Positive Rectifier To Battery Wire, Fused Or Not?

mrtwowheel

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Looking at wiring diagrams I see the positive wire from the rectifier connected in two different ways. One way is to connect at the battery side of the 20 amp fuse (between battery and fuse). The other way is to connect on the ignition switch side of the fuse (between fuse and ignition switch). Yeah, either way will work, but is there an advantage to one way over the other way, will there be protection for some component one way and not the other way?

Scott
 
If the fuse was between the regrec and the battery it would theoretically protect the battery from a couple of theoretical possibilities... If I had a choice I would probably put it there -- nothing to lose. The other way, the fuse doesn't protect the battery from what the regrec might theoretically do, turn into a dead short for example. Other than that no difference, the way I visualize it.
 
Factory has a 20 amp fuse between them on the standards after about 1972 and all the specials.

fusebox detail.jpg
 
Clymer shows no fuse on the TX650A:shrug:. Clymer has the wire connected between the battery and fuse on the XS650B & C. Clymer has it between the battery and fuse on the CB750 DOHC fours. Other diagrams that I'm using have it both ways. I can do it either way, simplest with the less wire would be to the solenoid, stacked on top of the battery cable. Tomorrow it gets connected, one way or the other.

Scott
 
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OTOH if you put it before the fuse and the battery explodes, you have a free ejection seat :)
 
Clymer shows no fuse on the TX650A:shrug:. Clymer has the wire connected between the battery and fuse on the XS650B & C. Clymer has it between the battery and fuse on the CB750 DOHC fours. Other diagrams that I'm using have it both ways. I can do it either way, simplest with the less wire would be to the solenoid, stacked on top of the battery cable. Tomorrow it gets connected, one way or the other.

Scott
Factory TX650A manual wiring diagram has the fuse between, where it pretty much stayed from then on. I love Clymers, they have kept several of my work benches from rocking for years.
74_tx650a-png.22980
 
There is only one correct way to wire it. The diagram in post #3 shows it correctly.
The purpose of the 20 amp fuse, is to protect the wiring downstream of it from melting and catching on fire, when a short circuit occurs. Diodes in the rectifier have been known to short circuit to ground, and so wired as in post #3, the fuse would blow. If the rectifier was connected in between the battery and fuse, any short circuit in the rectifier could cause the wiring harness to catch on fire.
 
Wired either way, the fuse would blow, and the bike would quit running.

Edit, No this is wrong. If the wire was connected between the battery and fuse and the fuse blew, the bike would quit running.

If the wire was connected between the fuse and ignition switch and the fuse blew, the bike could still be running even disconnected from the battery.
 
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If you don't wire it as per post #3 diagram, you run the risk of the wire from the rectifier to the battery melting the insulation and may catch the whole wiring harness on fire.

mrtwowheel.......................you don't understand what the 20 amp fuse is for. The battery is a huge source of amps of current. The battery can supply 100s of amps for a short duration. The 20 amp fuse is the only protection to prevent harness fires when a short circuit to ground occurs. It does not matter whether the bike is running or not. The wiring harness will still catch on fire.
 
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There is only one correct way to wire it. The diagram in post #3 shows it correctly.
The purpose of the 20 amp fuse, is to protect the wiring downstream of it from melting and catching on fire, when a short circuit occurs. Diodes in the rectifier have been known to short circuit to ground, and so wired as in post #3, the fuse would blow. If the rectifier was connected in between the battery and fuse, any short circuit in the rectifier could cause the wiring harness to catch on fire.
 
I think the factory fusing is a little goofy. There's no reason to blow the main fuse if the taillight shorts. There's no reason to have the 10A fuses in series with the main fuse. And there's no reason to blow the main fuse and the whole bike if the regrec shorts. All these things should have their own fuse. OTOH you want the ignition switch fused and that kind of forces you to have the series fuses if the different systems get their power from the switch.
 
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No, the fuse would blow, the alternator would not be excited any more and the bike would quit running. All is protected.
Possibly. The battery voltage would be zero until the short burned away. The fuse wouldn't blow though if it was connected the other (wrong) way.
 
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Wired the other way as in post #3 the fuse would blow because of the wire heat but the alternator could still be excited by the current from the rectifier, all is still connected and unprotected and burning.

Scott
 
Possibly. The battery voltage would be zero until the wire burned in two. The fuse wouldn't blow though if it was connected the other (wrong) way.

Yes it would, it doesn't matter which side of the fuse has the hot wire to blow a fuse, it's just the weakest link.
 
Yes it would, it doesn't matter which side of the fuse has the hot wire to blow a fuse, it's just the weakest link.
Ok, we're talking about what happens when the reg shorts to ground, right? If the reg is connected on the battery side of the fuse, then there's no current path through the fuse and the shorted reg to blow it.
 
Ok, we're talking about what happens when the reg shorts to ground, right? If the reg is connected on the battery side of the fuse, then there's no current path through the fuse and the shorted reg to blow it.

No, not the regulator.

We're talking about what is protected and not protected when the rectifier positive wire is connected either side of the 20 amp fuse on the bikes that were manufactured with the ONE 20 amp fuse.

I've been thinking about this all day. I'm at the point now of thinking that Yamaha had this all wrong.

Scott
 
Ok, we're talking about what happens when the reg shorts to ground, right? If the reg is connected on the battery side of the fuse, then there's no current path through the fuse and the shorted reg to blow it.

I see you meant to type rectifier instead of reg. That current doesn't know which way to GO and the fuse will blow anyways, whichever side of the fuse gets hot.
 
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