Alternator specs

[Muckroot]

Hello,

I took some measurements on the alternator I have and I need to know if they are good readings. It will eventually get replaced with a PMA kit from Hugh's but those are expensive, I am broke, and they are out of stock at the moment anyway. So for now, I am hoping to be able to use this stock Stator and Rotor set to break in my hardtail project. I did my best to make sure I had good contact between the leads and the bits I was measuring because these parts are pretty filthy. I measured with a cheapo meter, so that might be a factor in the weird readings I got.



My manual does not have a procedure for checking the alternator or the specs to go along with it, so I had to google the process as well as what numbers to expect. The readings I got almost all read 0.2-0.3 ohms higher than the upper bounds of the specs for this alternator. I thought this was suspicious because this thing is visually in pretty poor shape, and is also very old. Any input on whether this alternator is suitable for 3-6 months of use is welcome. I am also happy to re-measure stuff if that'll help diagnosis.

Best, Muckroute.

 

[5twins]

I think your parts are OK. With the stator, I think the only thing you measure between is the 3 whites. The exact reading you get isn't as critical as having all the readings near the same. This is outlined in the factory shop manual. Free copies are available on-line if you don't have one. Your rotor seems good at around 5 ohms. Clean the slip rings up, make sure the brushes are still long enough, and I think you'll have a working system. There's absolutely nothing wrong with the stock system. It works well and with these bikes being so old and many still functioning fine, you can see it's very robust. Frankly, I don't see the point of switching to a PMA. With it comes it's own set of unique problems. It's no charging system cure-all by any means.

 

[Muckroot]

It's no charging system cure-all by any means.

thanks for the info! what issues have you heard of with the PMA? and how can I best clean up the slip rings inside the stator without damaging the coils around them? for the rotor im guessing it's as easy as taking a bit of scotch brite to the slip surfaces because the coil is protected inside the rotor. Also I figured I'd go ahead and get new brushes because the one's I have are really rusty around the springs and probably wouldn't seat because of the weakened springs. Finally, how big a battery do I need to magnetize the rotor enough to get the bike running? this project is going to be a kick-only for the foreseeable future (although I'm keeping all the starter components in case I decide to reinstall it at some point).

 

[5twins]

I don't think there's slip rings in the stator. I just wipe the inside clean as best I can with rags and Q-tips dipped in solvent. For the slip rings on the rotor, I "polish" them clean with a little chrome cleaner on a rag. Cleans them up nicely without much effort. Once cleaned, I wipe them down with electrical cleaner to remove any chrome polish residue.

The problem with most of the PMA kits sold for the 650 is they contain cheap Chinese components that aren't up to the task. A PMA operates a bit differently than the stock system. On the stock system, the alternator output is controlled by the regulator. It produces more or less charging output depending on the need. A PMA isn't like that. Once the revs pick up, it pretty much runs full blast all the time. Extra output not needed is bled off through the regulator in the form of heat. The cheap Chinese regulators provided in the kits are not up to the task many times and burn out rather quickly. Now, you can buy a good, quality replacement but they cost around $100. So, that makes the system you just spent several hundred dollars on even more expensive. And on top of all that, if you have an '80 or later 650 with the factory electronic ignition, you'll lose that if you replace the alternator. You'll need to buy an aftermarket electronic ignition and that will lighten your wallet by another $100 to $200.

So, like I said, I don't see the point in switching. It's certainly not a very economical solution. It's much cheaper to maintain and upgrade the stock system. You can upgrade the two important components, the regulator and rectifier, to more modern ones for about $40 or less. This will lessen the strain on the other two "big ticket" components (stator and rotor) and give a better regulated and consistent charging output.

 

[Muckroot]

You can upgrade the two important components, the regulator and rectifier

this is excellent info! do you have any input on what regulator/rectifier unit to go with for mostly LED lights? I'm assuming that lowering the draw from the alternator will lessen the strain on it (and result in it lasting far longer) because as you said the stock alternator doesn't run at 100% all the time, it produces more power based on the draw of the bike. Is this assumption correct?

