Field Coil/Charging problem...

[JimJam]

Hello,
I am hoping someone can help please…
Bike is a CB750 F1 SOHC 1977
Following a 2 year restoration, I finally took the bike out for a first test. Largely all went well, apart from the distinct lack of charge to the battery.
Checking the stator wires with the bike running at varying rpms (2000- 4000) showed 0 Ac voltage across all three.
Stator resistance is consistent 0.8ohms with no continuity to ground
Field coil resistance is 7.2ohms with no continuity to ground.
The replacement solid state R/R gave correct results on the diode test.
I believe the issue is the field coil is not receiving 12+v from the R/R. As I understand it, with the ignition on the Regulator should supply 12+vdc to the field coil which will then magnetise. This is clearly not happening.
Could someone please confirm my wiring is correct?
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3 Yellow R/R wires to 3 Yellow Stator wires
Green = direct to ground
Red to Battery +
Black to ignition
White to White Field coil wire (being 12+v supply)
The green wire from Field Coil is direct to ground.
With everything connected and ignition on, I expected to see 12+vdc at the white field coil wire, but I am currently seeing 0v. What has gone wrong?
The wiring guide from the R/R manufacturer is:
RED: Positive      YELLOW: Phase input from stator      WHITE: Field Output for Alt.
GREEN: Ground      BLACK: Original sense input for Regulator
Any help greatly appreciated!
James

[AshimotoK0]

I can't comment on the regulator/rectfier as no experience with them. However, why not temporarily feed 12 to the field coil and see if you get any charge? (disconnect from RR unit when doing this !) Did you check for infinite (open circuit) resistance between each of the 3  yellow stator wires and the mag-frame of the stator?

Welcome to the forum BTW    cheers Ash

[JimJam]

Cheers Ash,

Yes, good idea on the direct feed. will give that a go.

I checked each of the stator wires for continuity to ground against the Alt. engine case.  There was no continuity. Is that sufficient? 

[BigAl (Alan)]

You would require a 12 volt + supply from the regulator to the field coil to start the charging process. A higher voltage insulation tester (as image) would also confirm that the windings within the stator & field coils have not shorted to the frame/ground, as the low voltage multimeters may not provide the correct reading.

[JimJam]

Thanks Al.

Could you please clarify that with the ignition on (only) the white Regulator wire leading to the Field coil should be reading 12+v and that the green Field coil wire is sent directly to ground?  Y/N


Thank you.

[AshimotoK0]

Cheers Ash,

Yes, good idea on the direct feed. will give that a go.

I checked each of the stator wires for continuity to ground against the Alt. engine case.  There was no continuity. Is that sufficient?

Yes that's correct .. Back in the day two of my 400/4's broke down insulation between the copper wire and the mag-frame (and hence I got continuity) . I don't think this is a problem on the 750 though as the stator runs in oil.

[BigAl (Alan)]

Hi James,

Simplified wiring diagram (as image) which may help. PM me if the image is too small to read

Alan

[JimJam]

Thanks Alan.

I put a direct 12v feed to the Field coil and it magnetised. So that's a good start (Thanks Ash)

I think the BLACK regulator wire should feed the Field coil rather than the WHITE. Contrary to the instructions. I will have a look tonight..

Many thanks both for help thus far.

[BigAl (Alan)]

Hi James,

It can be a bit confusing as to why Honda selected these colours (as image) The original regulator has a BLACK + input and a WHITE+ switched output.
The 7 wire sub-harness (part#31110-300-154) that connects to the alternator/coil will have a white wire, a black wire is not present within the sub-loom

Alan

[JimJam]

Hi Alan
Based on this diagram (and my manual) I have wired the R/R correctly. But with the ignition on there is no voltage going to the field coil via the white wire. The only way I am able to send voltage to the field coil through the R/R is to switch the white and black regulator wires.

If I do this I assume I will be bypassing the regulator and will cook the batttery!

I think the R/R is faulty... would you agree?

[BigAl (Alan)]

Hi James,

Its possible the combined rectifier/regulator is faulty? or the battery voltage is high, therefore the voltage regulator would switch-off as normal.
Try leaving the lights on for a while to reduce the battery voltage, the regulator may switch on at the combined R/R spec (none Honda component, not sure what this would be?)

[JimJam]

Hi Alan,

Yes, I have tried that. The battery voltage even dropped below 12v and still nothing.

After about 5 minutes of riding the battery voltage is under 12v and and the bike starts to misfire.

The RR is an electro sport. Not cheap £65. I think I will have to order another and see if it solves the problem. If so I’ try and get my money back on the faulty one.

[AshimotoK0]

Do you still have the original fitment electromechanical one to try? Personally I never had any probs. with the original one and I had a succession of 4 off 400/4's 'back in the day'.

[JimJam]

Sadly not. The bike had been sat outside for 10 years and the majority of parts were not salvageable. None of the original wiring or electrical components remain.

It has been a fair old challenge and this (I hope) is the last hurdle.

Here is a picture.

[Bryanj]

I have seen a lot of combined units go duff, it only takes a fraction of a second of incorrect hook up to total them