AC - DC system help please...

[minkey]

Hi Guys,

I need to pick the brains of anyone good with the start and end points of charging system on the XS.

Mine is a 1981 400SE UK model. I’m very comfortable working with 12V DC Vehicle electrics so am rewiring this bike from scratch. I’m just previously used to four wheel charging systems with Alternators that just give you the DC direct from the unit. Not had to deal with AC on a vehicle before, although I am also used to working with 240V AC Main power so working with single and three phase AC is familiar.

I’m needing a bit of help confirming my thoughts on the bike though, before I get the AC Charging part of the bike wrong.

It’s a Permanent Magnet Rotor stator setup, with points and condenser ignition which I’m happy to keep as I grew up working with this type of ignition.

The first thing that threw me, was my stator has FOUR white wires from the outer coil as well as the black and blue pair for the Neutral light and oil pressure switch from the inner coil

The first thing I’d like confirming is that on this model is, the stator being three phase for three of the wires, and there is a forth that is unused, but could go direct to the headlamp.

So, am I correct in thinking that I can use any three white in any order to feed the rectifier?

Then blank the fourth, as I will be powering the headlight from the DC circuit.

If that’s right, then I’m on to Regulator & Rectifier. The original loom has both separate units and unless there’s any reason not to, I’d like to change to a single Reg/Rec unit to help keep it tidy and reduce wire numbers.

So… Stepping away from standard OEM units, is there a load or spec that I’d need to consider for this bike.

I’m sticking with the standard 12Amp battery. Keeping the starter and changing all but the H4 Headlamp bulb for LED, so the load will be very similar to stock, apart from the very slight drop in load from using a few LEDs. Certainly no increase in load.

I’ve only ever needed to replace like for like on a Reg/Rec on more modern bikes, so am thrown by seemingly suitable units ranging from £30 - £130 ?!

Advice on choosing something that will last but not be unnecessary over cost would be a great help also.


I look forward to some answers.


Thanks all.

 

[amc49]

I'm looking at a wiring diagram here onsite that shows the 4th white stator wire simply ends at the connector, the other matching connector is blank there. Not used, it is obviously a wye tap, they just don't use it for power. You need to use the original 3 wires for charging, the 4th one will send more signals down the line since it taps into the ends of the other 3. You will get 3 pulses out of the 4th wire for every 1 out of the other 3 wires. The correct 3 wires to use will be the ones that connect across the connector to send power further down the line.

http://www.xs400.com/threads/yamaha-xs400-manuals.4503/

Go to post #2 and download the part 3 section and then go to .pdf page 29 or real pagination page 119 (same page) in the pdf and look at the wiring diagram there for 250-400.

 

[minkey]

Cheers amc49, I'll have good read.

Forgot to mention, this came to me with burnt and butchered stator wires so have had to rewire from the coils.
No indication of which was which so can't make out which one was the 4th wire.

Thats whats throwing me... I am having to make dangerous assumptions about wiring which I don't like.
Can I literally use any three of the four in any order, or do I need to know and eliminate the correct fourth from the new connectors?

What I can't make sense of is that you can have single phase on two wires, or three phase on three, but four phase isn't a thing...

 

[minkey]

Amc49,

I did manage to find that diagram in my manual after reading the dpf.
I'd got so head locked by it, I'd forgotten that the manual shows the fourth wire coming from the centre and not a coil

So... the question wis now... How do I identify it if they all have the same potential?

 

[amc49]

'...the fourth wire coming from the centre...'

That makes it a 'wye' tap, it taps into the middle 'Y' there. Look it up on the web.

Short course on A/C.....each stator lead of the 3 sends both positive and negative out BOTH ends of the loop, they are just reveresed, one is P then N the other is N then P. The middle join simply allows them to get out to complete the circuit. We use the outside fired ones, the rectifier trims out the one polarity we don't need and then the 3 add up to make a constant repeat of positive pulses closer to direct current. When you tap into the middle wye though you are getting 3X the +- pulses because you get the P and Ns from all 3 of the inboard bound stator sections all at once.

