Topic: Chasing a discharge. Where to start looking

[fatcaaat]

I finally got my 750k model fixed to be ridable.  Brake caliper rebuilt, carb rebuilt and electronic ignition.  Now, I have to figure out the one thing that has been plaguing me...my battery is discharging.

Anyone know the common reasons why the battery could be discharging?  I put it on the charger and a week later it won't spin the battery or honk the horn.  Frustrating.  The battery is fine if I disconnect it from the lead and let it sit for a week, but if I leave it connected, it will be dead. 

Any ideas on where to start looking?  Somthing is drawing power when the switch is off.  Oh...and it did this even before i put the electronic ignition on. 

[BobbyR]

What you are describing is a classic symptom of a short circuit draining you battery. It requires a point by point inspection of your wiring. The first places to look is where a wire runs close to the frame, which is about everywhere. I have read that under the clutch cover here have been some problems. The headlight bucket is a rats nest of wires so that would be a prime candidate also.

[kghost]

Well it seems simple but.....make sure your not taking the key out in the wrong position.

Leaving the tail light on....


I've done it lol

After that its checking wires

[sandcastcb750]

Find out if the charging system works. Should be about 14 volts at a fast idle at the battery leads. If not, bad stator, other or wires disconnected or corroded ect.

If it charges, you must find the short. systematically.

That is why I replace all the wires after a restoration with as much NOS wires, switches as possible.

[TwoTired]

Does the battery still drain if you remove the main fuse?

If so, it's likely the charging system.  I'd check the rectifier first.  It's always connected to the battery and if the diodes inside it fail, then the battery drains into the stator windings. 

There's and electrical FAQ on this site.

Cheers,

[mark]

I would likely start by disconnecting the battery ground and connecting a test light between the battery and cable. If there is enough of a draw to light the bulb, unplug things like rectifier, stator harness, ign. switch, etc. until the light goes out.

I found a nasty intermittent short where the strain relief(sharp metal thingy) on the ignition switch had bit into the + wire(nicely hidden inside the rubber boot, I might add).


Good luck.

[fatcaaat]

Great suggestions.  I can rule out the battery charging issue.  No problem there.  Once I get it started up and ride it for a while.  I can shut it off and hit the button and it turns right over just fine. 

I guess it is just going to be a fun time to figure this out!  Ahhh...the joys of owning a vintage bike!

[hymodyne]

Are you running a stock headlamp or a halogen replacement? I was running a halogen bulb from a car which was drawing too much juice, killing my battery within about 45 minutes of running. The 60-50 watt halogens are  kinder to our batteries than the higher wattage replacements sold for car applications.

hym

[InaneCathode]

I'd probably start with pulling fuses until it goes out, then unplugging things. That'd be easier than unplugging everything straight off.

[fatcaaat]

Thanks guys...looks like I'll play detective this weekend.  I've been using my multimeter for this type of thing...its about time I get a test light I suppose. 

[TwoTired]

Thanks guys...looks like I'll play detective this weekend.  I've been using my multimeter for this type of thing...its about time I get a test light I suppose. 

You don't need a test light if you have a multimeter of sufficient capacity.  What is your meter's amperage measuring capacity?  As long as your current drain is below what the meter's capacity is, that is a superior troubleshoot tool.  Just insert the meter in series with a battery connection.  The scale will read just what your current drain is.  Remove the main fuse.  Is is still there?  If so, you just eliminated most of the bike as a problem.  Anyway, when you find the drain load by disconnecting it, the meter will cease to show a drain.

I still wouldn't be surprised, if you find the rectifier partially bad.  Just because it still charges, doesn't prove it isn't causing the drain.  One bad diode won't stop if from charging, but it will still drain the battery.

Cheers,

[scondon]

Does the battery still drain if you remove the main fuse?

If so, it's likely the charging system.  I'd check the rectifier first.  It's always connected to the battery and if the diodes inside it fail, then the battery drains into the stator windings. 

There's and electrical FAQ on this site.

Cheers,

  +1

    My rectifier was draining the battery with key in off position. About 1.2 amps/volts(i can never get this straight) drain was measured. Took about a week to kill the battery. A new rectifier cleared things up.