Rectifier, Alternator Only Work At Over 65MPH

I have determined that my charging system only works when I'm going fast. The battery is new. (5 days old.)

The charging system is draining the battery when parked. I drove 80 miles at speeds over 65mph on Sunday after I installed the new battery and replaced a few burned wires, and the fuse box with parts from a KZ750.

On Monday I drove it to work at Hwy speed except when traffic got thick. When I had to slow down it began to misfire. After work the battery was dead.

I got my truck and charged it for about an hour. Because of the route I could only go 45MPH for the first 5 minutes. The bike died. I charged it for another 45 minutes and was able to get right on the highway and bring it up to 70MPH right away. I had to pause at 3 lights on the way, but it was after I had gone several minutes at Hwy speed. I made it all the way home(15 or 20 minutes away).

Does this sound like it is a problem with the Alternator or is it more likely to be the rectifier going bad?

Post edited by: idkrash, at: 2007/05/08 15:49

sounds like it is only charging at high rpms, nothing to do with your speed. I'd look at your alternator(stator).Get a multimeter and find out the specs, its pretty simple process if you have the manual.

idkrash wrote:

The battery is new. (5 days old.)

The charging system is draining the battery when parked. . . after I installed the new battery and replaced a few burned wires, and the fuse box with parts from a KZ750.

I guess more information would help here.

Replaced "burned wires" and "fuse box."

Just a few.

Which wires and fuses were replaced?

Do you know what caused your meltdown?

Do you have a wiring schematic?

How many wires come off your alternator?

Maybe there is still an open in the circuit somewhere.

Or a short.

Or both.

With a multimeter, you can test battery draw with the key off.

I'm guessing You have a burned(or broken) wire coming directly off of the alternator.All signs are there...to Me anyway.
Does Anyone know if the GPZ 750 uses the 3-phase system like the KZ's?
If they do,then I would bet My money that the problem is right in there with the wires coming from the alternator.:whistle:

i may have the same issue, and since im at work and not near my bike, where is the stator?

boomboom45 wrote:

i may have the same issue, and since im at work and not near my bike, where is the stator?

Sitting on Your bike,it will be on the left side of the engine...towards the front,and behind the cover.

got it, now i need to test everything.

Hi, I'm back (Twins Game, pulled calf muscled push starting bike, spent a day at the Dr., other stuff)

It seems that the alternator is the popular culprit so I will focus on that. I will post test results this weekend.

The 1982 GPz750 is aka KZ750-R1. My pulled parts are from a 1982 LTD750 aka KZ750-H3 (not an exact match). My weekdays are pretty busy, so I have not done any multimeter test yet, but I will be doing that tomorrow, Saturday.

Alternator: Three-phase AC.
Rated output 17A@8,000 rpm, 14V
Voltage regulator: Short-circuit type

The wire diagram shows 3 yellow wires coming off the alternator going to the regulator/rectifier.

The regulator/rectifier has a brown wire going to the Rear Brake light switch split to the Reserve lighting indicator. A black wire that becomes black and yellow and goes to the IC ignitor, Horn button, indicator array, NEG battery terminal, and tail lights. AND a RED/WHITE wire that goes to the POS battery terminal. I suppose this one charges the battery.

The red/white wire coming from the Reg/Rect to the pos. batt. term. joins 2 red/white wires that go to the electrical accessory leads (I have no accessories can I disconnect these with out causing problems?), and 1 red/white wire that goes to the 20A MAIN fuse.

I replaced the stock fuse box with the fuse box from the LTD. I think the fuse box burned up (melted box, browned wire insulation near fuse holders), because of irregular power comming from the alternator. It holds the 20A MAIN, 10A Reserve Lighting Device, 10A Ignition Switch (the brown wires from the 10A fuses join and connect to various lighting switches and lights, and the ignition switch.

I have a Stator Ring that I pulled from the 1982 LTD (Rated output 17A@10,000 rpm, 14V) If this fits will it cause the bike to run in a grossly irregular manner or can I get by with it? I'm ok with getting by.

The book says that the stator may short, or lose rotor magnetism. I've looked on the Old Bike Barn website for Alternator parts, but they don't have them. Any suggestions?

EPILOGE

ok. The alternator stator had broken loose and was being ground up by the rotor. This apparently initiated a short that was draining the battery.

The replacement parts from the '82 LTD. It's alternator is supposed to produce a lower output than the Gpz.
LTD= 17A@10,000 rpm, 14V
versus
GPz= 17A@8,000 rpm, 14V

The Kawasaki Maintenance Manual states that the GPz should test as follows:
Charging Voltage = "About" 14.5V@4,000rpm
Alternator Output Voltage = "About" 50V@4,000rpm for each lead pairing.

I'm getting ~14.8V, and ~60V both @4,000rpm. So I'm on the high end of normal. I guess.

The red/white wire from the Regulator/Rectifier to the Battery is warm, but not hot, and not melting or browning its wire jacket. All the lights work fine and the battery is staying charged at 12.52V overnight.

ADDITIONAL INFO:
The engine on the GPz 750 produces 80hp@9,500rpm.
and torque 6.7kg-m@7,500rpm

The engine on the LTD 750 produces 74hp@9,000rpm.
and torque 6.4kg-m@7,500rpm

The LTD alternator stator looked to be the exact shape and size of the messed up one I took out.

BIG QUESTION: what initiates the different alternator output? Is it the alternator stator or is it the engine capacity.

I've been running the GPz with the LTD alternator stator for 3 days, and everyting is working great.

Good work. Happy riding!