Cb125 charging system. How does it work?

[InkandIron]

I have a 1975 cb125s, build that I am just wrapping up, and have run into an issue.

When I purchased the bike, the previous owner had made a comment along the lines of "these bikes don't have charging systems." An I thought that was really weird. So I assumed the charging system was maybe just not working correctly. Upon year down I found numerous bad connections and whatnot so I figured that was probably the issue. Buttoned everything up, and have ridden the bike numerous times during the day and it runs perfect. The last few nights I have taken small trips and the last night I had it out I started to develop a slight stumble at lower rpms. It got worse until it would die upon deceleration.

Long story short, I have a dead battery. Runs great with no headlight on. Dies or stumbles with it on.

It's the stock 6v system. The only thing I have changed is a new battery (sealed lead acid) so it could be tipped on it's sides and tucked away, but the specs should be close to stock.

How do these charging systems work? Do they only charge with the light on? How do I test if it's charging? How do I know which component to replace of it isn't charging?

I've heard a little bit about a 12v swap, and this might be a good time to do it I I need to replace components anyways. What would I need for that? Any insight into how this thing is "suppose" to function would be great! Thanks


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[jungalist]

first of all, search 'cb 125s wiring diagram' and try to figure it out a bit, you've got 3 lead wires (yellow) coming from the charging coil, those go to your rectifier which puts out the 6v dc. So what your rectifier does is converting that 3 phase AC with unstable voltage into 2 phase DC 6V.

Buy yourself a multimeter and see if you can measure some voltage over the 3 yellow wires (from your coil).

6V to 12V conversion includes a new rectifier, new ignition coil and ofc lightbulbs, blinker relay,.... Charging coil normally puts out enough voltage to charge a 12V system so can be kept (if it's in good working order) so that's what you need to find out first.

but first try to find the source of what's wrong before converting it to 12V

 

[jungalist]

Just went quickly throught your previous posts, and dude, you really need to print out a wiring diagram of your bike and figure it out. It's not that hard!

It can save you lots of time to just be able to quickly solve a tiny problem instead of asking it here waiting for a answer.

 

[InkandIron]

first of all, search 'cb 125s wiring diagram' and try to figure it out a bit, you've got 3 lead wires (yellow) coming from the charging coil, those go to your rectifier which puts out the 6v dc. So what your rectifier does is converting that 3 phase AC with unstable voltage into 2 phase DC 6V.

Buy yourself a multimeter and see if you can measure some voltage over the 3 yellow wires (from your coil).

6V to 12V conversion includes a new rectifier, new ignition coil and ofc lightbulbs, blinker relay,.... Charging coil normally puts out enough voltage to charge a 12V system so can be kept (if it's in good working order) so that's what you need to find out first.

but first try to find the source of what's wrong before converting it to 12V

Thanks for the reply! I do have the wiring diagram, and I also have a downloaded Manual. Unfortunately the manual doesn't provide much information on this topic. I wasn't sure if this bike was in some way unique in the way it charges, based on what the po owner had told me. I did also read through sonreirs sticky about charging systems, but once again that was more or less based on 12v systems and my particular make and model seems to have far less components then were listed in that thread. I will buy a multimeter and get to testing I suppose.

Based on the fact that it runs fine without the light on, is there anything I can rule out and focus on one or two components?


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[InkandIron]

Just went quickly throught your previous posts, and dude, you really need to print out a wiring diagram of your bike and figure it out. It's not that hard!

It can save you lots of time to just be able to quickly solve a tiny problem instead of asking it here waiting for a answer.

Ha ha, I agree. After some of those more trivial posts I have downloaded the proper learning materials. Electrical stuff is like black magic to me, so in more cases then not, I need the guidance of somebody who knows what the hell they are doing!


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[jungalist]

Based on the fact that it runs fine without the light on, is there anything I can rule out and focus on one or two components?

not that i can tell for sure, but my guess would be the coil, because if the regulator was fried it wouldn't give any current, so the bike would only run until the battery was empty and then die, it sounds like it just doesn't get enough current...

