Topic: 1975 Hond CB550 Charging Issue

[vintage@5280]

Okay, I have been pulling my hair out (what's left of it) for the last week now.  I'm having a charging problem and I will start from scratch.  OR maybe I'm not.....

I bought the bike from PO and the old rectifier (stock OEM) was totally melted.  I was thinking "Okay, new combo unit should solve that".  I went through the bike and made sure everything was hooked up properly, points adjusted, timing in check, valves in check, complete carb overhaul (down to the bodies).  I put new rubber boots on and slapped the carbs on.  I fired it up (no air box, so the choke proved to be no use, it wanted to be wide open).  I used the stock mains and pilots.  I went with 98 main and pilot was #35.  The bike fires up beautifully, I barely tap the start button, and it cranks right up.  I just wanted to walk you through my first process.

I had a Rec/Reg combo sitting in my shop for another build (eBay special), so I figured I would slap it on, and see what I got.  I realized the big red wire going to the starter solenoid into the stock harness was nasty, so I wired up a new one.  I ran the same exact position of the stock, no changes.  I smoked the new reg/rec, my own fault.  I bought a Motobatt AGM battery and quickly realized the posts are interchangeable and I missed it. I did the bench test on that unit and it fails without question on the middle yellow.

When I start out, I check the battery, and I'm at 12.89 no juice and no charge for 2 hours.  I turn the key and battery drops to 12.4.  I fire up the bike and it consistently sits at 12.02 at idle.  I rev it up and it only jumps up a little bit if not at all.  I know I should see 13.5 at idle, right?   It just sits at 12.02 and basically doesn't go up or down, 2 mins of idle.

I have checked all the wires in the harness going from the stator and all is good.  I ran the test the manual says about static testing the stator and they all come out fine.  It says in Ohms that it needs to read .35 at 100 (r x 100), but my multimeter starts at 200 and it reads 3.5 on all the yellows.

I check it with the bike running on AC Volts (my meter again starts at 200) and it reads .3 on all the yellows, no matter what combo I put the leads on.  I rev it up and it goes up to 2.5 at 5k RPM. 

I'm almost positive I have a charging issue.  I have checked the Reg/Rec and I'm not 100% sure it passes the static test on the bench.  I put my multimeter to diode test and I get one false reading doing the full spectrum of testing back and forth (black to red wire with blacks going to yellows and all the other options).  Could I possibly have yet another bad Reg/Rec out of the box???

Question, what should I be reading when I'm applying the leads to the yellows while running?  I can't find anything stating what the stator should read (value while idling) while running.  I have a buddy telling me my meter sucks (so I went ahead and got a Fluke on the way, it's probably time).  I have a decent Home Depot Commercial Electric MAS830B and it seems to read fine, but maybe I'm reading it wrong.  I'm using the V with the squiggle line, AC, I'm 99% sure. 

I either have yet another bad reg rec or I have a bad stator / magnet that need to go to Rick's for wiring.....

I'm sure I'm missing a few other things I have tested, but I'm going nuts thinking the issue is one or the other, back and forth like a ping pong....

[bryanj]

Cant remember exact figures but if the field coil (white +green wire) is getting power you should have over 20 volts AC berween each pair of yellow wires comming out when disconnected.
On the bike with ignition on the 2 wires going to the field coil should have battery voltage accross them.
I have NEVER seen a field or stator go bad electricaly only bad connections or physical damage

[vintage@5280]

I checked the field coil wires (Positive Lead attached to the Black and Neg Lead attached to white and green) and I'm reading AC 23.8V on the meter.  Are you saying I should be reading over 20V AC on the yellow wires?  I'm not getting that reading at all.  The key was on when I read this.  When I tried the leads both ways on the just the white and green I get nothing, absolute 0 reading.
I don't see any physical damage on the stator, I opened it up last night.

https://imgur.com/YZb9IMz

[bryanj]

Cant open your picture,
Leads going to field are white and green no black
Disconnect multiplug to engine and check resistance between white and green going to engine, now with key on check for voltage on the white to green on the frame panel.

