To Fastback - Boyer Powerbox - battery setup

Jerry Doe

May 21, 2003
Country flag
Hi Phil and anyone else,

I am just about to wire in a boyer power box along with my boyer ignition. I was reveiwing the swingarm spindle post and noticed you have a powerbox and small battery.

For me this is a first and I am not sure if I should use a small battery along with the powerbox or go without a battery. I only plan on riding the Commando every few weeks or once a month so would prefer without battery.

I have been told ignition, low rev running and starting are fine without a battery, but find that hard to believe with boyer ignition. I dont use the lights much.

What size and type of battery are you using? Have you ever tried running without the battery?

Best Regards,

Jul 18, 2004
Hi Jerry,

I haven't tried running without the battery, I was wondering if I could skip the battery with the Sparks alt. when I did my setup. At the time the forum's collective wisdom, and especially Dyno Daves analysis on the Boyer needing a minimum voltage of 10.8vdc to operate reliably, convinced me to just shell out $14 for the sealed cell. 12volt 3amp

Dave's info is here

I have the first stop on my ignition switch set to just ignition for starting or serious idling. The 55/65 H4 Halogen will drain that little battery pretty quick without a charge on the other end.

Here's the battery:
I hope that helps.

Dec 15, 2006
Country flag
I have a '70 Fastback that I installed a Boyer onto back around 1997. All the rest of the electrics are original OEM, i.e., RM 21, Lucas rectifier, Lucas zener, and "blue can" cap. One day a few years ago I was driving down the inerstate & noticed that my ammeter (in headlight) was showing no charge; normally it will register above 0 when the engine is running. But the bike was running right & everything else seemed ok, so I kept on going. When I exited the highway all was fine - engine idled fine, but when I pulled on the front brake to hold the bike on the uphill exit ramp, the bike died. I was able to kick it back to life easily and made it home. Long story short I finally discovered that my fuse was blown due to the insulation on the front brake cable switch being worn through & it was shorting out on the lower triple clamp, blowing the fuse. It must have been the output side of the switch that was shorting because the bike would start & run fine unless I pulled the front brake, and only at idle.

The point is that my alternator put out enough current & voltage to operate my Boyer without a battery, even for start-up. I think if your blue can is ok, a couple kicks prior to turning on the switch is enough to charge up the cap & fire your Boyer.

I don't have any technical data to back this up, just my own experience. Might be interesting to see if your bike will start with the batterry disconnected.