CB750K2 Charging problem

[Bigbadbob]

Hi all, I'm really struggling with my bikes electrics, I've been speaking on and off to a member called Brian who's been really helpful but I think even he has ran out of ideas and said he would need to see the bike but he lives to far away from me.

The bike has never charged since I owned it and I've tried to live with it until this year.

After investigating if the stator is working as it should, the tests I have carried out confirm it is ok, I think?

I've recently fitted a new main wiring loom, but there is a spare red and white wire with a bullet connector which I believe should be connected to the positive cable from the battery to the solenoid, the old one only has one red wire that goes to the main and only fuse.

Looking at the correct cable, it should have a red and a red and white cable also. 

I thought I would simply replace this positive cable from the battery to the solenoid with a new cable and that would resolve the spare red and white wire problem.

Unfortunately this red and white wire is producing somewhere between 47 and 53 DC volts between 1000 and 3000 rpm!!

I've tried swapping the voltage regulator and the rectifier from another bike without any success.

I connected this red and white wire and an earth from the bike to an old battery which is only producing 11 volts and the voltage dropped to between 17 to 21 volts again at low revs.

If I connect this red and white wire to my positive cable from the battery to the solenoid I'm assuming it will burn out my battery and new loom?

Has anyone came across this problem before?

Hopefully someone can help.

[Trigger]

I can only recall one red/white on a 750 and that goes from the solenoid to the rectifier . There is a junction in the red/white that goes to plain red and that goes to the 15a fuse 


Block with red/white

[ Guests cannot view attachments ]


The red/white on the battery to solenoid sub loom goes to the main loom and the red on the sub loom is spare.


[ Guests cannot view attachments ]




I did have a charging problem on a K2 many years ago which was just a bad earth problem. Run a extra earth from battery in to the main loom solved it.

[Bigbadbob]

Thanks for your reply, I'll try and and follow your photos with my loom and see where I get,

I'll also try an extra earth as you've suggested.

I'll be back in touch one way or the other.

Cheers

[Lobo]

Hi Bob,

If the Brian you mentioned is the Bryanj with 7000+ posts here, the below is likely for naught as he is the guru on all things Honda.

Tbh am unsure why your old loom had ‘just the red’; and you are quite correct that the Red/White (ie from the Silicon Rectifier) goes to one of the LARGE posts of the starter solenoid. Connected to this same large post will be the RED loom feed wire (which goes to the fuse and then ignition switch) and of course, the thick (8mm or so) cable from the battery +ve. (see pic #1, and the red circle in pic #2)

Before you proceed you need to be certain all components are working correctly.

(1) Disconnect the two loom plugs to the ALTERNATOR & the RECTIFIER (see pic 2)

ALTERNATOR FIELD COIL: using a multimeter set on Ohms scale, verify the resistance between the WHITE and GREEN. It should be about 7.2 Ohms. Also check the coil isn’t grounded; ie measure between the White and battery -ve. ... it should read infinity. (ie open circuit) (See pic #2)

STATOR COIL. Again, unplugged from the loom. Measure the resistance between all 3 pairs of YELLOW, noting each reading should be about 0.2 Ohms. And again verify none of the 3 coils are grounded by measuring each yellow against battery -ve (ie should be infinity / open circuit)

SILICON RECTIFIER. Again, disconnected from the loom, and with your multimeter set on the DIODE Setting. Put one lead on the RED and the other on each YELLOW in turn. Verify flow in one direction only. (ie by swapping the meter leads around)

Now check flow between the GREEN and each of the YELLOWs - verify flow in one direction only. (ie by swapping the meter leads around)

Finally, check the Resistance (Ohms scale) of the RED and each YELLOW against the negative of the battery; they should all be Infinity / Open circuit.

GENERAL: At each loom plug (whilst disconnected) verify good continuity (ie 0 ohms) between the GREENS and battery -ve, between YELLOWS (ie plug-to-plug) ...and finally the RED/WHITE between the Rectifier plug & Solenoid post.

(2) Reconnect the two loom plugs.

