Topic: CB400F charging issues using M-Unit **sort of fixed**

[Dave87]

G'day All, I have been an avid reader of this forum for some time now and it is only now that I am posting my first post.

Firstly I cannot thank those more knowledgeable who post on here answering to the many questions and queries. The time and effort you put in is really very much appreciated! We would be lost without you.

The story: back in 1979 my dad rode a 1975 CB400F  from Texas up to Alaska. He sold the bike before he came back to Australia, although old mate who he sold it to never received the rego papers apparently.
Skip ahead a couple decades and Dad finds this American imported 1975 honda that is identical to the one he rode in the States (could it be the same one..?). Naturally he struck a deal and bought it.
He owned if for a while before life made him sell it.
12 years later, I'm talking to Dad about bikes and he tells me the bloke he sold his bike to is wanting to sell a pair of CB400Fs... So of course I went down with a mate and bought one each, me buying back my old man's.
Since then I have been working on it, not a resto but a custom job in a way that I liked and that still threw back to it's classic origins. As it had been sitting under a tarp for almost 10yrs it wasn't in great shape once I started breaking her down.
Well she's now all but done.

So the issue.

I am not getting a signal current/voltage to activate the field coil via the white wire coming from my rectifier/regulator.

The setup I'm running with is an M-unit, an Anti-gravity 13V, 4 Cell battery and a Forsetti Rectifier/regulator

Regulator black wire to M-unit Lock.
Regulator white wire to field coil white
Reg/Rec green wire to earth
Reg/Reg red to Battery + (also M-unit power supply as it is all connected)
3 Yellows to 3 yellows.

I have read and read and triple checked my wiring and connections and everything seems in order. The Alternator and Field Coil are both good. I ran all the resistance and continuity  checks in manual and any extra that I could think.

I can get the Alternator to work by bypassing the Regulator which indicated to me that it must be a dud. I bought a new one and hooked it all up only to have the same problem. I then hooked up the Regulator straight to a 13v car battery and hey presto the white wire came alive, indicating to me that the Regulator is not actually cooked.

Is there anyone out there that knows what could be the issue here... I have heard that it might not be enough grunt (despite having 12.8 +- V to the Regulator Black wire) to trigger it to activate.

Buggered if I know...

Thanks a heap!

****In short check that the Regulator/Rectifier is not earthing out to the frame! I wish I had known earlier! ****
 

[RAFster122s]

Do you have a diagram of your wiring scheme with the M-unit? That would be helpful.
What is the wiring for your rectifier/regulator...all the connections...where do you have them hooked up?

[Dave87]

Thanks for your quick replies guys,

For better or worse, I completely rewired the bike to work in with the M-unit etc...

The Reg/Rec has 3 Yellows, 1 Green, 1 Red, 1 Black and 1 White. It is designed to be a direct replacement for the regulator and rectifier using the original harness.

The way I have it wired up is as follows;

Alt Yellow x3 - Reg/Rec Yellow x3
Alt Green - Earth (bike frame)
Alt White - Reg/Rec white
Reg/Rec Green - Earth (same point on bike frame as the 'Alt Green'. Both read 0 ohms)
Reg/Rec Red - M-Unit +ive which is also a direct link to Battery +ive
Reg/Rec Black - M-unit LOCK (this is where my Key wire is also located so it reads the same. When I turn the key, the light on the M-unit illuminates. AUX comes on with the Kill Switch.

I did try placing the Reg/Rec Black into the AUX but it didn't make any difference.
It is interesting what you said about earthing the Reg/Rec body as mine only has the one Green. I'll try earthing the body out the the frame and see if that makes a difference.

Thanks a heap to both of you, I greatly appreciate it!

[Dave87]

Here is the Wiring Diagram we get with the M-Unit. Just for Info.

Cheers.

[Dave87]

Depending on how long I have been playing around with it but I usually have between 13.4V and 12.5V at the battery and about 0.5V less coming from the Lock. My guess it that the M-Unit uses a bit in some way.

