Topic: CB 750 not charging

[aminemed]

Hi

My CB 750 is not charging my battery while riding. I would like to start running it through the electrical troubleshoot, but first i have a question

I know that the first step is to read voltage when engine is at 2000 rpm, 3000 rpm, etc. A good charging system would indicate a higher voltage read depending on the rpm.

My question is on the proper method to run this test. I start my bike using electric start. How much time later should i perform this test after riding the bike ? Then, should voltage reading be at battery + and _ ? I have difficulty to understand how my battery voltage can rise to 14.5 if above 5000 rpm? In my understanding battery voltage increases slowly when plugged to a wall charger so how can it jump so high when engine is pushed to 5000 rpm? Is that means that voltage reading should be elsewhere than at battery + and - ?

Thank you for your help

[Stev-o]

Youre over thinking it. 

Start the bike and check voltage at battery at idle, should be around 13V.   Then check it at 3000R and 4000R, each should be higher. 

[MoMo]

Youre over thinking it. 

Start the bike and check voltage at battery at idle, should be around 13V.   Then check it at 3000R and 4000R, each should be higher. 

Agree, you do not need to wait.

[oatmeal400f]

set your ohm meter to 20V,
then hook up the positive and negative terminal on the battery.
after starting your bike your meter should have at least 13V during idling
as RPM goes higher your voltage should go up as well,
but if you see 15V and above you are over charging your battery and that can damage your battery.

if voltage is too low and you are using the old school regulator (not the solid state regulator) you can actually adjust the voltage output, just take off the regulator cover, and adjust the screw on the regulator. you will see changes on the ohm meter.

if that regulator is not fixing the issue, you should check if your rectifier is functional.

check this link
https://www.youtube.com/watch?v=F-Bw9xz09FU

[evinrude7]

Hi

My CB 750 is not charging my battery while riding. I would like to start running it through the electrical troubleshoot, but first i have a question

I know that the first step is to read voltage when engine is at 2000 rpm, 3000 rpm, etc. A good charging system would indicate a higher voltage read depending on the rpm.

My question is on the proper method to run this test. I start my bike using electric start. How much time later should i perform this test after riding the bike ? Then, should voltage reading be at battery + and _ ? I have difficulty to understand how my battery voltage can rise to 14.5 if above 5000 rpm? In my understanding battery voltage increases slowly when plugged to a wall charger so how can it jump so high when engine is pushed to 5000 rpm? Is that means that voltage reading should be elsewhere than at battery + and - ?

Thank you for your help

simply put, you're also reading what's being put back into the battery when it's on the running bike and raising the rpm.  first charge your battery fully.  let it sit a couple hours.  test the battery.  you should see 12.8 v or there abouts.  put the battery back in the bike.  start the bike.  test the battery at various rpms.  post results.  make sure your volt meter is set to 20V DC.   

[aminemed]

Hi

thank you for the replies.

I went before posting on all the suggestions, my battery is fully charged but when plugged to my bike, it stays at 12.8 at the different rpm: 2000, 3000, etc..

I have changed the rectifier and regulator with a new combined unit: please see it on the picture (bought from electrex). This combined unit has a big plug with 5 wires: 3 yellow, 1 green and 1 red and 2 separate flying wires, 1 black and 1 white.

Wires should connect this way:

* The 2 separate wires, black wire and white wire, should be wired with the black and white wire that usually connect to the rectifier.


* The 5 other wires in the big plug should connect as in the picture, 3 yellow wires to the 3 yellow wires going to stator, 1 green to green (ground) i guess and red to red (battery +).

My issue is that in my wiring harness, i have a big plug connector with wires as follow (you can see in the picture)
 
* There are 3 yellow wires (that match the other 3 yellow wires, so ok for this one)
* 1 big red (i suppose battery +)
* and one another red (don't know what is this one).
* There is no green wire to match the combined unit green wire. Therefore, i suspect that this might be the issue.

Can you please help me to understand better this wiring ? Many thanks for your support

[aminemed]

Thank you for your help calj737

Im plugging this R/R to stock plugs. I believe that it should be plug & play without rewiring anything. I suspect that the PO has changed something in the wiring. Can you please tell me that indeed there is a big plug in the wiring harness that has 3 yellow wires, 1 green and 1 red and that connects to my R/R directly ? I can t find it on my bike, the only big plug i have with 5 wires is the picture i posted but it has 2 reds (1 of them might have been modified..)

I suspect this big red wire to be wrong (see picture, yellow arrow)

[aminemed]

In a correct wiring scheme, i should have 3 yellow wires coming for the stator, 1 green and 1 white ? right ?

which cover to remove, A or C ?

[MoMo]

Remove C first, you may be able to see if the PO hacked into the original wiring...Larry

[aminemed]

Ok wiring is all good, from the stator and under the cover i have 3 yellow wires, green, white but also the neutral switch wire and the oil pressure wire. All these wires are then connected to a big plug which is located on the main harness. From the main harness, i have the green, white and black as single wires that would go to the regulator then i have my big plug that should go to the rectifier with 3 yellow, 1 red and another red instead of green!! The sad thing is that understanding what is this red wire requires cutting all the main harness tape...i suspect that this red wire goes to the ignition switch..i should.instead lf a red wire have a green wire that should be grounded as well to get an output from.the alternator if i'm right

[aminemed]

Some more pics, checked everything again:

from the alternator to the wiring harness, all wires are good. You can see in the pictures the wire connectors as per the wiring diagram of a K2.

