500W alternator stator (again)

Maestro, SEI-V
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

500W alternator stator (again)

Post by penman »

Hi everyone,
I haven't been on here for a long time, but I'm still riding the 1978 500W - or at least I was until last September. On the Piston Rally, my modern electronic rectifier/regulator failed big time with smoke and suitable sound effects. This didn't last long and when the smoke cleared, I could still ride the bike and it was still charging the battery a bit, just enough to keep the lights on though the starter generally didn't work. On checking it over back home, one of the input wires (yellow) to the rec/reg had burned right through and the other wires were a bit melted. Not sure exactly what had happened and at the moment I can't explain how it was keeping the battery at least partly charged.

I've been busy with moving house, so it has sat untouched since then, but yesterday I finally found time to take the flywheel off to check the alternator coils. A bit of a sorry sight, all the windings are showing signs of severe overheating, so it either needs to be replaced or re-wound. I managed to find 3 advertised for sale, but the typical price is around £250 plus postage. That's a lot to pay for a 40+ year old stator which might well have its own problems.

So I'm gathering information on re-winding. The only real information I can find is on The Netherlands Club website, but I think it refers to an early 350, not a 500. I think the 500 alternator has more output, but I think the general principle of how the coils are wound and interconnected is probably the same. Number of turns and wire gauge are probably different. When I unwind it, I can easily count the turns, note the direction of winding and check the wire gauge and I could wind it back exactly the same, so that's one option. But I don't really need a centre tapped winding as at present because I'm using a normal single phase rec/reg. Has anyone tried re-winding one of these with a single winding on each bobbin? If so, please let me know how you got on. Also, I have been thinking about changing to the Sachse ignition system for some time. Much as I like the idea of the ignition being independent of the battery etc. there are now cracks in the pickup stator potting compound and both ignition CDI units ("transducers") and I am a bit concerned about their reliability. If I do this, the ignition winding on the alternator becomes redundant and could potentially be re-wound as an extra generator coil. With a single coil on each bobbin, even the phasing would be a lot simpler. Again, I would be most interested to hear from anyone who has done this, successfully or otherwise!

A few questions though. As originally configured, 5 bobbins are used for the alternator and one for the ignition. Each alternator bobbin has two coils, wound on two tall bobbins and three shorter ones. The ignition uses a tall bobbin. Each alternator bobbin has one clockwise winding and one anti-clockwise - that just keeps them in phase when connected in series. The number of turns varies, but adds up to 179 in each string. I'm not sure why there are tall and short bobbins and I'm just guessing that the varying number of turns is designed to balance the load around the circle of coils, which would otherwise be upset by the ignition winding. As I say, I'm also unsure why there are tall and short bobbins, maybe someone can educate me!

I need to unwind my existing coils and count the turns, but my first thought is to put 30 turns of thicker wire on each bobbin, tall and short, six coils in total with adjacent coils reversed. The existing 179 turns across 5 coils makes around 20 volts (rms) at medium revs.

As I say, if anyone has tangled with any of this, please let me know, and if you have any info which might be helpful, I will be more than grateful!

Regards,
Joe
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: 500W alternator stator (again)

Post by mbmm350s »

Hello Joe
I think you already determined this, but just going over it again.

The stator has five formers available for lighting coils and the rotor has six magnets.
Each magnet is North South, then South North so each winding must be reversed from its neighbour.
Since there must be an even number of forward and an even number of reverse windings
it is necessary to split the winding at the centre to give 10 in phase voltages.
This is why each bobbin has two windings.
Its the most efficient and balanced way to wind that stator even at an increased per unit construction cost.
The centre tap is not brought out on the 500 stator as a full wave rectifier/regulator is used and that is why the output is higher
Also the 500 and later 350s use a different flywheel with an improved magnet arrangement rather than the rather weak salient pole type used before 78
later stators also have a thicker laminated core

Even later 350s (X3 kanguro) feature bare wound alternator, and are higher output again.

