Low charging at idle

[Mmoto]

Greetings!
 

I have a 79’ GS1000 with a new Yuasa battery, Dyna ignition and coils. It runs perfectly but I recently tested the charging system and the volts seem to be low at idle. At idle with the headlight fuse removed it is 12.5+ volts, with no throttle applied it will slowly raise to 12.57 12.58 12.59. When the headlight fuse is replaced the volts drop to 12.38 and will slowly decrease to 12.37 12.36 12.35. 
 

With throttle applied the volts will increase and nearly reach 13v. 
 

The diodes have been tested and all test good with continuity only in one direction. The AC volts from the stator are 40v+ and increase with throttle to 50+

I’m afraid the battery will deplete if the bike sits at idle for too long and not replenish its volts. 
 

I’m thinking about installing low draw LED headlight and taillight bulbs. Thoughts?
 

Thank you! 

Edited January 15, 2023 by Mmoto
Typo

[Gixer1460]

Forget the lights, your reg / rectifier is goosed and needs replacing. The AC voltage from the Genny looks low - don't know what the spec should be - needs checking!

[Mmoto]

Thanks, I believe it does has a separate regulator and rectifier. The rectifier diodes tested good and it doesn’t over charge when revved. 

Edited January 15, 2023 by Mmoto
Typo

[TonyGee]

I don't think a healthy battery will deplete at idle, your not at idle for long enough normally,  but worth checking all the connections from the genny up, its an old bike/harness so won't be perfect, also check you have good earths.  the charging is a bit on the low side. 

[Mmoto]

Thanks Tony, I’ll re-check the ground and make sure there’s no resistance there. I’ve replaced the bullet connectors as they were certainly corroded. 

[Gixer1460]

12 hours ago, Mmoto said:

Thanks, I believe it does has a separate regulator and rectifier. The rectifier diodes tested good and it doesn’t over charge when revved. 

Its not a case of 'over charging when revved' - its barely charging at all!

At idle it should be 13+v and above 3000rpm around 14.2 - 14.6v! If the RR checks out ok then the genny is suspect - as said AC output looks low.

[gs7_11]

What he said.

If you've still got the original separate regulator and rectifier, bin them and get a modern unit such as an Electrex.

Also delete the switching loop that goes through the headlamp switch.

Check out the stator papers on the GS resources forum.

 

 

[Mmoto]

You guys nailed it! I was only checking AC on two legs, I didn’t check it on the third leg (green/white wire) that goes to the headlight switch. AC volts tested 40v, 40v and 10v. Pulled the stator cover and what do you know, fried stator. I’ll match a modern reg/rec with a new stator and bypass the headlight charge wire. 

[TonyGee]

yuck !!!!  a new one will make a difference   when i got my GSX1100 it wasn't charging very good so checked my genny and it was like new ????  not bad for an over 40 year old, turned out to be the reg/rec and plenty of dodgy connectors. so treated it to an AGM battery and an upgrade on the reg/rec plus a bypass of that silly headlight wire   charges perfect now  

[Mmoto]

New stator and regulator installed and charges great! 

[gs7_11]

That was quick!

The regulator looks quite small.....is it a combined reg/rec?

[johnr]

On 1/16/2023 at 2:27 PM, gs7_11 said:

What he said.

If you've still got the original separate regulator and rectifier, bin them and get a modern unit such as an Electrex.

Also delete the switching loop that goes through the headlamp switch.

Check out the stator papers on the GS resources forum.

 

 

this, do this!!!!