I was testing the rotor with actual current going through it rather than just a resistance test. The rotor resistance dropped to 3 ohms after the test. Now its changed again. I think Ill just replace it..
R100GSPD Not charging
- Thread starter Wierpig
- Start date
Larry Langford
Registered user
The rotor may act different when it is spinning in the motor as well. Make sure you get the right rotor, it should be 2.8 ohms for a 90's bike. There was a guy selling the earth magnet alternators over in these parts but I haven't checked on that for a spell so I don't know if those can be bought. It would be really trick though as the is no winding there on the rotor just very strong earth magnets. Spin a magnet inside of a coil of wire, the stator, and you get power. On the stock setup the rotor is an electromagnet and does the same thing. Your rotor doesn't look like the epoxy coated newer versions. Looks to be stock from what I can see.
The rotor is a generator, not a load on the circuit. Electrics are very straightforward - you are making it sound complex!
"The rotor may act different when it is spinning in the motor as well" - it is designed to do this.
"Spin a magnet inside of a coil of wire, the stator, and you get power." You actually get voltage. You need to connect another circuit to get power. I think Michael Faraday (English physicist and chemist) found this out on 29 Aug 1831.
I'm going to put a wet towel on my head.
Whilst the theory of electrical circuits may be straightforward, in practice many things can lead you astray from a first time diagnosis. Lack of knowledge of a particular system, incorrect wiring diagrams and ambient conditions.
A poorly or oxidised soldered joint that tests ok with the low current of a multitester, that breaks down with working current. Changes in temperature etc...
A poorly or oxidised soldered joint that tests ok with the low current of a multitester, that breaks down with working current. Changes in temperature etc...
Larry Langford
Registered user
clymer manuals do have good wiring diagrams, if you can figure out which one you need. I wouldn't feel wrong about changing out this rotor, as if you pull one apart and it doesn't have the epoxy, and you can see individual wire of the winding, then you change it out almost automatically ... like a battery that might give you trouble on the road later.
Larry Langford
Registered user
are you one of those ass hurt metzler fans I ruffled up about year ago ..... this comment doesn't deserve a response imo .... absurd
I didn't say it was easy...! But it is straightforward.
The straightforward bit allows you to eliminate components (like the VR) and concentrate on the most likely culprits. If your rotor is changing its resistance then it or the meter is suspect. Can't rule out the multimeter (a dying battery....). Just something to check.
I always turn to Rick Jones's 'Classic Boxer Charging' book to help out. I've quoted from it to help you. I can scan the pages and include them here if you haven't got a copy? That said, as before, if your alternator is only delivering 4VAC per phase then the rotor is not excited enough to deliver more. As the VR checks out, the issue is likely the rotor, or the wiring to it.
At post #16 I tried to help you along the diagnosis path using the facts you had found out and written about.
The straightforward bit allows you to eliminate components (like the VR) and concentrate on the most likely culprits. If your rotor is changing its resistance then it or the meter is suspect. Can't rule out the multimeter (a dying battery....). Just something to check.
I always turn to Rick Jones's 'Classic Boxer Charging' book to help out. I've quoted from it to help you. I can scan the pages and include them here if you haven't got a copy? That said, as before, if your alternator is only delivering 4VAC per phase then the rotor is not excited enough to deliver more. As the VR checks out, the issue is likely the rotor, or the wiring to it.
I tested the multimeter using a new 9v battery and a 5k ohm resistor. All good. I appreciate your input. Ill oder a new rotor tomorrow and report back...
Are the Motorworks pattern rotors any good? Ive ordered a copy of the electrics bible!
Are the Motorworks pattern rotors any good? Ive ordered a copy of the electrics bible!
Reading their description of the reconditioned secondhand ones, they sound pretty good. I've never needed to buy one as I still have a few spare alternators on the shelf to get through before I do..
I bought an uprated alternator (600W?) off Bob Porecha a while back for my RS for a trip to Spain. I think that's the only one I've bought off a shop. Rest came from secondhand spares buys, where you find one at the bottom of a box of other stuff. They have all checked out though. And I don't think I needed 600W!
It was the rotor. Thanks for all input
Incidentally, in Rick Jones book he advises testing the diode board with the ohms setting of the multitester. I couldnt get a reading using that setting. Tried the diode setting and got the expected readings.
yes i know you've fixed it .
