Topic: Brand new battery killing problem (K7 CB750)

[coma13]

A brief preface: The electrical on this bike (1977 CB750K) was a mess when I got it, none of the peripherals worked and I went through and greatly reduced the overall wiring volume. There are no turn signals, the electric start is wired, but never used (I suspect a problem with the switch as it worked before my rewiring adventure), and my light runs the high and low beam at the same time, whenever the key is on.

I realize that this is a less than optimal wiring setup as it stands currently, but it was running fine for the last several hundred miles.

Fast forward to last week: I start classes and that involves a 6 mile ride on the freeway and a 2 mile ride on a surface street to get there. On my first day of class, I ride up there just fine and then a quarter mile before school, I pull up to a stop light, clutch in, as as the RPMs drop to idle, the bike just dies. I push it to the curb and try to start it but to no avail, I can see one of the filaments in the bulb dimly glowing. I got a jump start, didn't let the idle RPM drop below 3K and zipped home. When I got home and turned the bike off the headlight was dimly lit and faded quickly.

I figured my battery had just run its course, as it had been less than optimal when I first got it and had been discharged from sitting for weeks at a time. I bought a new battery (AGM 12V 4AH) which I figured would be fine since I don't use the electric start.

It fired right up, idled strongly and took me to work and back without any hiccups (3 miles each way). Today I head up to class again and just as I'm parking my bike, it dies. I realized that my lights are out and there is no hint of a glow in any filament. I go to class and return to the bike an hour later, surprised to see that my lights actually turned on when I turned the key, I kicked it over and it fired up first kick. I used my same technique as before, keeping the idle up, and zipped back home. As I pulled into the driveway, I let the idle drop into the sub 2K range and the bike died instantly. No glow from any filaments at all.

WTF is going on!?

I literally JUST got a multimeter and haven't the slightest idea how to use it, but I really need to get this figured out ASAP so I can use this thing to get to school and back on.

I'm a little perplexed as to why this would have just started happening as I've ridden it on numerous 50-100 mile rides without any similar symptoms at all, as recently ago as 3 weeks.

[audiofile]

There are several threads on this subject within the forums. Try OregonMotorcycleParts.com, He has a nice section covering pretty much all the troubleshooting for this problem, and more.

[coma13]

So I just came back to the bike an hour and a half after riding it home and having ZERO glow in the headlight and turned the key on and the headlight turned right on. Not full brightness, but about as bright as it was when I turned it on in the school parking lot.

Thank you, audiophile, I'll go have a look around.

[TwoTired]

Batteries supply power from a chemical conversion reaction.  They don't generate or store electrical power directly.  Electricity is used to make the chemicals convert (charging) and electricity is produced when they convert the other direction.

Battery depletion is when most of the chemicals have converted, leaving the rest sparse.  A battery exhibits limited self recovery as chemicals migrate or redistribute within the electrolyte.

The reason why you need to rev the engine to stay running is because that is the only time the battery recharges.  At idle, the alternator doesn't supply enough power to run the bike.  So, the battery makes up the difference in depletion mode.

Keeping the battery charged then becomes a balancing act of keeping enough charge in the battery to compensate for what the alternator can't make, vs the duration of higher RPM operation when it can.

Normally, the electrical load of the bike is less than the alternator makes when revved.  Any excess power generated can be used to restore a depleted battery.  However, the excess produced is small, and the battery is large in capacity.  It will take 10-12 hrs to fully restore a depleted battery while revving the bike at 5000 RPM.

So, your bike's electrical load now comes into question.  As stock bikes don't have nearly so severe a problem, the first question is "Has the electrical load been changed or increased from stock?"  If yes, you may have exceeded the maximum available from the stock alternator.

It is also possible that the charging system has been damaged in some way.  Reversing the battery connection polarity is a good way to do that.  Also, smacking the alternator with pavement is another.