What about current? If the M-unit wasn't allowing enough current through to activate the regulator side of things, could that be a issue? just trying to think outside the box.

If I just connect the Reg/Rec GREEN to the Alt GREEN, how will it EARTH? They are currently share the same earthing point on the frame and are in fact contacting each other so in theory it should all be the same right?

I connected my kill switch up as per the M-unit manual. on the CB400F it is a toggle switch so to activate the coils the KILL needs to be ON, thus providing the power from the AUX to the coils. rotating the KILL to OFF kills the engine by removing power from the coils by using the AUX port.

The LOCK purely allows the M-Unit to be powered up. That's why it should be a good spot for the Reg BLACK to go, well both the AUX and the LOCK should have worked in the same way, right?

Sorry that it's not a simple problem.

[scottly]

If I just connect the Reg/Rec GREEN to the Alt GREEN, how will it EARTH? They are currently share the same earthing point on the frame and are in fact contacting each other so in theory it should all be the same right?

Both the green reg wire and the green Alt wires are indeed connected to frame ground (Earth). With the stock wiring harness, the solid green wires are all connected to frame ground, either at the coil mount under the fuel tank or near the battery under the seat, depending on model. If the green Alt wire is connected only to the green reg wire, the system won't charge, and is a common mistake when noobs try to wire a system from scratch. Your reg/rect unit does not need to have the body grounded, as clearly stated in the instructions you posted.
Try connecting the reg black wire directly to the battery + terminal. (Disconnect after testing, lest the draw from the field drains your battery)

[scottly]

Learn how to read a schematic, Cal. All solid green wires on Honda's are connected to frame ground. Ground is ground, the whole Earth 'round.

[Dave87]

Thanks for the continued support guys!

I will post a rough wiring diagram of how I have the charging system set up.

As for testing the Yellows and the coils (both field and alternator), I have carried out resistance checks and continuity checks on all IAW the workshop. They came back in spec and all connections were solid.

The problem I'm having is that power is getting to the R/R from the M-unit via the BLACK but I'm not getting anything out of the WHITE which should be used to activate the field coil.

I'm wondering if the M-unit is some how not allowing enough CURRENT through to the R/R to allow the circuitry to send it through to the Field coil? Anyone know how these things work internally?

[scottly]

I can get the Alternator to work by bypassing the Regulator

 

This would rule out the yellow stator wires, and the field coil. How exactly did you bypass the reg?

[Dave87]

Here is the wiring of how I have the charging system hooked up. I think it is pretty accurate...

To bypass the Reg, I just made up a jumper wire to go from the LOCK terminal to the WHITE field coil wire.

By using this method I managed to get the YELLOWS give me some voltage readings. I can't quite remember what they were exactly but I know that once I hooked the 3 YELLOWS up to the Rectifier it was producing between 13ish V to 14.5ish V depending on RPM.

I currently am not with the bike so further testing and trouble shooting will have to wait for the weekend but keen to hear of any more thoughts you might have.

Thanks again!

[Dave87]

Ah my bad.  It's missing on the diagram. Sorry about that.

[Dave87]

Sorry I may have confused you. I swapped the Reg/Rec out with a new item. It is still the original Alternator. I guess you could be right Cal in saying the Alternator is not putting out enough Volts due to it being slightly old etc. But if you could explain how this would stop power been sent to the WHITE signal wire that would be great. I think I must be missing a concept.

The Rectifier side of the R/R is clearly working as it is putting out DC. The Regulator is still an unknown I guess as the only way I have managed to get the field coil to work thus far is to jumper past the Regulator (jumping the black to the white prior to reaching the R/R)

I too previously came to the conclusion that it must be the BIKE and my wiring. So to try and isolate the faulty wire, I systematically went throught and bypassed my original wires at each connection. I even pulled apart my plugs and triple checked them all.

Cheers mate.

[Dave87]

Ah ok thanks again Cal.
I haven't had a chance to try your troubleshooting as I'm not with the bike atm. I will give it a go this weekend and let you know how I go. I'm using the stock key switch. Moving the black from LOCK to AUX made no difference.