I think the physical design is dictated by the ignition winding, and hence the tall and short bobbins,
but I can only offer conjecture there.

As you say if you sacrifice the generator winding for the CDI then you can wind a single turn,
remembering that the neighbouring coil must be wound in reverse direction (or connected thus)

You can fit any stator 350 or 500, and if it has the red centre tap wire just leave it unconnected (taped to prevent shorts).
If rewinding - it should be rewound the same. Conversion to LED lights will dramatically reduce the power required.

The standard 500s regulator is a surprisingly sophisticated regulator for its era. The circuit on the Dutch site is my reverse engineering of the regulator, apologies for its scruffy nature.

The regulators shunt excess power to ground, I suspect therefore that the thyristor connected to the burnt out yellow had gone almost short circuit.
It may then have blown completely leaving the other half of the regulator functional as a half wave rectifier.


My electrical machines lecturer Mr AT Morgan's book "General Therory of electrical machines" might be of interest.
Mark
BSc Electrical Engineering (30 years in design)
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Hi Mark,

Many thanks for all that, you have encouraged me by not saying it's a daft idea!

My bike is an early 500 from 1978 and it had a centre tapped alternator and a rec/reg which (presumably) had a full wave rectifier. Unusually, the regulator gave a negative output and the centre tap was the +ve. As I received it, the bike hadn't run for many years. Among numerous other faults, the alternator was open circuit as was the rec/reg. I re-wound one coil and re-connected the two halves of the winding in parallel, using an eBay 200W single phase rec/reg. This worked pretty well and on a test it was giving about 160W at 3000rpm before the voltage started to drop. I have to say that this was a rather rough and ready test, no guarantee offered! This arrangement has worked fine for about 3 years and around 5000 miles until the rec/reg did the firework imitation. I think your assessment of the burnout incident is probably correct, but I'll have a closer look at the charred remains for the sake of interest.

I think my rotor has three magnets - three N poles and three S. I think that should work fine with 6 coils and alternate ones reversed. When I re-wound the one coil a few years ago, I found I got about 0.11v per turn, per coil at medium revs, so with 6 coils I reckon I need something like 30 to 40 turns per coil. A bit of experimenting needed here! I'll report back as soon as I have any more data, I would certainly appreciate your comments.

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: 500W alternator stator (again)

Post by mbmm350s »

I think my rotor has three magnets - three N poles and three S
yes, I should have said the rotor has 6 poles! doh.
My bike is an early 500 from 1978 and it had a centre tapped alternator
Do you mean it has a red wire from the stator plate?
Its possible some early 500s may have had the 350 stator, or this one has had the 350 stator retro fitted.

It seems that you originally had the 350 regulator as the centre tap arrangement is usually used with the
350 push pull regulator that has no diodes only two thyristors. The centre tap is connected to the battery +12V.
The 2 thyristors regulate the voltage by shunting excess power to ground.

standard winding is from a drawing I have (a = anticlock, c= clock) which is 179 turns give or take a turn.
Yellow1 25c,41a,24c,41a,48c, TAP=red, 48a,41c,24a,41c,25a Yellow2

can you do a diagram of how it was connected? as with the standard connection you can't put the yellows in parallel


We are agreed that if you wind all 6 coils with a single winding alternating each coil then it is fine. One thing is the open circuit voltage will be around 6/5 times the original system and the regulator shunt thyristors may have to dump more power when lightly loaded.
Probably not an issue for a new regulator
Unless you are running lots of accessories though isn't 120W enough ?

Its only the generator winding that makes a wierd setup
Scooters by the way use one of the bobbin positions for the ignition pickup, one for the CDI generator thus leaving 4 for the lighting coils , so that complexity doesn't affect scooters (or the 125H)
Mark
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Hi Mark,

Your winding "code" agrees exactly with mine, so that's a good start!

