Charging problem diagnostics (bike died on the way home)

robbiecampbellsoup

XS400 Enthusiast
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Hey Folks,

I just picked up a 1983 Maxim XS400 from a nice fellow locally - it rode decently well on a test ride and the price was pretty good so I picked it up - I knew the battery wasn't holding a charge on it when I was looking at the bike, but I was hoping that it was just a case of a super old battery - however I think it might be more than that after I didn't quite make my ride home - I am assuming that typically the bikes can run themselves without a battery when they are already running (Am I wrong?).

I guess I'm looking for pointers on where to start and next steps.

Here's what I've done so far:

1. Got it back to my shop finally (a bit of bump starting and then pushing)
2. Put the battery to a multimeter, 11.86V pretty flat.
3. Put the battery on a power supply at a charge voltage of 14V - 2A, battery immediately went to 14V with less than 0.01A current. Battery must have massive internal resistance (I assume that this means it's sulfated to crap)
4. I replaced the battery with a new one - it's currently doing an initial charge to 13.5V at a charge current of 0.5A.

Here's what I think I need to check:

0. Are things plugged in and or corroded?
1. Is the stator/generator outputting AC voltage?
2. Is the rectifier putting out DC voltage?

Any tips/pointers on what else to check would be greatly appreciated - otherwise I'll default to reading manual and fudging around (which would waste time if I'm overlooking something simple).

The old dead battery lasted me about 30min of riding around before I started to lose power and the bike would just die (this is what makes me think there's something up with the charging system, as wouldnt the bike normally be able to power it's own ignition system?? if the engine is already idling??)

Thank you for your time!

-Robbie
 
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Welcome to the forum.

You didn't mention what year your bike is. I have read on here that some if these bike need to have the battery charging to run.

I recently had an issue with mine not charging, I checked the ohms on the generator and it was good, but there was nothing with the field coil. The manual indicated these can fail. Mine was actually missing a brush, moron PO. Anyhow a new set of brushes and I was good to go.

My 83, the field coil is the green and red wires coming from the generator.

Good luck.
 
Ah! What sillyness of me. The bike is an 83 Maxim XS400 - not sure what else there is model wise after that.

Thanks for the tips. I'm going to check general voltages while running tonight (will report back), status of brushes on the field coil, battery voltage at Idle, 2000, 5000rpm.
 
Early update. Didn't sleep so well, so I went into work early.

Here are some numbers. I believe they point to the charge system, not sure which part of it yet as I've not measured the field coil resistance, stator resistance or checked to see if either of these have good connections running to them.

I do know the following;

1. New battery started the bike way better, headlight brighter, lights brighter etc.
2. Battery voltage on idle: 12.18V
3. Battery voltage at 2000 RPM 12.17V
4. Battery voltage at 5000 RPM 12.17V

Something tells me my charging system isn't quite working....

So next for me is to dive into the wiring diagram and manual and start doing some measurements on the charging system.

I work at a company that designs and manufactures electric bicycle components, accessories etc, we have a bunch of nice high power Neodymium permanent magnets lying around. Has anyone done a PM conversion of the field coil? I imagine that gluing the magnets in with all the oil could be a problem...
 
Measure the resistance at the 3 white wires coming from the generator. Mine measured 1.2 at all three wires. Then check the resistance at the field coil, green and red. After I replaced the brushes it measured 4.5.
 
Thanks for the welcome!

Bad news on the stator front - open circuit at the connector going into the voltage regulator/rectifier.

The field coil measured 9.0 Ohms, which is out of spec (4.5 Ohms) for the 82 manual (couldnt find an 83 manual, but Im guessing they are pretty darn similar).

Going to dive into the side casing and see what I see.. woohooo!

I'll keep everyone posted on this adventure. It might turn into a PMA swap quickly.
 
Corroded stator wires they are disconnected at the stator itself.

The stator/field coil are not where I thought they were. Above and forwards of the front drive sprocket. Would have assumed that it was in line with the crank... Pictures didn't make sense - I must have been looking at the xs650 too much.
 


The bike!



I thought the charging components would have been at the crank-shaft. Now I'm a bit confused - I need to see a diagram..



2/3 of the stator wires, and the winding center point (I'm guessing it's a Wye winding) were completely corroded inside the housing. They were not making contact at all.



I'm going to attempt to repair this as it is.

I've resoldered the Wye connection point as well as beefed up the insulation on the three phases leaving the stator. I've also conformal coated the entire assembly. Put glass insulation on the connection above as well as the other connections. Tie down with nylon thread. Epoxy thread in place. Win.

I will have to rip out the 3 phase wire harness and re-install a new one with the appropriate or new connectors to the regulator/rectifier.

Hopefully tomorrow I'll be able to;

0. Clean out all the gunk behind this cover. Holy shit it is messy.
1. replace the wiring on the stator, test and re-install everything
2. test charging system while motor is running
3. change motor oil and filter
4. bleed front brake and adjust banjo so that right turns full lock dont pinch the front brake hose!! :doh:
 
I know it may be a long shot but the PO put the wrong tail light bulbs in my bike and after I replaced the VR and those bulbs it is charging great.
 
I ended up crimping and soldering the connections. I used larger gauge wire that had insulation as well as fibreglass for heat resistance, so it was a bit of a challenge getting everything to fit in. However, I accomplished it using zip ties to hold things down, followed by nylon thread (rated to 220C) that was then epoxied down.





Charging circuit is running fine now.

Showing about 13V at idle, and 14.5V at 5000rpm.

Success!

Now.. to solve my low RPM torque problems, fix the front caliper bleed screw (it's broken off in the caliper of all things...), bleed the brakes, adjust the front brake banjo so that the front hose doesnt get squished between the tank and fork, replace the front disk, and do an oil change.

Apparently I should also clean the carbs or something?
 
Welcome to the site. You rewired that like you knew exactly what the heck you were talking about, electricity-wise at least. Electrical issues are always an issue around here and I for one am sure glad to add more electrical knowledge to the site. Can't wait
 
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