 

[5twins]

The fact that you're using LED lighting won't effect the kind of regulator you need, the version of the stock charging system you have will. There were two versions of the stock charging system used. The early version used up through 1979 uses a regulator that supplies regulated power to the outer brush. The 1980 and later system uses a regulator that supplies a regulated ground to the outer brush. So, your '75 would need the power regulating type of regulator. In the automotive world, this is know as a type B regulator. The one we most commonly use on our 650s is the VR115 or one of it's equivalents. You can get them from an auto parts store for about $30 or off eBay often for less. I got a couple over the years from eBay and never paid more than $10 to $15 for one. Search "VR115" on the site here for more info. Lots has been written about this topic.

The rectifier was the same on all 650s. This bike has an automotive style 3 phase alternator so you need a 3 phase rectifier for it. Many of us use this one from Windy Nation .....

https://www.windynation.com/Rectifier/35-Amp-3-Phase-Bridge-Rectifier/-/218?p=YzE9MjA=

 

[Muckroot]

The fact that you're using LED lighting won't effect the kind of regulator you need

That's a relief, should make hunting down a reg/rec a lot easier! I thought the LED would matter because the PMA that Hugh offers comes with an LED reg/rec and a Incandescent reg/rec, but if im tracking fully this is because the PMA outputs 100% power for the RPM that the bike is running at, so the regulator has to turn a lot more amps into heat when you're draw is low (like when the headlight and tail lights aren't on) than on a stock system, and especially so if your running LED's.

I was hoping to get a one piece reg/rec to go with the stock alternator, is that something that can be done or is it required to go with separate reg/rec units? I was hoping to get one with the sort of "block with heat fins" design because I planned out the electrical box with a mind for getting this style of reg/rec lots of air flow.

 

[5twins]

Yes, there are aftermarket motorcycle specific combined units like you've pictured for your early style alternator but they won't be cheap, probably around $80. Due to their cost, I never really considered one so I can't give you much info on them. I knew there was a good lower cost option so that's what I went with.

 

[Team Junk]

The 1980-83 TCI bikes don't have a seperate rectifier. The rectifier is incorporated into the regulator. It will require some rewiring and modification to one of the brush holders. Amazon has the late combined units starting at $27. Search for xj700 unit. It works better than the steam punk stuff the bike came with.
The difference between the LED/Incandescent PMA regulators is the LED units can sink more current

 

[Muckroot]

Search for xj700 unit

Alrighty! I'll certainly do that! you mentioned before that the difference between the two types of regulators for the XS650 was whether they regulated ground vs power, if I am building all the wiring from scratch anyway will it matter that I'm getting an XJ700 regulator/rectifier? I should just be able to just tailor my wiring setup to correctly utilize the stock alternator and the XJ700 reg/rec, right? is the stock alternator identical between the two different version of the reg/rec on the stock bikes? and lastly, what modification to the brush holders were you referencing? is that the nylon screws mod I keep hearing about? Thank you for all the information, the wiring is finally starting to make a lot of sense now!

 

[Team Junk]

Subtle differences between early and late alternators. The late rotor has a magnet added for the TCI system that won't matter in your case. The other difference is the brush holders. The early alternators has one of the brushes grounded to the stator frame. That is what the nylon screw is about and yes to use a late regulator you must do the nylon screw thing. There are several threads covering how to do this. Wiring is pretty close to being the same. It all happens at the connector you have disconnected.


With all this said if you have the brush holders squared away and you still have a problem when you reconnect the alternator then it's time to check some components for shorts to ground.

1) Your rotor could be shorted internally . Check the resistance between the brown and green wires on the suspect connector. If not in spec see Jim.

2) Same with the stator

3) could be a short in the rectifier. thats on the other side of the connector.

4) check the alternator wiring as it exits the alternator and goes past the chain etc.

 

[650Skull]

Stay away from the $29 ones............If your bike is a points model, here is a link for the 70-79 Combined SS Reg/Rect........there are some that have different colour'd wiring than the Factory set up.

This link shows the wiring diagrams for the Factory wiring set up ..........This thread shows the wiring diagrams for the SS Reg/rect that have the non Factory wiring ............

MikesXS instructions for the early, (points models), is up the shit and completely off the wall.......He used to sell the different colour'd wiring SS Reg/Rect, not any more.........there are some still being sold with the odd wiring by some sellers...........

http://www.xs650.com/threads/wiring-in-a-70-79-combined-reg-rect-to-a-points-model-xs650.52339/