RR question on kz750ltd w/ upgraded battery

koolaid_kid wrote: The biggest difference between the MOSFET and the series R/Rs is heat. The MOSFET will generate much more heat in the stator because the stator continues to run full tilt. The series R/R turns the stator off, saving your stator life.
This issue has been beaten to death over on GSR so I will not repeat all the technical details. If you want to know more, just visit there and look for threads started by posplayr.

Hi George,
I thought the stator makes power any time it spins. No way to stop it because the magnets generate the electrical field? My understanding is that with a shunting R/R any EXCESS power not consumed by the bike proper gets shunted back to the stator. That's the problem. The shunted current increases stator temp and can burn it up. The series R/R doesn't shunt current back to the stator, thus the stator lives longer. Not sure what happens to the extra power though. Turned to heat in the R/R? Power's got to go somewhere.

This is from a Super Hawk forum, very informative. Here is the meat of the thread but the entire thread can be found HERE

"What is the difference between a thyristor and a MOSFET based R/R?

The switches in the Regulator part are either type, but they both do the same thing... The rapidly turn on and off, shortcircuiting power to ground to keep voltage constant... That's called "Shunting", and almost every type of bike R/R used now is made this way...

Every time you short circuit something, it creates heat, just from the short circuit... That's the same for both types... But, the difference is in how you switch!

On a thyristor based R/R the most heat isn't from the shortcircuit, it's from the switching... A thyristor is basically a diode with a separate leg, acting as a switch... But the switch has a delay... The thyristor relies on the current flowing through it, to keep it open...

Basically the switch opens the door a crack, and then waits for the current to crash into the door, slamming it open... Closing it is similar... You slowly, slowly push the door closed enough until the current looses power and cant hold the door open, slamming it shut...

As a result, the thyristor is horribly inexact and inefficient... It takes time to switch, and it creates huge amounts of heat while doing it...

The MOSFET is a bit more intelligent... It doesn't rely on the current for opening the door, and it doesn't try to close it slowly... Instead the switch is really a switch... Switching it on means it starts to conduct fast, and switching it off means it stops almost as fast... That creates a lot less heat, and makes it more exact... A lot more exact..."

"

Ed, you are correct. I should have worded it more like "it turns off the return, or shunt, back to the stator,which causes the rise in heat". Jim is the one who did all the research and reporting on them when he was promoting the HD Compufire units.
I would never claim to be an expert on them, but his research and data proved beyond a shadow of a doubt that the series regulators were better, even better than the MOSFET shunt regulators. IIRC, he even supplied circuit diagrams of the differences. He also reported differences in temperatures in all that data.
All regulators shunt the power back to the stator except the series ones. Again, you would have to track down his data, which does prove it is a superior design. And the only series R/Rs that he found were the Compufire units and the one Polaris SH-775 unit. All others were shunt.

It's not an issue of whether a shunt or series design would be better for the stator or not, I don't think anyone would ever argue that. Series pass regulators are obviously more efficient from the stator's standpoint since they only let the stator generate the necessary current when it's needed. when not needed it essentially turn off the stator.

Stators only generate current when they have a path to do so. The series regulator, by being in series with the stator path, can turn off the stator.

Why would anyone use mosfets for a shunt regulator? SCR's are cheap and have shown they work for decades. We won't even know what the mosfet regulator's track record will be for another 20 or 30 years compared to SCR regulators.

Don't have an answer to your question, loudvhx. R/Rs are a HUGE issue on the GSR site because a poor design causes massive failures in the charging systems on GS bikes. Not so with KZ bikes, AFAIK. I got into this discussion with posplayr. He attempted to tell me that KZs MUST have the same issues, and refused to believe that I never had an issue with either one I owned.

Yeah, the only regulators I've had problems with on KZ's were nearly 30 years old, unless someone tried to jumpstart from a running car. But Honda's seem to spit them out like a kid eating broccoli. I think the same companies make them for both companies, so maybe it's some issue outside of the charging system.

George knows GS charging systems, he actually rewound his own GS1100 stator :woohoo: