help please - rewired my triumph 34 2/1 to positive earth

[Daveh67]

Hi all
Ive just rewired my triumph 34 2/1 to positive earth. Im filling a wassels 6v neg earth reg. I can only get 0.5 to 0.6 volt on the d terminal.
Can anyone please advise me. either my dynamo is not putting out or ive got something wrong.
I have polarised the field and wired as per instructions.
pics attached of my dynamo, my wiring circuit and wassels instructions
I wish i was working on the A10 instead.
regards
Dave

Adm edit: edited title, ref rules > https://www.a7a10.net/forum/index.php?topic=4723.0

[Swarfcut]

    Well, that confused me! If the regulator is designed for a negative earth system, then that's what you do, simply connect the frame earth wire to battery negative, repolarise the dynamo to suit, job's a good 'un.

    It appears from the wiring diagram that the dynamo needs a change to its internal wiring, so as a first step I'd suggest removing the  new Wassel Unit, putting things back as they were, and then testing the dynamo.

   Low output suggests a field coil problem, so first test the dynamo in isolation.  Bridge F & D, and put a 12 volt high wattage bulb eg car headlamp bulb ,or a multimeter if you have this luxury, between the bridge and dynamo body. If the dynamo is working the bulb should glow then shine brightly as revs increase. A meter voltage reading will start low and similarly increase. Assured the dynamo is working, repolarise as usual to match your negative earth system.

   No output from the dynamo, try a measurement of the resistance between Terminal F and earth. Open circuit is a poor or broken connection, or a break in the winding. With resistance near published figures, try a quick temporary connection from battery to Terminal F to energise the field windings. This is the equivalent of polarising.

  Stick with the official Lucas test and polarisation procedures, those crappy Wassell instructions look like they were written by some desk jockey. What looks like a third central brush is in fact a common earth connection for one brush and the field coil on a Lucas 2 brush dynamo.
   Connecting the field to Terminal D internally seems wrong, but its converting the basic field coil wiring circuit from original series wound to shunt . Maybe someone with one of these units can add some explanation. Remember the dynamo body needs a good earth connection to the engine and thence the frame. You don't want dirt, grease, paint and rust. So with a working dynamo, reconfigure the internal wiring as shown, add the regulator and reconnect the battery and that's it.

 This may help
   https://www.matchlessclueless.com/electrical/lucas/repolarising-lucas-dynamo/   

   Information here on all aspects of the charging system, including dynamo fault diagnosis.


 Swarfy.

[RDfella]

Beware testing output with a multimeter. Recently had a real run-around doing that. System not charging, so bridged D&F and used multimeter. Got wild readings - 3v, 18v, 0v etc so stripped dynamo (two or three times) and found nothing wrong. A member here suggested using a bulb and it glowed brightly, leading me to find the real problem in just a couple of minutes. Appears digital multimeters have a nervous breakdown trying to read a dynamo.

[berger]

I agree RD my digi meter goes on a dance but behaves a bit better with a new battery--- for a bit

[Daveh67]

Thankyou everyone. I appreciate the advice, Bike wiring was a melted mess so i though why not do it negative earth. Anyway I can see some issues so a few beers and back in the shed tomorow to try it all again.
Something so simple can get very confusing. The bulb trick is perfect, i have many times had to use a bulb instead of a meter chasing earth issues on tractors.
thanks again and I will update secess or failures.
Dave

[groily]

From what I see in the sketch, the field is indeed wired from D to F.
This is not standard Lucas practice (it's Miller, Bosch and most others' though) but it is correct and what the instructions demand - see the Wassell schematic for Neg earth units you posted. (Their positive earth ones require the standard Lucas field coil wiring - all very confusing!)

Therefore - and 'This Matters' - in this case the standard dyn output test of hooking F and D together and measuring from the pair of them to earth won't work.

This unit regulates on the earth side, not on the live side, so the proper test for dynamo output is to bridge the F terminal to earth, and put a bulb or (decent) meter between D and Earth and spin the thing the way it's meant to go.
That will tell you if the dynamo works - as long as you have got the rotation correct. If you have the rotation wrong, you'll see maybe half a volt  . . .  I'm assuming the polarity has been set for negative earth, which it needs to be.

If it does work, see whether you can get a decent output from the A lead off the regulator. (As Swarfy says, make sure you've got a decent earth from reg to dyn body.) 'Decent' means about 7.2v when things are spinning at a reasonable speed, which voltage then should hold steady as revs rise to any level, and should be maintained with loads applied.
Some of these particular regulators struggle actually to maintain battery voltage (which is 6.6v fully charged), but that's another story that can't be addressed until you know whether it does anything at all!

[Greybeard]

Beware testing output with a multimeter. Recently had a real run-around doing that. System not charging, so bridged D&F and used multimeter. Got wild readings - 3v, 18v, 0v etc so stripped dynamo (two or three times) and found nothing wrong. A member here suggested using a bulb and it glowed brightly, leading me to find the real problem in just a couple of minutes. Appears digital multimeters have a nervous breakdown trying to read a dynamo.

Makes me think about image persitance on a TV screen. A bulb does not react to rapid changes the way a digital meter can.

[Swarfcut]

Mr G.  Well said.    The standard test for dynamo function will not work if the dynamo remains in its newly configured format. When I said to put things back to how they were originally, I meant to restore the original dynamo internal wiring, as a means of ensuring that at least the dynamo was capable of producing an unregulated output.

 Shunt wound and series wound dynamos have different output characteristics. Looks as if this Wassel Unit  controls  the dynamo output in a completely different way to the original design.

 Thanks Groily for the expert enlightened overview.

 Swarfy.

[Triton Thrasher]

Weren’t most 1930s bikes negative earth?

[JulianS]

Was this dynamo originally a pre compensated voltage control 3 brush model? If converted to 2 brush are you certain that the connections are correct?

[groily]

The standard test for dynamo function will not work  . . .

Just wanted to be thorough, in case further tests were done without reverting to std wiring per your first suggestion  . . .

Why on earth the neg and pos versions of the Wassell gizmo regulate on opposite sides, I'm darned if I know. Maybe they were thinking most neg earth applications will be on machines with field already wired F to D. But as TT says, in pre-war days neg earth was normal - and if Lucas-equipped, with Field to Earth. The Continentals never flip-flopped on the polarity, being Negative since for ever.
I fit more Neg DVR2s over here in France than positives, because folk very sensibly tend to stick with what they're used to and aren't looking to confuse themselves in their sheds. Nor do I (want to confuse myself) so all my own  bikes are + earth, me being an anglais all contrary.

[Daveh67]

Just an update on progress.

I removed the dynamo and found it was not putting out any voltage, Stripped down and the armature looks new and measured ok. The field seems old and measured average. So cleaning and reasembly and all of a sudden I now have 2.8v at 1000 rpm. But this soon faded away and the brushes were leaving a very black mess on the armature. So re cleaned and voltage came back.
I suspect my brushes are the curent issue. So I will order new brushes and update when i can fit themm and re test the dynamo.
Dave