1980 XS400G electrical revamp

DarthGrt

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Hey all,

Wanting to learn about a regulator in this bike. One that is separate from the rectifier. It appears to lead to the field coil on the alternator, but then at the connector it appears green from the regulator is actually ground as it become black to the coil and the field coil is tied into a wire at the fuse box. Its very confusing to me what this regulator does. is it to keep the field coil at a safe 12v? It certainly isn't regulating the whole system based off this diagram, is it?

If it is, could I just remove it when I put in my replacement reg/rect unit? I am replacing electrical components of this due to its age. I want to modernize it a little. I have an advancer unit and an XS-Charge unit on the way to replace the ignition system. That way I don't have to rely on the proprietary igniter unit.
1981 XS400 G_SG.PNG
 
The charging system on this bike is a lot like the ones you find in cars. The voltage regulator senses the system voltage via the brown wire and adjusts the alternator output. If the voltage it too low, it will raise alternator output and if the voltage is too high it will lower the alternator output. If everything is working well, voltage will be controlled in a small range around 14.3 volts. A knowledge of Ohms law and understanding of how wires produce electromagnetic fields is helpful, but I will try to explain this without making you take a physics course

The way the regulator controls the alternator output is by means of the field coil. One end of field coil is attached to system or battery voltage (the black field coil wire is connected to the brown 12vdc wire from the main switch.) The other end of the field coil is attached to the voltage regulator using the green wire.

The regulator controls the flow of current to ground to maintain the 14.3 volts in the system, and it does this by changing the resistance to ground of the green wire. So, if the bike is running and the brown wire at the voltage regulator is 12 volts, the regulator will decrease the resistance to ground of the green wire which will cause current flow to increase through the green wire and this current will cause the electromagnetic field around the coil to go up and the alternator will increase voltage in the system. Similarly, if the voltage seen at the brown wire of the regulator is 14 volts, the regulator will increase the resistance to ground of the green wire, the electromagnetic field of the coil will collapse and the alternator output voltage will go down.

This is maintaining the voltage on the whole system as the alternator output is fed to the rectifier via the three white wires and the rectifier output is attached to the main, red wire in the system.

Hope that helps.
 
The charging system on this bike is a lot like the ones you find in cars. The voltage regulator senses the system voltage via the brown wire and adjusts the alternator output. If the voltage it too low, it will raise alternator output and if the voltage is too high it will lower the alternator output. If everything is working well, voltage will be controlled in a small range around 14.3 volts. A knowledge of Ohms law and understanding of how wires produce electromagnetic fields is helpful, but I will try to explain this without making you take a physics course

The way the regulator controls the alternator output is by means of the field coil. One end of field coil is attached to system or battery voltage (the black field coil wire is connected to the brown 12vdc wire from the main switch.) The other end of the field coil is attached to the voltage regulator using the green wire.

The regulator controls the flow of current to ground to maintain the 14.3 volts in the system, and it does this by changing the resistance to ground of the green wire. So, if the bike is running and the brown wire at the voltage regulator is 12 volts, the regulator will decrease the resistance to ground of the green wire which will cause current flow to increase through the green wire and this current will cause the electromagnetic field around the coil to go up and the alternator will increase voltage in the system. Similarly, if the voltage seen at the brown wire of the regulator is 14 volts, the regulator will increase the resistance to ground of the green wire, the electromagnetic field of the coil will collapse and the alternator output voltage will go down.

This is maintaining the voltage on the whole system as the alternator output is fed to the rectifier via the three white wires and the rectifier output is attached to the main, red wire in the system.

Hope that helps.
Thank You so much! You confirmed my suspicion. I knew that regulator had to be regulating to ground cause thats the only why for the coil to connect to ground.

I have a couple questions for you. Is this regulator to ground necessary if I put in a rectifier/regulator unit?
 
I guess in general what should I do about this regulator? By the sounds of it I am going to leave it in regardless. But I'm no expert in charging systems.
 
If the regulator works, I would leave it. Most reg/rec combo devices you buy are designed for bikes that have a permanent magnet field alternator and not an "adjustable" field like the XS400. A recent thread here also noted that there are two types of adjustable field regulators, A and B types. The A type regulates the field coil to ground (the type the XS 400 has) the B type regulates +12v to the field coil. So, you need to know a bit about what you are buying as there are big differences in how they work.

@tstidham has a good thread to read on this - www.xs400.com/threads/re-ring-dodge-vr-and-starter-clutch-springs.20579/

And if you need to replace your non-operational regulator, he has a working replacement identified.
 
If the regulator works, I would leave it. Most reg/rec combo devices you buy are designed for bikes that have a permanent magnet field alternator and not an "adjustable" field like the XS400. A recent thread here also noted that there are two types of adjustable field regulators, A and B types. The A type regulates the field coil to ground (the type the XS 400 has) the B type regulates +12v to the field coil. So, you need to know a bit about what you are buying as there are big differences in how they work.

@tstidham has a good thread to read on this - www.xs400.com/threads/re-ring-dodge-vr-and-starter-clutch-springs.20579/

And if you need to replace your non-operational regulator, he has a working replacement identified.

Thank you. I really appreciate you explaining this to me. I have a way better understanding of this charging system now. I am replacing the rectifier and I haven't found a single one that does not have a regulator in it.

