New Stator(s) - No Charge

[JT-NZ]

My 1979 GS750 was charging a little low. I could get no more than 13.2 volts out of it, so I did the normal tests including measuring the stator's output (original Suzuki stator). The DC voltage output was a little low as I couldn't get any more than 55 VDC regardless of the engine revs. The battery and RR (new) both checked out ok so I decided to renew the aging stator. The first replacement only put out a max of 13 VDC, measured directly from all three phases. The supplier refunded me on the basis that it was faulty.
I have just fitted another new stator (different manufacturer) and this is even worse with a max output of 11 VDC !
I haven't changed anything else in the system - only the stators. The rotor seems fine and has plenty of magnetic pull when I put the stator cover back on.
Surely, I can't have two faulty new stators.
Any thoughts ?

 

[Redman]

///////////QUOTE
..................................out a max of 13 VDC, measured directly from all three phases.
///////////EndQUOTE

When measuring voltage output of stator should be 60 or 70 voltsAC (each pair of two wires, three readings).... AC.... meter on AC volts.

 

[Redman]

Make sure you specifed was a 1979 model.
79 and prior were 12 pole stators.
80 and after are 18 pole stators.

 

[JT-NZ]

Oops - should have stated AC volts and not DC. Definitely only getting 11 AC volts.
Stator is definitely for a 77-79 GS750.

 

[JT-NZ]

Redman - I went and checked the number of poles. Both replacement stators have 18 so I think you are on to something.
Even though the supplier states they fit 77-79 models, perhaps they are selling these wrongly thinking they will work on pre-1980 models ?
Thank you - JT

 

[Grimly]

Redman - I went and checked the number of poles. Both replacement stators have 18 so I think you are on to something.
Even though the supplier states they fit 77-79 models, perhaps they are selling these wrongly thinking they will work on pre-1980 models ?
Thank you - JT

That's it exactly. The fact of the 12-pole existence seems to have been forgotten by suppliers.
However, there are a couple of them around, I spotted in the last couple of years. Whether they're still around is another story - you'll have to look.
Otoh, I think you can fit the later 18-pole rotor and stator from the GS850 (from 1980 onwards) to the earlier 750 engine, as the 850 was basically a bored-out 750 and it's highly likely the crank end and rotor are the same.
Note - I'm not saying that this is definitely the case - you need to find someone who's done it or have access to a bike breaker who will effectively lend you the parts for sizing up.

 

[JT-NZ]

Thanks Grimly. I found a new 12 pole unit with good reviews so I've gone with that.
Should be able to sell the 18 pole units (one of which was refunded anyhow) so won't be out of pocket.

 

[Redman]

. . . . . . . . .. I found a new 12 pole unit with good reviews so I've gone with that.
. . . . . . .

Glad I could help.

ANy update ?

 

[JT-NZ]

Still waiting for the unit to arrive. I'm in New Zealand and it only needs to come across the Pacific ocean from California.
It's estimated to arrive in 8 days time, so that will mean it's taken more than a month to get here.
Could have rowed over in a boat and picked it up.

 

[Nessism]

Be sure to rewire the charging system, removing the stator loop going up to the hand control.

 

[srsupertrap]

Be sure to rewire the charging system, removing the stator loop going up to the hand control.

Ed, May want to provide JT-NZ a link to the thread about removing the stator loop going up to the hand control.

JT-NZ Does your GS750 still have the OEM Denso Regulator and separate Denso Rectifier, or has the PO installed a single R&R unit?

 

[JT-NZ]

The bike has a new separate R/R and the stator loop is not plugged in.
Does it need to be physically removed ?

 

[srsupertrap]

I will assume you have a 5 wire R/R installed. If that is true, you likely connected the three stator phases directly to the three inputs rec/rec, which means no stator output passes though the light. No other action required.

We don't know what brand R/R you installed but most agree a used SH775 is the best cost effective R/R for our GS models.

 

[JT-NZ]

Ok, thank you.
Didn't use a SH775 but it is a 5 wire with the three stator phases plugged in to it.