Come back to me with readings

[vintage@5280]

Will do.  So, the white / green / black going to old regulator are not the field coil wires, right?  I must have that wrong.
I will snap some pics tonight.  I need to figure out how to post pics in this forum. 

TY

[bryanj]

They do eventually but not for these purposes.

[vintage@5280]

I'm reading 0 with leads on White and Green from the main engine harness.  I have the setting on 200 AC of multimeter

I tried it with Key on and Bike running, so I did both.  I'm getting nothing. 

[HondaMan]

The alternator wires (Yellow) will output over 20v AC when the engine is running if there is any field coil current.

Maybe this will help: it works like this - when the field coil draws power from the battery, it makes an electromagnetic field in the center of the alternator. The metal 'rotor' spins in that field and the openings in between the metal plats of the rotor lets the magnetic field hit the poles on the stator windings, inducing magnetic fields in them as on-off-on-off... magnetic pulses. Those windings around the poles of the stator then collect this and turn it into the 20v AC power you can see with the meter on the Yellow wires. It is anywhere from 18v at idle to 26v (AC) at 3500+ RPM on those wires. They go to the rectifier where they all get forced into one direction to become DC power, and the battery filters (smoothes) the peaks of the AC waveform into a 12-ish volt level.

It sounds like your stator wires are OK: they are very low resistance. Many modern voltmeters (especially digital ones) do not measure very well below 1.2 ohms, due to the input protection circuits those meters have (that's for when you forget to switch it to "volts" from "ohms" and try to cook the meter...not that I've done that...    ) . It sounds like your field coil is OK, too.

Keep in mind: the 500/550 has a very small output. it does not start charging the battery until 3000 RPM in most cases. Below that, it is losing power.

[HondaMan]

I'm reading 0 with leads on White and Green from the main engine harness.  I have the setting on 200 AC of multimeter

I tried it with Key on and Bike running, so I did both.  I'm getting nothing.

If that's the case, try temporarily hotwiring the field coil to +12 volts and Ground (Green) wire (I use clip leads for this, it draws about 1.6 amps). This will turn the field coil fully ON. Then run it and see what voltage appears on the Yellow wires. You should be measuring Yellow-to-Yellow, though, and not Yellow-to-ground: they are isolated from the rest of the bike.

[vintage@5280]

Okay HondaMan!  I got my FLUKE 115 in the mail today because I was convinced it was a meter issue.

I'm wrong and you are right.  I hot wired the field coil (green to ground / white to hot on the starter solenoid) and I'm reading 19v roughly on all three yellow wires at 1,200 idle.  I have another buddy who works on these all the time and said I should be hovering around 40-70 volts......so do I rip it out and send it to Rick's, or ride it around, and see what the battery reads.  I took my fancy new FLUKE and did the test on the rectifier (black on red wire coming out / black lead on the yellows and it fails the test on both reg/recs I have when selected to the diode tester).  I get a fail on both reg/recs.  Do you think I'm chasing something I don't need to be and both of these reg/rec combos are bad or should I be well into the 40-70v range coming off the yellows when running hot?

TY!!!

[vintage@5280]

And just to give you guys an idea of what I'm working on.  As I stated, I overhauled the carbs completely.  This is by far the most original CB550 I have ever got my hands on, it's a time capsule.  I'm glad I bought this bike.  I recovered the seat this weekend as well.  With the #$%* going on in the world I have plenty of time to get to these projects. 

[bryanj]

20 at 1200 is OK rev it to 6000 and you will get higher volts.
You have either a wiring fault or a regulator fault. I am a bit too far away to tell you which!!