The green wire is going from my alternator to my regulator and also have the green wire grounded to the frame.

Bike is starting, i have all lights, etc..

But in my rectifier wires connector, instead of having the green ground wire, i have a red wire which is finally different from the red wire going to the fuse block and then to ignition. I need to cut all wiring harness tape to be able to track it

Anyways, is this lack of ground in the rectifier a good explanation of why my battery is not charging while runnning ? As i have the electrex RR24 combined unit, with the following wiring: 3 yellow, 1 red, 1 green and 2 flying wires: 1 black and 1 white, i'm left with the green wire that should connect to the old regulator. Can I cut the strange red wire that i have in my rectifier plug and replace it with this spare green wire that i have that should have been connected with the old regulator ?  I guess it should do the job, given that it is grounded to frame and coming from the alternator..please give me your thoughts.

[aminemed]

After reading in the forum, it seems that the first issue to check if my battery voltage is not increasing with the rpm is the alternator. R/R is only here to capture & regulate the alternator output. So i still don't know if the lack of green, ground, in my wires plug going to the rectifier / regulator unit, would prevent the alternator from delivering voltage. I have measured voltage at battery POS and NEG.

[aminemed]

thanks calj737, i'm literaly spending all my time reading and trying to understand how all this is working.

I'll definitely hook up the spare green wire that should connect to my regulator inside my wire connector instead of the unknown red one, to provide my R/R combined unit with a ground and test again at battery POS & NEG voltage at various rpm.

Hopefully, this should provide me with a positive result..

[Yamahawk]

You don't need to cut apart your wire harness to find where it goes. Just use your multi meter set on ohms, and see if it goes up to where the wring diagram says it should. If it doesn't then you might have to start tracing physically. But, see with the meter where it does go. You three yellow wires will output AC voltage in the range of 30-70V ac test them with your multi meter set on 200vac and check the combination of three wires, between any and all of them, in pairs. Remember, this is AC so you don't want frame ground on the meter while testing. Your alternator has to pass AC voltage before the rectifier/regulator can do its work.
Charlie

[aminemed]

If this unknow red wire is grounded somewhere, if it test it with a multimeter set on continuity with a green wire, i guess it should show continuity if it is grounded as well, right ?

[aminemed]

Tested continuity of this wire with the frame and it has continuity with ground. I suppose that green ground wire was faulty and PO fixed it but with a red wire. I need to look somewhere else to find my issue.

[dave500]

check the field coil and stator coils resistance first.

[aminemed]

Ok i'll run through resistance tests.

I remember that lately, my green wire grounded to the frame broke while i was riding. It happened to me twice and of course, it drained all my battery.

Do you think that this can destroy the alternator ? riding the bike without any ground.

[dave500]

stop losing sleep!just check those resistances.

[Yamahawk]

after checking your resistance, check your ac output also lol...
Charlie

[dave500]

a lotta charging issues are just corroded connections,unplug and look at all of those,the regulator and or recifier is often blamed when its an open field or dodgy stator,the rec/reg often gets swapped out to no avail blaming the new rec/reg,a proper diagnosis of the entire system is the only way to avoid #$%*,check the #$%*ing stator and field first!

[dave500]

ok cool calj,whats his stator/field resistance?ya gotta start from there or its an unknown,and ive seen plenty chase their tail to find a dud stator or field,after #$%*ing around with the rec/reg.

[dave500]

always work it backwards,be sure the source is fine first!

[aminemed]

OK i run the resistance tests / continuity test, on both field coil and stator

Field Coil: between white & green, resistance of 7.0 ohms and no continuity

Stator: resistance is a bit higher than what manual says, 0.2, i have a resistance of 0.6 and there is no continuity

i now suspect that my bike plug, that should go to the rectifier, has its red/white wire not connected properly. It can slide inside/outside of the connector and therefore, might have been grounded somewhere, or not even connected to R/R red wire.

What i should do next is run again voltage tests across the POS / NEG battery

[Yamahawk]

POS/NEG tests will confirm that your battery isn't charging while the bike is running. Once you have confirmed that, follow the instructions for testing the alternator's AC voltage output. At idle, the voltage between any two sets of the three yellow wires at the connector to the VRR will confirm if it is indeed output of proper AC voltage. It should be about 20-30VAC at idle, and as much as 70VAC at 3000rpm.  Not sure of exact voltage, but you should be reading a higher AC voltage than DC voltage at battery. These are values I have found on other non-field coil excited alternators. If you have no VAC on the three sets of yellow wires, then your field coil isn't acting like an electromagnet, and you can trace the lack of DC voltage from battery to the field coil. If you have ever taken off the three screws in the alternator cover and started the engine, you have twisted those wires right off the field coil... ask me how I know...
Anyway, you should be able to determine AC voltage next,and go from there.
Charlie