Well, I'll be darned. PMA stuff.

[weaselbeak]

My son got the pma and regulator from Hugh. We wired it up (correctly). I pretty much solder, crimp, and shrink wrap everything. We put on 2 tiny batteries the size of a cigarette pack. They are 0.8 amps each, for a total of 1.6 amps. The bike would start, but run like absolute crap, even at higher rpms. We couldn't get decent voltage readings across the batteries either. While messing with it we ran little jumpers to a small battery off to the side and it all straightened out. He ditched the batteries and we went with a small battery of 8.0 amps. Everything is peachy now. 14.59 across the battery, runs great, battery came back from our run fully charged. I've noticed a lot of guys having problems trying to use capacitors & such. Our little batteries, of which one should have been enough, were not up to it. They test out OK. I find it odd that the pma was worthless even at speed until we went to more battery. There are certainly no substandard or inadequate connections. With just a bit more battery....golden.

 

[chizler62]

Its really dependant of what ignition system you're using.

On my XS650 (CDI) I don't need any amps (battery) to drive the ignition. On stock or many cam driven battery powered ignitions you do.

Did your PMA suggest the use of low amp batteries?

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[weaselbeak]

We are running a single coil, dual output wasted spark system. Points, as I prefer stuff I can deal with in the middle of nowhere.

 

[Brian902]

Your coil is probably drawing 3 amps and the small batteries just can't supply the constant voltage required. And couldn't hold any amount of amperage to maintain the current the coils were looking for even at higher rpm. That would be my best guess.

Saw an 8amp battery setup, must have been an AGM type, laying on it side under the seat. Really compact and light, pictures somewhere on this site.

Check this sweet setup for a small battery and kick start; http://www.xs650.com/forum/showpost.php?p=410720&postcount=131

 

[weaselbeak]

Yes, we used an AGM battery, in a traditional setup. It's physically small. Regardless of the current needed by the coil I would have thought that the pma would have supplied it while running.

 

[Brian902]

The PMA had no where to store the current the coils are calling for.

Even the no-battery setups use a 25v capacitor.

You just proved 2 x 0.8 amp batteries can't.

 

[weaselbeak]

I suppose that is correct. But I had a battery so dead on my GS last year that it wouldn't light up an indicator on the dash, and we push started and rode it home from Dayton, Ohio, over 400 miles. The battery was a total dud, but it push started easy and ran like a top all the way. Must be a much different or better pma.

 

[pamcopete]

I suppose that is correct. But I had a battery so dead on my GS last year that it wouldn't light up an indicator on the dash, and we push started and rode it home from Dayton, Ohio, over 400 miles. The battery was a total dud, but it push started easy and ran like a top all the way. Must be a much different or better pma.

Even a dead battery has some effective "capacitance" to smooth the output from the PMA. Either a battery or a capacitor is needed to fill in the lows in the cyclical output of the alternator. A standard field excited alternator is the same except it needs the battery to provide the current in the rotor to start the process as well as smooth out the cyclical output.