If I do leave this regulator in would putting in a reg/rect unit just be off the table? would the regulators fight each other and burn one of them out?

Or would I just have to splice that green wire to the ground wire and cap off that brown 12v on the regulator and have the field coil run at voltage and just let the rect/reg unit do it's job without another regulator in the system?
 
So, a couple of things to try and answer your question and a question of my own...
1. I don't know if adding a reg/rec combo unit would work. I don't know enough about the internal wiring of the combo units to feel comfortable trying it on my own bike - I wouldn't know how to hook it up, and I don't think the results would be good. But others on this forum may know (and probably do) more that I do about this!
2. The rectifier is nothing more than six diodes (a very basic electrical component) hooked up in a bridge. The XS400 wiring diagram shows exactly the six diodes and how they hook up. In a pinch I, or anyone else could make one up, if really necessary. I will have a look around for a stand-alone bridge rectifier that might work for you. But first I need to ask a question:
Why do you think you need to replace the rectifier? Is it missing? Rectifiers are typically pretty stout pieces of gear. If you suspect your rectifier is bad, they are pretty easy to test and we can walk through that if you want.
 
These combo units the regulator will shut off current from the stator and let the battery run the system. I was just wanting to replace it as a revamp. I understand they may work fine, but the fact still remains it's a 40 plus year old electronic. I will check to make sure it is working I know how to test the diodes since they only allow current one way. There's a lot of vids on testing rectifiers.

The replacement I have will be direct wire up, just it has a regulator included in it. It is actually for a 12v system on a Polaris. It's 3 phase so 3 AC wires from the stator to the rectifier then a ground wire and hot wire tying into battery positive.
 
Try it. The only thing that might be a concern is the potential of frying the TCI, but that risk can be eliminated if you disconnect the power feed to the TCI and wire it to a separate 12v battery. That way if there are any power spikes on the bikes electrical system during the test, they won't damage the TCI.
 
Try it. The only thing that might be a concern is the potential of frying the TCI, but that risk can be eliminated if you disconnect the power feed to the TCI and wire it to a separate 12v battery. That way if there are any power spikes on the bikes electrical system during the test, they won't damage the TCI.

Ignition control is torn out putting in the XS charge electronic ignition from Mike's it's all 12v so amps needed will be pulled. I don't think anything will fry but we're giving it a try. Thinking of it's all done and successful I'll make a thread documenting. Course I'll give it some test time to prove itself.
 
Try it. The only thing that might be a concern is the potential of frying the TCI, but that risk can be eliminated if you disconnect the power feed to the TCI and wire it to a separate 12v battery. That way if there are any power spikes on the bikes electrical system during the test, they won't damage the TCI.

So I found a reg/rec that addresses the variable field coil resistance. I am just going to buy this as it says it's spec'd to fit and it'll still just replace both pieces into one.
Voltage Regulator For Yamaha XS 360 400 500 1975-1982_ OEM.png
 
The combination units are hit-or-miss.
From 1979+ they are like yours, with one field coil wire going to 12V and one to ground through the regulator.
From 1976-1978 they are the opposite, with the regulator "regulating" the 12V supply and the second field coil wire grounded.

The ebay listing says it covers all years, which isn't really possible, so you have no idea how it should be wired.
If you understand the concept it is pretty easy to rewire the +12V/grounds to work either way. Might just take some trial and error.

A small caveat, since you are investing in various aftermarket electronics, the stock regulator setup control the alternator INPUT (field excitation) in an attempt to regulate the alternator output.
Nothing in the system actually regulates the alternator output.
The system voltage can easily spike to 14, 15-16+ volts.

Modern bikes are the opposite. Permanent magnets provide a constant field excitation and electronics (mosfets) regulate the actual output from the alternator, usually to no more than 14.5V.

If you really want to protect your new electronics it may be worth installing both a field excitation regulator (stock) and a more modern mosfet/shunt/series regulator that will actually limit system voltage.
It also reliably limits the voltage for lithium batteries.

I discovered that the regulators off CBR125 bikes use the same connector as the stock rectifier and also reproduce its function, but you will still need something to fill the role of the stock regulator.
 
I think the reg/rec combo shown will probably work as you would need to bypass the existing wiring and hook the field coil, the alternator output, the power/ground and sense lines directly to the reg/rec and let it do its thing. It shouldn't make any difference if the field coil is +12v regulated (B circuit) or ground regulated (A circuit) as you connect both sides of the field to the reg/rec. This should replace the two existing devices on the bike.

I have seen a new offering from NWT Cycletronic that will be coming out at the end of March with a similar approach as this device (https://nwtcycletronic.com/wp-content/uploads/DRR-F.pdf). This may be that device in a slightly different package as NWT Cycletronic is located in Canada also.

I vote "go for it" and let us know how it goes.
 

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Thank you

I have decided to return to google and found a reg/rec, it is spec'd for my bike as it has my reg and rect part numbers listed as OEM replacement. Some of the ones I found didn't list any part numbers

This is from Ricks Motorsport Electrics.

https://ricksmotorsportelectrics.com/OEM-Style-Yamaha-Rectifier-Regulator-10_411

This will be the one I pull the trigger on and use.
Hey there! I'm about to pull the trigger on the lithium version of this one for my new battery on my xs400 1979, wondering if you installed it, and how easy was the swap? do they provide instructions with the kit? Thanks
 
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