Topic: Chasing my tail with the 750F charging system

[nholden98]

Hello all,
I've been trying to track down the cause for my faulty charging system on my '76 750F for a couple months now. I am a college student living away from home so I have had limited time to work on it but now that I am home for winter break, I have been trying to get things sorted out. Initial/current problem is the obvious battery dying and not being recharged while riding. Voltage does not hit 13V regardless of engine speed when tested at the battery terminals. Here is what I have done so far:

1. Replaced rectifier with a solid state unit, bike still has separate OEM regulator. This did not fix it.

2. Had a reputable shop diagnose the issue. Diagnosis sheet from the tech says "Stator is bad. 24vac registering on two pairs @ 3500rpm, 3rd pair is going to 18vac and cutting back to 1.2vac." They also said the battery needed to be replaced due to sitting dead for a couple of months between the time I replaced the rectifier and brought it to them.

3. Brought the bike back home last week, threw a new battery in it and also replaced the stator with a new unit, trusting that it would solve the problem. WRONG! Battery voltage is still reading sub-13V with a new battery and stator.

4. I resorted to the guide found here http://www.hondachopper.com/garage/troubleshooting_charging_system/troubleshooting_charging_system.pdf and dove into it with a digital multimeter.

Here is where I have gotten stuck, it says that the resistance between the three yellow leads from the stator should be 0.2Ω. For both the old stator as well as the new one I am consistently getting a 0.8Ω reading on all three leads. Part of me wants to say that this could be due to some inaccuracy of the multimeter itself, but I am not entirely sure. Moving on with the guide, I tested the output of the stator. I could not get more than 1.2vac out of any of the yellow leads while running. Guide says that it should be 50-60vac when at operating speed. Lastly, I also tested the field coil to ensure that there was no shorting and it was within spec at 7.2Ω and no continuity to the case, cool.

In addition to this, I also went through as much of the charging system as I could to confirm that there were no shorts in the wiring itself between the stator, rectifier, regulator, and field coil.

According to the guide, I should have a faulty stator...however, this is a new unit and I would like to think that it is not at fault. I remember my rotor and field coil having the slightest amount of rust or corrosion on them in a couple spots, but I did not think much of it while the bike was apart. Could this be causing virtually no output? If so, I have no problem pulling it apart again but I would like to get some other opinions before I order a new set of gaskets to do so (working on a college-kid budget here lol). Any insight as far as what direction I should go next would be greatly appreciated as electrical issues are not my strong point (there is a reason I am in school for mechanical engineering and not electrical  ).

Sorry for the long post, I just figured I would try to include everything I have done/found until this point. Thank you in advance for any help and have a Merry Christmas!

[nholden98]

Williamsburg is home, I go to school up at VCU there in Richmond.

Voltage at the battery with the key off is 13.1 volts. It's a new AGM type battery. At 4,000rpm the voltage reads 12.5V.

Regarding the bullet connectors, the stator side of them is new being that it is a new stator. They appear fine and that is where I tested the stator output from. Just rechecked and am getting the same output reading up at the rectifier connection with the bike running as I did doing the same down at the bullet connectors. The bike was a frame-up build last winter and the previous owner re-did the majority of the wiring, so most of these connectors are relatively new/clean as well.


Sent from my iPhone using Tapatalk

[nholden98]

I haven't tested the regulator specifically, I never really found a clear method online to doing so. So that should probably be the next step. Rectifier is a solid state model made/sold by Oregon motorcycle parts.

I took the bike to Moto Richmond across the river from downtown. I had been through there a couple times earlier in the fall to check out the shop and the folks there are very cool. Went to the release party they hosted for the new Triumph bobber, awesome event. One of the sales guys even invited me earlier in the semester to swing by anytime and try out any bike in the shop but sadly I never had time to with my school/sports schedule.


Sent from my iPhone using Tapatalk

[scottly]

Disconnect the white field wire from the regulator and measure the resistance between the wire and the battery negative post; it should be the same 7.2 ohms you measured on the field coil. If that checks OK, re-connect the white wire to the reg and measure the voltage at the white wire/reg junction with the key on, motor not running.

[Jerry Rxman Griffin aka MuthaF'er]

What's the resistance across your ignition switch?

[nholden98]

Disconnect the white field wire from the regulator and measure the resistance between the wire and the battery negative post; it should be the same 7.2 ohms you measured on the field coil. If that checks OK, re-connect the white wire to the reg and measure the voltage at the white wire/reg junction with the key on, motor not running.

Resistance is 7.3 ohms so that checks out. When you say the voltage at the wire/reg connector, is that still with one of the multimeter leads on the negative terminal? I got 0.1V doing that with the wire and reg connected. Voltage passing through the connection at the white wire/reg is 0.6V when both leads are at the connection. These were both with they key and headlight on.


Sent from my iPhone using Tapatalk

[nholden98]

What's the resistance across your ignition switch?

Resistance across the ignition switch with the key on is 0.4 ohms. I unplugged the main connector at the key and tested it on the red and black wires.


