1930 T6 600cc

[walabat]

Hi all, as a new douglas owner I am after some info on my bike
from info & no.s I have identified it as a T 6. but unsure as to its original state.
does not have generator or BTH light set, need feedback or photos of what its supposed to look like. I am guessing that it had a carbide light & bulb horn as per an EW, also has bodgy handlebars.
would appreciate if any one has photos to share or info
walabat

[Doug]

Here is a catalog picture of a T6:



Larger view

Very similar to the S5 and S6 models except in detail. Such as the old fashion rear carrier with leather tool boxes rather than cast alloy toolbox in chainstay of the S5/S6. Slightly lower overall gearing, heavier flywheel clutch (larger rim.) Continuation of the old duplex extension spring forks rather than the single central compression spring fork new for the S5/S6. Footboards rather than footrests. 

J. Withers has reprint parts and service books for the T6/S5/S6 models here. PVIN700 and PVIN701 would be of interest, as well as the year catalog for 1930.

The lighting set would normally be electric, as seen here from the same catalog:



Larger view

The generator was a four pole BTH 'pancake' dyno that plugged into a large diameter opening in the timing chest.  Head and tail lamp would also be BTH, the headlamp changed slightly depending on year, though you ar lucky to get any BTH lamp from this era.  There was a cheaper option of acetylene lighting, but I have not seen a S5/S6/T6 so fitted. Earlier machines (1926-1929) had alternate timing covers with and without the dynamo, but I not yet seen a S5/S6/T6 timing cover without the dynamo provision.

-Doug

[Manley]

If you do decide to locate a lighting set for your machine may i suggest that the pancake dynamo is left out of the hunt.  My experience tells me that they are not great and after trying everything to re-magnatise the ring (4-pole split ring) magnet it still wont produce even a small charge.  Im almost (i did say almost) thinking about fitting a modern alternator and hiding it under the BTH cover (gasp!).  Good luck anyhow.

  Rob. 

[Doug]

The BTH, Type P.A., Form B (Pancake) dynamo starts to charge at 1400 rpm, and puts out a maximum 3~3.5 amps at 3000rpm. So even in tip-top shape, output is meager. I've not tried to remagnetize one yet, but always thought bridge pieces would be required so as to do all four poles at once.

I'm almost (i did say almost) thinking about fitting a modern alternator and hiding it under the BTH cover (gasp!).

There are some fitted to the small industrial Kubota diesels that might work, the main difficulty finding one short enough. Though the Lucas alternators fitted to later bikes just might work too. Or you could fill the empty housing with Ni-Cad batteries! 

-Doug

[trevorp]

also take into account an alternator needs starting current so needs a battery

[Doug]

Some alternators rely on residual magnetism to self-excite, or at least initiate excitation. In the case of the six-pole Lucas alternators fitted to motorcycles, these have a solid magnet armature, and do not use excitation at all, and need no current input to initiate output. The infamous emergency start and capacitor ignition for dead or no battery coil ignition situations.  Typically excitation is seen in automotive applications, where you have slip rings and winding on the armature, and even there I do not think they apply battery voltage to the armature to get excitation, rather they use residual magnetism to start and then tap off the fields to provide power to the armature windings.

You will have to rectify the AC current output of the alternator into DC, which you do not have to worry about with a dynamo. And like a dynamo, you will need voltage regulation. There are two basic types. The three lead stator (field coils), for six or twelve volts where they successively short out field coil pairs manually (via headlamp switch) to reduce the output. Then the two lead type, twelve volts only, wired internally for full output all the time. Excessive voltage being dumped to ground (and heat) through a zener diode.

The BTH pancake dyno is unregulated, as quite frankly, the output is not high enough to ever ever worry about overcharging the battery! Only a cutout was fitted, to prevent the battery draining down through the dyno when the charging voltage was too low. Which was probably most of the time!

-Doug

[trevorp]

Is not a solid magnet armature  a generator, and an alternator exicted field magnets, all vehicles automotive wise need 12v to excite field whereas in the old generator days u just needed them to turn
i may be wrong but dynamo and generator(same thing really) work on one principal and alternator another although im more from the auto field and not so much bikes

[Doug]

Trevor,

All dynamos and alternators generate alternating current. A dynamo will have a commutator to convert the AC to DC at the unit, where as an alternator has the AC converted to direct current via a rectifier.
It has more to do with the output being DC or AC, not whether the armature has windings or a magnet, though if you wanted to point to a constructional difference, I would use the presence of a segmented bar commutator. There are plenty of dynamos with armature windings and even dynamos that excite or energize the field or armature windings (the ubiquitous Lucas dynos fitted to motorcycles for example.)

Early on there may have been some subtle difference between calling something a dynamo-electric machine or a generator that would have a Victorian engineer tut-tutting, but if there was, I do not know it. I think the definitions are interchangeable, and it is just yet another example of one group a electro-chemical storage device a battery and another calling it an accumulator.

-Doug

[trevorp]

mmmmm now u have me thinking this explains it most clearly i think
http://www.rowand.net/Shop/Tech/AlternatorGeneratorTheory.htm

[Dave]

Trevor,

That's an informative link you found there. Would you like to post it in Other Links also? Might be easier for people to find in its own topic.

Dave