The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: snowbeard on 03.09. 2007 04:52

Title: should both wires of my dynamo be grounded?
Post by: snowbeard on 03.09. 2007 04:52

I tried to test my wiring to see if the carb fire shorted any of it out, and I found that both the yellow and green wires are "connected", i.e when I test the yellow at the regulator for continuity it's good, but so it is also good at the green on the regulator when testing it to the yellow at the generator.

in addition, they both ground to the frame as continuous from the generator.

is this normal? or has my generator shorted out...

thanks!

Title: Re: should both wires of my dynamo be grounded?
Post by: fido on 03.09. 2007 07:27

The resistance figures for the armature and field windings are very low so they could well appear as short circuits, depending on what equipment you are using to test them. The dynamo is wired with one field coil and one brush wire connected to its casing inside, the other 2 connections being the F (field) and D (dynamo i.e. brush) which go to the regulator via green and yellow wires respectively. I suggest you rig up a 12 volt bulb eg a car turn indicator bulb to test the dynamo. To do this you take off the wires to the dynamo, join it's F and D terminals together with a short wire link and connect this to one bulb contact. Connect the other bulb wire to the bike ground and start the engine but don't rev too high or the bulb will blow.

Title: Re: should both wires of my dynamo be grounded?
Post by: LJ. on 03.09. 2007 08:22

Here is a handy little tool most of us could make for testing dynamos at some time or other...
As already been said... plug the two plugs into the F & D (doesn't matter which way round) and crocodile clip to earth somewhere and then start motor. A good dynamo should output around 17 volts so don't rev too hard or the 12volt bulb will blow. This then determines that your dynamo is working.

Title: Re: should both wires of my dynamo be grounded?
Post by: snowbeard on 03.09. 2007 16:56

I was just using a decent multimeter on buzz for connection, at the lowest setting. I'm glad to hear it doesn't mean certain death for my dyna, Thanks again!!

is there a problem with running the bike without a battery tho?  Does it require a battery to properly dissapate the generated energy?  will something overheat?

thanks again

Title: Re: should both wires of my dynamo be grounded?
Post by: fido on 03.09. 2007 19:18

If you were going to do much riding without a battery it would be a good idea to remove the dynamo chain. It might not cause any damage to the dynamo but it is better to be safe than sorry.

Title: Re: should both wires of my dynamo be grounded?
Post by: snowbeard on 03.09. 2007 22:15

so would that include removing the cover on the right side of the cranks?  just trying to gauge the options, just buy a battery now or disconnect...

thanks a ton!!

Title: Re: should both wires of my dynamo be grounded?
Post by: dpaddock on 07.09. 2007 17:01

You may safely ride without a battery as long as your lights are always ON. Take away the battery and insulate the hot lead to prevent it from grounding.

Title: Re: should both wires of my dynamo be grounded?
Post by: snowbeard on 07.09. 2007 17:10

thanks again!  ;) 

So I disconnected the leads from the generator,  and separated the fused wires above the carbs (this bike has experienced a carb fire)  so if my light works (!) with it all connected and the hot battery lead insulated, it should be alright?

would running it with the leads simply disconnected from the gen hurt it? (I only got about 200 ft  *whistle* )  I'm still only testing it gingerly to see if it likes to move anymore.

Title: Re: should both wires of my dynamo be grounded?
Post by: dpaddock on 07.09. 2007 17:55

You may safely ride with the generator leads disconnected.

Title: Re: should both wires of my dynamo be grounded?
Post by: snowbeard on 09.09. 2007 19:10

great!  that's the plan for now, while I get the rest of finding a battery, etc, sorted out.  thanks again!