Topic: Custom 750K drains battery rapidly when key is turned on

[BB63gunner]

Greetings all.  Any help would be welcome.

This is a chopped 750 I've had most of my life.  Basically trouble free until now when I'm thinking about selling it.  It's like the thing knows.  Anyway it has the most basic wiring imaginable, so I'm feeling sorta like a dumbass for not figuring this out myself.

Long story short, after troubleshooting by disconnecting wires until the problem went away led me to the wires going to the points (blue and yellow).  When I disconnect them, the battery no longer drains (with one or both points closed and grounded of course).  This baffles me as the points are working as designed and spend most of the arc closed.  So why didn't I notice a voltage drop before?  The fuse does not blow but the drop is rapid.  I'm going to list a couple of possibilities below that may have some bearing on this.

- My old ass hasn't been riding much lately, the hardtail takes it's toll these days.  So I had to replace the battery recently.  Instead of going with the good old reliable Yuasa wet cell I have always run, I went with a less expensive dry cell bought online.  It is rated as 12V14AH like the bike calls for.  But I doubt that it's as strong.  Is it possible that if I have a weak battery the points would cause a voltage drop that would be unnoticeable on a strong battery?

- I noticed this problem at first, because when checking battery voltage it was low.  But when charged it would hold voltage without the key on.  Only drop when the key was switched on.

- I would really like some input before replacing another battery at today's cost.

Any help from an electrically minded SOHC rider/mechanic would be greatly appreciated.  Thanks.

R/,
Mike.

[kerryb]

I would start with an ammeter connected between the battery post and ground to see how many amps are being drawn.  Don't be buying a battery until you know why or what the problem is.

You could take the battery to autozone to put it on a load test to see if the battery is capable.  Suggest charging it first.

[scottly]

First of all, just how fast does the battery voltage drop? Each coil will draw about 2.5 amps when it's respective point set is closed. The stock regulator will add another 1.8 amps of load. When the motor is running, does the battery voltage go up?

[Bodi]

As nothing else has changed this seems like a bad battery. The original battery just got old, and the new one is a dud. The regulator and coil(s) draw quite a bit of power, a good fully charged battery's voltage should not drop very quickly: you should measure the amps and confirm there is no unusual load. Rotate the crank to where the points close and open for both coils. Points should close for roughly half the rotation, mostly only one will be closed but there is some overlap with both closed so if lights are off the load should vary from around 4 to around 7 Amps as the crank is turned.
A good 14AH battery should stay above 12V for at least an hour with this load applied. Weak battery... nope.
There are two basic battery tests: max amps and capacity. Usually auto stores can only test max amps.

[Deltarider]

Most likely a bad battery. What brand is it? You could try to revive it by connecting it to a multiphase charger for 24 hrs (max. load 1,5A).

[BenelliSEI]

So...... ? What happened??

[BB63gunner]

All,

Apologize for the delay in responding.  Especially since your inputs were awesome quick.  I can't stay on this problem every day as i'd like, keep getting dragged away.  I'm also new at this forum and posting stuff.  I know the goal is to benefit everyone, problem and results.  So if I'm screwing up, I'm open for advice.  I'll answer your posts below:

calj737 -

Good reminder/info on the coils energizing and the voltage drop.  I am leaning towards a crap battery more and more.  Thank you.

kerryb -

I'm not familiar with an ammeter.  I'm no electrical genius.  I do have the amps function on my multimeter with three ranges; 200m, 20m, and 2m.  I hooked the leads (with jumpers) between the neg. post and the grounded battery cable and got no reading whatsoever in any range when i turned on the key.  I am going to consult with someone with a better electrical knowledge than me, should be here in a couple of days  As far as autozone doing a load test,  I have to disassemble the whole back of the bike to remove the battery, so I am going to do other checks first.  I appreciate your advice and will keep it in mind.

scottlv -

Voltage drops from 12.5 to 9 volts in about 5-7 seconds before I freak and shut off the key.  Then it rebounds but not back to the starting voltage.  As far as voltage increase when running, I now have other issues.  It's only banging on 3 cylinders at the moment.  It's prone to clogged jets and yes I've cleaned carbs, replaced hoses and filters.  The damn thing doesn't want to be sold I'm telling ya.  Also I broke one of the brittle wire connectors from the field coil to the electrical box so it's not going to charge right now.  I know I have to get those things right to continue sensible troubleshooting.  I was hoping to solve the voltage drop issue first in case it had something to do with the other issue.  I've been told troubleshooting can be waylaid unless battery voltage is good and I agree with that.  By the way all these other things happened after the first posting.  Thanks for the input.

Bodi -

I want to agree with the bad battery theory, especially the way you describe it (1 hour under the load of coils and regulator should be fine).  I am planning on doing the amp check as soon as I get educated (see answer above) and thanks for the response.

Deltarider -

I am tending to agree with the bad battery.  The one I purchased online is a dry cell Sigmas Tek STX14AHL-BS.  I have done the charging routine several times with the same voltage drop result.  I was thinking maybe dry cells act differently than what I'm used to, but a battery is a battery..........right?  Thanks for your time and input.

BenelliSEI -

What happened is this.  Every turn sends me down a different rabbit hole.  It's the voltage drop when points are closed that has me stumped, but is getting clearer.  I will work each issue until I get it right and respond.  As previously stated, I can't stay on top of this every day.  But I certainly appreciate every ones input and help.  So please don't think I am ignoring anyone.  Thanks for asking.

All -

You post to help other riders/wrenchers.  In my book that makes you all right and I hope you have a great Christmas and New Years. 

Thanks,
R/,
BB63gunner

[scottly]

scottlv -

Voltage drops from 12.5 to 9 volts in about 5-7 seconds before I freak and shut off the key.  Then it rebounds but not back to the starting voltage.  As far as voltage increase when running, I now have other issues.  It's only banging on 3 cylinders at the moment.

Your battery is toast. The running issue is most likely due to too low of voltage supplied to the ignition coils.

[BB63gunner]

To all that posted, thank you.  Pretty much all the info and advice was spot on.  I

I want to finish up now I have some results, so other riders can benefit and finally put some closure to this.  So sorry it took so long.  Let it suffice to say , "life happens".  I got back to work on it about a month ago, the results are as follows:

- First of all I found brittle and broken wiring under the electrical box.  These intermittent voltages sent me down numerous rabbit holes and threw me off on most troubleshooting.  This almost cost me money on parts I didn't need.  Lesson learned.
- Me buying a cheap ass battery was the main problem.  Thanks for educating me on the ignition coil and regulator drawing voltage at key on.  Went back to the good old Yuasa and no more problems there.  Lesson learned.
- The charging problem was a combination thing.  Those intermittent wiring issues prompted me to buy a combination regulator/rectifier.  That and the more available space deal.  The unit I received was faulty.  No voltage out the white wire means the field coil won't work, the alternator in general won't work.  Replaced with the original reg/rec and she charges just fine.  Almost spent more money on stator before I figured that one out.  Lesson learned.

So, new parts (battery or rectifier/regulator) doesn't mean they are good and will work.  Electrical troubleshooting is hard enough for someone like me without having intermittent faults.  So I hope this will help someone else down the road, like the help I got on this site.

Many thanks,
R/,
Mike.

[madmtnmotors]

Way to stick with it! Electrical problems can be the toughest to get sorted and often requires eliminating what it's not.