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Discussion Starter #1
man, I had to buy a new diode.

I hooked up a 12v source to my field to see if the stator was putting out a charge. It fixed my tach, and made plenty of volts for the rectifier....
burned up my diode something fierce....

What would cause this?
 

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In this situation, only two things: more reverse voltage than it is rated to block, or, more likely, more forward current than it is rated to conduct.
 

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Discussion Starter #3
experimental testing

It would have been a good idea to disconnect the regulator with a full charged battery behind it, when I jumped the field to create a charging condition on the stator... I am considering replacing my idiot arct regulator with a new one, I have already ordered a new diode. The old one isn't completely gone, it is reading about 585 instead of the original 1163, but it isn't reverse engineering.
I am getting a bit of heat in the main link also. the only thing that is on that line besides the entire bike electrical system is the main fuse, and I thought it was supposed to blow before any thing burned up...
this is bothering me something fierce.
 

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Do you know the ratings of the diode? If the coil is ~3 Ohms, then it will try to draw over 4 Amps - (14.4 - .6)/3. Because of that, a 5A rated diode will get really hot.
 

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Discussion Starter #6
so the math is important on 1981 yamahas electric systems?

I am sad to say that your last post said something like one sixth tenth of the highest voltage attainable = diode capability.

problem with that is if you try to divide any kind of current with a diode, it will burn up. diodes control current flow, not current. They are not rated by amps, but by their value..(I think I remember this.. (I could be delusional and farting the star spangled banner)
 

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No, diodes ARE rated by how much current that they can conduct before overheating. There are .1A diodes and 100A diodes, and just about everything in between. Some switching diodes are limited to less than .1A, and some power diodes go over 100A. They are also rated by how much voltage that they can block before failing, from a few Volts to over 1000V. That is for switching and rectifier diodes. There are also Zener diodes, designed to conduct in reverse at a fixed voltage and current range. Tunnel diodes are even stranger.

If you are using a rectifier diode to steer current, you have to make sure it can conduct all the current that the device after the diode will draw, plus some to spare, so it doesn't over heat.
 

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Discussion Starter #8 (Edited)
schem of problem circuit

On my bike, the wiring is different. There are 3 stator wires. One feeds this diode circuit but without the tach, another feeds only the tach, the other just jumps to the rectifier.

The relay has a ground, and a straight connection to the fuse box, which is where I think the relay gets its power at key on. still doesn't explain why this diode is in there, or why the stator wire terminates at the relay.

The manual does not show a relay with a diode in it, where this is, but everything else on the bike is working, so I am assuming it is something else.
 

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So, that diode turns the relay on when the stator begins generating power, allowing the various lights to come on; until the engine starts, there are no lights (except maybe the neutral and other warning lights). If that diode only goes to one side of the relay coil, the only current it should see is what it takes to switch the relay. When the R/R is working, it connects the stator output, through diodes, to the battery, limiting the voltage at the stator to about 15V, but if the rectifier/regulator is not connected to the stator, the voltage will rise, possibly to 50 or 60V. At 15V, the relay coil should draw about .05 to .1A, so, unless you have a small switching diode, it should not get hot. Unless, of course, the R/R is disconnected from the stator, then the current through the diode goes up a lot, which could make it very hot, and the relay coil, too.
 

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Discussion Starter #10
kind of.. not quite

The key turns the relay on. All lights power up and so I am assuming the fuse box wire is where the relay is getting its power.

The stator doesn't start producing AC until after the bike starts up, and never when the battery is over 12v.

If this wire is spliced to one of the white rectifier wires, It has AC in it, and not DC, this is strange to me.

The alternator wire that is connected here has to power or drive something.
the secondary headlight or something.
 

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I can't guess what the diode that routes the stator signal to the instrument panel is for, then, unless it is to switch the warnings off after the engine starts, like oil and over-temp, assuming, of course, they aren't actually active. With AC on the stator side of the diode, you get pulsed DC on the other side, as the diode alternately conducts and blocks the current from the stator.

The stator has to generate some AC, even when the battery is fully charged, if only to operate the tach. Also, the battery, by itself, won't keep the lights lit, so the stator is operating at a level to keep the battery from discharging at all times, if the regulator is working properly.
 

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Discussion Starter #12
After what you said, I may take the regulatar replacement route, if not but to only see if I fried my other one.

I just wonder what they were trying to get away with when they stuck a DC powered relay in an AC line straight from the stator.

The reserve lighting unit is supposed to do 2 things, light the instrument panel when the headlight goes out, and switch from the burned out filament to the reserve headlamp filament. It doesn't seem very likely that this device is driven by the stator, but it could be, in an emergency, like if a bird or rock flew into the headlight it might short out the battery and cause the bike to die, if the reserve unit bypassed the short using the stator power, it would not require the battery to get home.
but the diagram in the main repair maunual has a relay with no diode, and the wire that goes to the alternator stator, is yellow, not white. the yellow is excluded on the H model of this bike.
 

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Now you've lost me - that diode goes to the coil of a relay that switches a backup headlamp on, if the main headlamp goes out? Can you scan the schematic and post the picture to a photo site, so I can see how this is supposed to work? I can't figure what could keep the reserve lamp off while the main lamp is on.
 
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