Topic: Charging Mystery

[breasley]

Hi All,
I have a CB750 K "everything" I have had for 40 years.
Just the other day the AGM battery was suddenly flat.
Am running an after-market reg-rec as the original reg finally died.
The stator and reg-rec seem to test fine with a multimeter but testing for volts there is no rise with the motor running.
Anyone have any idea what to look at next?
Thanks in advance.
Steve

[bryanj]

How have you tested the reg/rec?
With ignition turned on but lights and kill switch off voltage at black wire and at white wire to ground should be same as battery voltage with a max drop of 0.5v

[Bodi]

Measure field coil voltage. Check harness connections and wires from alternator to reg/rect. Try temporarily connecting field coil directly to power and see if you get charging.

[breasley]

Thanks for the replies guys.
So far I have -
- cleaned all harness connections - alternator to reg/rec to battery (including the ones behind the drive sprocket cover)

- Checked stator
-phase to phase - all came up at 0.7ohms
-coils to ground - all open circuit
- all three phases show AC with motor running

-Checked reg/rec
with meter set to diode
-neg lead to +on reg/rec - fwd bias - all 3 diodes read 0.46
reverse bias - all open circuit
- pos lead of meter to - side of reg/rec - all 3 diodes read 0.46
reverse bias - all open circuit

As you suggested bryanj I comared voltage at black and white wire to battery with ignition on (I don't have a kill switch).

Battery - 12.32V (bit low as I have drained it a bit starting bike etc)
- black to ground - 11.65V  - diff=0.67V
- white to ground - 10.84V  -  diff=1.48V

As you can see, both higher than the max of 0.5V you suggested  -  what does this mean?

At this stage I can only think the reg/rec is defective despite all the diodes checking out.
Perhaps I should order another one and give it a go. It will take about a month or more from the states the way things are now, but it seems the only logical answer.

I am interested in your answer re the black and white wire difference.

Thanks in advance,

[bryanj]

Black to ground lower voltage is volt drop due to bad/dirty connections between battery and black wire, could be
Battery connections
Fuse connections
Ignition swition connections
Any wiring connections
Battery to ground connections(at lot of people dont clean paint/powder coat from frame or engine plate where ground goes.
Extra drop to white is a problem with regulator.

From your comments i suspect you are in UK, there are several UK Suppliers that sell aftermarket reg/rec.
Are you on the UK site as well?

[breasley]

Just checked resistance across the other 3 wires. Are these the field coil?
White to green - 7.8ohms
black to green  - open circuit
white to black - open circuit

[bryanj]

White to green on engine is field coil, required value is in manual BUT dont forget to deduct the meter resistance.

Where are you testing the others?

[Bodi]

Connect the white wire to black (disconnected from reg/rect) and start the engine. This should power the field coil to give maximum alternator output, battery voltage should rise with revs: if it does, you regulator has failed. If not, something else is wrong (many possibilities and bad rectifier is most likely - but you checked that as ok).

[PeWe]

Shop manual ch 8 available?
That chapter make it easier to see how the wires are connected.
https://r.tapatalk.com/shareLink/topic?url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D54044%2E0&share_tid=54044&share_fid=13548&share_type=t&link_source=app

[bryanj]

Manuals and parts books are available to down load on the UK site in alladins cave

[breasley]

So, today cleaned every connection I could get to and re-connected them with dialectric grease. No notable changes in readings....except...
today white to ground 0V and white to green field resistance was open circuit!

I have been testing at the side cover point.

Ran bike with white connected to black and no V increase across battery.

Maybe the field coil and reg/rec are both toast.

I am in Fremantle W.A. There is a guy in the Eastern states who will have a good field coil and I have found a reg/rec with the connector block with the 3 seperate white, green and black wires. Most of the ones available have only 2.
I bought the bike for AUD250 forty years ago and made money when I re-built it in 2000 from selling the donor bike I got cheap and left over parts so I don't mind spending money on it.

Thanks for your help boys

[bryanj]

Check the coil resistances closer to the coil, if your coil is gone its the first one i have ever heard of BUT the solder joints sometimes fracture

[breasley]

As suggested, checked closer to the coils (behind sprocket cover - no different).
Have decided to concede defeat and wait for the reg/rec and field coil ordered.
Thanks for your help but it seems I am once again defeated by the electrics gods.
Will ride the other bike for now.

[PeWe]

- No charging att all when revving 5000 rpm?
 I have not seen if you have tried another battery.
- Regulator correctly set,  not touched?
I adjusted to decrease max voltage.
Suddenly no high charging relay function at all so I had to increase to get the regulator relay function back.

Regulator made for 14.5V, possible to reduce a little.
I reduced for GEL battery max recommended voltage which is lower than std wet.