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Alternator / Stator Charge Voltage #791795 12/01/19 8:54 pm
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DarrenJ Offline OP
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Hi lads,

I have a Lucas Rectifier / Regulator fitted on my 1968 T100C.

I have a new battery, ignition switch and ammeter and Boyer ignition.

When I put a voltmeter across the battery with the engine running I see that the voltage fluctuates a few times a second from anything as low as .1v to 14.5v.

This couldn't be right?

Resistance between the wires from the alternator is 1 ohm. I believe around .5 ohm is normal, so 1 ohm should be fine.

I have checked all connections and replaced many connections and wires just to be sure.

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Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791796 12/01/19 9:03 pm
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kommando Online Content
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Digital voltmeter ?

Not many can cope, an old analogue meter works better.

Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791801 12/01/19 9:27 pm
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htown Offline
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Yep, these old bikes send a digital voltmeter into spasms sometimes. If you can find an old analogue meter they damp out the noise.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


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Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791802 12/01/19 9:35 pm
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DarrenJ Offline OP
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When I had the solid state rectifer and Zener fitted it read a steady voltage. But 5k resistor plug leads were fitted at that time.

By noise, do you mean the interference from the non-resistor plugs and caps etc?


I removed the earth wire from the Zener and attached it to the back of the bolt in the headlight. Maybe it would be better to send an earth directly from the battery to the new rec/reg rather than depend on the earth so far away in the headlight. I will run a jumper earth to the red wire on the rec/reg to troubleshoot this.



Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791833 12/02/19 5:42 am
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An earth connection in the headlight has to go the headstock race bearings plus whatever mounting the headlight has to the forks. Not a good connection. What are you grounding with that wire, the battery or just the lights?
I presume the Lucas unit is a self contained rectifier/regulator, not the old zener diode and rectifier stack? The red (presuming positive ground) wire should go to the frame or directly to battery positive.
You can put a 0.01uf ceramic and 10uf electrolytic capacitor across the leads of the meter to filter out noise from the ignition. Or use an analog meter that cannot follow the noise spikes.

Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791837 12/02/19 8:26 am
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Originally Posted by DarrenJ
When I had the solid state rectifer and Zener fitted it read a steady voltage. But 5k resistor plug leads were fitted at that time.
By noise, do you mean the interference from the non-resistor plugs and caps etc?

the noise in this case is produced by
the rapid and repeatable switching of the rec/regs power switching components .
Quote

I removed the earth wire from the Zener and attached it to the back of the bolt in the headlight. Maybe it would be better to send an earth directly from the battery to the new rec/reg rather than depend on the earth so far away in the headlight. I will run a jumper earth to the red wire on the rec/reg to troubleshoot this.

your current wiring may be causing a ground Loop signal error
a better ground at the battery
may allow your digital meter to read correctly .

Re: Alternator / Stator Charge Voltage [Re: DMadigan] #791845 12/02/19 12:02 pm
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I'm only using it as a ground for the lights. The Boyer, coils and engine are grounded with a wire going from the battery.

Yes, I have a Lucas rec/reg in the one unit.

What I'm wondering is, on the factory charging system, does the red wire that is attached to the old solid state rec only go to the Zener? If it does, I removed this wire from the earthing connection on the Zener and pulled it up into the headlight casing and connected it to the bolt going through the headlight casing and the headlight ear.

Would it be a better idea to attach the red wire from the new Lucas rec/reg straight to the battery?

The negative runs up to the ammeter through the brown/white wire and back through the blue/brown wire.

Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791852 12/02/19 2:10 pm
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Re: Alternator / Stator Charge Voltage [Re: kommando] #791858 12/02/19 4:10 pm
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DarrenJ Offline OP
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Yeah that answers my question clearly!

I will wire the postive back to the battery terminal!

Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791860 12/02/19 4:39 pm
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I expect that, even when everything is properly wired, you will still get erratic readings on your voltmeter with the engine running, unless you use an analog meter, or a digital meter that has what's called "True RMS". I don't know what "RMS" stands for, or how it works, but my good Fluke meter that has it gives me steady voltage readings, whereas my less expensive Radio Shack meter does not.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791868 12/02/19 6:44 pm
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RMS Root Mean Square. It's a kind of average of AC voltage. It's way over my head...
Cheers,
Bill


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Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791883 12/02/19 9:44 pm
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Originally Posted by DarrenJ
Yeah that answers my question clearly!

I will wire the postive back to the battery terminal!


is your bike fused on the positive side ? ( your years bike originally was )

if so , the new Regulators red wire goes to the fuse , just off the battery... and not the battery .

... for a positive ground/fused bike ...all ground wires new or original need to go through the fuse ... to be a fuse protected .
.

Re: Alternator / Stator Charge Voltage [Re: Mark Z] #791886 12/02/19 10:25 pm
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Originally Posted by Mark Z
I expect that, even when everything is properly wired, you will still get erratic readings on your voltmeter with the engine running, unless you use an analog meter, or a digital meter that has what's called "True RMS". I don't know what "RMS" stands for, or how it works, but my good Fluke meter that has it gives me steady voltage readings, whereas my less expensive Radio Shack meter does not.




A good explanation of RMS.
https://www.britannica.com/science/electricity/Alternating-current-circuits#ref307209

The reason small/inexpensive meters have a problem with noise is that they tend to have very high impedance inputs
and use very crude sample/hold front ends. Any radiated noise may be picked up by the leads and little or no input
suppression is incorporated.
Dave Madigan's suggestion of using a couple of caps (100uf + 0.1uf is a better choice) will help considerably with
conducted noise but may not help with radiated noise if the actual meter pcb is poorly screened..

Re: Alternator / Stator Charge Voltage [Re: DarrenJ] #791890 12/02/19 11:06 pm
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RMS defines the area under the curve of the AC wave, it's a calculus thing. Typically 1v peak equals 0.707v RMS. Meaningless when measuring DC.
BTW: The voltages given in your shop manual for alternator output assume the use of an analog meter, which typically reads "average", not peak, AC volts.


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