18 S Electrickery

Steve Martin · Post by **Steve Martin** » Tue Mar 21, 2006 8:53 am

Don't worry Lawrence, it's 'Tin Chaincase Syndrome' again!
Cheers, Steve.

itma · Post by **itma** » Tue Mar 21, 2006 8:59 am

IS your avc Properly earthed? nor mounted on rubber? have you polarised the dynamo?

rob the rebuild · Post by **rob the rebuild** » Tue Mar 21, 2006 12:51 pm

Now we are really speaking electrickery jargon. Me poor mechanical engineer so what do you mean by avc? do you mean the voltage reg? The current Lucas RB108 does have rubber grommets. It has also been tampered with before but I am going to investigate further.
The dynamo is pumping out (note good mechanical speak) a good 6.5 to 7 volts at tick over so that should be ok? The only other thing I did notice last night was that when inserting my wire link between the terminals on the dynamo (engine not running) I did get a bit of a tingle (similar to that if you test a 9v square battery on your tongue to check the charge) so wonder if something is not quite right with the dynamo after all.
So how would polarising the dynamo help?

itma · Post by **itma** » Tue Mar 21, 2006 2:26 pm

AVC = voltage control box
FADE, the prince of darknesss mantra
F = field ie F on dyno
A=ampmeter
D= dynamo D on dyno
E=earth
you should make sure the earth wire runs to a good metal to metal fix on the frame; lost count of the number of times I`ve seen earth leads under the head of a rubber mounted bolt or one running through a grommet; while you are messing with wires it pays to run an earth wire the lenght of the machine from the head lamp, instaed of relying on the earth through the frame.

It always pays to polarise the dyno to make sure it agrees with how you have the battery earthed.
you certainly seem to have a short somewhere; another thought; have you had your bits finished in epoxy paint? this stuff I have decided is a curse, really hard to get an earth through it.

rob the rebuild · Post by **rob the rebuild** » Tue Mar 21, 2006 5:54 pm

Firstly my bits are not epoxied.
Will check the earth from the AVC to the frame.

As I am getting volts out from the Dynamo, definitely +ve earth as shown by my multimeter with negative probe on the link wire, is it worth polarising?
If so, which connection on the dynamo do you connect the wire from the negative terminal on the battery?
Will also take the cover off the AVC and clean the terminals.
Whats the best way to check the set-up?

Don Madden · Post by **Don Madden** » Tue Mar 21, 2006 8:11 pm

You are stumbling around in the dark with a Lucas lamp! Follow Biscuits good advice & search the Archives website. Once there go to Technical Bulletins\Electric\Technical Tips\Practical Dynamo Maintenance. All your questions are answered there.
Cheers, Don.

Biscuit · Post by **Biscuit** » Tue Mar 21, 2006 8:28 pm

Thank you Don. How many times does it have to be repeated?.

rob the rebuild · Post by **rob the rebuild** » Tue Mar 21, 2006 8:45 pm

Many thanks Don and Biscuit for the subtle hints and will investigate using the article.
I have nothing to loose and everything to gain even if it is just knowledge and experience.

But why the tingle like a 9V battery?

Also chain cases can be of cast ally!

itma · Post by **itma** » Tue Mar 21, 2006 9:41 pm

Are you using one of those Hawker batteries? they pack quite a punch.
To polarise your dynamo, disconnect avc box and flash the live terminal from the battery to the F terminal on the dyno, check and check again the earth, most troubles like this stem from bad earths.

rob the rebuild · Post by **rob the rebuild** » Fri Mar 24, 2006 6:59 pm

Well peeps the saga is over! Well hopefully.
Oh joy for not having to work on a Friday afternoon!.
Took the lid off the old Lucas RB108 and lordy lordy the fault stares you in the face.
I've posted a picture of the winding coil to the post where the solder joint has failed. Click on the link:
http://homepage.ntlworld.com/robinson44 ... CN0908.JPG
So now temporarily repaired by wire wrapping and soldering back to the terminal post. A new solid state is on the way so at least that should be reliable.
The contacts were also in a pretty bad state with pitting and carbon so have cleaned and reset them. So it will probably now cook the battery.
As to which size of battery to run with. Talking with some, size does matter! Small batteries cycle the regulator more and so increases the stresses on contacts and therefore increases heat within the assembly. So the moral is use a big battery with plenty of capacity.
Edited by - rob the rebuild on 24 Mar 2006 7:11:00 PM