R/R Upgrade - Field Coil to Regulator?

Hey all,
Question - I own a 1976 Twin KZ750. The electrics were bust on the bike so I have performed a complete re-wire, with some simplifications as I'm taking her towards a scrambler look.

I've bought a combined R/R. I can see the three wires that connect from the stator to the regulator, and the green and red wires coming out of the R/R that connect to positive and ground respectively.

Where I am lost is what now happens to the other wires coming from the field coil that previously connected to the regulator? There are four wires coming from that part of the engine? If you are upgrading to a combined R/R what should be done with these?

Thanks!

H-BOMB

H-Bomb wrote: Where I am lost is what now happens to the other wires coming from the field coil that previously connected to the regulator? There are four wires coming from that part of the engine? If you are upgrading to a combined R/R what should be done with these?

EDIT: never mind. I'm not familiar enough with the 750 twin to comment properly.

The early 750 twins used excited-field alternators. Not only that, they used solid state regulators that controlled the ground side of the field. That makes them unique among Kz's. A plug-n-play reg/rec will need to be specifically listed for that application or it will not work.

You can re-configure the wiring to use a solid-state regulator to control the positive side of the field coil, as is done on a few other KZ's, or you can get the one from www.oregonmotorcycleparts.com for one specific to the 750 twin.

Loud, what are the advantages to that kind of system?
Steve

swest wrote: Loud, what are the advantages to that kind of system?
Steve

They operate like the alternator in your car. The rotor uses chunks of iron and wire as electromagnets unlike the permanent magnets in most bike charging systems. An external power source supplies varying amperage to the rotor's electromagnets which generates a voltage in the stator windings as the rotor rotates. Increasing/decreasing the current to the electromagnets will increase/decrease stator output.

IMO their advantage is in how they are regulated - alt only generates as much power as needed. Our permanent magnet style always outputs 100% and the regulator converts the excess to heat. I believe they can put out far more power as well (never seen a large permanent magnet alternator)

Downside is commutator or slip rings can wear out. An external power source is also required to charge the rotor.

The early 750 twins used excited-field alternators. Not only that, they used solid state regulators that controlled the ground side of the field. That makes them unique among Kz's. A plug-n-play reg/rec will need to be specifically listed for that application or it will not work.

This is very interesting, and something I have never heard before. Most field coil style alts regulate the positive side but the concept is similar.

I was also thinking it would reduce drag created by the rotor. When I had mine off the bike had noticeably more power. Race bikes don't have it for that reason so I guess my question was to confirm this.
Steve

Yes, the upside is that the alternator's power extraction from the engine is determined by the electrical load. This makes it more efficient. As a side effect of that, there is less energy wasted as heat in the alternator and rectifier/regulator. It also allows you to fit an alternator with a larger range of output in case you want to add accessories, etc. Many big touring bikes still use that type of alternator for that reason.

The Kawasaki system does not use slip rings, which is one of the failing points on car alternators and slip-ring-alternators found on some Yamahas and Hondas, which are notoriously probelmatic. The field coils tend to fail since they are vibrating and spinning at engine RPM. The Kz uses a spinning field-inverter, while the field coil, itself, stays fixed. This is far superior in reliability, but more expensive.

Regarding the 750-twin's solid state regulator: the reason it controls the ground side of the field coil, rather than the positive side (as is done on the relay-regulated version), is that an NPN transistor is used. That type was more common, and more reliable, in the 1970's (and may be even now). The type of circuit, using that type of transistor as a switch, is much simpler to design when the transistor is connected directly to ground.

Thanks for all your advice.
Could I run a standard modern comnbined R/R, and then use an original part regulator alongside it for this model. I ask because I've bought the R/R combined unit, but as your advice says it will not work, so would running an original Regulator alongside it suffice?

Thank you,
HBOMB

No offense intended, but it sounds like you are fighting a losing battle. You bought the wrong unit, so why not simply return it or if that's not possible sell it on eBay? In any case you will need the correct unit, and I highly recommend you contact the folks in the link below to determine exactly which unit you need. They make very high quality motorcycle regulators and rectifiers, and they are very familiar with the KZ750 twins, so they can tell you what's needed. Ed

www.oregonmotorcycleparts.com/vregulators.html

Yeah I think you are right - I have contacted them and they have advised on the correct part at $145.

Thanks,

What voltage regulator did you get?
You may not want to do this, but you might be able to swap the charging system components with the later type found on the 440s or 82-84 750-Twins. the 440 stator may be different (less output?). I think the electronic ignition from one of those could be swapped as well. Here's a quote:

by steel: Other than the emission ports, the motor is the same as a 78-80, but has a different charging system than the 76-77 though, and even that can be swapped. .... steell & bountyhunter are two of the more knowledgeable 750-2 owners.

The 78 and later 750 twins used 1-phase, permanent magnet alternators. At least on the diagrams I've seen. (I have one as late as 1983 West German.)