stators / rotors testing

sinclairlaw2 · Post by **sinclairlaw2** » Mon Apr 28, 2003 2:16 pm

new to posting. I have a 79 CBX that is not charging. I replaced brushes, and still no charge. A few questions> 1) what should be the ohm reading on the rotor? 2) anyone have test procedures for checking the system? eg. stator/rotor etc. 3) Looking for a tech tip manual that someone may no longer be using and wants to sell. 4) if I need to replace stator/rotor, any suggestions on sources? what about rewinds? thanks!!!

Jim-Jim · Post by **Jim-Jim** » Tue Apr 29, 2003 11:29 am

Look at the topic - Alternators for some measurements.

Guest · Post by **Guest** » Tue Apr 29, 2003 4:11 pm

thanks Jim-Jim, I will check out the alternator measurement topic for info. I did find out that the reading between the rotor slip rings should be between 3.5 and 4.0 ohms with a setting on the ohmmeter at Rx1 scale. My rotor reads to 15 ohms, so I guess I must replace it.

Jim-Jim · Post by **Jim-Jim** » Tue Apr 29, 2003 11:09 pm

Whoa!! Not so fast!! I'm no expert but that seems unusual. Have you checked your meter for accuracy? I would like to see an better qualified Xer chime in here (Mark???) - I would think that the rotor would short out and show LOWER resistance or ground out to the metal - not increase in resistance. Not to insult your intelligence but were you right on the copper rings with good contact? I'm not sure how a rotor winding could GAIN in resistance but not totally open up. Maybe someone else can add a thought or two. By the way, if you DO have to replace the rotor, I would like to buy your old one from you to see if I can figure out how it did increase in resistance (fair price + shipping, of course). Let me know.

Tom Whaley · Post by **Tom Whaley** » Wed Apr 30, 2003 12:41 am

On thing you might keep in mind is that it takes quite sometime for the alternator to start charging after new brushes are installed. Charge up your battery and take a 5 to 10 mile ride and see what happens. I know it sounds silly but it just might start charging for you. If you have already done that, then I'm stumped also. Best of luck.

EMS · Post by **EMS** » Wed Apr 30, 2003 7:42 am

I am not an expert either. I don't like Electricity. Especially when it is used to power vehicles.

Have to live with it, though. Resistance increase is a sign of conductivity drop. A long thin wire has a higher resistance than a thick one of the same length. I would assume, if the wiring in the rotor is damaged or cut, the resistance would go up.

Jim-Jim · Post by **Jim-Jim** » Wed Apr 30, 2003 11:52 am

C'mon, guys, it's not that hard. I've been involved in electric/electronic diagnostics for boocoo years and that makes me some kind of expert (the 'ex' is a has-been and the 'spert' is a drip under pressure), that's why I am so puzzled about the high resistance he measured in the rotor. It could be a result of a bad/cold solder joint within the rotor; it's possible one turn could be partially broken/weak but not cut. A cut would be an 'open' and there would be no resistance at all (0 ohms). Since it is a single winding, as opposed to the stator's three, it's pretty simple. If a second check still shows the 15 ohms resistance, I guess I might try to re-solder the ring connections to the winding. But I'd really like to get my hands on that rotor to see what's what; it would make an interesting project. I'll wait to hear what he comes up with.

Guest · Post by **Guest** » Wed Apr 30, 2003 2:20 pm

I think I better toss out that meter I just bought at wally mart for 10. bucks! I got hold of another meter and brought the dial down to RX1 and measured across the rings, it now measures about 2 ohms (still off the recommended readings) , I ain't no rocket scientist, so this electrical stuff is a bit above my head. Thanks Jim-Jim, EMS and Rocketman for your responses. I don't quite know what to do now, replace rotor? I checked the three yellow stator wires and they all measure consistent at about 2 ohms, so I am not sure if that is a problem or not. By the way, Rocketman, I saw a post regarding bearing numbers, are those numbers still available?

Guest · Post by **Guest** » Wed Apr 30, 2003 3:00 pm

Man,,, I feel like a really dummy, ok... I am looking at the posts in response to CBXAL, appears that he is suffering from the same problems that I have with my cbx. ALTERNATOR. Jim-Jim, you have provided a great detail on the procedures for reading. You mentioned that the stator leads should all read around .32- .40, so I must be reading this darn thing (meter) wrong. I interpreted the reading as a 2. When I get off of work today, I will go home and re-evaluate the meter readings that I have. Thanks !! Also, I have not ridden the bike yet to see if it will charge, that sounds like the best idea. Thanks to you all, I really appreciate the quick responses here

(now if I can only figure out how to post replies properly).

Jim-Jim · Post by **Jim-Jim** » Wed Apr 30, 2003 5:55 pm

One thing everyone needs to keep in mind (file away for future reference) is that when you are dealing with the stator/rotor measurements, you are dealing with very low ohms and you MUST have a VERY GOOD meter

- Flukes are among the best. A poor/cheap meter will read poorly ESPECIALLY at the low ohms range. So that's first. Next, the Stator has three windings (yellow/yellow/yellow leads) that produce the charging/running voltage/current. The alternator is a 350 Watt job, that means it can put out up to 30 amps, that's a lot of current through the stator so it's windings are really low in resistance (0.32 - 0.40). I wouldn't worry if the resistance was up to 0.5 ohms in each winding but if it was the same for all three windings, I'd say OK. The rotor is a different matter. It has only one winding and only generates the magnetic field to interract with the stator so it doesn't draw as much current to do that so it's resistance will be higher (3.5 - 4.8 ohms). I wouldn't worry if it was 5-6 ohms but no higher. If it was lower than, say, 3.0 ohms, I would worry; it would mean some of the turns in the winding have shorted. Shorted windings will draw more current and overheat the copper, burning it up. Then the rotor would 'open' (0 ohms). If, somehow, the resistance DID go way high, then the rotor would not draw much current and would not generate enough magnetic field for the stator (low output from the stator). The optimum resistances for the rotor/stator will ensure a correct running charging/running circuit.

Again, if you DO replace the rotor, I'd like to get ahold of it to check it out (that's how you learn new stuff) to see exactly what's wrong with it.
Let us know.

busaboy · Post by **busaboy** » Wed Apr 30, 2003 8:50 pm

An "open" circuit will result in infinite resistance; 0 ohms would be a short circuit, e.g., if some windings were touching each other or the rotor or stator.

Jim-Jim · Post by **Jim-Jim** » Thu May 01, 2003 9:13 pm

OOOPPPsss!!! Eric, you're right!! I was trying to find some way to put an infinity sign in and ended up with the '0' and forgot about it. Glad you caught it, I hate to see someone put out bad/inaccurate info and looks like I did it myself. An open winding will show NO resistance at all. The meter needle (analog) will not move; the scale (digital) will usually show just a +/- sign with nothing else.

busaboy · Post by **busaboy** » Fri May 02, 2003 10:23 am

Wait a minute - I think you just said again that an open circuit has no resistance, vice infinite!

EMS · Post by **EMS** » Fri May 02, 2003 11:28 am

Actually, he said "it will SHOW no resistance" "the meter will not move"

which may be the meter's way of telling you infinite resistance???

busaboy · Post by **busaboy** » Fri May 02, 2003 12:04 pm

Any analog meter has an "infinity" side of the scale - it will point to that when being used to measure an open circuit. I think my analog meter has the "infinity" side to the right, and swings to that side when confronted with an open circuit.

The International CBX Owners Association