XS2 Not Charging

[freddy3]

The charging system in my '72 XS2 is once again not working (i.e., the battery drains (especially when I switch the headlight on!) and the bike dies by the side of the road with no lights, horn, etc.). Once the battery dies, if I let the bike sit for a few minutes, it'll start up again and get me home without any problem as long as I don't use the headlight.
This time, however, the problem wasn't preceded by the rectifier burning up, so it's probably something different (and not the rectifier).

Unfortunately, the 9V battery in my Fluke digital multi-meter just died as I was trying to test the resistance between the rotor rings, so I can't (yet - I'll get another battery tomorrow) report much in the way of results from the Troubleshooting section of the factory service manual.

However, yesterday, I installed a new, fully charged Shorai battery (out of the bike, it measured 14.2V at the terminals). After the battery was installed and with the engine running at 2,500rpm, I measured 13.2V at the battery terminals. When I switched the headlight on, the voltage dropped to ~12.9. Switching the headlight off, it went back to ~13.2.

As I kept testing the voltage over a five-minute period, the voltage slowly dropped so that I was getting ~12.8 and ~12.6 when I switched the headlight on (it went back, briefly, to 12.8 when I switched the headlight off).

Then, I removed the cover on the regulator and tried adjusting the screw, but it had absolutely no affect on the voltage at the battery terminals:

Revving the engine from idle with the headlight on produced no change in brightness.
So, clearly, the charging system's not doing its thing.

As you can see, the left-side alternator brush is near its minimum length limit, so that may be related:

Also, the bike DID pass the "SLAP" test, so I'm kinda wanting to point the finger at that worn alternator brush and/or the regulator (since the adjustment screw doesn't affect the voltage readings at the battery)??

Does that make sense, or should I run through the rest of the factory manual's troubleshooting steps first?

In case it's useful, here're photos of the alternator...

...and rectifier

 

[cra-z1]

After you get new brushes I would dump the stock regulator and rectifier and replace with a modern electronic regulator/rectifier. The stock regulator was not very reliable as you probably know or have found out. I mounted one I got from Mikes about three years ago and am very pleased with the results. When ever i restore one of the older bikes of any brand those are the first components I get rid of.

 

[freddy3]

Thanks cra-z1, but I forgot to add my usual disclaimer: I've owned this bike since '75 and, until the OEM rectifier burned up and caused charging system problems a couple of years ago (which were history until a coupla weeks ago when this new problem appeared), it's been very reliable (including the charging system). So, while I realize there're many reasons to upgrade the electronics, unless I'm absolutely forced to, I'm trying to keep the bike totally stock. But your point is well taken.

Re the brushes: Since you said "after" I get new brushes, does this mean you concur with my suspicion that the short brush may be the cause of my current charging issue? Or are you suggesting it simply to cover all the bases?

 

[retiredgentleman]

You can try adjusting the regulator...............Yamaha service manual has details. A better way would be to buy an automotive NOS VR-115 regulator. With the VR-115, no more regulator problems.

 

[freddy3]

Thanks, retiredgentleman (I remember you being very helpful the last time), but I'm trying to keep the bike stock (in spite of the known shortcomings of its vintage electronics).

 

[weekendrider]

Get some new brushes go from there. You've gotten your moneys worth out of those.

 

[freddy3]

Thanks, weekendrider. Brushes en route and should arrive tomorrow. I'll post back with results after they're installed.

 

[freddy3]

UPDATE: Unfortunately, the new brushes weren't the problem.

QUESTION: When testing the OEM rectifier, does the rectifier need to be installed on the bike (i.e., so its case is grounded to the bike frame), or can I test it on a bench?

I went through the factory service manual's troubleshooting procedures and found that the rectifier's bad (fyi: this is the 4th Yamaha rectifier to go bad in the past 5-6 years - I know that solid state ignition's more reliable, but I'm keeping the bike stock). So I bought a used OEM rectifier on ebay and decided to test it -before- I made the trip over to the storage where I keep the bike. Unfortunately, it was passing current in both directions, so I sent it back.