(on a guzzi )
rotor resistance is 3.6 - 4.2 ohms ( isolated ) then i check from the connecters , through the rotor. about 6 ohms . had loads of bikes with many more ohms , this is now ( for me ) a standard check.
DON'T FORGET TO " FLASH " THE ROTOR .
(on a guzzi )
rotor resistance is 3.6 - 4.2 ohms ( isolated ) then i check from the connecters , through the rotor. about 6 ohms . had loads of bikes with many more ohms , this is now ( for me ) a standard check.
DON'T FORGET TO " FLASH " THE ROTOR .
What is “flash the rotor” ?
Please educate a thicko…….thanks
OK , thicko ! 
@Bubb
engine running , take wire from battery+ down to the connection from regulator to brush pack ( rhs as you look at it from the front ) D+ or DF marking ? hold wire to terminal for a count of 5 , gen light will go out , remove wire , turn engine off , restart , rev engine while watching gen light , light should go off as revs rise.
this procedure just polarises the rotor . some work straight out of the box , some don't . so i just do it as a matter of course , if i'm working on a Bosch system.
@Bubbengine running , take wire from battery+ down to the connection from regulator to brush pack ( rhs as you look at it from the front ) D+ or DF marking ? hold wire to terminal for a count of 5 , gen light will go out , remove wire , turn engine off , restart , rev engine while watching gen light , light should go off as revs rise.
this procedure just polarises the rotor . some work straight out of the box , some don't . so i just do it as a matter of course , if i'm working on a Bosch system.
You do not need to flash the rotor as it is not a self-exciting system, the battery supplies the field voltage and Faraday does the rest.
Without being rude I'd say the vagueness in the instructions in #34 could lead some owners to seriously fuck their electrical system if they were not absolutely clear about what they were doing. And if they were clear about what they were doing, they would know that Bosch charging systems of Airheads we are talking about do not need to be flashed.
Without being rude I'd say the vagueness in the instructions in #34 could lead some owners to seriously fuck their electrical system if they were not absolutely clear about what they were doing. And if they were clear about what they were doing, they would know that Bosch charging systems of Airheads we are talking about do not need to be flashed.
just re-read what i wrote , seems clear enough to me . which bit do you think is vague ?
whether they need to be flashed or not , I do it so i know it is done.
have you never had a rotor lose it's polarity ?
whether they need to be flashed or not , I do it so i know it is done.
have you never had a rotor lose it's polarity ?
If you took a B+ to Df you are bypassing the VR and putting B+ on both sides of the GEN light. No wonder the GEN light goes out. It would do that if the engine wasn't running. And if the engine was running, the GEN light would probably be out (unless you are at the normal state of the alternator not giving enough output to balance the battery voltage). So this action is totally pointless.
AI backs this up, "Applying 12VDC directly to the DF (Dynamo Field) terminal while the engine is running bypasses the voltage regulator. The alternator rotor receives maximum field current. This forces the alternator to produce its absolute maximum output continuously, causing system voltage to spike well above 15V and potentially boiling or frying the battery and sensitive electronics.
The rotor is not a permanent magnet so it does not have or need polarity (your 2nd question is therefore irrelevant). When it is spinning in a working engine it has field current in its windings and 'THEY' cause the alternator to generate power (see #23 Faraday reference). To think the rotor is a permanent magnet unfortunately displays ignorance of the Bosch charging systems. That you do it and tell others not to forget to 'flash the rotor', well I'll leave you to be the judge of that.
well I've been flashing rotors for 30 years , this way.
i haven't yet fucked up something . ( yet )
what do you do when a rotor loses its' polarity for no known reason ?
i haven't yet fucked up something . ( yet )
what do you do when a rotor loses its' polarity for no known reason ?
I've only ever heard of "flashing" like that with dynamo systems.
Never done it, or needed to
Never done it, or needed to
Thank you …you truly are “the on and only”OK , thicko !
engine running , take wire from battery+ down to the connection from regulator to brush pack ( rhs as you look at it from the front ) D+ or DF marking ? hold wire to terminal for a count of 5 , gen light will go out , remove wire , turn engine off , restart , rev engine while watching gen light , light should go off as revs rise.
this procedure just polarises the rotor . some work straight out of the box , some don't . so i just do it as a matter of course , if i'm working on a Bosch system.
Even a thicko like me can understand that.
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