This bike is only number 32 of the 500s and probably has a few differences to the more "established" models. Some years ago, I removed the red wire. The link between the two winding strings was on the short bobbin to the right of the ignition coil. I broke that link so that I could parallel the two halves of the centre tapped winding by reversing one to bring them back into phase. I was a bit unsure if the varying numbers of turns on the different bobbins would unbalance the two halves as the rotor turns, so with the alternator disconnected, I checked for any current circulating in the loop formed by the two parallel windings. There was up to about 50mA at times, nothing dramatic. I can't remember the open circuit voltage, I'm sure I wrote it down somewhere (!) but I think it was about 20v. I know it was a bit lower than I expected.

As I think I said earlier, this all worked fine for at least 5000 miles, so as a solution it worked well. By the way, I only used the parallel connection rather than series because I thought the voltage with light load and high revs might be a bit high for the rec/reg. The upside of series of course would have been a lower cut-in rpm. Anyway, right or wrong, that's what I did!

As you suggest, I'm sure 120W would be fine. I use an LED headlamp and some other LED lights. The only other accessories I use are satnav and sometimes a phone charger, which don't add up to much. I just like to know I've got some headroom if I need it, and if I do fit Sachse ignition, that'll need maybe 40W (not sure) anyway.

I am hoping to get a bit of time this afternoon and I might start unwinding to see what I have to start with. This stator may not be the same as the 350.....!

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: 500W alternator stator (again)

Post by mbmm350s »

This bike is only number 32 of the 500s and probably has a few differences to the more "established" models.
Possibly, the very first 500s may have had the same regulator and stator arrangement as the 350s of the same age (1978)
The link between the two winding strings was on the short bobbin to the right of the ignition coil. I broke that link so that I could parallel the two halves of the centre tapped winding by reversing one to bring them back into phase.
Understood that make sense.
I can't remember the open circuit voltage, I'm sure I wrote it down somewhere (!) but I think it was about 20v. I know it was a bit lower than I expected.
Interesting as it should be 30V rms, though depends on the rpm measured at.
As I think I said earlier, this all worked fine for at least 5000 miles, so as a solution it worked well. By the way, I only used the parallel connection rather than series because I thought the voltage with light load and high revs might be a bit high for the rec/reg. The upside of series of course would have been a lower cut-in rpm. Anyway, right or wrong, that's what I did!
The 500 stator evolved from the 350, earlier 350s pre 77 suffered from needing too high rpm to load balance, when braking and indicating at the same time as the lights are on, the rotor was improved, however I think the lower operating regime of the 500 means the serial winding and the full wave rectification leads to a lower load balance rpm than a parallel wound even though theoretically the losses would be greater with the serial wound.
Unfortunately without test equipment and rigs its quite difficult for us to decide, and using a live motorcycle to test these theories a bit risky.

The 500 stators that I have seen have an extra keeper plate rivetted to the end of the generator winding, this was introduced to the 350 stators too and its purpose is over voltage protection

Mark
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Hi Mark,

Thank you for your reply once again. I have made a bit of progress and have now un-wound all the alternator coils - one thing for sure, they were unusable , the insulating varnish having peeled off large parts. I'm sure there were shorted turns all over the place. Some were showing more evidence of overheating than others, but all were in poor shape. I'll try to insert some photos if I can remember how.

Image

I think this first photo will tell you why I thought it needed a bit of attention!

Image

In this view, 1 is the ignition pole, so 2, 4 and 6 are the short bobbins and 3 and 5 are tall. I'm not sure why there are two holes drilled in no. 4 pole piece, or why it has a bit cut out of one side. Similarly, why is there a hole drilled at the base of 2. There was a square copper plate on top of the ignition coil - I guess that is the "keeper" you mentioned.

All coils were wound with 0.8mm wire and the windings were as follows:

COIL 2 (short) outer 25t CW
COIL 2 " inner 25t CW
COIL 3 (long) outer 41t ACW
COIL 3 " inner 41t ACW
COIL 4 (short) outer 25t CW
COIL 4 " inner 25t CW
COIL 5 (long) outer 41t ACW
COIL 5. " inner 41t ACW
COIL 6 (short) outer 25t CW
COIL 6. " inner 25t CW

So each half of the centre-tapped original winding had 157 turns, so using all 6 poles, it would need around 26 turns per bobbin to achieve the same voltage. Do correct me if I've gone astray anywhere!

