Yes, the VR115 auto regulator is the way to go. The original mechanical regulator is usually pretty robust but it's output is very erratic even when it's working properly. My best guess is this bike's vibration messes with the points inside the regulator.
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1978 XS650 Special Project
- Thread starter Melnic
- Start date
Low 12's is pretty normal for these at idle. The RPMs are so low, the charging system isn't putting out much yet. And I lose almost another volt when I turn the lights on, lol. But that's only at idle. Once revved, the lights don't effect the charging output much.
Well, I wish I had tested the rectifier and regulator last weekend when I had the time.
I just tested the rectifier at the top of the bike under the tank at the 6 terminal connector and one leg is open circuit to the + of the Battery terminal.
I then went to the main connector at the regulator itself and same thing. I take it I get to the mounting bolt from under the rear tire at the front but I could not find my small socket adapter to 3/8. I do have one of those offset angle adapters. I'll order a replacement rectifier anyway using info from the thread Jim linked
Is just pulling that nut off the bottom of the Rectifier all I need to do to remove it or will it be stuck on there or need another nut/bolt removed?
I just tested the rectifier at the top of the bike under the tank at the 6 terminal connector and one leg is open circuit to the + of the Battery terminal.
I then went to the main connector at the regulator itself and same thing. I take it I get to the mounting bolt from under the rear tire at the front but I could not find my small socket adapter to 3/8. I do have one of those offset angle adapters. I'll order a replacement rectifier anyway using info from the thread Jim linked
Is just pulling that nut off the bottom of the Rectifier all I need to do to remove it or will it be stuck on there or need another nut/bolt removed?
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I'll sometime refer to the parts manual for disassembly when I'm working on a new to me bike.
I am dumber than a box of rocks but I wired in a VR115 to my 77 tracker. I didn't post pictures out of shame....
Already did...VR115 is a regulator, Need a bridge rectifier to complete the overhaul.................................Jim and 5Twins made an excellent ""how to" tutorial to do this..................Maybe someone could post a link
https://www.xs650.com/threads/1978-xs650-special-project.65053/post-812769
I had pulled apart the regulator and it passed all the resistance testing. I think the original problem on why it was not regulating is the adjustment on the side of the relay which I"m guessing sets the voltage that it switches to the low voltage (low magnetic field) mode. Its a screw that contacts a spring that sets the resistance to the coil powered by the ignition power (brown) wire. Out of curiosity I'm going to bring to work and hook up to a variable Power supply to see what voltage it switches.
Good idea. If you can also adjust the current, the rotor draws about 2.5A at max charge rate... would be a good starting point anyway.
So after looking at the regulator circuit I can now understand how it works.
Ohms Law (V=IR or I=V/R) and that regulator is either passing the Brown wire direct to the coils or dropping it down with a resistor once the relay engages.
So if the coils are 5 ohms and its at 12V then it will be 2.4V. @ 13V its 2.6A
Once the relay switches fully, its 8ohms added in series so that would drop it down @ say 14.5V to be 1.1A (5ohms + 8ohms)
So, if the coils are higher than 5 ohms, then current is reduced. With brushes there and the wiring, not sure how much extra resistance that adds.
So, if that screw is out of adjustment and the relay does not switch soon enough, or the relay is bad and does not switch at all, the coils could exceed 3A while running easily.
If I wanted to keep this regulator and limit the current, I'd have to add some series resistance.
I do have a solid state current meter so I could measure the coil current while running if I think to do that.
Ideally a solid state regulator would do just that, regulate the coil power by varying the coil voltage to keep the output at a known good voltage level. I'm expecting the VR115 not to just switch back and forth but vary the coil voltage with feedback from the brown wire.
Back in the 70's solid state electronics to do this must have been more expensive than a relay and large resistor. not so today. Especially the copper in those coils.
Ohms Law (V=IR or I=V/R) and that regulator is either passing the Brown wire direct to the coils or dropping it down with a resistor once the relay engages.
So if the coils are 5 ohms and its at 12V then it will be 2.4V. @ 13V its 2.6A
Once the relay switches fully, its 8ohms added in series so that would drop it down @ say 14.5V to be 1.1A (5ohms + 8ohms)
So, if the coils are higher than 5 ohms, then current is reduced. With brushes there and the wiring, not sure how much extra resistance that adds.
So, if that screw is out of adjustment and the relay does not switch soon enough, or the relay is bad and does not switch at all, the coils could exceed 3A while running easily.
If I wanted to keep this regulator and limit the current, I'd have to add some series resistance.
I do have a solid state current meter so I could measure the coil current while running if I think to do that.