VOLTAGE REGULATOR Check
See Pic #4. Honestly though, I’d grab a 12-30V Car Voltmeter off eBay (from around a fiver), sellotape it to the handlebars and connect the +ve to any Black lead in the headlamp shell, and the -ve to any GREEN. Then, as you ride, you can ascertain it’s behaving as you’d expect IAW RPMs.

————

You say the RED/WHITE voltage is around 50V at 3000RPM - honestly you should not run the bike with Rectifier disconnected as high voltages can destroy the diodes (ie the RHS trio in pic #2, which have one side connected to Earth). Hopefully this is not the case. Open circuits can have unpredictable readings: I’m not prepared to disconnect my Rectifier to verify your findings!

Any battery has internal resistance, and in the circuit will ‘clamp’ the voltage down to typical values. I don’t think you can read too much into this open circuit voltage...

Your Check with an external battery...

The Voltage REGULATOR works by applying varying current through the Field Coil, ie the more the current, the higher the Alternator output.
At low RPMs (and low Loom voltage) the REGULATOR outputs 1.7 Amps to the Field Coil; when Loom voltage reaches 13.5-14.5V or so, this reduces to 0.7A, and above 14.5V reduces again to 0A. In this way, the output voltage of the Alternator is kept in check.
Your test (with an external battery) effectively took the RED/WHITE charge voltage out of the bike circuit, and fed it to your external battery. Your bike loom voltage therefore remained at its own (low) battery voltage of (say) 12V. The REGULATOR was fooled into thinking that the Alternator output was low, and kept applying the full 1.7A to the Field Coil. The alternator output would therefore keep rising with RPM, which might explain the 17-21V you saw.

If it were my bike, I’d ensure the battery was tip-top, the Rectifier & Alternator components verified as above, all connections made... and with all lights OFF (just in case the over-voltage is genuine) start it. Have a multimeter connected (VOLTS Scale) across the battery terminals (or your eBay product) and check the voltage doesn’t rise above 15V.
If it does, but only minorly I’d suspect the Regulator and service or swap it. If a major over-voltage - you’ll have to check the RED/WHITE is not somehow directly connected to the WHITE of the Voltage Regulator.... implying that the Alternator output is directly feeding its own Field Coil - ie ‘regulation’ is simply not happening.

Hope this helps,
Simon

[Bigbadbob]

Hi and thanks for the replies,

After looking at your photos and comparing them to my situation it appears I have the correct wiring i.e. the white block connector that goes to the rectifier has the red and white wire together with the 3 yellow wires and the green wire. 
The spare red and white cable with the bullet connector appears that it should return to the battery and I need to simply buy an original Honda battery to solenoid cable which makes allowance for the red wire and the red and white wire with the bullet connector.
see attached photos.
I'll try and carry out checks that have been suggested and see how I get on, albeit as BrianJ has found out, I'm not the best with electrics hence why this problem is on going.
If any of you out there have the time, I would gladly pay for your services as I'm keen to see this problem resolved.
Thanks again.

[Trigger]

It looks like all you need is a feed from the battery to the loom 

I have had time to look at the set up on one of my K2's and the red/white feeds the loom and the red with the spade goes to the fuse box .


[ Guests cannot view attachments ]

[Bryanj]

You dont need to buy the new Honda lead just make up a short lead with a ring terminal on one end to bolt to solenoid along with the main battery one and the appropriate bullet one the other end

[Bigbadbob]

Thanks for all your help, I connected the red white wire directly to the battery and the bike is producing about 14.5 to 15.50 volts maximum at varying revs.

This same RED/WHITE wire was producing around 50V at 3000RPM when not connected to anything.

I've now just got to buy a new battery solenoid cable but I'll most probably do the modification BryanJ suggested.

Can someone advise if I can leave things as they or should I try and adjust my voltage regulator or even replace it, I can see Lobo's post and my voltage at the battery appears to be on the high side?

[Bryanj]

As long as you buy a lead/acid battery and not one of these new fangled ones it will be fine, charging voltage will probably drop with a decent battery

[Bigbadbob]

All sorted, many thanks all of you. Just need some weather suitable to enjoy the ride