Yamaha Banshee magneto swap

[CaptDan]

Sparx Electrical has just released their Yamaha XS650 alternator kit. Price is £200 and comes with stator/rotor, reg box, adapter ring, and nut. You can have single or 3 phase. Check with Andy Gregory [e-mail].

Sparx has been making alternator upgrade kits for older Triumphs (which were designed to run with dead/no battery). The cool thing about the Sparx kit is that it has a "button" rotor (with timing marks!) that spins inside the stator, instead of the large XS/RD/RZ/Banshee/Powerdynamo rotor that rotates outside the stator.
As much as I would like to see an OEM alternator upgrade for the 650, the Sparks unit seems to offer many positives. www.sparxelectrical.com
I'll try to get more information and relay it back...

[Burns]

I've been pondering a generator upgrade for some time and was about to go with the Bosch stuff (BMW/Guzzi) and SHAZAM two companies start marketing off the shelf bolt-on stuff. It's like the world is starting to sing to my music or something.

'bout time.

[CaptDan]

More info on the Sparx kit...
- By adding a capacitor (p/n SPX027) in line with your battery you will be able to (kick) start your XS with a weak/dead/or no battery.
- It is based on a proven design with over 5000 units sold.
- We'll want the 3 phase stator with 210 watts at 7000(?!) rpm.
- They're working on having all the info in a down-loadable format on their website soon.
Could it be that the little internal rotor would allow the 650 to rev quicker?

[Burns]

I wonder how long that capacitor will hold a charge. Probably a good idea to augment the battery but it seems pretty iffy to me for a battery-less set-up. Also, if the flywheel weight is reduced enough to allow quicker revs it will make the bike more apt to stall on take-off, and generally be less tractable at low engine speeds. That would be made worce with more cubes or higher compression. I think this motor needs all the flywheel that it was born with and maybe even a little more.

[CaptDan]

The capacitor set-up appears identical to the arrangement my 2 battery-less Triumphs had. They would always start with 1 or 2 kicks (but then they also had switched lighting).

My thought is that if these (Sparx) units have been running in all manner of Brit bikes (stocker, custom, resto) with good results, our bikes should not be all that different.

Good point on flywheel weight. British bikes historically have had lots of flywheel, so their use of an internal rotor design was probably dictated more by convenience or cost than performance.

Out of the 9 bikes I've owned, the XS650 is the first one that had a battery, and frankly, I don't like having the battery dictate whether or not the bike will start. The sooner I get rid of the battery-dependent charging system, the more confident I'll be.

[Burns]

Captdan.

Would the capacitor on your Brit bikes keep a charge for a week or more? I'd like to be battery-free to, but I'm leaning toward a mag. It seems to me that the ideal set-up would be a mag that included a spark advance mechanism with a curve optimized for the 650 and a built in regulator. That would be a bolt on solution for 90% of this bikes inherient weaknesses (ignition and charging).

[CaptDan]

With my Triumphs, I would go weeks - maybe even months - without riding them. I think the capacitor only stores its charge in-between firing cycles - just like the capacitor on older points-type cars. I think the permanent-magnet alternator generates current any time the rotor spins, so when kick-started, there is just enough juice to fill the capacitor. When triggered (by the points or electronically), the capacitor dumps its charge to the coil, and away we go! With the XS' non-PM system, the alternator only made current if the battery was 'front-loading', so-to-speak, the system with power.
I think many of the OEM "magneto" systems out there are really just PM alternators (like this Banshee).
That's my best estimation. (Did you notice now many times I wrote, "I think"?) ;D
Thanks for the back-and-forth, mburns!

[Burns]

I thought (it's catchin') that with a PM you don't need a capacitor.
Isn't the capacitor just for exiting the EM's? PM'swill make electrons flow anytime you spin 'em but with EM's it's no juice in no juice out- right?

ON points systems I think that the condensor's (a.k.a. capacitor) job is to prevent arcing at the points by taking the peak surge, it doesn't excite the coil.

I'm thinking out loud here so, anybody please feel free to disabuse me of my misunderstandings.

Did your Triumph alternators with the capacitor set-ups have PM's Captain?

[Burns]

On the distinction between alternator/generator/magnito. Doesn't a generator put out DC, a magnito is a generator with a permanant magnet and an alternator puts out AC (which is then converted to DC by a rectifer). I'm reaching a little but I think that an EM alternator's output can be regulated by reducing current to its EMs but a generator's output, which increases with speed, is regulated by shunting excess current to ground at a heat sink.

