Why you should or shouldn't fit a PMA stator conversion…
Another fad we keep hearing about, mainly on the interwebs, is the PMA (Permanent Magnet Alternator) conversion for XS650's. So, this little article will help you decide whether it's a good idea.
The stock XS650 has an EM stator (Electro Magnetic). This system is actually very good and is also the type fitted to all the old Honda fours. The troublesome CB350 twin charging system was a PMA, so that tells you that either system can be bad if it's not in good working order. Most people go for PMA systems because they think the original is crap. This is not true... it just needs to be made good again.
If an XS650's charging system is a good working order, it is arguably a better system than a PMA, as a PMA's regulator is constantly dumping power because it is charging all the time. This can cause the regulators to burn out often (like many sport bikes do that are made today).
An EM system regulates the power to the electro magnet thousands of times a second to regulate the power coming out of the stator, instead of dumping unused power. The main difference between the two systems is that a PMA can run without a battery (although a large capacitor is needed, otherwise known as a 'battery eliminator') and an EM system can't, because it needs power to make the magnet magnetize. In other words with an EM system, no power = no charging system.
If you like stable, non-flickering lights and turn signals at idle... it's better to have a battery regardless of what system. So, below I have listed the advantages and disadvantages of both systems.
1. A battery-less bike.
2. Simple and easy to wire in.
1. Burns out regulators more often (partly because most new aftermarket regulators are garbage, except for Oregon Cycle Supply... his ones are great).
2. Loss of timing marks, which is a major down side.
3. Extra weight on the end of the crank, which robs a small amount of power and throttle response, but gains a small amount of torque.
4. Running battery-less gives you flickering lights at idle, no electric start and you have to kick the bike quickly to get enough power to spark (unless you have a good battery eliminator... which you can also get at Oregon Cycle Supply)
Stock EM system pros:
1. Very reliable and does not eat regulators (NOTE: Any of the Electrosport units, like Mikes XS sells are probably not going to work out the box, go for an Oregon Cycle Supply unit. It will work and they are adjustable).
2. Lighter weight on the end of the crank (see above).
3. Keeps stock timing marks.
Stock EM system cons:
1. Slightly more complex to wire and brushes need occasional replacement.
2. Rotors sometimes break down internally, but then again... so does any type of stator.
3. Will not work without a charged battery.
So, now you have all the information you need to make a decision... and not be swayed by all the forum stuff.