Burning through regulators

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Mittons
Cucciolo - the Lil Pup
Posts: 5
Joined: Sun Jul 14, 2024 11:53 pm

Burning through regulators

Post by Mittons »

Hi All,

Hoping someone can give a litle advice. I have recently installed an st2 rotor and electronic ignition and something seems to be wrong as i have damaged 2 regulators. They start out fine at around 14.2v then after running for a while they spike to 18.2v. Any help would be greatly apprecieated.

Mick.
Mittons
Cucciolo - the Lil Pup
Posts: 5
Joined: Sun Jul 14, 2024 11:53 pm

Re: Burning through regulators

Post by Mittons »

Hi Guys,

So I realise that my post is a bit vague so I’ll try and explain in a bit more detail.
I have a fairly new to me 1974 gt750. When I received the bike I decided to go through the new bike document that Steve has made available for us. I also installed an electronic ignition and happened to get an ST2 rotor at a reasonable cost and installed that as well.
When I installed the rotor I observed that the stator had two wires connected to the winding and the red wire was connected to ground under one of the stator fixing screws. Does this sound correct? When I had everything back together and went through the tuning process I got the bike running really well however the charge voltage from the regulator would be steady at 13.6 to 14.6 depending on revs and then spike to 18v after running for a while.
I figured the regulator must have failed and replaced it but the same thing happened. I have tested the AC volts coming from the stator and got 11-12vac at idl and around 25-30vac at 3000 rpm. Does this sound a little low?

Any help would be greatly appreciated.

Cheers,

Mick.
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BevHevSteve
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Re: Burning through regulators

Post by BevHevSteve »

all 3 wires should be connected directly to the stator. IF you have the right stator then there would be 3 posts sticking out that the wires connect to.
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wdietz186
Cagiva Alazzura
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Re: Burning through regulators

Post by wdietz186 »

I did much the same on my 750, ST2 rotor and a modern single phase regulator. The 750/early 860 had a different alternator stator than the later 200 watt alternator. The red wire was what they called a center tap and had something to do with the rectifier curcuit [1/2 or 1/4 wave] and the internal componentry of the rectifier. It is mostly explained a few posts down in this section "Wiring Tri Spark Regulator on 750 GT". The later [modern] reg/rectifiers are configured to not need the center tap, only need the AC voltage from the two yellows. Remove/or isolate the red wire from the alternator lead. I did that on mine and the output is good and stable at 13.8 to 14.5v. Sick firefly light output no more!
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