I hev to come back on my comment of the '3 yellow wires' i know with my cb 125T that are the colours, but seems that your bike might have different colours. anyway, you should be able to indentify where they come from... check your wiring diagram perhaps.

you should measure the voltage between each of them (so between cable 1 and 2, 2 and 3, 3 and 1) while the bike is running without disconnecting them (so poke a bit where the wires are inserted into the connector).

if the 3 voltages are the same the coil should be good (measured at idle= more or less constant rpm). and don't forget to put your voltmeter in AC!

 

[Sonreir]

first of all, search 'cb 125s wiring diagram' and try to figure it out a bit, you've got 3 lead wires (yellow) coming from the charging coil, those go to your rectifier which puts out the 6v dc. So what your rectifier does is converting that 3 phase AC with unstable voltage into 2 phase DC 6V.

Buy yourself a multimeter and see if you can measure some voltage over the 3 yellow wires (from your coil).

6V to 12V conversion includes a new rectifier, new ignition coil and ofc lightbulbs, blinker relay,.... Charging coil normally puts out enough voltage to charge a 12V system so can be kept (if it's in good working order) so that's what you need to find out first.

but first try to find the source of what's wrong before converting it to 12V

Sorry that I'm getting in on this one so late, but this is a lot of misinformation that needs to be corrected.

Depending on your year, your bike will have three wires coming from the alternator, but only one will be yellow. The other two will be pink and white (or possibly yellow/white).

These wires do go to your rectifier, but the rectifier most certainly does not put out 6VDC. The rectifier puts out voltage relative to what is being generated, and that varies depending on RPMs. More RPMs, more voltage. Again, depending on year, your bike will probably not have a voltage regulator. Your system is, instead, setup to be sort of self-balancing. You get about 2/3 of your charging power when the headlight is turned off and the other 1/3 of the capability it added into the mix when you switch the headlight on.

You may have noticed that your battery is pretty big considering the size of your bike. Stock battery is 12Ah which is the same as the CB750. The reason for this is that your battery is your voltage regulator. It helps to absorb the extra power generated by your bike by boiling away the electrolyte. Make sure you keep your battery topped up with water or the battery dies.

To begin testing your system, the first steps are to start with a charged battery (about 6.2V) that hasn't been on a charger in the past 24 hours. Next, start the bike and measure the DC voltage across the battery terminals. It shouldn't be much different than when you measured with everything off. After the bike has warmed up a bit, give it some revs. At around 3000 RPM or so, you should see the voltage begin to climb. At 5000 RPM you should be close to 8V. Repeat this test with the headlight on.

If you're not getting an increase in voltage, turn off the bike. It's time to test the stator. Between each of the yellow, pink, and white wires you should be getting around 2 Ohms on the multimeter. Repeat the test between each of the three wires and the negative terminal of the battery. You should not get any reading at all.

If everything checks out, test continuity between the wires at the rectifier and at the alternator plug.

If that's OK, check AC voltage between the stator wires with the bike running and the alternator unplugged. Wear rubber gloves. You should see around 60V when you get some revs on it.

Assuming everything still checks out, it's probably time for a new rectifier. If you can find a combined R/R in 6V (I have a couple left in stock), then it might be worth installing a replacement.

 

[InkandIron]

Sorry that I'm getting in on this one so late, but this is a lot of misinformation that needs to be corrected.

Depending on your year, your bike will have three wires coming from the alternator, but only one will be yellow. The other two will be pink and white (or possibly yellow/white).

These wires do go to your rectifier, but the rectifier most certainly does not put out 6VDC. The rectifier puts out voltage relative to what is being generated, and that varies depending on RPMs. More RPMs, more voltage. Again, depending on year, your bike will probably not have a voltage regulator. Your system is, instead, setup to be sort of self-balancing. You get about 2/3 of your charging power when the headlight is turned off and the other 1/3 of the capability it added into the mix when you switch the headlight on.

You may have noticed that your battery is pretty big considering the size of your bike. Stock battery is 12Ah which is the same as the CB750. The reason for this is that your battery is your voltage regulator. It helps to absorb the extra power generated by your bike by boiling away the electrolyte. Make sure you keep your battery topped up with water or the battery dies.