Oh and just to clarify, I tested the Reg on a Car Battery not a  donna vehicle. Both R/R are brand new also.

Thanks a heap for everything. I'll let you know how the testing goes.

[Dave87]

Can't remember the exact Voltage we got from the White but it was pretty solid.
How we achieved it was by connecting the Red and Black to the +iv and the Green to the -ive of a car battery that read about 13.something volts. We then checked the voltage output of the White with a multimeter. We found that the White was now active. As it was not installed in the bike and had no working Alternator we figured there was no point testing the Yellows during this test.

It may have been a bit agricultural but we were running out of ideas.

[Bodi]

This keeps going in circles.
The alternator makes power from the field coil electromagnetic field. Voltage on white means pretty much nothing, the coil has to pass current... is the other field coil wire grounded? Are you sure your R/R works (like the OEM regulator) by controlling the positive? Some (ie DOHC4 type) control the negative and want the other field wire at +12V.
If unable to measure field coil current, you should be able to tell the coil is working by holding a steel tool near the alternator cover, it will be attracted by the magnetic field when the coil is working.
If that coil is making magnetic field, a spinning rotor will induce voltage on the stator yellow wires. Disconnected, I think over 25V should be expected yellow-yellow (all three combinations )but I've never measured it.
So measure the field current or test for the magnetism with a screwdriver or something.
The alternator must be fully assembled - field and stator coils on the cover, mounted over the rotor - to make power. If you have a good field, the rotor is turning, and all the wires are connected... it doesn't have many ways NOT to work.

[Dave87]

Thanks Bodi for entering the discussion!

Not sure exactly how this aftermarket R/R works but it is meant to be a direct replacement.

The other field coil wire goes to earth.

Interesting to hear about the current. I'll have to test that over the weekend and let you know. Thanks for that tip!

[Dave87]

G'day all, 
Sorry for the lack of activity, have been rather occupied with moving etc.
I am very happy to report that my charging issue is fixed!
The culprit... The Regulator/Rectifier body was earthing to the frame. I have seen a lot of people having similar issues to me with new R/Rs so the first thing I will recommend is make sure the body is isolated! I would have saved myself a lot of time and heartache if I had known that they needed to be installed like thus.

I have added the wiring diagram I used which is correct and working. Sorry for the lack of colour etc. Yes the black from the R/R goes to the AUX of the M-unit.

Thanks a heap everyone!

[scottly]

The body of the reg/rect shouldn't have to be isolated from the frame??

[Dave87]

Not sure Scotty,  this was a Forsetti direct replacement. Not sure if they are all the same but that's what's worked. It was earthed out and not working. Now it is not and it is working.  I won't argue with that. Haha.

[scottly]

With the key on, engine not running, measure the voltage between the reg/rect case and earth.

[vortexuk]

I am having the same problem but not with m unit. Complete rewire of bike, including upgrade to combined reg/rec, I have wired red to battery positive (has power) black to power when switched on (has power) green to earth, but when the bike is on no power to white field coil wire? i have tried 3 reg/rec with no joy. Battery i am using is lithium ion, could this be the reason?

Also i have tried wiring field coil direct to power and it energises. I am at a loss to work out what the problem is

[Dave87]

I'm sure others will have more to say on this but I'll give you my 2 cents worth in case it helps.
It seems you have it wired correctly and I highly doubt that you have a problem with the battery.
I would hazard a guess that the culprit is something to do with the earthing.
In the end I went with a 'Ricks motorsport' R/R. It has 2 earth wires instead of the just the one. Since installing this it worked great!
I feel that with some of the generic models (I found the same cheap unit sold by a few different brands) like the first 2 I tried with just a single combined earth that the signal coil signal gets lost somewhere in the unit's circuitry.
My recommendation is if you haven't already try a 'Ricks. As annoying as it is I think you'll have the issue fixed.
If not I have no idea where to go. Sorry mate.