I think at this point, I run out of any clear guidance and it's into trial and error territory! Doing any tests is going to be tedious because I'll have to wind all the coils pretty carefully, mount the bobbins on the stator, re-assemble it onto the engine and run it to see what happens. I don't need to put the starter and side casing back, that should save me 5 minutes!

Unless you have a better idea, I think my first attempt will be 30 turns of 1.0mm wire on each coil. I'll wind them all the same way to avoid mistakes or confusion, but I'll reverse the connections to alternate coils. Perhaps I should go a little higher, say 35 or even 40 turns - what do you think?

I can't predict the effect of the holes etc in the laminated core, especially around coil 4. I presume that coil will be a bit "weaker" than the others, and I'm tempted to add a few extra turns to that one to compensate, but really I think that's a bit too close to "poke and hope" for my comfort! It would also be difficult to tell if it had helped.

Ideally I would just like to wind this once, but it might take two attempts. I'll order the wire and see how I get on. By the way, I bit the bullet and ordered the Sachse ignition unit. I have one on my Guzzi V65 and it does work well.

Regards,

Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: 500W alternator stator (again)

Post by mbmm350s »

Hi Joe,

That doesn't look like a 500 stator, which I have to hand and whose provenance is known
reasons:
1. The 500 stator has a partially thickened laminated core reaching coils 3,4,5,6
2. I cannot see the white wire which is an earth.
3. The generator winding relative to the slots is different position on 500 stator,
with slots upwards its at 7 o clock. Giving better cooling for the lighting coils.

I can't see the additional rivetted keeper plate.

The 500 stator is wound with what i think is 1.0mm by vernier caliper measure (i cant measure easily with micrometers)
but its definitely thicker than a 350 stator which is for sure 0.8mm

I don't have an X3 stator, but from memory these have less turns of thicker wire.

If series wound I think stick to the same total turn count but use 1.0mm wire, if it can be fitted.
For parallel wound then you could place more turns if possible.

Will try to up load a photo

Mark
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Hi Mark,

Interesting! There never was a white wire, the ignition winding earthed via the mounting screws - you can see the earth tag. I wonder if this was a transitional design used on early 500s. The number of turns is quite different to the 350 but as you have verified, it is also different to the later 500s. I'll give it some thought, but having got this far I guess I'll carry on and see how it turns out. Since I'm going for a single coil on each bobbin, I'll have plenty of room for thicker wire.

The keeper plate, if that's what it is, is a copper plate with a square hole in it on top of the ignition winding, and with a cardboard spacer between it and the plastic bobbin. You can just about see it in the first picture, though you are viewing it edge-on. It's not riveted to anything and literally fell off when I straightened the bent over laminations.

If you can post a photo of the later 500 stator I'll be most interested to see it.

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Hi Mark,

I have just been looking at used 500 stators on eBay and sure enough they are exactly as you describe. It is visibly wound with MUCH thicker wire than mine, probably something like 1.2mm at a guess. I can see two yellow wires, a green and a white, so there is no centre tap and from what I can see, just a single winding on each coil. I can also see that adjacent coils are wound in opposite directions. Hmm!

Well I guess the white earth wire was added at some time to improve the return path for the ignition winding so I'm not bothered about that. But I am worried about the obvious changes to the laminated core. I can only assume that was to improve magnetic coupling through the core, but the steel plate doesn't go inside the coils (at least I don't think it does) and it is cut to avoid the ignition winding. Not sure how much difference it would have made, but they must have considered it worth doing even though it's a bit of a bodge! Just to complete the picture, I would be obliged if you could count the laminations on your stator. Counting from the mounting plate side, mine has 2, then a thick one and then 22 more. The thick one is 2.5mm and the whole stack is 14.5mm.

