Author Topic: CB400f alternator fried? (Read 4356 times)

Baune · « **on:** April 20, 2018, 04:37:58 AM »

Hello all,
Just created my account today, but i have been reading a lot on this forum, and it seems like you guys have the knowhow to help me out!

I have been having a LOT of charging problems on my cb400f, and have followed posts from this forum to find out what is wrong. I narrowed it down to being the alternator, and so i bought a new one off of Ebay. It ran for a few minutes and charged the battery at a little over 15 Volts, and I then turned it off thinking i had fixed the problem. The next time i started it up i realised it wasn't charging, and i started to look elsewhere for the problem. Now 3 months later i have circled back to the alternator, and i measured it and found out it is shorted to ground (i've heard this is bad).

My question is, how do i know if the alternator were bad from the get go or if my bike did something to fry it?
It would be pretty stupid to buy a new alternator if it is going to get fried once again.

Also a bonus question; I have attached two pictures, one of the old original stator and on of the new one from Ebay. They both have signs of heating the same place(on the writing), is this normal for these alternators?

Best regards

Bodi · « **Reply #1 on:** April 21, 2018, 07:54:41 PM »

The alternator coils are hard to kill, rarely failing unless damaged in a laydown. Problems are typically in the harness connectors, regulator, regulator, or the battery to frame/engine ground connection.
You should have roughly equal and fairly low resistance (low resistance is difficult to measure accurately with a typical multimeter so don't worry about your reading vs the spec) in the three possible measurements between the three yellow stator wires, and another low reading across the field coil. With all wires disconnected you should not have any connection to ground on any wire ("infinite" ohms). The field coil has one wire connected to ground in the harness, so that's OK if you can't find the connection. You should inspect the alternator bullet connectors under the sprocket cover as these are famous for corroding and overheating, the cover tubes should be clear... brown or black is not good, those will need attention. Inspect the engine connector as well, the spade connectors are not as prone to decay as the bullets but can cause trouble, the housing usually looks burnt/charred if things got really bad.

Baune · « **Reply #2 on:** April 22, 2018, 02:04:22 PM »

Thank you, both of you, for your answers. I have done all the tests previously, more or less in that order. Giving attention to the stator i found out that it is indeed shorted to ground (when measuring with three connectors disconnected), and that is clearly my problem.

What bugs me is, this stator is completely new off of Ebay, and now it's shorted after only running for a minute or so. How do i find out what is killing it? As i said, i don't want to go out buying a new stator once again just for it to break whenever i start up the bike.

TwoTired · « **Reply #3 on:** April 22, 2018, 06:01:49 PM »

The stator wires have to be routed outside the housing. And that gives the opportunity to short against housing. Check that. Could be installation/routing issues.

Cheers,

evinrude7 · « **Reply #4 on:** April 22, 2018, 06:13:07 PM »

You say it was charging at 15 volts. Isn't that a little too high?

Sent from my LG-H871 using Tapatalk

scottly · « **Reply #5 on:** April 22, 2018, 10:10:44 PM »

There was a guy with a 500/550 some years ago that had a similar problem with stators shorting to ground; turned out the stators had been installed wrong side out in the alternator cover. The clue was when he mentioned a "crunching sound" when tightening the stator mounting screws. The crunching sound was the varnish insulation being scraped off the windings where they hit the inside of the cover.

Baune · « **Reply #6 on:** April 22, 2018, 11:52:43 PM »

As far as i can see the wires going out of the altenrator cover has not been damaged. It is unfortunately though a real possibility that I have installed it the wrong way. Can anybody attach a picture of wich way it should be installed? Normally i do it with the wires facing towards the crankcase.

Regarding the charging voltage, i think it's a little high, but nothing catastrophic, maybe somebody with more knowledge than me can chime in.

EDIT:
With this post i am now able to post pictures, so i have attached a schematic of the generator assembly. Is this the right way to install it, because mine is installed opposite of this.

scottly · « **Reply #7 on:** April 23, 2018, 12:19:57 AM »

Quote from: Baune on April 22, 2018, 11:52:43 PM

Can anybody attach a picture of wich way it should be installed? Normally i do it with the wires facing towards the crankcase.

EDIT:
With this post i am now able to post pictures, so i have attached a schematic of the generator assembly. Is this the right way to install it, because mine is installed opposite of this.

The schematic is correct; the stator wires face the outside, and then loop back towards the inside. I can get you a pic, but it may take some time as I will have to pull the motor out of the crate it's been hiding in.

Baune · « **Reply #8 on:** April 23, 2018, 12:47:24 AM »

Oh alright, i think the "looping back" of the wires is what made me turn it the wrong way in the first place. Is it almost certain that installing the wrong way will short it? Could i be lucky enough that i will work if i install it the correct way?

Also if it's not much trouble i would like a picture of how it should fit in the cover, especially with the wire looping back up.

I really appreciate the help!

