The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: tonyairconchap on 24.03. 2019 17:16

Title: another dynamo question...sorry
Post by: tonyairconchap on 24.03. 2019 17:16
Hi All, sorry its another question about dynamos which know doubt has been answered many times, i have read up on the forum and think i have followed everyone advise for checking.
Field coil to earth on terrminal f is aprox 3.4 ohm, d terminal to earth is about 0.8 ohm.  I have disconnected the f and d terminals connected them together and connected to meter lead and the other to earth,  no joy no output.
i have flashed the f terminal,still no joy.
anything else i can check?

Thanks for reading and thankyou in advance for any advice.

Tony
Title: Re: another dynamo question...sorry
Post by: tonyairconchap on 24.03. 2019 17:51
Forgot to say i am getting about 0.5 to 0.9 amp when checked
Title: Re: another dynamo question...sorry
Post by: lawnmowerman on 24.03. 2019 18:32
Forgot to say i am getting about 0.5 to 0.9 amp when checked
Hi Tony

Not sure what you mean by this - where was this reading taken?

I normally connect the F and D together and take it to one side of a 12v bulb (the unregulated output will blow a 6v bulb). The other side of the bulb will go to earth.
If the bulb does not light then check the brushes and give the commutator a clean.

Jim
Title: Re: another dynamo question...sorry
Post by: tonyairconchap on 24.03. 2019 19:27
Hi,  output test was done as you say but instead of a bulb i used the multi meter.  The resistance reading was taken with  the  f and d wires removed. Set meter to ohms and checked both to earth.
Tony
Title: Re: another dynamo question...sorry
Post by: trevinoz on 24.03. 2019 20:15
Did the generator ever work for you?
If it set up for the wrong rotation you won't get much out of it.
If rotation is correct, checked by motoring, have a good look at the armature, by that I mean get it tested.
Title: Re: another dynamo question...sorry
Post by: tonyairconchap on 24.03. 2019 20:25
Hi , yes  it worked , but bike was laid up for 8 years. Had to have the magneto rebuilt,  so assume the dynamo did not like sitting there all those years.
I have flashed the f terminal  as per lots of useful websites say. But i still only get a low output of  aprox 1 volt when tested.
Cleaned commutator and brushes, ohm readings on field coil and D circuit all seem to be ok.
The only thing i am doing different is flashing the F terminal with 12v as i have a 6 to 12v solid state regulator fitted with a 12v battery. Does it matter that i am flashing with 12V instead of 6V?
tony
Title: Re: another dynamo question...sorry
Post by: chaterlea25 on 24.03. 2019 20:43
Hi Tony,
Try this,
disconnect both loom wires from the dynamo
Provided the field connections have no been messed around
Connect a 12v 60w bulb between D and earth
Connect the battery live to the F terminal as the engine is running about 12/15 hundred rpm
The bulb should light brightly,
If it does not, try pushing the brushes harder against the  commutator
If this fails the armature winding is dead

John
Title: Re: another dynamo question...sorry
Post by: tonyairconchap on 24.03. 2019 20:54
Hi John , thanks for the advice, my bike is positive earth, so i assume i connect the battery negative wire to the F terminal,  is that right?
Title: Re: another dynamo question...sorry
Post by: trevinoz on 24.03. 2019 21:00
Adding to John's advice re the brushes, I have had the same problem after the generator had been standing unused for some time.
Try slipping a piece of fine abrasive paper between the brushes and the comm, rough side to the brush, and move the armature while holding the paper to it so that it abrades the brush face.
You are right, connect neg to F.
Title: Re: another dynamo question...sorry
Post by: RichardL on 24.03. 2019 21:02
Since you are going to be right there, a basic check I like to make for motors and such is to put my nose real close (not while its running) and have a whiff. While I haven't experienced this problem myself, if you smell something burnt, maybe it could be the field coil from too long a "flash" of 12V.

Richard L.
Title: Re: another dynamo question...sorry
Post by: mikeb on 24.03. 2019 21:37
if the coils measure ok, brushes intact and you've 'flashed' the field coil then...
... mine was dead after years laid up. after checking everything I just ran it (without charging) for a  couple of hundred miles while fetling other things. the dynamo came back to life by itself. i figured it had demagentized itself - and the running remagnetized it somehow. true or false?

so best kind of maintenance: do no work and ride your bike!