Well I suppose I've nothing to lose if I soldier on as planned. I'd love to know how many turns there are on those later coils though! I have some 1.0mm wire on order, I'll see what that looks like compared to the pictures on eBay and if it still looks a bit thin I might buy a reel of something thicker. Fingers crossed!

Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
huub
Posts: 194
Joined: 24 Jul 2006 15:11

Re: 500W alternator stator (again)

Post by huub »

i have been looking for a replacement stator for morini's, ended up with a aprillia scooter stator that just slots into the morini, only to find out the aprilia uses a six magnet rotor.
i'm still looking for a replacement, the diameter of the stator is pretty standard, and scooter parts are cheap.
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: 500W alternator stator (again)

Post by mbmm350s »

Early 350 and 500 stator compared.
https://photos.app.goo.gl/HswU6NDyZkgft6vn7

Later 350 stator K, K1 and K2 is more like 500 stator but with centre tap red wire.

Mark
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Thanks for the comments and the photos of 350 vs 500 stators. Mine certainly looks more like the later model 350 version - maybe that was fitted to the early 500s, I don't know. I used to have a 1986 K2 and I do remember that had a centre tapped stator. I may well have a photo somewhere, I'll have a look.

I'm away now for a few days, but hopefully there will be some progress by the end of next week. Watch this space!

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

Well. I have re-wound the coils with 30 turns of 1mm wire on each and re-assembled the stator back on the bike. I can't start the engine at the moment because I haven't yet fitted the new ignition system, so the best I could do was take the plugs out and spin it over with a drill. I reckon it was managing about 200rpm at best and the alternator was producing 3.9 volts rms. I know the voltage is proportional to the revs, but I don't know the actual relationship. Using the kick start with the meter set to hold the max reading, I was seeing about 2v, so very roughly, doubling the rpm was doubling the volts, at least in that low revs area. I will have to have the engine running to really understand this.

Winding the coils and getting them in phase was quite difficult - very easy to make a mistake! Before I reassemble it completely I shall temporarily attach wires to just one coil to check the volts and make sure it is about one sixth of the total. That's how unsure I am of my interconnections!

Anyway, comments and suggestions gratefully received!

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
penman
Posts: 325
Joined: 08 Mar 2016 09:20
Location: Milton Keynes, UK
Location: Milton Keynes

Re: 500W alternator stator (again)

Post by penman »

First of all, I'm sorry this update has been so slow coming!

Well with the stator wound at 30 turns per coil, 6 coils is producing about 30 volts at 4000 rpm - that is rms voltage, measured open circuit. That fell to just a few volts at idle speed, so I felt it was not enough and decided to do another re-wind. As I mentioned before, it is quite difficult to wind and interconnect the 6 coils so that adjacent coils are wound in opposite directions. This is necessary to ensure that as the magnets rotate, the coils are all in phase. So for my next attempt, I wound the coils in situ with one continuous wire. That was a lot easier - if you have just wound a coil clockwise, the next will be anti-clockwise and so on. This time I put 40 turns on each coil, which then gave about 40 volts open circuit at 5000 rpm.

This time I connected up a single phase rectifier/regulator and with the headlight on, the battery was maintaining 14.4v at about 3500 rpm. Connecting extra load soon brought the voltage down though and I would estimate it was only producing about 60 watts. A bit disappointing, but if necessary it'll just about do.

Ideally, I would like to put another 20 turns on each coil, but I don't think I can fit that in, at least not with 1mm wire. It will probably fit OK on the tall bobbins, but not on the short ones. This is partly because of the space taken by the wire, but also because it is so difficult to wind it neatly with such thick wire and you end up with a lot of wasted space. I'll give some thought to what I do next.

Regards,
Joe.
1984 Moto Guzzi V65
1969 Honda CB450
1975 Triumph T160 Trident
2019 BMW F750GS Sport
1978 Morini 500
Post Reply