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Premium Member
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Discussion Starter #1
Hi Gang,

I've got some charging issues on my 1997 748, so I'd like to methodically test everything in the charging circuit, beginning with the stator.
This bike has a single phase (2-wire) charging circuit.
I'm aware of the ElectroSport fault finding guide:

http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf

This guide seems to be written for three phase charging systems, but I'm sure most of the procedures are the same.
In any event, I'm looking for a sanity check so I don't waste time and money on this issue if I don't need to!


Here's the deal:

Let's call the two yellow stator wires 'lead A' and 'lead B'.
Let's call the battery negative terminal 'GND'.

With my meter on AC volts, here's what I measure at three places (with the engine at 4000 RPM):

lead A to lead B - 50 VAC
lead A to GND - 48 VAC
lead B to GND - 1 VAC

With my meter set to measure continuity, I test the following:

lead A to lead B - continuity? yes
lead A to GND - continuity? yes
lead B to GND - continuity? yes

This has me concerned, as I did not expect there to be continuity between either of the stator leads to GND!
In fact, I tested the stator on a spare engine I've got, and there was no continuity beween any of the stator leads and the GND lug on the engine.

At this point, I suspect there is a short in my stator. What do you think?

:(
 

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Old Wizard
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3,006 Posts
Lead A should have continuity with lead B (about 0.3 ohms.) Neither stator lead should have continuity with ground, so you've got a short or bad insulation.
 

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5 Posts
+1 there shouldn't be a path to ground. since you have one the power is grounding out instead of going to the rest of the system.
 

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Premium Member
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Discussion Starter #4
Rats....it looks like I need another stator. On the bright side, that will give me an opportunity
to rewire the leads of the replacement stator all the way to the internal lugs! ;)
 

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Premium Member
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1,087 Posts
Discussion Starter #5
Well, I removed my existing stator and I can see exactly where the short occured...there is a big burn mark on the coil.

My replacement stator is in hand, and I'd like to replace the two undersized leads before installing it.
I'd like to replace the leads entirely, including inside the cover all the way to the lugs on the stator.
We've got some 12 gage PVC jacketed 'Machine Tool Wire' here at the office that I'd like to use for the job:

http://www.generalcable.com/NR/rdonlyres/64684582-E6C4-4224-A515-AFB2072FD67F/0/76502.pdf


Is it adequate, or should I search for something better?
The temperature rating has me a bit concerned, as does the oil resistance of the PVC jacket...

:confused:
 

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Old Wizard
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3,006 Posts
12 Gauge PVC insulated wire is good to use given the current carried and the environment that it sees. PVC is what's on the replacement stator. It's resistant to motor oil.

http://www.perspex.co.uk/documents/technical/chemical-resistance/PVC.pdf

The main issue with replacing the stator wires is to reduce the electrical heating from the 30+ amp current they have to carry. A different aspect of this is that any in-line connector becomes a hot spot because, as corrosion occurs, that causes the connector resistance to increase and the heat generated to increase in this region. This damages the connector (melts the plastic ones) and overheats a few inches of wire both sides of the connector.

It's essential that the stator-to-regulator in-line connector be eliminated to avoid future problems, on ALL bikes I might add.. See this the excellent solution by davyj below.

Any wire, no matter what size, has resistance (so many ohms per foot) so any wire will heat up. Obviously the larger the wire, the less resistance it will have to current flow, and the less heating that will occur for a given current.

Different materials have different temperature allowables for continuous operation. For example for 10 gauge (AWG) wire in 30ºC (86ºF) free air:

55A will heat high density polypropylene to 90ºC allowable
58A will heat Polyvinyl Chloride (PVC) insulation to 105ºC (220°F) allowable
75A will heat Kapton, Teflon, and Silicone insulation to 200ºC allowable

(Stator wires see 30-40A.)
 

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Premium Member
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Discussion Starter #7
Hi Shazaam,

Thanks for the information! I'll give the MTW a shot....
 

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Shazaam, I'm curious why you think the terminal block you show in your picture is better than another type of connector? The terminal block is a connector as well... It has plated metal innards that corrode just as easily (depending on the type, thickness and application quality of the plating) as another connector. The difference is where the corrosion would probably be. Since you're not soldering the wires to the connector body (and thus making the joint gas-tight), you can get corrosion in two spots - between the metal in the terminal block and the end of the wires going into it on both sides of the block. A standard connector would get corrosion where the two mating portions of the connector joined together. Additionally the terminal block is not designed to be on a vehicle - it has no provision for sealing out moisture. So unless you go to a lot of effort to seal it up with RTV or whatever, it's probably going to corrode faster than an automotive style connector.

I guess the terminal block is a lot easier to replace when it does go bad than a stock style connector...
 

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Old Wizard
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3,006 Posts
My first choice is always to eliminate the connector entirely, but if you want to be able to remove the regulator, the terminal block type of connection would over time assure a better mechanical and electrical connection than a slip together fitting. Neither type will be sealed against moisture or be corrosion free.
 

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Premium Member
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Discussion Starter #10
Hi Gang,

My stator rewiring project turned out well, but I had to compromise a bit on the wire size.

The wiring at the solder lugs inside the case was discolored, brittle, and fragile....so I removed it all.
Each solder lug has a thru hole to accept the flying leads. This hole was too small to accept 12 gage
wire, so I settled on 14 gage. In addition, it would have been difficult to get two 12 gage leads through
the existing grommet in side of the case.

I fashioned two leads and soldered them to the lugs:







A bit of heatshrink and a few tie wraps were added for strain relief:





And the assembly was reinstalled into the case:





I left the leads extra long so I can relocate the rectifier if I choose to. While I would have liked to use
a larger gage wire, the 14 gage is about two sizes larger than stock. Also, the wires are not jammed
together in a common jacket like the original setup! Once installed on the bike, I will solder the leads
to the rectifier to eliminate the connector.

With any luck, this will be a lasting repair that will perform better than the factory setup!

:)
 

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Holy crap Mike, this stuff sounds and looks complicated! :)
 

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Premium Member
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1,087 Posts
Discussion Starter #12
The stator has been reinstalled, and it is working like a charm!
To complete the project, I also replaced the rectifier/regulator with a new one from ElectroSport.
I eliminated the connecton between the two by splicing and soldering the wires directly.

Hopefully this repair lasts a good long while... ;)
 
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