Apologies if this has been asked before here (I'm sure it has). But I must have missed it.

Does the battery need to be in the circuit for the charging to work properly?

I've got a feeling that it doesn't. But either I've simply got a dead battery stopping the volts from getting through, or there's another fault somewhere.

Any advice/opinions?

email (option): dannydefazio@sumpmagazine.com

Hi Danny,the battery must be in the circuit to complete the circuit,otherwise there is nothing to charge.Also the battery energises the field coils to make the dynamo produce a current to re charge the battery.hope this helps
cheers Rick

email (option): richardholt@rocketmail.com

Yep... the dynamo does not have enough residual magnetism to start charging. You must have a battery to provide the stationary magnetic field to allow the armature to produce current as it rotates within that magnetic field. This is different from other charging systems like a modern bike alternator which use a rotating magnet to create the rotating magnetic field that then creates an electric current in the stationary coils surrounding that magnet.

The Lucas magdyno system on just about all WD bikes is regulated by increasing or decreasing the magnetic field in the field coils. This differs from say, an alternator as used in most 60's and later British bikes. In those bikes, since the magnetic field can't be increased or decreased, most commonly a zener diode is used to convert excess charging system power into heat when the engine is run at a high RPM.

That's more than you probably wanted or needed to know, but I couldn't help myself. I'm an engineer. An engineer will tell you the stochiometric ratio of lighter fuel to air when you ask him for a light.

Kevin

Its not static. The proof I described produces the maximum power from the dynamo. Normally of course its regulated by the cut out and regulator box (MCR1 or 2)

Thanks to all for the responses. But I'm still not sure of one thing; perhaps I should have made it clearer. Should the lights and horn work without the battery if the engine is running?

email (option): dannydefazio@sumpmagazine.com

Yes they should, Danny. But without the battery the circuit is disturbed and an overvoltage may blow your bulbs.

When using a dynamo with a mechanical regulator,
You do not really need a battery, and it is used only
When the engine idles or on very slow revs.

Actually, as the regulator contains also a "Cut out" part which
disengages the battery from the charging system on low revs
or when the engine is off,
(In order to prevent discharge of the battery into the dynamo)
The dynamo starts producing energy from the residual magnetism,
which starts to feed the "Field" coil, which in turn becomes an electromagnet,
Which then, with the help of this magnetic flux, help producing higher voltage,
As the armature turns "cutting"/crossing this flux.
This voltage is being monitored by the regulator,
Who disconnects the voltage feed to the "Field" coil whenever the
Output voltage goes over 7.2 Volts, ideally,
(For 6V systems, or 14.4V for 12V systems), then feels
that the voltage in too low, and quickly feed the "Field" coil again,
So we actually get a very quick pulsing DC current.

Electronic regulators, however, do need the battery as "load" to release the
energy, and can otherwise burn quite fast..

Noam.

email (option): noam10@gmail.com

Hi Danny - I agree with Keith's comments and would add that the residual magnetism may dissipate over the long term and the generator may need to be flashed if it has been in storage to start it. See tech section http://www.wdbsa.nl/lucas_dynamo.htm.

email (option): watsond@xnet.co.nz

I stand corrected. Very interesting information. Thanks!

Kevin

Thanks again for all that. Very helpful. My M20 obviously has a problem then. It's got an old battery that's well past its sell by date. Meaning that it's dead. Bike runs fine, but no lights or horn.

I've had this before, and it usually wakes up after a few revs and a few miles. But it's not waking up now. Wiring looks okay. Bulbs look okay. But I've got to check output from the dynamo. Not sure how to do that, but I've got a service book, so I'll figure it out.

Just wanted to know if the lights ought to work without a battery, and now I know. Actually, I've got a vague memory of Ian Wright telling me all about this ten years ago when I bought the bike. But the older you get, the more you have to remember, and the more you're apt to forget.

Appreciate the advice, all.

email (option): dannydefazio@sumpmagazine.com

Hi Danny,

Yes, all should be working with a dead battery or no battery,
As long as you rev it enough to pass the "Cut out" point of the regulator.

In order to measure the output to batt, you can just attach a Volt Meter
On to the battery terminals and measure the output.
(Should not go above 7.2V, can be min about 6.8V)
If no output there, you can test if the dynamo is working like so:
You can try to disconnect the "F" and "D" terminals from your system,
Short- circuit them together, and attach a wire to one of them,
and then try to measure with a Volt Meter to see if there is a voltage
Between this terminal (which is connected to the shorten "F" AND "D")
And the chassis. as the voltage is not regulated now,
it can get as high as 20V or more, on high revs.
Or, instead of a Volt Meter, a bulb (6 or 12v) can be connected between
the chassis and the "F" & "D". if it lights when reving the engine
Then the dynamo is alive.

Noam.

email (option): noam10@gmail.com

Thanks, Noam. I'm on the case.

email (option): dannydefazio@sumpmagazine.com

Thank you, Noam, for your clear and convincing explanation. That was a tour de force.

Jeff

email (option): jjbandoo@aol.com

The 'dead' battery may actually be the cause of the problem if you have suffered a dynamo or regulator failure...
The system is demand driven and designed to 'cut in' as required to maintain the battery charge (or rather balance input against output)..

However, when not required to do that (when the battery is fully charged) the system 'cuts out' and no current is produced...

A defective battery that won't hold charge is effectively always 'flat' and the system will run continuously at full output in an attempt to correct that condition, something it is not designed to do...Ian

email (option): ian@wright52.plus.com

Hi Danny
If your battery is as dead and knackered as you said then its possible it may have developed an internal "short circuit". That would definately stop the lights working and may even have damaged the dynamo and wiring.
Regards
Keith H

Danny,

When the dynamo is constantly charging because of s flat or short circuited battery the solder from the collector might melt because the dynamo running very hot. If you take of the cover band at the end and you see a lot of silver shiny particles you know what you have got to do. DAMHIK!

Regards,
Leon

email (option): leonhop3@planet.nl

Thanks all for the advice. I'll pick up a new battery tomorrow and runs some checks. I haven't actually been running the bike for any length of time with a dead battery. I just started it a couple of days ago after a few months at the back of the garage (to keep the oil where it's supposed to be and generally check it over in anticipation of a few autumn rides).

The battery was old and frail when I laid up the bike, and I think it's since passed away quietly.

It's back to first principles, of course. Thanks again.

email (option): dannydefazio@sumpmagazine.com

You might want to put a modern fuse in there while you're at it if you haven't already. I put in a weather proof rubber sealed fuse holder with a micro fuse. It's very cheap insurance. There are a lot of great sealed 6 volt batteries out there now too, that will last a long time and have high amp-hour ratings. Once again, if you haven't already gone that route.

Good luck and may the smoke stay in your harness!

Kevin