TOPIC:

Go to JC Whitney and buy this conversion light and a bulb, it's cheap and very good.

tinyurl.com/2eqjuv

Now if he could only harness that voltage for the coils only:dry:

Well, I appear to have everything worked out (except for the flashers, which is in a different post). I do have one more question, though.

With enough voltage going through the system to fry all those bulbs, I'm wondering why it didn't blow any fuses. Personally, I'd much rather deal with fuses blowing than bulbs.

Is that a system design issue, or, is it a problem unique to my bike?

Thanks

Fuses are really only there to protect against shorts. If a wire would short against the frame the fuse would blow to protect the wiring from frying and potential for a fire. Current=volts devided by the resistance of the circuit and I would imagine any fuse rating on a motorcycle is at least twice what max current will ever flow through it. So say you were expecting 14v on a normal working motorcycle to the bulbs and in your case you had 21v, what this would do would to be raise the current drawn by 50%, not enough to even be noticed by the fuse, and as each bulb burned out, that load would go lower, so less current. Quick explanation, but if you really wanted a fuse to protect against over voltage you'd have to add a zener diode or similar rated at the max volts you'd want to ever run through the system after the fuse. So if you had a 16v zener in there your voltage would attempt to rise above 16v but either be clamped at 16 by the zener or it would short and blow the fuse.

It would have to be a huge zener to do that. Most zeners are 1watt. That means they blow up at about a tenth of an amp... not enough to blow the 20amp fuse.

In order to blow a 10amp fuse, the zener would have to be a 200 watt zener, (I never heard of one), or you could use 200 1-watt zeners. Either way it's kind of pricey.

That's what I meant. Put 200 zeners in there
No, I guess I didn't think. In TVs and such they put a 18v zener across a 12v supply for example and if the volts go wild the zener shorts and the fuse blows. So you're saying in a motorcycle with high current instead of blowing the fuse, the zener would simply be blown apart instead of shorting. Makes sense.

Yeah, the Zeners can handle a short spike of high current before they blow up, so maybe if the fuse would blow quick enough it would be ok. But if the fuse doesn't quite blow, the Zener is a goner.

The power dissipated by the zener is simply the voltage on it times the current through it. If the typical Zener is rated at one watt, you can calculate the maximum sustained current allowed in the Zener.

Maximum allowable sustained Current = 1 watt divided by the voltage.

It's a heat issue, so if the current is brief enough, I've seen Zeners handle several times their theoretical current limit. So instead of 200, maybe 30 or 40 would be enough as long as the fuse blows.

Post edited by: loudhvx, at: 2007/07/27 21:12