If you don't get the correct 3 wires not only does your current interrupt incorrectly to get not full power, but you will overlay a 4th pattern over the top of that that messes things up even worse. It would show I think on an alt ripple test. which measures the equality of the individual pulses. It would show as more ripple, which is an indicator of the power pulses being uneven. Think of your power like this coming out of alt correctly each stator lead combining to pulse as 123123123 evenly spaced, solid power. One stator lead breaks and you have 1-31-31-3 with the number 2 stator lead broke. The - shows on the test as a no power moment, the test 'ripples' for a fractional second as no power was there. Now you add the 4th lead and you blow up a single pulse there; we''ll use 1 to make it; instead of just 1 it becomes 1+4, next one is 2+4. next one 3+4 to make again a repeating pattern but more complicated.

 

[amc49]

You should be able to ohm test the different stator leads to figure out which is the wye one, it is the one with the least resistance by half. Start testing all possible pairs of leads and carefully watch the behavior ohms at the lowest they will go. When you have two of the normal three leads the resistance has to go through TWO coils to get out meaning more resistance, when one of your wires is the 4th one you will get only half that when it combines with any of the other three because you are only going through one coil of winding instead of the two normally. When you find that half amount wire it will show that half amount matched up to any of the other three. The other three will show double resistance in any combination of THEM ALONE. The half amount wire is your 4th wire.

 

[amc49]

FYI, if somebody has one of those alts with the 4th wire one could add another plus and minus diode to then patch it into the regulator to get a high output alternator with 10-15% greater output. Most cars do that nowadays, the alts changed from the usual 6 diodes to 8 to cover the extra wye tap lead.

 

[minkey]

Amc49... You sir are a gent and a scholar.
The AC lesson bit i was familiar with as for work I deal AC mains and in the UK, three phase mains is 415V so it's definitely something to know the hurty end of.
Funnily enough, I was chatting to an electrician mate thus morning about the bike and he said as a youngster, his trainer said "When working live, always keep one hand in your pocket, but never hold your balls!!"

So, Where I have had a school day today is the Y tap. Thats new to me and makes a lot sense the way you put it.
What I had discounted when measuring, was the small difference in resistance. Its certainly way away from half, but one wire gives 0.8 Ohms to the other three and the others are 0.9 Ohms. Its a tiny difference id put it down to either a small but acceptable defect in the windings or more likely my new wires, which I had fitted right from the coils.

I'm also picking up a new meter tomorrow which may be more accurate and show a bigger difference but I get now that the lowest is the tap and I'll test again in highest sensitivity.

Genius !

Have a great weekend. You've just improved mine

 

[minkey]

Amc49... You sir are a genr and a scholar.
The AC lesson bit i was familiar with as for work I deal AC main and in the UK, three phase mains is 415V so it's definitely something to know the hurty end of.
Funnily enough, I was chatting to an electrcmate thus morning about the bike and he said as a youngster, his trainer said "When working live, always keep one hand in your pocket, but never hold your balls!!"

So, Where I have had a school day today is the Y tap. Thats new to me and makes a lot sense the way you put it.
What I had discounted, was the small difference in resistance. Its certainly way away from half, but one wire gives 0.8 Ohms to the other three and the others are 0.9 Ohms. Its a tiny different id put it down to either a small but acceptable defect in the windings or more likely my new wires, which I had fitted right from the coils.

I'm also picking up a new meter tomorrow which may be more accurate and show a bigger difference but I get now that the lowest is the tap.

Genius !

 

[amc49]

I expected it to be half amount resistance but just a guess, the wires are so low resistance it may not be that different at all. At that low an ohm it is hard to get exact too and a new (better) meter may well help.

The important thing is to find the solid lower resistance difference in that one wire as compared to the others and it repeats with more testing and it marks it.

You'd be interested to know that I have no formal training in electrical at all, just what I have picked up keeping my eyes open, rebuilding car alts has helped me with some of it, when I hit new territory I self-learn just like you did. Occasionally a self rule I have in head gets popped or readjusted like the half amount idea here. You have to be willing to modify ideas to learn..........