[Bodi]

The alternator stator output voltage is never going to be 40-70VAC with a good rectifier and battery connected.
AC voltage between any yellow and either of the other two yellows goes to the rectifier, and when the voltage gets above battery voltage - current flows through the rectifier diodes to the battery (this happens simultaneously on all three possible pairs of the three yellow wires). Readings at the yellows is higher than battery voltage by about 1 to 2 volts due to the diodes' forward voltage drop, plus some from voltage drop in the wiring, plus the battery's internal resistance adds a bit... so 20V or so is believable: with a good rectifier and battery 40-70VAC is just not possible.
Measuring with the stator yellow wires disconnected, the voltage is higher since there's nothing to draw current. I expect that 40-70VAC may be possible then.
So don't worry about the alternator itself. It's fine. The coils are very rarely bad unless physically damaged.
Since you've proven there is power out of the stator when you hot wire the field coil, look for problems with the regulator, its wiring, or the field coil wiring. Roughly battery voltage has to be on the regulator black terminal with key on. Green must be ground. With key on and engine stopped, white should be close to battery voltage - and if you can measure current (between the regulator and the white wire to the field coil) it should be a few amps DC. Not sure how many... 3 or so probably. If no amps, check the other field coil wire is grounding properly. Both are white directly from some (or all) field coils although the wiring diagram shows green and white: the wires at the bullets under the side cover are usually green and white though and which way the field coil wires connect does not matter. The bullets for the field and stator wires under the engine cover are very prone to corrosion and bad contact after 40+ years getting heated and cooled with the engine, so give them a good look and probably clean them regardless of how they look. If the plastic sleeve over a connection is burned dark brown or black it definitely needs attention.
If you show no voltage on its white terminal with key on and +12VDC (or so) on the black terminal: the regulator is bad. Pulling the green off and doing this test tells whether the relay is bad and can't make contact (still no volts on white) or if it's triggering on too low a voltage (12V on white with green disconnected but no volts with it connected). Either way a new regulator is advisable.

[HondaMan]

The alternator stator output voltage is never going to be 40-70VAC with a good rectifier and battery connected.
AC voltage between any yellow and either of the other two yellows goes to the rectifier, and when the voltage gets above battery voltage - current flows through the rectifier diodes to the battery. You lose about 1 to 2 volts in the rectifier (diodes' forward voltages) and some in the wiring and battery impedance, so 20V or so is believable... but with a good rectifier and battery 40-70VAC is not possible.

^^ What he said...the highest I EVER saw on these bikes was with a battery that had an open cell (10 volts sitting), and the AC was 32 volts while connected to it and running at 3000 RPM with hotwired field coil.

[vintage@5280]

Okay, got out there right now and ran some tests.  I hooked up the reg/rec combo unit (I should have mentioned that is what I was using)
With the key on I'm getting 12V DC from both the black and white wire that would be running to the old regulator, now the new combo unit.  I have it hooked up.  When I didn't have it hooked up I was reading 0V on either one of the of the black or white with the other hooked up. 
I turned the bike on and let it idle at 1,200.  I put the leads on the battery and it reads 12.45V DC.  I rev it up and it went up to 12.5V DC, but that's it.  I went to about 3K RPM and held it there for 30 secs. 
I guess the biggest question I should be asking is with the reg/rec hooked up, shouldn't I be seeing 13.5V DC or am I missing something?  Maybe I have no issue and I just need to install this and move onto the next task.  I thought I should be seeing way more than 12.4V DC with the unit hooked up. 

[bryanj]

Only if the battery is fully charged and no lights on

[Bodi]

Unless the battery is fully charged, it will absorb current and charge until its voltage gets around 14.5V, above that it's electolysing its water into oxygen and hydrogen. If it's not fully charged, the voltage will be whatever the battery gets to with all excess current (over the bike's load current to be running) going to charge the battery. This voltage will slowly rise as the battery charges, but there isn't a huge amount of excess power available from the alternator for that so it will take a while even when riding, and at idle it won't charge much if at all.
Disconnecting the headlight reduces system load by whatever wattage your bulb is. There are still some unavoidable loads - the ignition and the alternator field coil - plus minor loads from the tail and instrument lights.
This testing is best done after fully charging the battery, disconnecting the headlight, and starting by kick to eliminate the starter discharging your battery.

[vintage@5280]

Great, thanks.  I'm also going to rewire the red and green on the back of the bracket.  I think those wires might not be totally okay, so I might as well replace with new and than see what I got.  I appreciate all the help.  I have a new rec / reg on the way as well, so I want to see what that does.  I think with all the testing I know the field coil and stator are in good shape, I just need to narrow down the issue under the seat area now.  I think new wires might do the trick.