Then, a few days ago, I found another OEM rectifier, this one advertised as NOS (although it looks anything but!):

But, unfortunately, I'm still getting the wrong readings.
Of course, it's no surprise that people will sometimes describe defective gear as working, but I'm beginning to wonder if it's got something to do with the way I'm testing these replacement rectifiers (i.e., out of the bike), since two-out-of-two didn't work.

Again, the question is do I need to install the rectifier to test it?

 

[retiredgentleman]

Rectifiers do not need to be installed on the bike. Bench testing is just fine.

If you have an analog VOM, you should measure about 6 or 7 ohms in one direction and open circuit in the other.

If you have a digital meter, the "diode" selection should show about 580 to 700 forward voltage drop, and open circuit the other way.

I think you're flogging a dead horse, by trying to use the old stock style rectifiers and regulators. Technology has moved on, and silicon diodes and soild state regulators make life better.

 

[freddy3]

Thanks, retiredgentleman. I'm still confused as to why the factory and Clymer service manuals both spec readings of 75-150 ohms?

Anyway, as it happens, I've got both analog and digital meters, but I'm still not getting the right numbers--either yours or those specified in the Yamaha (or Clymer) service manual.

With the analog (1,000ohm scale): I'm reading 5 ohms on 2 of the white wires and an open circuit on the third (the white wire in the center of the connector):

Reversing the test leads reads open on all white wires.

With the digital (diode scale): Testing from the black wire, I'm reading ~.485 at the same 2 white wires and an open circuit on the same white wire as above. Testing from the red wire, I'm reading ~.516 at the same 2 white wires and an open circuit on the other white wire:

Reversing the test leads reads open on all white wires.

At this point, I've no idea whether the variance in readings between the red and black wires in the connector indicates a problem, but the open circuit readings for that white wire in the center of the connector pretty much validates my original conclusion that this "NOS" rectifier was probably pulled from a bike that had the same problem I've got.

Is it possible to just replace the individual diodes in this rectifier? I mean, can't I just pick some 12V 75-150ohm diodes up from Radio Shack or somewhere online and solder them in place of the bad ones?

 

[retiredgentleman]

Thanks, retiredgentleman. I'm still confused as to why the factory and Clymer service manuals both spec readings of 75-150 ohms?

Anyway, as it happens, I've got both analog and digital meters, but I'm still not getting the right numbers--either yours or those specified in the Yamaha (or Clymer) service manual.

With the analog (1,000ohm scale): I'm reading 5 ohms on 2 of the white wires and an open circuit on the third (the white wire in the center of the connector):

Reversing the test leads reads open on all white wires.

With the digital (diode scale): Testing from the black wire, I'm reading ~.485 at the same 2 white wires and an open circuit on the same white wire as above. Testing from the red wire, I'm reading ~.516 at the same 2 white wires and an open circuit on the other white wire:

Reversing the test leads reads open on all white wires.

At this point, I've no idea whether the variance in readings between the red and black wires in the connector indicates a problem, but the open circuit readings for that white wire in the center of the connector pretty much validates my original conclusion that this "NOS" rectifier was probably pulled from a bike that had the same problem I've got.

Is it possible to just replace the individual diodes in this rectifier? I mean, can't I just pick some 12V 75-150ohm diodes up from Radio Shack or somewhere online and solder them in place of the bad ones?

With your analog meter, use the X 1 scale for ohms. Check all 6 diodes, and see what readings you get. It does appear that you have an open circuit in a diode.

Here's a pic of the rectifier I made up, and it works just great. I bought 2 bridge rectifiers from an electronics supplier her in Canada (we don't have Radio Shack anymore). Each is a single phase bridge rectifier rated at 25 amps.

They cost me $5.99 each or $11.98 total, 3 years ago. The 2 have a total of 8 diodes, and they get wired up so that you are only using 6 of the 8. You only use 6 diodes because you are making up a 3 phase rectifier. You can buy them at Radio Shack in the USA.

