Stator / RegRec Wiring Question

[Elder]

Gents, be gentle with me here...
I'm not a mechanic and this is my first bike. That said, I'm also not a total dummy. I have the manual(s) and have some experience with working on small engines. But if I call the magneto the stator or call the stator the alternator... I'm sorry in advance. This part is all new to me.

So here's the rub. I've got, to the best of my knowledge, an '81 xs400H Special II that does not charge. I've replaced the battery with a Lithium, chopped the tail off to build a single-seat, and gotten the ol' girl running on just battery to power the sparks and lights, replaced all the lighting with new LEDs, and rebuilt the entire wiring harness from the ground up. Everything works fine with one exception... The battery (even the original one) has NEVER charged properly. Finally got around to that part of the rebuild and am realizing that I have no idea what I'm doing.

I have about 4 "wrong" reg-recs sitting on my bench. I'm pretty sure I have one that will work now, but there's no wiring diagram for it and the site documentation is pretty vague. I think I've identified the main issue with the original charging system (goober before me pinched off/crushed all the wires between the block and the component that houses the stator). I assume the three white wires from the magneto are just matched up with the other white ones on the RR. Then I lose confidence in my guesses. The RR also has red, black, gray, and green wires. I can GUESS that the red and black run to the battery, but I'm not sure. The gray and green wires apparently go to "switched ground from alternator field" and "voltage sensing input from ignition switch", but I don't know where those are. The magneto also has two additional wires (other than the white "outbound" wires) that I'm unsure of their use. The sheathing on these two is too oil-stained to identify colors on them, but according to the book's wiring diagram, once upon a time they were black and green.

Can any of y'all bike-geniuses help a newbie out and with getting the right wires run to the right places?

I can provide images later if that would help.

Thanks, folks.

 

[CaptChrome]

I will give it a shot. I don't know if the newest reg/rec will work (not a lot of specs and info is given for it), but I can probably help with how to hook it up to try it out. Not having the factory wiring harness might make this more complicated as we could go by exact wire colors if the old harness was used

Anyway, what you should have and will need is five wires coming from the stator/alternator/generator/thingamabob that exit at the bottom of the left-hand engine side cover. You indicate that they are cut, so you are most likely going to have to remove the side cover and solder on some new wires. But what you should find there are five wires - 3 white, a green and a black. The easy part is that the three white wires from the engine need to be connected to the three white wires on the reg/rec. The green wire from the engine is from the field coil in the alternator and is switched to ground by the regulator in the stock bike. So, hook the green wire to the green wire of the new reg/rec. Simple so far, right? The black wire on the bike that remains is positive voltage supply to the alternator field coil. It does not get hooked to the reg/rec directly, but it should be from switched power on the bike - whatever wire gets switched on when you turn the key on. That takes care of the wires from the alternator.

The reg/rec still has three other wires that need to be connected somewhere. The black wire on the reg/rec goes to a ground point on the frame or engine. The red wire looks like power to the reg/rec and the grey wire is the voltage sensing wire. Most regulators I see don't have separate wires for these as they get everything from one wire, so I would hook them together and terminate them at the same switched main power point that you hooked the black from the field coil to.

To test what you have:
1. Install a fully charged battery and put voltmeter test leads across the + and - terminals. You should have a reading above 12 volts. Note the value.
2. Start the bike and let it idle. Look at the voltmeter reading at the battery again. It should be above the value from step 1. Maybe like 13.5 vdc or similar.
3. Rev the bike up to maybe 4000 or 5000 rpm and look at the voltmeter reading again. It should be somewhere in the neighborhood of 14.5 or 14.7 vdc, but should not go above it. ( I am using approximate ranges here because the specs are not listed for the unit you bought.)

 

[Elder]

Cap, every time I browse this forum, you're out here coming through for the community. Thank you.

The bike actually lived in a cow pasture for about 10 years while I was out doing my time in the Mil. Before that, it was "abandoned" in a different field for an unknown amount of time before making its way to my possession. The harness was Completely shot. I would say I tried to keep it as stock as I could, but I absolutely did not have that luxury... I made it work the best I could figure out and that was the most I could expect from myself on that project.

I'm glad I asked here. This is absolutely Not a wiring configuration I would have just guessed and landed at. I've been dreading this step for over a year, so I'm grateful for the assist. Hopefully with this and a new set of tires, the bike is ready to take for a test ride. You're fantastic.

I'll update and let you know how it goes!

 

[CaptChrome]

Thank you.

You are welcome.

I made it work the best I could figure out and that was the most I could expect from myself on that project.

No issues. You are attempting to bring a dead bike back and that is good enough for me.

I'll update and let you know how it goes!

