Showing a discharge on tickover?

[shaunstaples]

75w continuous would do nicely, some really useful information on here thank you.
I went in garage at lunchtime and ran it with a voltmeter across the battery, the ammeter is accurate as the battery was initially 12.4v before starting and climbed fast when ammeter showed positive and dropped down under 12.4v slowly when showing discharge.
If this discharge can be minimised or better eliminated by fitting a DVR2 then happy days.
I think its worth changing regulator before touching dynamo, if after riding it, the battery has had some charge (Sounds like a plan)

Thanks again

[SPRIDDLER]

Shaun, I think you'll find this an informative read wrt conversion/output/revs/testing etc......

https://www.matchlessclueless.com/elect ... onversion/

[shaunstaples]

Thanks Spriddler, Another good read...

[shaunstaples]

This happens because the cut-out is not always very crisp with descending rpm on some regulators. They cut out a little 'late'. You will see it with many mechanical ones too. So it is not abnormal to see an amp or two discharge at tickover.
One of the reasons I particularly like the DVR2 version of the modern electronic generation is that it does not allow a drain back towards the dynamo from the battery at tickover so you see no equivalent discharge.

So The discharge is because the regulator has detected some voltage and "cut in early" or "cut out late" from charging and the voltage trigger point is below 12v (while dynamo running too slow). Then this allows the battery to discharge back through field coils ?

The DVR2 must either have a higher trigger point or able to block current under 12v ?

[Groily]

Basically yes and yes.

The discharge at low rpm is because the cut-out isn't cutting out until the dynamo voltage is lower than the battery voltage.
Ideally it should cut-out the instant the voltage from the dynamo drops to battery voltage.

If the battery has a higher voltage than the dynamo is producing then it will try to turn the dynamo like a motor and you'll see your discharge at tickover. It's common enough, if not ideal. The system makes up the tickover battery losses quickly when the revs climb again though.

If the cut-out stayed 'closed' with the engine stopped then the battery would feed the dynamo full blast, the current would work it's way through the wiring loom and the dynamo windings and there would be a mega-problem and probable need for the Fire Brigade.

For reference if it helps, an edited version of some words from the Jampot from years back:

The five stages of operation of a dynamo: static ; excitation; avalanche; unregulated charging; and regulated charging.

Static
1. The cut-out is open.
Battery not connected to the dynamo. If it were, it would try to make it turn like a motor. But it needs to be connected if it is ever to be charged. So, in ‘FADE’ terminology, wire A (to ammeter, switch and battery) is only connected to D when the cut-out is shut. A and D are never connected at rest or at low dynamo rpm.
2. Contacts (or electronic equiv) on the voltage regulator connecting D and F are closed.

Excitation & Avalanche
The dynamo body contains a small amount of residual magnetism from the last time it ran. So the armature turns in a weak magnetic field when started. That weak field produces a small voltage between D and E which is fed from D straight back to F through the closed circuit on the voltage regulator. This fires up the electro-magnet to increase the field strength: power builds up fast from D. This is the ‘avalanche’ phase.

Nothing shows on the ammeter until the voltage from D exceeds battery voltage - which is present at A. Then the cut-out closes. D and A are connected now, so power can go to the battery while still feeding the Field.
D, F and A are connected – F to D through the regulator contacts, D to A through the cut-out. This is the start of unregulated charging.

As Dynamo rpm increase further so does output. At a speed around typically 1800-2000 rpm (but according to load as well), the regulator says 'that's enough output or we'll overcharge the battery, blow bulbs etc' so, it starts to regulate by rapidly opening and closing the connection between D and F. 'Open' cuts the feed to F from D, 'closed' restores it, thus maintaining a steady(ish) average output to A. This is the fully regulated phase.

As dynamo revs fall the whole process is reversed until the point is reached where the cut-out senses that the battery needs to be disconnected – and opens to prevent the battery trying to drive the dynamo as a motor. A is disconnected from D, while D and F remain fully connected at the regulator.

Cut in and cut out speeds are typically not quite the same, to prevent interminable flutter. Cut-OUT speed tends to be set lower than cut-in, hence the discharge often shown on the ammeter at low rpm, which disappears when the engine stops.

[ChrisTheChippy]

My brain hurts ...

[shaunstaples]

Thanks Bill,

That's how I need it!

Reading & Digesting it has took me back to 1979/80 at Rotherham Tech. Mr Bramhall drawing with his coloured chalk on the board and us lot shouting back at him were never gonna need it! Should've paid more attention, took 40 years but he was right!

[Groily]

Ha! I expect your Mr Bramhall waved his hands around explaining Fleming's Left and Right Hand Rules, and all that sort of 'Force / Current / Magnetism' stuff Shaun! I know the poor so-and-so who had the misfortune to try to teach me anything back in the late '60s / early '70s did.

Never found a lot of it to be of much practical interest at the time either.
However, I decided later that I was darned if I was going to spend the rest of my life without a basic understanding of the electrical bits on my bikes, and that something had to be done belatedly to grasp at least the basics. (Amazing what having passionate hobbies can do to force us to re-look at things we dismissed as irrelevant before we got the bug . . . !)

I have absolutely no real idea WHY many of these things 'are'- they are the fundamentals of the Meaning of Life the Universe and Everything after all and I am neither a physicist nor an electrical engineer.
Sometimes we have to be like children and accept that something just IS without saying 'But Why Mum?' all the time . . .

[shaunstaples]

Yes Flemings Left and right hands are shelved somewhere, We all probably stuck 3 fingers up at him with that too.

I left the motor trade in 1988 and swapped repairing vehicles for repairing telephones, always been interested in cars & bikes but much more enthusiastic about bikes. I can remember the banter with the old guys, you always got " I've forgot more than Tha'll ever know" and I'm there now!
I can go upstairs and forget why I've gone up!
I always have to take things to bits and at least try to understand what's going on, It all started with my Mamod traction engine...

Thanks again Bill for sharing your knowledge

[SPRIDDLER]

I can go upstairs and forget why I've gone up!

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