Odd stator readings.

[Guest]

Hi. I have a 81 GS650GT UK spec shaft driven and it will not charge the battery.

With the the stator disconnected I get a reading of 0.6ohms across each winding with no reading between the windings and ground. With the stator disconnected and the engine running at approx 5000rpm I get about 68vac. So far so good.

With a brand new 3phase 25amp regulator fitted the output voltage is 10v dc at tickover and 5v dc at 3000 rpm??? And this is with no load, I am confused.

Can anyone help please?

Andrew

[UK-GT]

DMM for a start then got out old faithful, a proper AVO8 meter. Its weird, so I got out a 5amp bridge rectifier and connected it across one of the stator windings, about 45-50vdc at about 4000rpm, tried a different phase, nothing , then remembered to turn the lights on (as one of the phases is wired through the light switch), got about the same readings, all looked ok.

Then got a 15vac transformer and connected it up to the same bridge rectifier and got about 16vdc no load, as expected, then connected the transformer to the bikes rectifier and got about 5vdc again, WTF.

The new regulator was from 'Brooks-Barn' and is described as "SUZUKI GS850G, 80-81 regulator/rectifier THREE PHASE 25 AMP 5 wire" and as far as I can tell it is the same one used in whole GS range from that era.

Just connected an old indicator across the output of the new rectifier as well as the dmm, about 10vdc at tickover and about 5vdc when revved, the voltage went down when revved and not up!!!!!

[posplayr]

You should not test the r/r with it disconnected from the battery. Can you do a Quick Test (see link below)and post the results. If you fail the first part the you need to get the battery charged.

There is also a link for gs charging system health. You need to reconnect that r/r.

[UK-GT]

The battery has been on charge for a couple of hours. When I got home from a 60mile ride this morning I turned the bike off, then went back to it later to go to the shops and the battery was flat, I put my ddm across the battery and got just under 11v.

Just checked the voltage 12.75 with ignition on. Started fine, still 12.75v running, revved engine and voltage went down?

[posplayr]

The battery has been on charge for a couple of hours. When I got home from a 60mile ride this morning I turned the bike off, then went back to it later to go to the shops and the battery was flat, I put my ddm across the battery and got just under 11v.

Just checked the voltage 12.75 with ignition on. Started fine, still 12.75v running, revved engine and voltage went down?

Voltage went down to what??? I'm purely guessing but you have very poor connection between battery and harness. Revised phase a tests can confirm.

I also have never seen a Moro battery hold 12.75v with the key on. Is that with lights? Test should be done that way.

[posplayr]

At least the way your shunt r/r works is ghat if there is no load connected then the voltage quickly climbs about the regulator set point at shove time the regulator shunts the windings usually making it and the stator very warm.
Series r/r like the compufire and SH-775 given the same situation will just open as they don't short stators

[UK-GT]

Completely re-wired charging circuit and took the light switch out of the equation, I always ride with my lights on anyway. Rectifier now has new earth point by the side if the fuse board. New 4way Tyco connector for the rectifier, need to do a little more tidying but I will do that after I have used it a few times to make sure everything is ok. The only Suzuki wire left is from the power connector to a new soldered join and then 2.5mm cable to the new connector and then onto the rectifier.

Results so far are looking promising:
Ignition on + lights on 12.18v
Ticking over at 1000 rpm with lights on 12.7v
As above lights off 13.5v
2000 rpm 14.3v
4000 rpm 14.5v

I think I have fixed it, but not totally sure what was wrong, earth, one of many joins, light switch etc.........who knows!!

[posplayr]

Completely re-wired charging circuit and took the light switch out of the equation, I always ride with my lights on anyway. Rectifier now has new earth point by the side if the fuse board. New 4way Tyco connector for the rectifier, need to do a little more tidying but I will do that after I have used it a few times to make sure everything is ok. The only Suzuki wire left is from the power connector to a new soldered join and then 2.5mm cable to the new connector and then onto the rectifier.

Results so far are looking promising:
Ignition on + lights on 12.18v
Ticking over at 1000 rpm with lights on 12.7v
As above lights off 13.5v
2000 rpm 14.3v
4000 rpm 14.5v

I think I have fixed it, but not totally sure what was wrong, earth, one of many joins, light switch etc.........who knows!!

Your quick test looks good, but I would also do the revised Phase A tests to insure that the voltage drops are below 0.2V.

How much resistance does it take to get a 1 volt drop when you are pushing 10 amps?

The answer is 0.1 ohms.

On most peoples DVM that is 1 LSB.

so it only takes 0.5 ohms to drop 5 volts.

And if you think you are confused, think about that shunt R/R. It gets confused and shorts all the stator windings resulting in the inevitable death of itself and the stator.

That is the predominate mode of failure for most charging systems.