Your first course of a action is to fully charge the battery from a source separate from the bike.  Mind the polarity connections.
Next after charging, is to monitor the battery voltage at idle and at 1000 RPM increments up to 5000 RPM.
You should report these findings to us as well as all specific changes to anything electrical made to the bike since it was brand new.
We have access to stock wiring diagrams in which to trace electrical flow.  But, not the custom diagram you made for your bike.  Please post that.
With those tools we can get you on your way toward restoring your bike to reliable function.

Cheers,

[bollingball]

You have all ready increased the load by having the high and low beams on at the same time plus any thing else you have added. Like TT said get a good charger/maintainer (automatic) don't want to over charge it with a big car charger.A few more times of draining and charging will mess up your new battery

[coma13]

Awesome. Thanks for the response. I'll get all of the info to you guys by the weekend. The knowledge base on this forum never ceases to amaze me.

[coma13]

OK! So I haven't had a chance to map out my wiring diagram yet, but I did get to put the multimeter on the battery (my "old" battery since I had stuck it on the charger when I put the new one on) and got some readings at different RPMs.

Also, I just remembered, recently my taillight stopped working, but my brake light continued to work. In need of a quick fix to avoid getting run over at night, I just manually fixed the brake switch in the "ON" position, so that the brake light runs any time the key is on. That, plus the fact that my high and low beams are running simultaneously should be the only extra pull on the electrical system while it is running.

First of all, can anyone tell me if I was using the right setting? I had it here:


The voltage I recorded was as follows:

Wired up to bike, key switch on: 11.77V
1000RPM: 11.9V
2000RPM: 12.2V
3000RPM: 12.4V
4000RPM: 11.92V
5000RPM: 12.02V

Weird, right? Was I on the wrong setting, or is this indicative of any particular charging illness in and of itself? I'll try it again with the new battery tomorrow after it's charged back up.

Thanks again for all the help.

[TwoTired]

That is the correct setting on the meter.

Charging system isn't working very well, it appears.
But, you have to do the test with a good, fully charged battery.

Looks like you tested with a depleted battery  And a sick battery can't be mended/or charged instantly even with a good charging system.
You actually WANT the battery to change it's voltage slowly.

[Spanner 1]

Your bike is not charging the battery and depleting it every time you ride. You must be putting it on a charger every night and not riding more than a few miles between charges ! If that's your bikes lifestyle then O.K., don't need to mess with anything.... if your of a curious mind and like to know why/how it's not right , then ask questions here. But do the responders a favor and do like they suggest ( simple tests with your meter ) and hang-in there until fixed... shouldn't be too involved. Or just throw parts at it until solved, both paths work... just please choose one !!
TT responded just as I was going to post, so I defer to him.... except for choose your path part 

[coma13]

Alright! Sorry for the delay. Various life happenings have kept me from being able to get back at this. I went digging through the wiring and found a bunch of exposure in the wires emanating from the alternator, so I went in and reconnected and covered all of those up. I'm in the process of just finishing the rewiring now and I wanted to post my wiring diagram before I finish it all up.

Does anybody see any reason why this setup wouldn't work? I've omitted wire colors except where absolutely necessary to illustrate my intentions (I think.) Please let me know if it isn't clear. (One thing I'm not sure if is the placement of my single fuse, and also how many amps it should be.)



Thank you!

[TwoTired]

You've drawn a kill switch that is the grounding type.  It will, kill the spark alright. It will also blow the fuse each time it is turned on because it will connect the hot side of the battery directly to the neg side of the battery.  If the R/R doesn't isolate the black from the red, the kill switch will smoke that up, too.

What you want is a kill switch that opens the power line to the coils when activated.

Without knowing what coils, headlight, and taillight you are using, it is unwise to state minimum fuse size.  However, 15A is what the stock bike uses.

[coma13]

Thanks, TwoTired! Precisely the kind of input I wanted. I was totally unclear on the operation of the kill switch and just drew my conclusion based on the wires that came dangling forth from it.

