GSXR charging system 101

GSXR charging system 101.

This information is based on the K6-k9 600/750 GSXR charging system, since that is what I have.

Most GSXRs for at least a decade before and to current models are 99% the same.

There are generally two ways to approach a charging system problem;

1. Just throw new parts at it till it works (hopefully) again or,

2. Diagnose what the actual problem is and only change what is needed.

The first method works frequently, but can be costly, may not fix the problem and each “repair” that you do has the risk of introducing other problems. i.e. damaging the stator cover by trying to pry it off, etc.

Personally, I like to know what is wrong so the correct repair can be made in an efficient, practical and economical manner.

To easily perform a good diagnosis, some system and simple electrical knowledge really helps.

THE BASICS: The good news is that this is a very simple charging system with really only three components:

#1 The stator. (and flywheel/rotor/magnet)

This is where the magic happens or at least the power is produced. If you didn’t sleep through your basic science class, you’ll remember winding a length of wire around a nail, hooking the ends of the wire to a voltmeter and seeing the needle move when a permanent magnet is passed along the winding. Pass the magnet the opposite direction, and the needle moves the opposite way. Remember that last part, it will come up again. The stator is just three coils of wire, joined to each other at the ends with a wire tapped off of each of these connection points. That is why there are three yellow wires coming out of the stator.

Delta diagram.

Yes, when you look at a stator, there are more then three coils (18 on my model stator). Not to despair, every third coil is connected in series so there are actually only three circuits.

Ricks stator. 

So we have the nail and the windings times three, where is the permanent magnet? Why, they are glued into the flywheel/rotor, mounted to the crankshaft that spins around the fixed stator which is mounted in the stator cover. You can see the shadows of the magnets on the inside of this rotor.

Rotor pic.


So we have magnets swinging past coils and the faster they pass each other, the more voltage/current the stator is capable of producing. But Houston we have a problem. As the magnets pass north south on opposite sides of the coils, they induce current first in one direction then in the opposite direction. Otherwise we have alternating current (AC) and our bike needs 14-15 volts direct current (DC). This is where the second component comes in.


#2 The R/R (Regulator/Rectifier)
This is the most complicated part of the system, the most prone to failure and the hardest to accurately test. Just as the name implies, it has two functions.

The first thing the R/R does is rectify the AC current into usable DC current. That is done through the use of diodes that act as one way valves for electricity.

As you can see, the diodes are arranged so positive voltage is always supplied to positive side of the battery/electrical system.

When the polarity changes on the coil and current wants to flow the other way? No problem, the diodes take care of that.

This happens with all three coils and when melded together, the result is a relatively smooth DC current output. The second thing the R/R does is regulate the voltage/current output to the bike.

Our bike system is different then most automotive type systems.

On the automotive side, the voltage regulator actually controls the strength of the electro magnetic field. The stronger the field, the higher the output.

On our bikes the magnetic field is permanent magnets so we can’t control the field. It is always basically wide open.

So how do we control the charging voltage? We throw the excess overboard! T

hose SCRs are actually controllable one-way electrical valves. They are controlled by the IC which is monitoring the system voltage. When the voltage gets to the correct value, the IC tells the SCRs to start shunting the excess current back to ground. Of course sending current directly to ground generates a lot of heat and that is why R/Rs run so hot.

This is not the most efficient system, but it is simple, compact and light.


#3 The wiring and connectors.

The stator plugs into one connector on the R/R and the bike harness plugs in to a second connector on the R/R. The most common problem is the connectors getting old, corroded and loose. Damaged wiring is a less common problem. Yes, that is it. Don’t make it more complicated then it is.

Next, how do we figure out if our charging system is working correctly and how to find out what’s wrong if it isn’t? (These procedures are basically right out of the service manual) It’s best to go from the easiest to more difficult tests. You will need a good, digital, Volt Ohmmeter for these tests. First, make sure your battery is in good condition and fully charged. It should be over 12.8 volts with the bike off. SYSTEM VOLTAGE CHECK Connect the voltmeter to the battery and select DC voltage measurement with at least 20 volt full scale. Start the bike and rev to 5k rpm. You should read 14.0 – 15.5 volts DC. Most bikes seem to be about 14.4 volts, slightly higher at idle. If the voltage is in the correct range, put the seat back on, nothing to see here. So what if the voltage is OVER 15.0 volts and keeps going higher if revved higher? Stop the test and replace the R/R before you ride the bike again. The R/R has failed in the over volt mode (not uncommon with the $39 Ebay/Chinese crap kits) and will boil out the battery(rotten egg, sulfur smell), blow bulbs and then fry expensive electrical components. The R/R is the only part that will cause an over volt condition. What if the voltage is lower then spec, but higher then the bike off voltage? Otherwise, there is some charge. The R/R rarely, if ever, fails at partial charge. They either go open (no charge), short out (this blows the main fuse and the bike stops) or fail in over volt mode (wide open charging). The reasonable things to check for partial charging are poor connectors or a bad winding in the stator. If the charging voltage is just below spec, the battery could be weak (high current draw) or you might have a cheap voltmeter that is off a couple of tenths of a volt (yes, I’ve seen this happen a few times). What if there is NO charge? Otherwise the battery voltage goes down when the bike is started and never rises with rpm. Again, easy stuff first. WIRING, CONNECTORS CHECK Check the wiring for obvious damage and or burned parts. This is very rare but it could happen and just takes a minute to look over the harness. Check the two connectors in and out of the R/R. The one between the R/R and the stator is prone to overheating if it gets loose or corroded.



