Overcharging issue -recitifier?

[Big T]

My 78 GS 1000 started blowing its headlight filaments after I revived it last week.

I thought it was an age issue at 1st, but then it blew the low beam last night as I revved it up to pass someone on the freeway

So, I started testing it today.

My static reading at the AGM battery is 13.8V, which is high

So, I started it up, hooked up my Sears vom and tried to test the charging.

The voltage readings jump all over the place, flashing up 4-5 readings/ second, making it hard to determine what's going on. It goes from 11 V to 18V.

This bike has the separate regulator and rectifier. I thought the regulator was bad, so I swapped in the one from my 79 and tested - same weird results. I tested at the battery and the headlight connector to confirm the problem.

I'm in the process of swapping in a spare rectifier, so I thought I'd ask if this is more likely the problem.

Don't tell me I need a combo R/R - I'm trying to keep this original.

Plus, it has to be on the road 1st thing Saturday AM.

[posplayr]

My 78 GS 1000 started blowing its headlight filaments after I revived it last week.

I thought it was an age issue at 1st, but then it blew the low beam last night as I revved it up to pass someone on the freeway

So, I started testing it today.

My static reading at the AGM battery is 13.8V, which is high

So, I started it up, hooked up my Sears vom and tried to test the charging.

The voltage readings jump all over the place, flashing up 4-5 readings/ second, making it hard to determine what's going on. It goes from 11 V to 18V.

This bike has the separate regulator and rectifier. I thought the regulator was bad, so I swapped in the one from my 79 and tested - same weird results. I tested at the battery and the headlight connector to confirm the problem.

I'm in the process of swapping in a spare rectifier, so I thought I'd ask if this is more likely the problem.

Don't tell me I need a combo R/R - I'm trying to keep this original.

Plus, it has to be on the road 1st thing Saturday AM.

Without a scope to see , you are gonna have to guess a little, but with anything that irratic, I would assume the rectifier is going out. Can you test it with a diode tester to ensure all 6 diodes are intact. Also if the Regulator section is disconnected you should still see relatively clean DC coming out of the rectifier (even with no load).

[Big T]

Thanks Jim

To test the diodes, I look for no resistance in one direction, the switch the pos/neg and it should have lots of resistance.

hard to believe I had at least a year of physics in college (getting old)

I'm cleaning the connectors on the replacement in copper reducer right now

Off to my wiring diagram

[posplayr]

Thanks Jim

To test the diodes, I look for no resistance in one direction, the switch the pos/neg and it should have lots of resistance.

hard to believe I had at least a year of physics in college (getting old)

I'm cleaning the connectors on the replacement in copper reducer right now

Off to my wiring diagram

Yes you should be able to get continuity with black lead on the R/R(+) from each stator leg. In other words current will flow from each stator leg input to the R/R(+) output.

On the R/R(-) side do the reverse (hook the red to R/R(-) )and current should flow to each stator leg as return current.

[Big T]

Okay, I'm not getting any readings at all (no continuity) by going from the 3 stator legs to either the red (+) or the black (-) wires

Looks like all the diodes are blown (?)

[tom203]

Don't tell me I need a combo R/R - I'm trying to keep this original.

OK, I won't,but you're making your life difficult.

[Big T]

OK, I won't,but you're making your life difficult.

Yeah, because the original was so weak, it only lasted 33 years!

[posplayr]

Okay, I'm not getting any readings at all (no continuity) by going from the 3 stator legs to either the red (+) or the black (-) wires

Looks like all the diodes are blown (?)

Maybe use the diode test.

Is the battery good for the Ohm meter?

[Big T]

Hmm, replaced the VOM battery and now I'm getting readings around 50 on all 3 legs in both directions (+,_)

Is that what I should be getting as far as the amount? (50)

[posplayr]

Hmm, replaced the VOM battery and now I'm getting readings around 50 on all 3 legs in both directions (+,_)

Is that what I should be getting as far as the amount? (50)

current should only flow one way so it doesn't sound right but hard to beleive that all of the diodes (6) are not working.

[Big T]

I just went to the store and got a new 9 V battery for my meter

Got the same values on the rectifier test

Tried the bike at the headlight - got the jumping values, turned off the lights and

Still got readings

Pulled the other 9V out of the 2 pack and it shows .1 V

So, a seriously screwed up VOM.

I just should have gone to HF and bought a new one (cheaper than the 2 pack)

Grrrrr!

[tom203]

Yeah, because the original was so weak, it only lasted 33 years!

My original is still running at 30 years, but when it goes, I will replace with a Shindengen unit- it's a more reliable unit. You have better choices if you opt for a combo R/R.

[Bill Alexander]

Yeah, because the original was so weak, it only lasted 33 years!

That was how I felt until just before Easter when my stator got toasted. I decided to transfer the whole set up my donor bike had (something aftermarket with an intergated R/R) across just to make sure I wasn't risking another stator. I have also added in a digital volt meter which now sits on top of the instruments and I monitor the battery/charging all the time. The new set up is much more stable than the old one was.

[salty_monk]

I have seen this a couple of times on the smaller 750/850 (82/83 era) combo RR units. Headlight blowing seems to be the first indicator... the 2nd one is a dry battery - not sure what the third one is...!

Personally I would switch to a Combo RR unit. If you want one of the larger Suzuki units (80 era GS1000) then give me a shout, I have a couple on the shelf.

If you must ride it Saturday & there is another bike going with same size battery you could disconnect the charging system & run total loss, just swap the batteries over a couple of times during the day. Disconnect the headlight if you want to give yourself more of a run before you have to swap...

[Big T]

Update:

A couple of notes:

1. My headlight switch actually works - easy to do on 78s
2. I've done the stator output conversion so that the one leg does not run to the headlight switch and back - so all of the stator output goes to the rectifier and VR
3. I went to HF and got another VOM, cause I just couldn't believe the readings I'm getting

So, I did the following tests:

1. Rectifier output is good and steady DCV
2. Main power fuse is steady DCV
3. The other 3 fuses test result is the jumping voltage
4, Battery static -13.8V, running 14.8-15.4
5. The headlight socket has jumping voltage on both high and low

So, based upon these results, the VR and the rectifier are good. There is a problem of some kind between the main fuse and the other fuses. There are two wires and the ignition switch between the main fuse and the other fuses.

I'lll be pulling the switch next

And yeah, the SFRC season opener is tomorrow at 9 AM. I've got to get the 78 up and running for it. The only other bike I have that runs is my GPZ, but that needs new tires due to age, so I definitely do not want to ride that ion the rain.