If it's not too much trouble, could you show me what type of kill switch is appropriate? I'd prefer something as simple as possible. If I understand correctly, I'm looking for something that closes the connection to the coils in one setting and simply disconnects that closure in the other setting. Correct? If correct, I could just wire in an on/off push button between my main switch and the coils, and mount it on my bars.

This is the one I was planning on using (thankfully JUST planning).

[coma13]

Without knowing what coils, headlight, and taillight you are using, it is unwise to state minimum fuse size.  However, 15A is what the stock bike uses.

Stock coils, stock headlight and tail light. I might wire the headlight to run the high and low beams at the same time, as I had in the past.

[coma13]

Does anything else in that wiring diagram look like it's going to cause everything to go up in smoke? Assuming that I install an appropriate kill switch in the appropriate place.

[TwoTired]

If it's not too much trouble, could you show me what type of kill switch is appropriate? I'd prefer something as simple as possible. If I understand correctly, I'm looking for something that closes the connection to the coils in one setting and simply disconnects that closure in the other setting. Correct? If correct, I could just wire in an on/off push button between my main switch and the coils, and mount it on my bars.

Seems you have the correct idea.  I've only used the stock ones, which (Surprise!) works quite well.  The stock has OFF-RUN-OFF positions, where power only passes through it in the RUN position.

Stock coils, stock headlight and tail light. I might wire the headlight to run the high and low beams at the same time, as I had in the past.

Power budget estimate for your diagram:

2 amps for the alternator
3 amps  - 5 ohm coils driven with points.
1 to 3 amps for the tail and stop light
4 amps for a 50 Watt headlight element.
3.2 Amps for 40 Watt headlight element.

15.2 amp total, or 206 watts

You should run a fuse at about 2/3 of its rating.  So, with 90 watts at the headlight you ought to run a 20 or 25 amp fuse.

The 210 watt alternator won't keep up with a 90 watt headlight (plus the other loads) at idle (where it delivers about 40-60 Watts), and just barely will keep up with the power load when revving the engine to 5000 RPM.  If you don't put a switch on your headlight, plan on pushing the bike a lot due to a depleted battery.  Or, don't stray too far from your "at-home" battery charger.

Cheers,

[coma13]

Great input! Thanks. It looks like a headlight switch is in order to take it easy on my poor little alternator.

[phil71]

the thing that's bugging me is, your updated reg/rectifier doesn't know that the headlight is wired screwy, so it ought to be trying to force the dynamo to make more power, even if the dynamo wont like it. At best, that scenario would result in losing horsepower, at worst, melting field coils, but neither of those things seems to be happening to you. I DEFINITELY agree you need to lighten the load by ditching the portable sun you're sporting, or at least picking one beam, BUT, that regulator may be toast too if you're getting those numbers at 5k.

[TwoTired]

The SOHC4 alternator is self limiting on output power.  It can never make more than it is capable of providing by design.
If the current limit is reached, then the voltage stops building in the stator windings, and the reduced voltage limits the power output.
While capable of making 14 amps with a load that demands that or less, asking for more than that 14 amps of power will actually reduce the output current.

This is one of the reasons why the stator is so robust and very rarely do the stator windings fail unless some physical (rather than electrical) trauma is applied to it.

Cheers,

[coma13]

the thing that's bugging me is, your updated reg/rectifier doesn't know that the headlight is wired screwy, so it ought to be trying to force the dynamo to make more power, even if the dynamo wont like it. At best, that scenario would result in losing horsepower, at worst, melting field coils, but neither of those things seems to be happening to you. I DEFINITELY agree you need to lighten the load by ditching the portable sun you're sporting, or at least picking one beam, BUT, that regulator may be toast too if you're getting those numbers at 5k.

Just to clarify, those voltmeter readings were all taken before I dove back into the wiring at all and had a different REG/RECT on there. The new one hasn't seen any electrical charge yet as I've still only mocked up the wiring. Hopefully I'll have time this weekend to flesh it all out with the advice of the forum.

