Voltage drop on white blue wire

EagleLakeWoodworking

EagleLakeWoodworking

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Oct 14, 2020
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I'm starting my venture to bring a 74 Commando 850 back to life. Very early on in the process and I'm fitting a solid state regulator / rectifier and a Pazon e-ignition.

Removed:
Selenium rectifier, zener diode, 2mc capacitor, ballast resistor, condenser. There's also no headlight right now.

My concern:
I've located the ignition-switched white/blue wire and measured voltage there at 12.15V

Temporary battery is 12.45V

What could be causing the voltage drop and is it anything to worry about?
 
Resistance.
Wire.
Connections.
Everything has resistance.
Do some basic electrical reading.
Inspect.
Perform individual component resistance tests.


Define "worry"
 
concours said:
Resistance.
Wire.
Connections.
Everything has resistance.
Do some basic electrical reading.
Inspect.
Perform individual component resistance tests.


Define "worry"
Click to expand...
Just wondering if this type of drop is normal and expected and it won't be a problem.

Should I expect that my voltage at each consumer read closer to the voltage reading at the battery than what I have measured?

I measured some more -
I have an inline fuse at the battery on the negative side. This is where the voltage appears to drop
 
L.A.B. said:
The original plate rectifier is silicon.

White/blue connects to the white/yellow from the kill button (fed by white from the ignition switch terminal 2) so the kill button switch would be one place to check.
Click to expand...
Thank you, that's helpful. The readings at my ignition switch vary quite a bit, so I'll be looking at that.

It appears the main voltage drop I'm experiencing is right after the inline fuse I have on the negative line coming from the battery. I should have checked there first 🤦‍♂️
 
My ignition switch and kill switch were both very corroded. Kill switch was worse. Check and clean it good.
All connections are sources of resistance so be aware.
Jaydee
 
A fuse have some resistance, needed to melt and break the wire in the fuse when current is too high. So some voltage drop over the fuse is normal.
As you did not say how much load when measuring, impossible to say if normal. Assuming ignition was on and drawing 2A, the voltage drop .3V gives resistance causing the drop is 0.15 Ohm. Nothing to write home about.
All car and motorcycle makers I know of, use as thin wires as possible. To use a minimum amount of copper, saving money. So small voltage drops are normal.
 
EagleLakeWoodworking said:
Just wondering if this type of drop is normal and expected and it won't be a problem.

Should I expect that my voltage at each consumer read closer to the voltage reading at the battery than what I have measured?

I measured some more -
I have an inline fuse at the battery on the negative side. This is where the voltage appears to drop
Click to expand...
💡🏁
 
Just for reference, a while ago I made these measurements on a 1972 750:
Voltage drop from -V battery terminal to
Master Switch terminal 1 = .182V (includes fuse and wire)
Master switch terminal 2 = .188V
Kill Switch white wire = .281V
Kill Switch white/yellow = .284V
White/blue wire at EI input = .350V

Current was measured as 2.34 amps

This was running a RITA EI.
 
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