1up3down wrote:My two alternator wires exit back of primary and I have them going to aftermarket regulator, from there there are two wires, one to positive ground and one to negative battery terminal for DC charging.
The other day I noticed the battery had stopped charging and that the 15 amp fuse had blown.
Everything had been working just fine for the past two years since I installed the Alton.
So to my questions, why did the fuse blow, was it because it was a 15 and not 20 amp
As it has taken two years for it to blow then probably not. I would say it's more likely to have been caused by a short, or vibration.
1up3down wrote:was it because it was a 15 and not 20 amp as my 45 year old workshop manual specifies? duh, yes that could be.....
Which particular "45-year-old workshop manual" specifies a 20A fuse?
Do you mean 15/20A continuous or 15/20A blow?
The standard fuse for all Commandos as stated in the usual factory manuals is 35A blow, 17.5A continuous and unless you buy the original Lucas type glass fuses the nearest modern equivalents are normally 15A or 20A. http://www.classicbike.biz/Norton/Repai ... mmando.pdf
1up3down wrote:the fuse is directly between the regulator and the negative battery terminal, am I correct that it blew because
too much DC from the regulator blew it?
Unlikely, but you said previously that the regulator negative wire was connected "to the negative battery terminal"?
1up3down wrote:and going to a 20 amp good chance that will not blow..?
No, as we don't as yet know the reason why the fuse blew.
1up3down wrote:would say turning my head light on when I ride "dump" or relieve some of that charging current or lessen the strain on that new 20 amp fuse or accomplish nothing in this regard? Maybe doing so actually increases charging?
or is my speculating about this a waste of time because I just had too weak of a fuse in the first place?
As the 15A (I'm assuming 15A continuous) fuse didn't blow for two years (and presumably you have done some mileage in that time?) I doubt the fuse rating is problem.
Did you try another (15A?) fuse?