[coma13]

Update time! My bike has been down for several weeks for other, non-electrical work and I had thought I had the wiring pretty much figured out.

I took it for a short ride today, and unfortunately my battery still wasn't charging.

This is my wiring diagram as it currently stands (the kill switch isn't actually in there, just a loop of wire running up to the handlebar where the switch will be installed when I get one that I like).



Any pointers on what to start checking at this point? I tested the voltage at the battery terminals up to 4K and saw no rise in voltage at any point.

Thanks in advance!

[scottly]

What is the voltage on the white regulator lead with the ignition switch on, and the motor not running? What is the battery voltage under the same conditions?

[Spanner 1]

Still don't know what rect./reg. is on this bike ?? Is it an aftermarket solid state one ?... If so, most a/m products use BLACK as Neg. - 12v whereas on all our SOHC Honda's BLACK = Pos. +12v. So if that's the case, your diagram is putting +12v to the NEG. side of the rectifier ( which may have blown the first time you connected it that way)  = no charge and battery deplete....
BTW... unless you wear sunglasses at night while riding  you need to go back to stock h/l wattage, no possible need for high and low on together.......which would grossly overheat the bulb capsule and cause both filiments to fail = no headlight to get home by. 

I guess the question is; what r/r and exactly what color wires are attached to it ? ( Just the unit, off the bike ).

[TwoTired]

Charge the battery first.  Then...

I would monitor the Black wire at the Vreg while revving the engine.

If battery voltage is present there, then move on to monitoring/measuring the White and Green at the alternator while revving the motor.  You must get some power there for the alternator to make any.

It is best to report the actual numbers on the digital display, rather thatn just use your own assessment of Good" or "bad".

Did you ever tell us the Reg rect brand and model you are using? (I didn't reread the entire thread.)

[coma13]

What is the voltage on the white regulator lead with the ignition switch on, and the motor not running? What is the battery voltage under the same conditions?

I checked this this morning with a fresh charge before riding (successfully) 30 miles to work (20 on the highway @5000+RPM). I brought my charger and the charger indicated the battery was topped up within an hour or so of putting it back on the charger.

Voltage @ white regulator lead with switch on:  11.65
Voltage @ battery with switch on: 12.16

After ride to work:
Voltage @ white regulator lead with switch on: 10.85
Voltage @ battery with switch on: 11.32

Still don't know what rect./reg. is on this bike ?? Is it an aftermarket solid state one ?... If so, most a/m products use BLACK as Neg. - 12v whereas on all our SOHC Honda's BLACK = Pos. +12v. So if that's the case, your diagram is putting +12v to the NEG. side of the rectifier ( which may have blown the first time you connected it that way)  = no charge and battery deplete....
BTW... unless you wear sunglasses at night while riding  you need to go back to stock h/l wattage, no possible need for high and low on together.......which would grossly overheat the bulb capsule and cause both filiments to fail = no headlight to get home by. 

I guess the question is; what r/r and exactly what color wires are attached to it ? ( Just the unit, off the bike ).

It's an Electrosport ESR240 solid state reg/rect. I'm pretty sure that the black wire on that model is + from the regulator. Also, I've got a headlight switch on there now. No double filament burning for me anymore.

Charge the battery first.  Then...

I would monitor the Black wire at the Vreg while revving the engine.

If battery voltage is present there, then move on to monitoring/measuring the White and Green at the alternator while revving the motor.  You must get some power there for the alternator to make any.

It is best to report the actual numbers on the digital display, rather thatn just use your own assessment of Good" or "bad".

Did you ever tell us the Reg rect brand and model you are using? (I didn't reread the entire thread.)

I'll check this out when I get off work. It's an Electrosport ESR240, by the way.


Thanks guys!

[Spanner 1]

That reg./rect. ( ES 240 ) is plug-and-play.... so no grounding issues there  ... correct for SOHC's.