So the wiring and the connectors are good?

STATOR CHECK The next test is to see if the stator is functioning correctly. There is no need to open the engine and look at the stator. The electrical tests will tell us what we need to know. There are three tests to prove the stator is good.

You will need to disconnect the plug between the stator and the R/R to gain access to the three wires to the stator windings.

Test #1 Resistance check. Check between each pair of wires (three pairs) for 0.2 to 1.0 ohms resistance. This will check for an open coil or internally shorted coil.

Test #2 Ground check.  As the stator diagram showed, all three coils are connected together but they are insulated from the engine.

So put one lead of the ohmmeter goes on a good engine ground and then probe each yellow wire in turn. You should not have any continuity. Otherwise infinite resistance or open circuit.

Test #3 No load stator test.  Set your voltmeter to measure at least 100v AC. Start the bike and rev to 5000 rpm. Check between each pair of wires (three pairs) for 65+ volts AC. Most say they get about 85+ volts, which is fine. ( In depth test  – How to test a stator !)

R/R CHECK There is a long and complicated process in the service manual to check the R/R. It also seems that many have done the tests, had positive results and yet the R/R was still bad. This is where the process of elimination come in. Remember there are really only three components to the charging system. If the wiring/connectors are good and the stator tests good, then it must be the R/R. It is that simple. I hope this helps.



WIRING AND CONNECTORS: As mentioned earlier, the connection plugs between the R/R and the stator are prone to over heating and failing due to corrosion and loose contacts. Finding the correct connector replacement parts can be difficult so the answer is to just cut the connectors off and splice the wires together. A crimp connector is OK, a soldered joint is better. No it does not matter which wire gets joined to which. Remember that the diodes in the rectifier will sort it out.


If you are lucky enough to have the bike totally die electrically, and the battery is good, it is likely the main fuse has blown. Suzuki put the 30A main fuse in the starter relay block. Just follow the positive wire from the battery to the first component. That is the starter relay. There should be spare fuse there also. A very common reason the main fuse will blow is that the R/R shorted out. If the fuse blows right away, unplug the R/R from the harness. If the fuse stays intact, replace the R/R. THE R/R: The replacement is pretty straight forward on most bikes. Two connectors and a few screws/bolts. They do hide the connectors on my K9 behind the frame and under the airbox. If you have a K6/9 bike, you might consider relocating the R/R from behind the radiator to keep it cooler. Do a search and you’ll find some ideas on how to do this.

THE STATOR: Replacing the stator is also a pretty straight forward job if you have average mechanical abilities.

You don’t even have to drain the oil if you tip the bike over to the right side. There are some common pitfalls.

Make sure you have all the stator cover screws removed! On the K6/K9 there is one hiding under the starter gear.

Consulting the service manual is strongly suggested. T

he magnets really hold the cover on tightly. Resist the urge to pry the cover off as you will damage the gasket surfaces. If you bike requires removing the starter gear, pay attention to how the parts, shims and washers came out so they can go back exactly the same way. Putting it back wrong will likely result in a locked up starter. Do use Loctite on the stator bolts and the little screw that holds the wire retaining bracket.

They can come loose and cause quite a bit of damage. (the correct torque for my K9 stator bolts is 8 ft/lbs. Check your service manual)

Here the stator bolts came loose and chewed up the stator and destroyed the magnets. Of course there is also lots of metal floating around the engine.




Here the little bracket screw came loose and found it’s way between the rotor and the cover. I’ve seen two of these. A drop of Loctite would have prevented this.



Do use a new stator cover gasket!

Gasket maker does not seem to work and can cause the stator to hit the rotor. The clearances are that small. A few have written in that their engine was locked up due to interference. Also, don’t forget a dab of gasket sealer at the corners of the rubber wire grommet if you don’t want an oil seep.

Watch your fingers when you go to put the stator cover back on.

Remember those strong magnets? They really snap in the cover the last 1/4 inch. If you read the manual, use good tools and take your time, the job will go smoothly. Carry on!



2 thoughts on “GSXR charging system 101

  1. Hi,

    Ive got a GSXR 750 2006/2007 model. ive replaced the stator 3 times now, the r/r is fine but still no charge… Im getting 30/33v AC out of each prope not anywhere close to the 65/60 mark…
    Is it the rotor that has lost its magnetic role?

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