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BTH Cut-Out



Michel

Well Known and Active Website User
VOC Member
#1
Hi everybody,

Paul Richardson - Fig. 98 - Wiring Diagram Mag-generator Lighting Equipment

On this diagram under the switch is drawn a circle with the letters B D E F T.
I do not understand which electric accessory represents this circle ?
Thanks.
Michel.
 

vin998

Well Known and Active Website User
VOC Member
#5
It's the connection terminal on the back of the BTH headlight switch. As a note that wiring diagram is for the pre A machines and the 1935 series A's that used the BTH headlight and switch. When in 1936 Vincent went to Miller lights which had a switch which is similar to the series B&C headlight switch except it had a charge resistor. For a while these bikes with Miller lights still used BTH mag-Dynamo to use stocks up. I have never seen a "hybrid" wiring diagram of Miller lights & BTH generator so a bit of ingenuity is required.
 

Michel

Well Known and Active Website User
VOC Member
#6
This is an explanation that I like because it's been months that I try to understand how I will redo the connections of electrical circuits. In three weeks I go on vacation with my Comet Serie A. I will dedicate a few days to redo these connections. The BTH generator is restored and installed and I recently found the BTH cut-out and the right Miller switch (4 positions and his charge resistor).
 

Michel

Well Known and Active Website User
VOC Member
#7
I still ask the question and I try my luck. Maybe an other VOC member has encountered the same problem and would have drawn the right diagram. Maybe I'm dreaming but if it exists I thank him for sending me this right wiring diagram.
Thank you.
Michel.
 

Michel

Well Known and Active Website User
VOC Member
#8
"...Miller lights which had a switch which is similar to the series B&C headlight switch except it had a charge resistor."

And except it had a dynamo with regulator and not a generator, isn't. And this is why no diagram available in general documentation is correct.
 

vin998

Well Known and Active Website User
VOC Member
#9
Michel
My series A is exactly the same as yours as in it has Miller lights & Miller switches but a BTH mag-dyno and BTH cutout. I basically made up the wiring diagram to work as I think it should and so far it does. If I cannot find the diagram I will redraw it but give me a few days.

Simon
 

Michel

Well Known and Active Website User
VOC Member
#10
Dear Simon,
You would be my saviour because I am not very smart in this kind of electric exercise. And I'm afraid of doing something stupid.
Michel.
 

vin998

Well Known and Active Website User
VOC Member
#11
Michel
I found the wiring diagram which is a mixture of several different diagrams to work for the Miller / BTH combination.
For anybody else looking this is for a 1936-37 series A single that the factory fitted with Miller lights and a BTH mag generator. There was probably approx 50-100 bikes fitted with this combination.
BTH-Miller combined diagram.jpg
Simon
 

Michel

Well Known and Active Website User
VOC Member
#12
Dear Simon,
Great, wonderful, beautiful ! Could you send it to me on my email address. I send it to you in PM. Do you come to the international rally in Belgium in 2019 ? If so, you will be entitled to one or more abbey beers if you like Belgian beers. I wish you an excellent weekend under the sun and driving your Vincent, of course :)
 

Michel

Well Known and Active Website User
VOC Member
#13
Dear Simon,
I followed your diagram and the electrical circuits worked perfectly. But you have to install a connection between the terminals n°5 and n°7. In the next few days, I install the BTH cutout but I already noticed that the BTH generator charges (very) weakly.
Thank you.
 

vin998

Well Known and Active Website User
VOC Member
#15
Michel
You should not need a connection between terminals 5 & 7. If you do then there is something different with your headlight switch. The speedo bulb and rear light bulb should be on a separate terminal to the pilot bulb and the switch connects them up depending on the switch position. Here is what each switch position should do on a series A single with Miller lights:

Off - no lights and no charging.
Ch - no lights and the battery charges through the charge resistor at a low rate.
Hi - Main headlight on, speedo bulb on, rear light on and charges full rate (resistor not been used). Note the pilot bulb is not connected or used in this position.
Lo - Speedo bulb, back light and pilot bulb connected. Note the main headlight is not connected in this position.

The above switch positions work exactly the same on series B & C bikes but as they have charging regulator on the dynamo and not a charging resistor then position 2 does nothing.

Simon
 

Michel

Well Known and Active Website User
VOC Member
#16
Simon, we agree.
Next step, replace the manual switch with the BTH cut-out.
Wait and see, as our English friends say.
Michel.
 

Michel

Well Known and Active Website User
VOC Member
#17
Hi everybody,
And that's it, the cut-out is in place and everything is working normally. Except that the cut-out has not closed yet because the battery is fully charged.
 

Michel

Well Known and Active Website User
VOC Member
#18
Hello Simon,
Considering the BTH generator, what is the capacity (Ampere / hour) of the battery 6 volts lead on your Comet and you advise ?
Michel.
 


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