Have I got that right?

[mrriggs]

mburnsxs650 said:

On the distinction between alternator/generator/magnito. Doesn't a generator put out DC, a magnito is a generator with a permanant magnet and an alternator puts out AC (which is then converted to DC by a rectifer). I'm reaching a little but I think that an EM alternator's output can be regulated by reducing current to its EMs but a generator's output, which increases with speed, is regulated by shunting excess current to ground at a heat sink.

Have I got that right?

Yes, the term generator is typically used in DC applications and alternator for AC, but alternators are commonly refered to as generators. The word magneto is mainly used to describe a self contained permanent magnet ignition system, but permanent magnet genarators and alternators are often refered to as magnetos as well.

The AC output from an alternator is a sine wave that fluctuates positive and negative. The rectifier only flips all the negative waves up so they are positive as well. What you are left with is not DC but DC pulses. A three phase alternator spaces these pulses out evenly so they overlap. That way the voltage will be closer to DC, never falling to zero volts between pulses. The battery is typically used to smooth out the riples into true DC. If there is no battery you can use a capacitor, which is like a little battery that will hold just enough charge to fill in the gaps between alternator pulses. Without a battery or capacitor the bike can be hard to start because the ignition may be trying to fire between the pulses from the alternator when there is little to no power available. This a problem mostly seen when running a conventional ignition off a single phase charging system. This is why batteryless bikes typically run a conventional magneto ignition or CDI.

You are correct that alternators with field windings can be regulated by varing the current to the field. Permanent magnet genarators and alternators have no way to control output so the regulator has to break it down. Older systems did this by grounding out excess power but newer systems use a switching regulator. Like the name implies, it switches on and off to control voltage.

[Burns]

Excellent post Mr. Riggs. Very informative. I now understand that an alternator can have a permanant magnet and that in such a system the capacitor does not excite an EM but merely bridges the DC pulses to keep constant current to the ignition coils. Learning is a beautiful thing.

I'm still foggy on the "switching" type regulator for a DC generator with a PM though. Do they work by taking a set of windings ("phases") out of the circuit?


Since an alternator will always need a rectifier, is a DC generator the cheaper and more reliable system for low-output applications?

[mrriggs]

mburnsxs650 said:

I'm still foggy on the "switching" type regulator for a DC generator with a PM though. Do they work by taking a set of windings ("phases") out of the circuit?

Switching type regulators are used for everything but EM alternators. The concept is pretty simple, its just a switch on the rectifier outlet. Like if you took the hot lead from the rectifier and touched it to the battery until you see 14.5 volts, then pulled it away. Only the regulator does it a thousand times a second.

Since an alternator will always need a rectifier, is a DC generator the cheaper and more reliable system for low-output applications?

There is a reason you can hardly find a DC generator on anything anymore. They don't work well. They can't be spun fast because of their armature design, they don't put out much power at low speeds, and they are current limited since all curent they produce has to go through the brushes. Alternators make more power, are more durable, and cheaper to make. Even with the need for a rectifier they are still the better bet for pretty much any application.

[Burns]

I wonder. I've never had a problem on any of the thumpers or two-strokes that I've had with PM generators. I have blown a few recitifiers in various alternator equipped bikes though. Piston airplane motors use magneto ignitions.
Still, I take your point, everything BUT the thujpers seem to have alternators, there's got to be a reason.

[mrriggs]

mburnsxs650 said:

I wonder. I've never had a problem on any of the thumpers or two-strokes that I've had with PM generators. I have blown a few recitifiers in various alternator equipped bikes though. Piston airplane motors use magneto ignitions.
Still, I take your point, everything BUT the thujpers seem to have alternators, there's got to be a reason.

DC generators all have multi-pole armatures where the brushes make and break multiple connections. Alternators have "slip rings" where each brush stays connected to the same connection. Alternators can also be brushless, by spinning the magnet instead of the armature. Generators can not be brushless.



I'll bet the bikes you are refering to are not running generators, unless they were built back in the 30's. Many offroad bikes run an alternator without a rectifier. If a bike has a magneto ignition or CDI, and no battery, then all that's left for the alternator to power is the lights. They run just as well off AC power as they do off DC power.

[Burns]

Thanks, you've clarifed my thinking on this topic. My mind-set was that the PM spark-makers were generators, and that alternators would all have rectifers. So I assumed all those two-strokes and thumper four-strokes had "generators." I'll stop thinking that now thank you.