edited by: loudhvx, at: 2008/02/20 23:18

Here's a pictorial view:

Here's a slightly different version. It eliminates D2, and allows the battery to feed the lighting circuit directly to take some of the load off the ignition switch. The problem is that it uses an $8 relay instead of a $2 relay.

AWESOME! And I appreciate the idiot version diagram:P I will probably go get parts tomorrow.

No prob.
I guess I should mention in case anyone didn't know, the silver stripe on the diodes is important. It must be oriented as shown.
The resistor can go either direction.

loudhvx wrote:

the silver stripe on the diodes is important. It must be oriented as shown.
The resistor can go either direction.

Hey Lou, does the silver stripe denote positive or negative?

Little B wrote:

loudhvx wrote:

the silver stripe on the diodes is important. It must be oriented as shown.
The resistor can go either direction.

Hey Lou, does the silver stripe denote positive or negative?

The stripe denotes cathode. If you want current to go through a standard diode, the cathode is negative. If you want the diode to block current, it is positive.

Zener diodes are generally used in the reverse direction from standard diodes, so there really isn't a standard rule to positive or negative.

However, the symbol for the diode is well chosen. It is an arrow, and the arrow points in the direction of normal current flow. (Zener diodes are the exception, and their symbol is slightly different). In the diode symbol, the line that the arrow points to is represented by the painted stripe on the diode.

That's really interesting. I have a lot to learn about electronics & sure appreciate you taking the time to teach this stuff. Are you some kind of electrical engineer or something? :woohoo:

I do some occasional engineering, but work mostly as a technician.

Loud, I built it and have yet to try it out. I have a question though. Will it still trigger i standard bulb is replaced with an LED bulb?

Why not just wire a double pole relay into the starter circuit (the bosch type that have 5 contacts instead of 4). Feed constant ground to one of the relay trip contacts. Feed starter power to the other relay trip contact. Feed keyed ignition power into the closed center pole so whenever the key is on the light is on (the normal outer contact for that pole goes to the headlight. When you hit the starter button and the relay closes the other pole contact (that isn't connected to anything), the headlight will be switched off. Then when the bike starts and you release the starter button the relay is turned off and switces back to feed the original pole and turns the headlight back on.
The relay will use much less power than having the headlight on while cranking will. It's late, I hope you understand this.

87 No Connection
87A Keyed ignition feed
30 To headlight
85 Constant ground
86 Wire from starter cable side of solenoid

This shows the relay at rest. When it is activated by the starter wire it closes the circuit for 87 and no power goes to the headlight.

Post edited by: The Milkman, at: 2008/02/29 03:44