Bodi · « **Reply #9 on:** April 23, 2018, 06:40:19 AM »

I don't know what you mean. I don't see any wrong way possible. Yellow to yellow and white to white. The order does not matter.

Baune · « **Reply #10 on:** April 23, 2018, 07:39:55 AM »

The wrong way im talking about is not the connection of the yellow or white and green wires, it is the way the stator coil is installed inside the cover, which according to scottly, and the attached schematic, is wrong.

I have ordered a new stator now, and I will install the correct way when it arrives. Anything other than that i should make sure of before i start it up so i don't fry another stator winding?

Bodi · « **Reply #11 on:** April 23, 2018, 09:16:01 AM »

I don't know how one can fry a stator winding. Was it physically damaged by mounting it upside down? That would make no difference to its operation anyway, if nothing was crushed in the process.

Baune · « **Reply #12 on:** April 23, 2018, 09:41:12 AM »

I don't know for sure if that is the problem yet, but the height of the stator coils is slightly increased on one side of the stator, which would make sense as tightening it down in the cover may have ruined the insulation and shorted it.

I just hope and pray that it is myself who ruined it instead of some obscure electrical problem that i am not able to find.

scottly · « **Reply #13 on:** April 23, 2018, 07:06:55 PM »

I was wrong, and so is that schematic. Look at the general export versions, and you can see the difference. In the pics, notice the clean surface where the heads of the mounting screws seat, and on the side that goes against the cover there is a clean ring around the outside, where it sits on the ledge of the mounting post.

Baune · « **Reply #14 on:** April 23, 2018, 11:04:16 PM »

Arhh bummer, just thought we had figured it out...

Can you do me a favor and measure if there's continuity from one of the yellow leads, and to the outer metal ring?
Both my stators have continuity there.

scottly · « **Reply #15 on:** April 23, 2018, 11:09:40 PM »

There should be no continuity between any of the yellow leads and the outer metal ring. Please post a picture of your "fried" stators.

Baune · « **Reply #16 on:** April 24, 2018, 12:00:37 AM »

I have attached some pictures i had laying around on my phone, if you want to see something specific i will take som new pictures later today.
What i have tried to capture here is the heat markings in the same place on two different stators.

Stator 1(old)
https://imgur.com/a/P72ovMS

Stator 2 (new)
https://imgur.com/a/jLSr8Lf

TwoTired · « **Reply #17 on:** April 24, 2018, 12:12:44 PM »

With the stator removed from the housing, do you still have continuity between the yellows and the iron core?

Baune · « **Reply #18 on:** April 24, 2018, 12:16:53 PM »

Yes, there's continuity when it is out of the casing.

strynboen · « **Reply #19 on:** April 24, 2018, 12:28:49 PM »

look burned at the last Photo...is that the good one?

Baune · « **Reply #20 on:** April 24, 2018, 12:48:44 PM »

Quote from: strynboen on April 24, 2018, 12:28:49 PM

look burned at the last Photo...is that the good one?

Yes, that's the one i bought off of ebay. What i think is weird is that the two stators have signs of heating in the exact same spot.

TwoTired · « **Reply #21 on:** April 24, 2018, 02:07:44 PM »

Well, the stator is three coils of wire all connected at one end in a wye configuration. If you supply unlimited power to any of the two leads, it will conduct current and possibly overheat and melt the wire insulation.

A big enough battery could do this, but that means the diodes that would normally block this sort of flow (in the rectifier) would have to be shorted, and the wire harness would also have to carry this destructive current (and get very hot, too).

The stator cannot make enough power to do this insulation melting/damage to itself. It is self limiting to is design capability. A direct short of the output would make any voltage build up drain off before current could be enough for heating self damage. One of the beauties of it's design.

You are looking at either physical trauma or external power source damage, to make it fail. A remote possibility is that the material used for the coil wire insulation has changed its physical properties with age or had applied external heat or both.

Toss a stator into a fire and it will likely be damaged.

Cheers,

scottly · « **Reply #22 on:** April 24, 2018, 07:04:13 PM »

Look at the inside of stator #2, it looks like it may have been rubbing against the rotor? The bluing on the outside means it has gotten very hot, possibly from friction. The cover has two counter-bored holes, one on either side of where the wires exit; look closely at the pic I posted. The counter-bores are for the alignment dowels; if the dowels are missing, the cover won't be perfectly centered over the rotor.

Baune · « **Reply #23 on:** April 24, 2018, 11:20:38 PM »

Yeah i think it has been rubbing against it too. The bike made som whining noises from the generator cover, and if i remember correctly i fixed it by tightening down the stator a wee bit more. I just did not think that it would create so much friction heat it could actually burn the insulation.

scottly · « **Reply #24 on:** April 24, 2018, 11:26:55 PM »

The stator is difficult to get seated squarely in the cover, and once it gets cocked it can bind. The surface under the heads of the screws should be flush with the cover in that area.

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Author Topic: CB400f alternator fried? (Read 4356 times)