Sent from my iPhone using Tapatalk

[scottly]

When you say the voltage at the wire/reg connector, is that still with one of the multimeter leads on the negative terminal? I got 0.1V doing that with the wire and reg connected.
Sent from my iPhone using Tapatalk

Now measure the voltage at the black reg terminal, with the black meter lead still on the battery negative post, with the key on. (For the purposes of trouble-shooting, turn the headlight off, or remove the 7 amp headlight fuse.)

[HondaMan]

You can also try this, to see if the connections between teh bike's wiring and the big white plastic plug is still working:
Unplug the White and Black wires from the regulator, and jump them together. Start the bike and rev it to 2500-ish RPM while watching the battery voltage. If it starts rising, so far so good: this means the 12 volts is actually reaching the field coil (this is "full charge rate" mode).

The resistance numbers you are citing, if using a digital ohmmeter, sound OK. The meter itself will have something like 0.6-1.2 ohms of its own: you can find this out by touching the leads together in Low Ohms mode, and mentally subtract that reading from the readings you get on the bike.

The alternator works like this: with no power applied to the field coil, the windings produce about 3-7 volts AC by themselves (depending on whether the bike is parked facing north-south (3-ish volts, typically) or east-west (up to 7 volts), due to Earth's magnetic field lines. This is called the "tickle current" and is used for triggering the fancy modern solid-state regulators, but is a way of testing the old units when unplugged from ANY regulator at all. then, when the field coil (an electromagnet) is powered up by the voltage regulator, it makes a stronger (for more output) or weaker (for less output) electromagnetic field in the center of the windings, and the steel rotor cut thru these magnetic lines to "alternate" them on and off. This causes the windings to 'see' alternating magnetic flux, and their coils then generate some AC power from this, based on how strong those fields are (from the field coil). This becomes up to 70 volts AC on these bikes (with no battery attached, if you can pull off that trick without burning out the lights), or about 28-38 volts with the battery and rectifier connected. The rectifier strains this out to DC pulses of about 18 volts peak (if all is working like brand-new) which average out to be 13.5 volts (depending on the battery's impedance) at full output.

[Jerry Rxman Griffin aka MuthaF'er]

What's the resistance across your ignition switch?

Resistance across the ignition switch with the key on is 0.4 ohms. I unplugged the main connector at the key and tested it on the red and black wires.


Sent from my iPhone using Tapatalk

Probably should have asked what are the input and output voltage values of your ignition switch instead. The switch passes through substantial system voltage which can affect it.

[Grabcon]

Look at the last three videos of these help videos. I used these to diagnose issues with the stator on my wife's bike. I found on hers that the ohm values were within range but once I tested the AC voltage from the stator things were obvious.

Make sure your battery has a full charge. I disconnected the stator from the rectifier and preformed this test. (See stator output test video). Check to see what the voltage output should be. The variance is really what was important. On my wife's VFR I had two leads at around 56 volts and the last at 19 volts. The stator had one set of windings fried, literally.

[Grabcon]

Forgot the link.

http://www.roadstercycle.com/Roadstercycle.com%20Videos.htm

[scottly]

Guys, his current issue points to the regulator, not the stator; less than 1 volt on the white reg terminal that feeds the field coil. This should be about 12 volts with a stock regulator, if the 12 volts is getting to the black reg terminal in the first place.

[nholden98]

Sorry all, family came over yesterday afternoon and I had to leave the bike for the remainder of the day. Been running around all day today and finally had time to look at it again tonight.

Hondaman, I unplugged the white and black leads from the regulator and connected them together (I assume this is bypassing the regulator entirely). Started the bike and the voltage at the battery hit 15V before the tach even got to 2k (I think it was around 1800rpm). Does this confirm that the regulator is the issue? Or are there any additional tests I should do to confirm? Also, thank you for that explanation of the charging system. My only electrical experience is from my motocross bikes and there is much less going on in them (the only thing electrical they are powering is the spark plug).

If it is in fact the regulator, does anyone have any recommendations of where to get one? I have a brand new solid state rectifier on the bike and it's a tight fit under my seat (cafe racer) so buying a rectifier/regulator combo would require a lot of rearranging as well as being a bit more expensive. The only place I can find that sells a regulator by itself is Oregon motorcycle parts (where my rectifier came from). I don't have an issue buying from them, but they are a bit pricey and shipping also takes awhile being on the other side of the country so I figured I would see if anyone had any other input.


Sent from my iPhone using Tapatalk

[scottly]

You might try cleaning the upper regulator points. These are "normally closed", and connect the black reg terminal to the white reg terminal, calling for full charge, like when you connected the black wire to the white wire. When the voltage rises above a certain level, the electromagnet pulls the movable point down, which reduces the field current. With both the black and white wires removed from the reg, you should read very near zero ohms between the black reg terminal and the white reg terminal.
 

[nholden98]

Forgot to update the thread. The issue has been resolved. HUGE, huge, thank you to Cal for taking the time to come out and assist in confirming that it is the regulator at fault, as well as hooking me up with a spare that he had. The previous reg was not letting any current through, therefore not charging the field coil if I understand correctly. Looks like this summer's task will be to clean up some of the wiring jobs on the bike but for now, we're good to go. Thank you all for the help with this. And Cal, I owe ya one


Sent from my iPhone using Tapatalk

[tlbranth]

http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf