Charging system inspection after battery died

[TylerLew89]

So last month I bought a used 2003 Ninja 250 off CL for my wife. The thing hadn't run in a few years and battery was shot.

Bought a new battery, changed fluids, slapped some new tires on there, replaced the fork seals, and serviced the chain and the bike was as good as new.

At the time I put the new battery in I "tested" the charging system by measuring the resting voltage of the battery and measuring the voltage at around 4000 rpms. Resting voltage was right around 12.6 Volts and running voltage was around 14-14.2 volts. To me, this meant I was good.
Just this past weekend my wife took the bike out and after filling up for gas, the bike was dead. Like, no dash lights dead. Battery voltage was at 8 volts. Tried to leave the battery on a charger for a bit but it wouldn't hold. Would read 12.5 volts only to go back to 8 volts after one click of the starter. I replaced the battery and rode the bike home.

After getting home I checked the manual for charging system trouble shooting. The stator checked out fine. At ~4000rpm the stator was putting out 45 volts of AC. When I checked the resistances in the regulator/rectifier I found some weird numbers. Most notably was flipped resistances through some wires. Manual said resistance should be infinite one way and ~400ohms the other but my multimeter was telling me the opposite story. Went to ebay and bought a "working" replacement off the same year bike.

The new part came in today and I quickly checked the numbers again. I am getting the exact same readings on every connection as I did on the old one. Now, my multimeter is chinese ****. I bought it for like $5 off amazon. I know its **** so I don't take the numbers as absolute truths, just the ballpark usually.

I am hoping to borrow a much nicer multimeter from work tomorrow but in the meantime can anyone think of another reason why the battery was dead so quickly? Is there another part I am overlooking that could have failed?

There is a small chance that my battery tender cable could have caused a short and drained the battery. It was hooked to battery and looped around the gas tank vent clamp. The cover on the cable was off as well. The bike was running fine prior to this event so I am not sure how quickly the drain occurred. Also unsure how a low voltage 250 reacts. Older larger bikes of mine wont crank below 11 volts so unsure how the ninja got to 8

Thanks

[InvisiBill]

That's about all there is to the charging system. The stator puts out AC, the R/R rectifies it to DC and regulates it down to ~12V. If you're replacing it anyway, I suggest looking into the MOSFET R/R mod.

I would expect it to have problems at 8V, both in actually cranking, and in working voltage for the igniter. Use your ammeter and see if you're getting any usual current draw while the bike is completely off, or key-on but not running.

Is 45VAC within spec? On the 500, they say 60. (The 250 may very well be a different number, but they use the same R/R.)

My Clymer's R/R test procedure says that you should get a high reading one way and a low reading the other way (at least 10x difference), but it doesn't say which direction you should get each. I'm thinking that your test may not have been conclusive of a bad R/R if the only issue was opposite directions.

[csmith12]

Welcome Tyler!

Always... suspect the battery first. The stator can be ohm tested so you don't just "throw parts at the problem" but the rectifier is a bit more tricky. Both high and low sides must be tested and CAN'T be tested with a meter. This is where friends with parts or the exact same bike come in handy.

Good luck sir!

[TylerLew89]

Originally Posted by InvisiBill

If you're replacing it anyway, I suggest looking into the MOSFET R/R mod.

Thought about it but got a replacement oem part for $15. Doubt my wife will want to keep this bike for more than a year or two. I like things simple.

Originally Posted by InvisiBill

Is 45VAC within spec?

Yes. Manual says that at 4000 rpm I should read "about 45VAC" from the stator.

Ive attached the chart for ohming out the rectifier from the manual. I am thinking that my multimeter just must be ****. I def have the + and - leads hooked up right so it makes no sense why I am getting reversed readings. I know ****** meters will give very inaccurate results but switched + and - seems like a horrible error.

Unless I am reading this chart wrong? To me, I hook up the positive lead to a yellow wire and the negative lead to the black wire, I should get between 200 and 600 ohms. My meter reads it as discontinuous. Works when I flip + and -

Csmith, what do you mean it can't be tested with a meter? I have only ever seen them tested by checking resistances. Do you mean that standard meters aren't accurate enough?

I am beginning to think that either the battery was defective and just went bad or that the leads I had on for the charger caused a short.

In my stupidity Invisibil I read your question about amp draw and said "Hmm, ill go check". Switched my meter to amp draw, swapped the positive lead over and stuck the thing against my battery. Very quickly learned why that was stupid...Looks like I can't measure amp draw anymore on this thing lol

[RacinNinja]

Amperage goes in line with the positive, IE battery terminal to positive battery cable, not positive to negative. However, most meters go to 10 amps so it's not enough anyway unless you're checking it with the key on and not starting.