Please do. This will be important knowledge for the forum. Plenty of people have posted with various regulator issues and there are some tried and true solutions for installing a replacement ground-switched regulator. However, a reg/rec combo that is ground switched and works in the bike would be useful info for a lot of folks. Knowing if this one is the unicorn or not would be valuable.

 

[Elder]

I wired everything together the way you recommended and I'm not positive we're in business, but I'm reluctantly optimistic...

With everything connected and the RPMs up (unsure exactly how high since the tach isn't connected), the voltage across the battery reads around 12.7-13.5. It's not as high as the 14+ that's targeted, but I can watch the voltage drop when running the electronics , but it does come back up. I'm also curious if the Lithium "smart" battery is affecting the readings since it may be trying to manage the voltage output somehow. So for now, I'm back in a holding pattern until I get some tires on the bike and take it for a couple test rides. If it dies a couple miles from the house, I'll have a pretty solid guess why.

More to follow once I pick up tires and test run it.

 

[CaptChrome]

I don't have any experience with lithium batteries in this application and you would have to read up on it to tell if it is outsmarting the troubleshooting here. What was the battery voltage without the bike running?

12.7 to 13.5 volts sounds low for the regulator to be working, but if it is higher than the starting battery voltage, all could be well.

 

[tstidham]

I would imagine if the battery has its own onboard BMS, it would reside between the battery terminals on the outside and the lithium cells inside. So you likely wouldn't have access to measure the internal charging voltages unless there exists some other wire connectors on the battery. When I first got the charging working on my 78 that also sat around for years, I found high voltage drop readings all over the bike, as high as 1.2 volts in some places. Many of the plugs and connectors had surface corrosion within them. I carefully went through the entire harness just unplugging and replugging them all several times to sort of scrape fresh metal connections and this was very successful. In doing this I also found two main power feeds in the headlight bucket that showed clear wire overheating with cracking and melting of the insulation and I spliced the bad sections out for new wire.

 

[donn29]

Pretty sure a lithium battery can only 'disconnect' the positive or negative post, and it will only do that if it's connected to a voltage that is too high, or if there is a drain on the battery and the battery voltage drops too low. If you have voltage between 12v and 14v, the battery should be working and should accept a charge.

 

[Elder]

Whelp... Time for that update I promised.
Short Version: No.
New tires, both carbs rebuilt, battery charged on the bench. Finally ready?
Made it to the end of my ~1/4 mile dirt road and about halfway back. Then she died on me. Checked the battery and it was Completely drained. So something's still funky. Everything wired up as described above. Might be time for a different tracing approach. Maybe it's the copper coil itself, maybe it's wired wrong, maybe the Reg/Rec is just a turd sammich, I have no idea. If anyone else stumbles down this thread, the battery is a Very fancy (not really) 12V 200A 26WH X2Power Lithium blah blah here's a link and the R/R is this thing. Been trying to get this old girl running for like 3 years now. But at least I got... *quick maffs*.... 0.4 miles out of it?

Okay, with story time out of the way, Any recommendations to tracing the issue at a lower level than "pull Voltage reading from between the terminals"? Can I try tracing the voltage on specific wires and checking those to figure out what they're up to? I would think the three white wires aren't constant current due to being magnetic field generated, but can I measure the pulse rate? or the voltage that Does get pushed down that line? Compare that against what's expected?

I got Incredibly Lucky recently and picked up two more frames and three more engines for the same bike for like $400. Must have done something right in a past life to find that deal. Would it make sense at this point to pull the coil out of one of those other engines and try it on this block? How would I even know if that one's outputting what's expected?

 

[CaptChrome]

Even without the charging system hooked up, I would think you could run the bike on a fully charged battery for more than what it takes to drive ¾ of a mile. But I checked out the battery you are using and it is only a 2 amp-hour battery. If you are using electric start that probably pulls most of the charge out of the battery before you even get rolling. Still, it should last longer than a few minutes, but a 2 AH battery doesn't allow much time for chasing down something causing a big current draw.

As a point of comparison, the gel battery I have is 12 amp-hours.

 

[tstidham]

Have you checked the AC voltages coming out of the alternator on the three white wires? The service manual has the procedure and target voltage ranges. If I recall, something like in the 30 volt range.

 

[Elder]

Have you checked the AC voltages coming out of the alternator on the three white wires? The service manual has the procedure and target voltage ranges. If I recall, something like in the 30 volt range.

I have not, but I think that's exactly what I'm looking for. Start with each individual end-component and see if it's doing what it's supposed to be doing. Work from the extremities toward the problem. Thanks for the pointer.

