DC Voltage Drops While Running

[blaat!]

‘66 Mach 1 starts so easy and runs great. DC voltage (at the white wire on the coil) with brand new battery is 6.3V, but drops to 6.1V once stated. It stays at 6.3V with the key on but drops once running. If I shut it off and turn the key back on it goes right back to 6.3V

If the battery is to charge, seems like the DC voltage should increase while running… no?

I swapped the coil (both brand new) and regulator (both brand new) and no difference.

Stator tests 24V-42V on a multimeter and has 6A+ AC with an ammeter in line on one of the yellow wires.

Bike seems to be running off the battery and eventually sputters out on short rides. I’ve been messing with this for weeks and I’m stumped.

Your knowledge and expertise is always appreciated

[graeme]

Lights on or off ?
I have a scrambler that would only run for a short 1/2 hour trip before it would stop.
The headlight bulb was 55/60 watt which was too much draw for the alternator.
Add in the brake and tail light and Sachse ignition and the battery would drain.
Lights off there was no problem.
Change the headlight bulb to LED and all fixed.

Graeme

[blaat!]

Good thought, but lights off

[themoudie]

Good morning blaat,

What happens if you take the ignition switch out of the circuit?

I suspect that the insulation in the ignition switch may be a bit iffy.

Good health, Bill

[Jordan]

High AC voltage without corresponding DC voltage sounds like the result of an unrectified alternator.
It is correct that to charge a battery, the charging voltage needs to be in excess of the normal fully charged voltage of the battery.
A nominal 6V battery is fully charged around 6.3 - 6.5V.

[mrkprsn]

6.3v is the standing voltage of a 6v battery. At the battery you should get at or close to 7v when running. As mentioned above I believe you have a rectifier issue since the stator seems to be working correctly.

[blaat!]

Good idea Bill. I'll get into the headlight to disconnect the ignition switch and jump it to see what happens.

Jordan and mrkprsn: Rectifier was my first thought too when this all started with the original '66 regulator. Since then I bought a regulator/rectifier from Lacey (Electrex World), and another cheap reproduction 6V reg/rec for a Honda. I seem to get the same result with all three of them.

I did measure the Hz of the AC coming out of the stator using my (good quality, but very basic Fluke) multimeter and it was like 350-400. Could that be the problem? Is it somehow just really high/poor AC frequency that these regulators can't deal with?

Any other ideas or things to test would be appreciated!
Jim

[Jordan]

I would expect the frequency to go up and down with engine revs, unless the regulator is an inverter type.
I'd guess it would be engine rpm x number of alternator poles x 60 Hz.

[mrkprsn]

I was thinking about this last night. I assume the battery is good. I've had some that voltage test OK but don't pass a load test.

If you test the voltage at the coil it might drop there because the coil is essentially a ground. I assume you also tested the voltage at the battery. Which should be around 7 when running without any lights.

Are both AC wires outputting the same voltage and current? It should be the same. Is there continuity between the wires? Is there continuity between each yellow wire and ground?

With three different rectifiers you can rule that out. I'm sorry I don't have more knowledge to test your ac generator.

[Jordan]

I'm often confused when someone just mentions coil, not knowing if alternator charging coil, or spark plug coil is meant.