Ideally a solid state regulator would do just that, regulate the coil power by varying the coil voltage to keep the output at a known good voltage level. I'm expecting the VR115 not to just switch back and forth but vary the coil voltage with feedback from the brown wire.
Back in the 70's solid state electronics to do this must have been more expensive than a relay and large resistor. not so today. Especially the copper in those coils.
Jim,
Interesting test. And good info that the Coil resistance changes as it warms up.
I expect 2 things change when on the bike. Rotating it may cool better, but being right next to the engine and being covered, it could be heating up even more.
So, I bench tested the regulator.
Variable Power supply from Black to Brown.
Volt Meter from Brown to Green (Rotor Coil Voltage)
With the regulator removed, the green voltage will drop to 0. (if it was in the bike, it would reduce to about 1/2 to 1/3 I think)
My regulator was moving off the primary contact at 16.5V. WAY too high.
There is an adjustment screw on the bottom (as its mounted on the bike) which would make it really hard to get to when mounted.
There is a nut to set it tight. loosen the nut then go CCW to weaken the spring and thus make it trip sooner to reduce the voltage.
Just to put this one on the safe side, I set it to 13.8V. Tightened the nut, then tested again for 13.8V. That is not necessarily how high the battery will go but the trip point to change the voltage going to the Rotor and reduce output. Running on the bike would be needed I think to get a better indication.
This does NOT appear to be in the Service manual I have and I feel a weak aging coil causes this to come out of adjustment and will only get worse as the coil weakens further. This also can likely be temperature dependent and act differently in the summer or winter. Since this is not direct to the battery but the Brown wire, I can also imagine if you have poor connections in various location and the Brown wire circuit is not at battery voltage, it can make the battery voltage higher than the brown wire too and switch later as well.
So, this is what I'm going to go with for the sequence of events that lead me here:
This is all academic cause I have a VR115 due in today.
Interesting test. And good info that the Coil resistance changes as it warms up.
I expect 2 things change when on the bike. Rotating it may cool better, but being right next to the engine and being covered, it could be heating up even more.
So, I bench tested the regulator.
Variable Power supply from Black to Brown.
Volt Meter from Brown to Green (Rotor Coil Voltage)
With the regulator removed, the green voltage will drop to 0. (if it was in the bike, it would reduce to about 1/2 to 1/3 I think)
My regulator was moving off the primary contact at 16.5V. WAY too high.
There is an adjustment screw on the bottom (as its mounted on the bike) which would make it really hard to get to when mounted.
There is a nut to set it tight. loosen the nut then go CCW to weaken the spring and thus make it trip sooner to reduce the voltage.
Just to put this one on the safe side, I set it to 13.8V. Tightened the nut, then tested again for 13.8V. That is not necessarily how high the battery will go but the trip point to change the voltage going to the Rotor and reduce output. Running on the bike would be needed I think to get a better indication.
This does NOT appear to be in the Service manual I have and I feel a weak aging coil causes this to come out of adjustment and will only get worse as the coil weakens further. This also can likely be temperature dependent and act differently in the summer or winter. Since this is not direct to the battery but the Brown wire, I can also imagine if you have poor connections in various location and the Brown wire circuit is not at battery voltage, it can make the battery voltage higher than the brown wire too and switch later as well.
So, this is what I'm going to go with for the sequence of events that lead me here:
- Bike ran fine
- Regulator Coil weakened over time and then did not properly lower voltage to the Rotor.
- This fried one phase of the Regulator
- This later fried the Coil on the Rotor.
- Owner put bike away for a period of time
- Friend purchased bike for $300 several years ago
- Friend traded bike to me for gun parts
- I fix Bike
This is all academic cause I have a VR115 due in today.
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Well done!
I don’t know how many years we operated with mechanical regulators, but it was a lot. 5 years ago, I was still teaching that technology in A&P school. Grasping it makes for a much better understanding of how the solid state stuff operates. That, and mechanical regulators are still in service.
Yeah... I'd guess I'd been a mechanic for a good 10yrs before I saw my first solid state regulator. Adjusting the old vibrating type was a fairly common task back then.
My how times have changed...
Thing I like most is you still teaching mechanical components recognising the value of it giving better understanding. Increases in value the more we live in a World where we all use tech we don't understand. Tech works because it works, unless it's broken, then replace it. But it'll be superseded by the next gen long before that happens.
Hopefully there's at least a few younger folk who want to learn about older stuff, maybe they're just interested or maybe they value the involvement and seeing how it all works.
This is why I always loved troubleshooting broken aircraft on the flight line before ordering parts and bringing them to the hangar for heavy maintenance.
If you truly understand the components and how they work together in performing their tasks with one another, troubleshooting is an exciting challenge.
Always loved getting it right the first time.
