Checking for a charge

[jOe]

I rewired and reinstalled the OEM voltage regulator on my '69 XLH. I wanted to see if the generator was charging and the regulator was functioning. So I fired it up,all normal, everything functioning as advertised.
I took the battery out of the system by removing the negative ground strap, kept running, all stayed normal. (I know this doesn't determine the output through the reg., but I just wanted to check the functionality).
Now long ago when I was a teenage gas station attendant in Reno I was told that to perform that test the positive lead should be detached to take the battery out of the system. Does it make a difference? I looked at the schematic and everything is grounded back to the frame/neg. ground strap....I figure that once the battery is disconnected on either side, it's out of the system. I'd like to avoid disconnecting the positive lead if possible.

[thefrenchowl]

It's like you asking us

""is it safe to check my home wiring by just disconnecting the return path (we call it "neutral" in GB...) or the earth...""

Good luck mate...

Patrick

[jOe]

I don't see it as a safety issue, all I wanted to do was see if the ignition was being supplied by the battery or the generator.....just a quick field expiedient.

[sportsterpaul]

Disconnection the battery from the ground side is fine to remove it from the system.

It is a not that great of a way to test regulator output, as it creates a "load dump". This is a big surge when the generator has been charging the battery and then poof-- the battery goes away. Also, a generator running without a battery can make a lot of voltage spikes, since the battery works to level out the generator output. Since you have no electronics on the bike and have a mechanical regulator, you can get away with yanking the battery off of a running bike. If you had electronic ignition added, or an electronic voltage regulator, this might cause them to fail.

It seems a simpler way to check output is to wait for dusk or night. When Sportsters idle, there is not enough output to keep the voltage up, and the headlight will dim as it it is running off 12 V battery voltage. When you rev the bike, you should see the headlight brighten noticeably, as the generator can now supply charging voltage-- 13.75 to 14.2 volts. If you have a voltmeter, you can just measure the output at 1500 RPM or so day or night. Its also nice to check with a voltmeter, to insure the regulator is not allowing too high a charging voltage, which will boil out your battery and shorten bulb life.

[jOe]

Thanks....I know. I just pulled the lead off for a few seconds for the quick check. I also looked at the lighting fluctuation---that seems pretty nominal 1500-2000 rpm +/-....I'll get around to putting a meter on it pretty soon and properly check it. It's a mechanical regulator.
I don't know why that positive battery lead idea persisted for all those years....I guess I was young and impressionable. Thinking about it now, it doesn't make any sense.

[EKHKHK56]

In the "old days" people used to say pull a lead off and if the vehicle still runs the generator is ok... a black/white diagnosis. some people actually thought you could do that with an alt also. Not good or effective for checking output. Any voltage spikes like that should be avoided, especially with an alt! Joe, on those plug wires I don`t have a source right now but I always use steel core wires for better performance. I have had high performance vehicles that the difference in running was very evident just changing from resistor to solid wire. Erik K