You must have a heat sink, so many lads just use a piece of aluminum. I used an old amplifier heat sink that I had laying around for years.

You could use the old connector, or do what I did, buy a new connector from Mikesxs.

 

[freddy3]

That's a very clever idea, but I'd really like to just replace the diodes in the rectifier so I can keep the basic OEM appearance/wiring. Also, my (current) electronic skills are pretty much limited to swapping components. I'm comfortable replacing diodes (for similar parts) in the current rectifier, but I wouldn't want to chance constructing a new rectifier block.

 

[retiredgentleman]

freddy3;

I understand your desire to keep things stock. On my bike, I replace/upgrade as required to maximize reliability. When I'm on a long trip and I'm 1000 km from my home, I don't want any breakdowns.

Those old OEM rectifiers may have been OK when new, but they have deteriorated over time. Even if they sat on a shelf for all those years, they still degrade. The voltage drop across the old rectifiers increases with age.

I'd say its quite difficult to repair the old rectifiers. Its actually simple to make up a new rectifier such as in my picture. If you want details, let me know.

 

[freddy3]

You do make a good point about time & degradation. Is your rectifier a bolt-on replacement for the OEM rectifier? That is, can I just remove the OEM part and bolt yours on using the same bolt without having to change/modify either the bike or any other components?

 

[retiredgentleman]

You do make a good point about time & degradation. Is your rectifier a bolt-on replacement for the OEM rectifier? That is, can I just remove the OEM part and bolt yours on using the same bolt without having to change/modify either the bike or any other components?

Here is a link that has 6 pages, to read all about making one:
http://xs650temp.proboards.com/index.cgi?board=Charging&action=display&thread=3473

You can make up any kind of heat sink you want. Then bolt the heat sink (with the 2 rectifiers) to the bottom of the battery box. With my heat sink, I drilled a hole in the centre, used a long bolt, and bolted that to the battery box bottom.

There's no changes to the bike itself. You use the same hole in the bottom of the battery box that the stock rectifier used. Use the same 6 pin connector, so that it will plug into your harness. When I made mine, I did not solder directly to the bridge rectifiers. I soldered spade connectors onto 14 gauge wire, and then just push the spade connectors onto the bridge rectifier terminals. I used heat shrink insulation on the terminals.

You can continue to use the OEM stock regulator if you wish to do that, or a NOS automotive VR-115 regulator could be used.

You do need to have some soldering and wiring skill.

 

[freddy3]

The basic construction/soldering/wiring isn't a problem, but the rectifier on my bike looks smaller than the units on the later bikes in that 6-page thread. Mine's also bolted to the frame under the left side cover instead of below the battery box (the rectifier's at right in this photo):

I found this 25A, 50V full-wave bridge rectifier on Radio Shack's website. Is this the one?

 

[freddy3]

Actually, I wonder if this 3 Phase Diode 50A 1000V Bridge Rectifier might be better since it's smaller so I could mount it in the same space as the OEM rectifier:

 

[retiredgentleman]

The basic construction/soldering/wiring isn't a problem, but the rectifier on my bike looks smaller than the units on the later bikes in that 6-page thread. Mine's also bolted to the frame under the left side cover instead of below the battery box (the rectifier's at right in this photo):

I found this 25A, 50V full-wave bridge rectifier on Radio Shack's website. Is this the one?

Yes, that appears to be the correct one from Radio Shack. The 3 phase one from China, also should do the job.

 

[5twins]

There are other adjustments on your voltage regulator besides that screw. There is a core gap and a point gap that must be within the given spec for the unit to perform properly .....

 

[freddy3]

I'm glad it's the right one, because I picked the rectifiers up from Radio Shack and put it together this morning:

Obviously, I still need wires and I ordered another connector from Mikesxs to put it all together. So, with a bit o' luck, I'll be back on the road again this weekend.