 

[LeBouc]

I wrote on Google: «can i replace a lead acid battery with lithium ion» and it came out with this in its answer:
Charging System:
Lead-acid and lithium batteries have different charging voltage requirements. If you are switching to lithium, you will likely need to adjust or replace your charging system (charger, alternator, etc.) to avoid overcharging or damaging the lithium battery

If I would be you, I would restart with a standard lead battery as those motorcyle electric components were designed with this type in mind

 

[Elder]

I wrote on Google: «can i replace a lead acid battery with lithium ion» and it came out with this in its answer:
Charging System:
Lead-acid and lithium batteries have different charging voltage requirements. If you are switching to lithium, you will likely need to adjust or replace your charging system (charger, alternator, etc.) to avoid overcharging or damaging the lithium battery

If I would be you, I would restart with a standard lead battery as those motorcyle electric components were designed with this type in mind

The only electrical components left that are stock are the Stator, Field Coil, and Spark Plugs.

I've replaced or removed everything else in favor or LEDs, Lithium, or Deletion (turn signals, gauge lights, etc.) Ignition coils seem to run fine, bike runs, it just isn't charging. I 100% get what you're saying and I'll probably rebuild one of these other ones as stock as I can get it. But this one is basically ready for Lithium. Just gotta figure out the right R/R and wire-up.

I've also googled if it's possible. The Google AI and/or ChatGPT responses aren't authoritative. They're GPUs hallucinating and making guesses. I'm not expecting it to be drop-in.

 

[LeBouc]

The only electrical components left that are stock are the Stator, Field Coil, and Spark Plugs.

I've replaced or removed everything else in favor or LEDs, Lithium, or Deletion (turn signals, gauge lights, etc.) Ignition coils seem to run fine, bike runs, it just isn't charging. I 100% get what you're saying and I'll probably rebuild one of these other ones as stock as I can get it. But this one is basically ready for Lithium. Just gotta figure out the right R/R and wire-up.

I've also googled if it's possible. The Google AI and/or ChatGPT responses aren't authoritative. They're GPUs hallucinating and making guesses. I'm not expecting it to be drop-in.

There is a video talking specifically about using a lithium battery on an older bike (not designed for that).

The title is «How To Choose The Right Regulator-Rectifier For Lithium-Ion Batteries». We have rectifiers on our XS but no regulator (the voltage changes with the RPM) and Lithium batteries need constant voltage at the end of the charging cycle....

 

[tstidham]

Our bikes do have regulators. My original was bad and only putting out about 11 volts, the rectifier however was working fine. I replaced my regulator with a Dodge pickup truck style from the 80s using a heavy duty adjustable Transpo brand. It's set for max of 14.2 volts. Because our bikes alternator is pretty weak (I think like 230 watts), the voltage at idle is low, but usually just above 12.6. it rises to 13.8 pretty quick above idle and stays at 14.2-14.4 in the upper rpm ranges.

 

[Elder]

There is a video talking specifically about using a lithium battery on an older bike (not designed for that).

The title is «How To Choose The Right Regulator-Rectifier For Lithium-Ion Batteries». We have rectifiers on our XS but no regulator (the voltage changes with the RPM) and Lithium batteries need constant voltage at the end of the charging cycle....

I mean... the stock bike definitely does have both a Regulator and a Rectifier.

 

[BBS360]

I mean... the stock bike definitely does have both a Regulator and a Rectifier.

Modern bikes user permanent magnets for the field coil in their alternators and regulators on the output of the stator that regulate the actual power coming out.
Our older bikes use DC electromagnet field coils and have a regulator that controls that field coil in the alternator. As a result they influence the stator output but do not actually limit the voltage out of the stator wires.

It is that finer voltage control that lithium batteries need.

It is possible to replace the stock rectifier with a modern reg/rec that does directly control the output on the stator wires.
The stock regulator would still be required to control the field coil unless one does a permanent magnet alternator, "PMA", modification.

 

[LeBouc]

I mean... the stock bike definitely does have both a Regulator and a Rectifier.

When you work with electronic parts, a regulator will give a very specific voltage output. The regulator that we have on cars and motorcycles simply limit the voltage to a maximum output (around 14.5V) to make sure that the alternator is not burning the battery. Lead batteries are designed to begin charging at, at least, 13,5 V. This is not the case with Lithium batteries. Which model of smart battery do you have? It could have its own regulator to avoid being overcharged!

 

[Elder]

When you work with electronic parts, a regulator will give a very specific voltage output. The regulator that we have on cars and motorcycles simply limit the voltage to a maximum output (around 14.5V) to make sure that the alternator is not burning the battery. Lead batteries are designed to begin charging at, at least, 13,5 V. This is not the case with Lithium batteries. Which model of smart battery do you have? It could have its own regulator to avoid being overcharged!

Battery and RR are linked in this earlier message (https://www.xs400.com/threads/stator-regrec-wiring-question.21606/post-191198), but see below for specifics.

https://www.batteriesplus.com/productdetails/cyl10087
https://4into1.com/regulator-rectif...50-tx650/?searchid=3519909&search_query=rr-20