Advice would thankfully appreciated,12v dynamo ? regulator ?

[Stephen Arsenal]

Hi,I bought a 1959 a10 flash from a guy who said it had been modified to 12v.Have restored most of the bike and am now on the cables.The bulbs were 12v and the amp meter is also 12v (however I cannot trust this guy 100% because a lot of the bike was really bodged together).Here is a picture of the control box,it is obviously not original,has only 3 wires,on the wiring plan it has 4.I cannot get into this box as it is a sealed unit,I have been advised not to try and test it because we cannot be 100% certain  if the dynamo has been modified to give out 12v or 6v.Apart from starting the motor up,(not an option at the moment) is there any way to test the dynamo.I have taken some photos,The lettering on the face is such  F 28 25 and D 8 ? It has to be all 12v battery dynamo control box or all 6 v or ? can anyone help ? thanks-steve

[MG]

Hi Stephen!

There are two ways of doing a 12V conversion.

The first way is to use the original 6V dynamo and couple it to a 6V-12V electronic converter/regulator unit. With this set-up charging starts at about 1500rpm (1000 rpm originally)
The second option is using an armature and a field coil converted (rewound) to 12 V. This means twice as many windings with thinner wire. Due to the thinner wire you also need an electronic regulator to limit the current in order not to burn the now much thinner wire.

Whatever type of conversion has been (or might have been) done on your bike, the battery should be a 12V type, when the system is run on 12V.


You can do the following check in case you are the proud owner of an ohmmeter (or multimeter):
There are two cables coming from the inside of the dynamo body, running through the bakelite base plate/brush holder. One of these is connected to the dynamo body and the other one is connected to the F terminal on the backplate. These are the ends of the field coil. If you measure the resistance between these leads, you will get a reading of approx. 2.8ohms for a 6V coil. A 12V coil should have at least twice as much resistance, probably even more due to the thinner wire. Oh yes, disconnect the earthed wire from the dynamo body prior to measuring!

As for the regulator: I don't know that particular type of regulator, but maybe the missing 4th cable is the earthing connection, that is done via the metal casing of the regulator maybe?
F usually stands for the dynamo field coil connection, D is for the dynamo output. A third connection is for the battery.
I don't know if your bike is positive or negative earth? I tend to believe that BSA changed that somewhen during the A10 range?

Sorry I can't be of any more help here.

Cheers, Markus

[G/F DAVE]

Hi, Stephen the control box you have is a JG 12V conversion. To use these you need to rewire the dynamo to suit. I have used one in past and it gave me no problems also ran a halogen bulb set up on my A10 .If you need a wiring diagram/instructions I still have them somewhere? Dave..

[Stephen Arsenal]

Hi Dave,are you sure ? there are no markings / names of any type on the box,I can also photograph the inside,although it is a closed sealed unit.If true,then if you could tell me which wires go where I´ll be forever thankfull.I´m guessing that the dynamo has been already been re-adjusted,but will check wether its a 6v or modified 12v later on in the week.Is there anyway I can test the regulator to see if it works,the bike has´nt been started for over 13 years or so.Any advice would be great,thanks dave,(and Marcus in Österreich).

[MG]

There is an easy test, but the dynamo has to be taken out of the bike, or at least the chain has to be taken off.

Connect the F and D terminal together and hook them up on the negative pole of a 6V battery. Then connect the positive pole to the dynamo body. The dynamo should now motor.

[MG]

Sorry, you asked for a test procedure for the regulator, not the dynamo, I misread that. But I will leave the post here, maybe it will be of use to you or someone else nevertheless.

I'd better go to bed now...  

[trevinoz]

Markus,
             Just a point re testing dynamo.
If this particular dynamo has had the connections changed for the regulator pictured and if, as I suspect, the field is then earthed through the regulator case, this test will have to be done differently.
Also note that a dynamo that motors will not necessarily generate.
Trev.

[MG]

Trev,
Thanks for the hint. I was not aware of that mod as I always refurbish and re-use the mechanical regulators, for nostalgic reasons mainly.  
When restored and set up properly, they work so well that I never felt the need to convert to 12V or buy some fancy part with semi-conductors in it.

Cheers, MG

[groily]

It's definitely a JG 12v box, and it almost certainly required the mods on the internal wiring unless they did 2 versions back then. I'm quoting word for word and/or paraphrasing here from the original (photo-copied type-written!) instructions that came with one I bought in the 1980s and which still works (although I've replaced it with a DVR2 as I think they're better).
 
"For positive earth only. The green wire is to Dynamo F; the blue to dynamo D; the black goes to ammeter or switch etc and the box has to be well earthed by its studs. Have to scrape paint for that.

The dynamo's wiring has to be configured to generate -ve voltage. Wire the field and brushes as follows:
* the nearer brush AND one field coil lead attach to the D terminal;
* the other field coil winding goes to the F terminal;
* the second brush simply goes to earth at the little screw on the dynamo."

(The difference between this and the original wiring is that the second field coil lead goes to the D terminal rather than to earth - ie the field is connected F to D, not F to earth.)

"To test the earth (polarity), first connect a wire from F to earth, then connect (they say a 6v) battery live (negative) to D and battery positive to earth. It should motor. If it motors the wrong way disconnect battery and swap field coil leads over."
(This by contrast with the usual 'Bridge F and D, run them to batt live and the dynamo body to batt +'.)
As Trev said, motoring isn't a perfect test - but it's a good start.

"There should be up to 14v at the blue lead as the revs rise" according to the data sheet in front of me.

Interestingly, the JG paperwork also blandly states 'it will boost the output power to twice the original specification'. Well, it won't, but you do get some increase . . . I happily ran a 60/55W halogen round central London for years with mine, and it just about managed it.

The box itself is an OK gizmo. Sometimes it needed a handful of rpm to get the thing to kick in from cold, it allowed a discharge into the field at tickover (same as most mechanical boxes do) but it generally maintained batteries well for those years. However, it's not as good as a DVR2, which kicks in better at 12v, allows no discharge into the field at tickover, and is smaller and easier to conceal for those who prefer to do that. Maybe the modern JG boxes are smaller, I don't know.

You should find the dynamo wiring change has been made already, and all the kit should be 12v. Unless someone's really made a dog's dinner of everything!

[G/F DAVE]

Hi. Stephen this is a jg instruction sheet I have yours is a 12 volt as the 6  volt ones have a brown wire instead of green. same as Groily has said dont give alot of trouble unless it has been wired incorrectly.Dave..

[G/F DAVE]

Stephen please note this was  12 volt instructions that had been changed to 6 volt then back to 12 volt. only the wire colour(brown/green and battery voltage. Dave..

[Stephen Arsenal]

Thanks everyone,not quite sure I understood everything,but know a man who would.Thanks again,really appreciated.-steve

[trevinoz]

MG,
           I agree with you about the mechanical regulators, they are excellent when set correctly and LEFT ALONE.
I have overhauled countless numbers of them for myself and others.
Spares are no problem as I must have 50 kg of regulators that have been stripped from their bases for electronic replacement as well as similar regs from cars.
 Trev.

[Stephen Arsenal]

OK so far so good,the next question is how do I turn the engine off,Have been told there must be a cable which earths the dynamo ? , where does it attacht itself ?

[trevinoz]

Steve,
               You do not earth the dynamo, you earth the magneto.
Depending on which end your magy has, the wire connects to a stud on the screw on type or it has a contact point under a bakelite nut on the side of the bakelite type.
Trev.