Measuring AC Voltage

I've got a 1965 Gilera with a 6V AC system, no regulator, no battery. When I try to measure voltage at a light, or anywhere, the reading are too erratic to see. They jump around like a crazy man.

And yes, the multimeter is set to AC voltage.

Is this usual?

Re: Measuring AC Voltage

Digital or analog? You have a spare condenser , put it in parallel with probes. Start with stator light coil unhooked for a bench mark . You may have a bad connection from coil or ground.

Re: Measuring AC Voltage

Is the bike running or are you just kicking it? Voltage is based on rpm. If you have a constant rpm you should have a sorta steady voltage, enough to get a close range.

Re: Measuring AC Voltage

This is with the bike idling, and I'm measuring with a digital multimeter.

Bike runs fine, but I'm doing some electrical work so I want a baseline reading.

Re: Measuring AC Voltage

Crappy connection? You should be able to get a good reading if everything is working properly. How many coils in the magneto? Can you check another one? I have checked my peds even when pedaling an got a good reading. Try revving it a little also when checking and see if that makes a difference in stability of meter readings.

Re: Measuring AC Voltage

There are two coils, a lighting coil and an ignition+tail light coil. I tried the taillight and had problems. I'll try the headlight too. Also see if reving it changes things.

It was strange. I also got readings, jumping around, just with one contact on the frame, and the other contact hanging mid-air.

Re: Measuring AC Voltage

I recall hearing that on systems with a lot of "noise" like my unregulated AC bike, the spurious signals can prevent good voltage readings.

But that adding a capacitor to the line dampens erratic noise and allows the meter to work. Anyone know what size or type of capacitor?

Re: Measuring AC Voltage

the quality of your meter affects the quality of your results, what meter are you using?

the ignition has a condensor built into it, i don't think that is the answer.

my best advice is the min / max feature, if yours lacks that, you may not get reliable results.

i have a few threads on multimeter testing.

Re: Measuring AC Voltage

Kiel the Canuck /

You'd probably get a more reliable reading on an analog meter, or a digital meter with a low impedance mode.

Most digital meters have an input impedance of 10+ Million ohms, so tiny low-current spikes of higher voltage will throw the measurements off.

Most analog Volt-ohm-meters come with anything from 20 thousand ohms per volt down to 1000ohms. The latter would certainly stamp down on very low current pulses... (edited)

Re: Measuring AC Voltage

A condenser is a capacitor. Got a spare, you should get one, any cheap one with a wire.

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