Stator phases to chassis resistance?

[t3rmin]

Well the battery stopped charging so I'm going through the stator papers troubleshooting guide.

When I got to section B (testing the stator), everything checked out except the part where you measure resistance between the three stator wires and the chassis. I get 0.9ohms between the stator wires and chassis.

I'm getting a healthy 80+ volts from all three phases of the stator, but how can that be if they're all grounding to the chassis?

I continued on through the troubleshooting process and after the diode mode test, it was obvious that the R/R was fried. It'd been getting pretty hot and one wire had melted its insulation a bit due to some bad connections (which have since been cleaned up), so that didn't surprise me.

I'm reluctant to sign the death certificate on this stator, though. I'm thinking of just getting a new R/R and seeing what happens.

Anybody else get similar stator to chassis resistance readings but good voltage, and did the stator end up working? I've seen lots of people give stator testing advice on these forums that consisted only of measuring the AC voltage output, and troubleshooting in that way has seemed to get results for several people...

[t3rmin]

Woot. Got a Honda R/R on eBay for $18.50 including shipping.

[fgh]

I don't know how you can have a short to ground and still get voltage between the leads, BUT IT DOES HAPPEN! A guy a while back had the same test results and didn't get it fixed until he replaced the stator. The Honda R/R's are the way to go. MY GS has one from a CM and its doing great. It could be the stator got the R/R, the R/R got the stator or coincidence. The bad stator will probably take out your new R/R soon. If you don't get a stator check your charge voltage and if it isn't right you should do the stator too.

[duaneage]

The stator DC resistance is around .8 - 1.0 ohm. However the stator is not a DC device, it is an AC device. When you pass a magnet wound a coil it generates AC voltage as the magnet moves. The coils have something called impedance. Impedance is a combination of resistance (.8 ohms) and reactance. But as a voltage source, the stator produced voltage, it does not use it.

Stators are voltage drive sources. The current capability comes from the high voltage and relativel low current of the stator. The voltage regulator converts the 3 pahse AC down to a much lower DC voltage but with greter current capability because there are three phases. Aircraft also use 3 phase power since it is efficent and requires smaller power supplies.

your lucky the RR did not take out the stator.

[t3rmin]

So you think the stator sounds ok? Perfect voltage and inter-phase resistance trumps apparent short to ground??? ;-)

[Boondocks]

Although the stator voltage is in the normal range with the engine running, if you are reading your meter properly it is failing the static test. With the three stator wires disconnected from the R/R and the engine not running, the resistance from each stator wire to the engine (ground) should be infinite, i.e., an open circuit with no resistance. The readings that you are getting would be OK and expected between stator wires, but not between the wires and ground.

With the low resistance readings that you are getting, it is odd that the stator voltage under load is within specs. I would double check my work to see if the meter reading is from the Ohms range and not Kilo Ohms or Mega Ohms. If the correct reading is more than 100 Ohms, the stator should be serviceable. If the correct resistance readings are less than 100 Ohms, I would replace the stator.

[Steve]

I am siding with Boondocks on this one, I think it is a case of a mis-read meter. If there is that little resistance between stator and ground, there can not possibly be enough active coil left to generate adequate voltage.

As he said (and as outlined in the Stator Papers), resistance checks from A to B, B to C, and C to A should be about 1 ohm. Resistance checks from A to ground, B to ground, and C to ground should be infinite. If there is any resistance showing there, you are not getting all you can out of your stator. Also make sure that when you are doing these checks that the three stator wires are not connected to anything except your meter.


.

[Keith Winter]

Here's a tip for testing,
Make SURE you don't touch the test probe's with your bare fingers. Most half decent ohm meters will register a slight resistance if you touch both probes at the same time with your bare finger's. My digital meters will easily register the resistance from finger to finger, and the reading will go up if your finger's are even slightly damp. Like Boondock said, from stator wires to any ground, there should be an open circuit.
Keith

[duaneage]

So you think the stator sounds ok? Perfect voltage and inter-phase resistance trumps apparent short to ground??? ;-)

In order to measure the DC resistance of a stator you have to zero the ohm meter first. Essentially you touch the leads together and either adjust for 0 ohms or else you can select a zero button ( on digitals) that will show the resistance as 0.00 ohms.

Then you can accurately measure the stator resistance. And yes, the short to ground is probably apparent but not real. The center of the stator is grounded, there has to be a reference to ground somewhere or you will not be able to generate any voltage. Each leg of the stator acts independently.

[Guy]

The center of the stator is grounded, there has to be a reference to ground somewhere or you will not be able to generate any voltage. Each leg of the stator acts independently.

More bloody nonsense to mislead people. No part of the stator is grounded. Simplest way to check if your stator is good or not is to disconnect the terminal block between the stator and the R/R. With the engine running at 4000 RPM you should get a healthy 75V AC across any pair. If it's significantly less, then you have a partial short somewhere. Simple.

[t3rmin]

Well with only $18.50 on the line, I'm going to just stick in the new R/R and see what happens. I do have a very encouraging 80+ volts coming from all three phases of the stator. If the new R/R fries, I'll rewind the stator and get another Honda R/R for cheap again.

[Keith Winter]

Well,
Here we go again, actually, they are BOTH kind of right. The stator body is grounded, as it's bolted to the bike. The WINDINGS however are not, IF, the coating between the stator body and windings is ok. The stator windings ARE grounded through the negative side diodes in the rectifier. Like duanage said, there has to be a ground (or closed circuit) or no current would flow. This is why you have to disconnect the stator wires in order to DO the resistance test on JUST the stator windings.
Keith

[Guy]

No, we're not both right. Now lookit..........

To do a resistance test on the stator you isolate it from the rest of the electrical system, so the theory about the continuity through the r/r is irrelevent for purpose of the test. The windings aren't connected in any way to the body of the stator, so if there is continuity between the windings and "earth" the stator is faulty.
The way I described to check the the stator, by measuring the no load AC voltage with a running engine is the simplest way. It's logical, fool proof, and leaves no room for confusion or misinterpretation.

[duaneage]

Considering all the bikes Guy owned I thought he had noticed the screw in the middle of the stator asssembly that provides the circuit ground for the three coils. In order to create voltage you must have flow from ground, through the leg of the stator, and then through the diode. This happens for each leg of the stator. If the screw comes loose in the center that holds it on the bike the stator output goes way down. All current comes from ground, really.

Now anybody knows the windings and attaching wires don't touch the grounded part of the bike. But when the windings end they must be grounded or it won't work. This has nothing to do with bench testing the part, or even testing the thing with the bike running.

I suppose I have to dig out my stator mounted to a side cover and snap a few pictures with my ohmmeter connected to settle this. (Sigh)
Try this, connect your voltmeter black lead to the bike's engine and connect the red lead to ONE of the three yellow stator wires. If you get AC voltage of 30-40 volts then how do you suppose the circuit is being completed?

[t3rmin]

Well it seems the stator isn't working. Hooked the Honda R/R up and I'm not getting much voltage rise with RPMs at all. And when I pulled the stator out, I broke one of the magnets in the rotor. So we'll see how it looks after a new stator and rotor...