Charging circuit test

[stevush]

Hi,
Have had a problem with my 400/4 regarding charging. It seems to be charging OK during normal riding, starts first time on the button even after leaving it for 1/2 weeks but if I ride with headlights on for say 10/15 miles it discharges the battery and next time I try to start with the button, the battery won't turn the starter but it will kick first time.  I've just fitted a new fully charged battery and I've connected a multimeter across the battery when running at 3/4000 rpm and I'm getting 12.02.  I've cleaned the points on the voltage regulator, swapped it with another 2 regulators but I can seem to get a higher reading.  I suspect the alternator is not working correctly, any further tests to prove this ?

Thanks
Steve

[paul G]

Should be much higher than that around 13.8v if I remenber correctly.
I have a load of info somewhere I will see if I can find it.

[TrickyMicky]

Hiya,
    Had similar problem about 18 months ago, did not possess means or know-how to check if it was alternator, rectifier, or voltage control unit. I'm afraid I took the easy option and replaced the rectifier and control unit with a single "potted" item from Silver's. Managed to concoct a couple of mounting brackets, and placed it where the control unit originally sat, there is enough slack in the wires to the rectifier to pass them through the frame to the left hand side. So far no problems, charging well, original units removed and placed in the Black Museum.

[stevush]

I have a few spares so maybe I'll swap the rectifier and see if it makes any difference. Looks like the alternator isn't difficult to swap either ?

Thanks
Steve

[Bryanj]

Sounds like either one of the yellow wires has disconnected or one phase of rectifier shot, check for AC voltage on the three pairs of yellow wires that exit the engine into loom

[paul G]

The fault I had as well was one of the phases to ground.
Check all the three yellow wires in turn to ground there should be no continuity.

[paul G]

have a look at these they are for the 550 but should point you in the right direction.

[mike the bike]

It does sold like one of the phases isn't doing anything, either the rectifier is faulty or the yellow wiring from the alternator is faulty.  Don't overlook the plug going to the alternator.  Do you have access to a multimeter?

[stevush]

I do have a multimeter but I'm a relative novice with it. I can check continuity, check voltage readings (thats how I tested volts across the battery) but not much more. Resistance is beyond me I think..

" check for AC voltage on the three pairs of yellow wires that exit the engine into loom"..
Not sure how I'd do that

Steve

[stevush]

So..
I've disconnected the multiplug connector from the alternator. There are 3 yellow wires from the alternator, I've checked all three and there is continuity to ground on ALL of them..

Steve

[Dave487]

Check where the 3 yellows exit from alternator cover. I recently had a similar problem and one of 3 had gone to earth at the bullet connector close to the cover and melted the plastic insulators on all 3. I fitted new connectors and all is well.

[Lobo]

Steve... to check for AC voltage ..

(1) select a suitable AC Voltage range on your multimeter. (Eg 50v AC)
(2) With all connections ‘normal’, start the bike
(3) put your multimeter probes across a pair of the YELLOW stator windings... and check the AC Voltage
(4) Do this for the next pair
(5) Ditto.

Attached a YouTube clip, not necessarily what you’re after, but useful general knowledge stuff..

https://www.youtube.com/watch?v=zCz735rFcYU

[stevush]

OK Lobo, Interesting, thanks for the info, I'll try that over the weekend sometime.
What readings would I expect to tell me if its good/bad  ?

Thanks
Steve

[mike the bike]

If you get continuity to earth on all 3 yellows, it doesn't necessarily mean all three are shorting to earth,  it will read a short because of the low resistance of the endings.   Check the insulation of the yellows where it exits the alternator casting.

[Lobo]

Steve - I honestly wouldn’t know typical AC readings as this test is not described anywhere I read - rather the resistance of each STATOR winding is the typical check. (should be 0.2 ohms ‘ish)

(Whilst you’re at it, you should check your FIELD Coil winding... the coil within the STATOR. This has WHITE & GREEN wires - this resistance should be 7.2 ohms’ish)

You mention you’re a little uncomfortable with reading Resistances... set your meter as the below pic RED circle. (No matter which way around you use the probes). Set the scaling correctly... or just understand why it reads 0.72 ... or 72 ohms etc!

I’m not near my bike(s) to do such an AC output coil check on a healthy machine... if I had to guess I might say 16vAC ?

BUT. The point is, it is highly unlikely all 3 windings would have failed in exactly the same way... ie. just as when looking at cylinder compressions - you’re mainly looking for a difference. Such a thing will point to an issue ... if all 3 readings are give-or-take the same (and > 15vAC) I’d reckon you could move on from the stator.

As Bryan has already mentioned, one of the diodes may have failed within the Rectifier (fin air cooled thingy with 5 wires (3 yellow + Red + Green) coming out. Have you checked this?

If you study the 2nd attachment below (drawing schematic) you can see that ALTERNATING (AC) current is fed into the middle of 6 Diodes. (via the stator output, ie the 3x Yellow wires)
Diodes only allow flow in one direction ... and so you can see that (to the left side of all #3 inputs) the positive part of the alternating flow will be allowed to pass through the ‘arrows’... to the RED/WHITE wire, the negative part will not. Equally, to the RHS of all #3 inputs.. all positive flow will be rejected, whilst the negative portion of the cycling current will be allowed to flow to the GREEN wire.
And bingo... Alternating current is ‘rectified’ into Direct current, ie +ve at the RED/WHITE and -be at the GREEN wires.

So... if one of those diodes has failed... your charging will be degraded.

Set your multimeter to the Blue (ie Diode setting) circle, and put:
(1) The Black probe on the first  YELLOW, and the Red probe on the RED/WHITE Wire. You should have continuity ... and if your meter so equipped, a B...E...E...P.
(2) keep the Black probe on the first YELLOW, and move the Red probe to the GREEN Wire. Should have zip.
(3) move the Black probe onto the second YELLOW, and put the Red probe on the RED/WHITE Wire. You should have continuity ... and if your meter so equipped, a B...E...E...P.
(4) keep the Black probe on the second YELLOW, and move the Red probe to the GREEN Wire. Should have zip.
(5) move the Black probe on the third YELLOW, and put the Red probe on the RED/WHITE Wire. You should have continuity ... and if your meter so equipped, a B...E...E...P.
(6) keep the Black probe on the third YELLOW, and move the Red probe to the GREEN Wire. Should have zip.

If any part of the above fails you’ve likely an issue with your Rectifier. (Don’t forget this issue could simply be corrosion in the plug etc - ie if it fails the test check the wiring / bullets etc)

Wrapping up... and having re-read your first post... the charging on these old bikes is minimal at best. If you’ve non-standard coils (?) which are ‘high performance’ there is every possibility you’re overloading the charging system with lights on etc. If you’ve non-standard lights, add-in electrics... ditto. Just sitting at traffic lights, foot on the brake, headlamp on, maybe indicators...  you’ll be depleting the battery. Bottom line, don’t begin to compare this charging system’s output with anything modern you might own! Use your electrics sparingly, avoid main lights if pootling about town etc, get the starting bang-on... ie no-need of excessive cranking.

Good luck,
Simon