To begin testing your system, the first steps are to start with a charged battery (about 6.2V) that hasn't been on a charger in the past 24 hours. Next, start the bike and measure the DC voltage across the battery terminals. It shouldn't be much different than when you measured with everything off. After the bike has warmed up a bit, give it some revs. At around 3000 RPM or so, you should see the voltage begin to climb. At 5000 RPM you should be close to 8V. Repeat this test with the headlight on.

If you're not getting an increase in voltage, turn off the bike. It's time to test the stator. Between each of the yellow, pink, and white wires you should be getting around 2 Ohms on the multimeter. Repeat the test between each of the three wires and the negative terminal of the battery. You should not get any reading at all.

If everything checks out, test continuity between the wires at the rectifier and at the alternator plug.

If that's OK, check AC voltage between the stator wires with the bike running and the alternator unplugged. Wear rubber gloves. You should see around 60V when you get some revs on it.

Assuming everything still checks out, it's probably time for a new rectifier. If you can find a combined R/R in 6V (I have a couple left in stock), then it might be worth installing a replacement.

Thanks for the info! I found a much better Manual online and downloaded it and it also showed pretty much the same tests to run. Although my Manual isn't specific to my year so there is some miss information but it gets me pretty close. I'm going to perform these tests tonight, and see what I come up with.

I don't know if you saw in the initial post, but I switched to a smaller (physically) sealed lead acid battery, but kept it as close as I could to stock stats, and possibly this is my problem? I didn't realiZe how the stock battery was used as a regulator. Would it be a good idea to switch a combo reg/rectifier like you had mentioned if I want to run a smaller battery like I did?

Even though I switched the battery, when I initially bought the bike, it had a stock battery and all stock components and the PO mentioned "theses bikes didn't have charging systems" so I'm guessing it wasn't working properly. So I guess I'll do some investigating and see what I can come up with. I really appreciate the Info for electrically inexperienced guys like me!

Just out of curiosity, how much do your 6v reg/rec units cost? Would it more or less be a direct replacement for stock? I'd be interested! Thanks!


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[Sonreir]

I think the sealed battery is definitely part of your problem. You can't use a sealed battery in a system without a regulator. If you do add a regulator to the system you should be able to significantly reduce the size of the battery needed. 6Ah and sealed would work fine in your system once a regulator has been added.

Our 6V R/R is $30 shipped within the USA. If you send me a picture of the plug I'll try to match it.

 

[InkandIron]

I think the sealed battery is definitely part of your problem. You can't use a sealed battery in a system without a regulator. If you do add a regulator to the system you should be able to significantly reduce the size of the battery needed. 6Ah and sealed would work fine in your system once a regulator has been added.

Our 6V R/R is $30 shipped within the USA. If you send me a picture of the plug I'll try to match it.

Sign me up for one of those! What is the best way to order/make payment/send a picture of the plug? Let me know and I can take care of it today! Thanks for your help!



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[Sonreir]

I can be contacted at sales@sparckmoto.com.

 

[InkandIron]

So, the test results are in... Grabbed myself a multimeter and with your direction arrived at these numbers.

Battery not running - 6.5 v
Battery while running - no change

Stator testing
Resistance:
Red-white: .3
Red-yellow: 1.8
White-yellow: 2.0

When retested against neg terminal showed no reading

Ac voltage while running and under a few revs
Red-white: 50+ v
Red-yellow: 70+v
White-yellow:40-50v

I thought the resistance was weird that it wasn't consistent on each path, but I came across a site that rebuilds stators (regulatorrectifier.com) posted these stats for a healthy stator on my model and year:

Testing the female 6 gang plug:

The red to white should read between .2-.3 Ohms

The red to yellow .8-1.0 Ohms

The white to yellow 1-1.2 Ohms

Non continuity to ground

Soooo... Looks like my data should be great in comparison. Am I correct to assume that my stator is functioning properly? Any input would be great. Thanks!


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[Sonreir]

Stator looks good to me.