Circuit Resistance

[pdqford]

Looking for some guidence - a little background first.

1980 GS750ET (only 23k miles and I'm the second owner for the last 26 years).

Because the idle was getting unstable I decided to do the carb dip (all done and the carbs are ready to reinstall). Then I decided I 'miteswell' adjust the valves as the tank was already off (all done and valve cover installed. And my son loaned me his Motion Pro to sync the carbs (but I have to yet make some drain plugs to measure the wet fuel level in the carbs.)

Then I figured I 'miteswell' go over the wiring harness (while everything is accessable) as the voltage to the coils was only around 10.5 volts and the horn was kinda weak and the charge rate was about 13 volts, etc.

Okay. Measuring the resistance from the battery + cable to the hot wire of the horn circuit was 11 ohms. Cleaning connectors and switches I got that down to 2.2 ohms. Is that a decent reading?

Also measured the resistance from the battery + cable to the connectors for the coils. IIRC, that was about 9 ohms, but cleaning the kill switch and the connectors in the headlight bucket ( I couldn't figure out how to get the ignition switch out to clean it, but it only showed .1 ohm resistance accross the switch) the resistance through the coil feed circuit now shows 1.0 ohms. Is that a reasonable reading?

If these are reasonable readings I will progress to measuring the resistance in the ground circuits . . . .

Just a thought,but has anyone thought about building a spread sheet of actual resistance readings for various circuits of the various GS years/models?

[Steve]

Good work on getting your resistance values lower, so far.

Are they now good values? I don't know, I have never gone through and measured a good circuit for comparison.

I do have a question, though. When you measured your 10.5 volts at the coils, was that with the engine running or not?

.

[pdqford]

I do have a question, though. When you measured your 10.5 volts at the coils, was that with the engine running or not? .

The engine was not running as I had the fuel tank off. I opened the connector at the coils and probed the connector with the key on.

I'm not sure how to check the voltage with the engine running as I would suspect that the voltage would be jumping up and down as the ignitor would be pulling the coils to ground and realeasing them quite rapidly. Probalby would need a scope to track the coil voltage while running???

[posplayr]

Looking for some guidence - a little background first.

1980 GS750ET (only 23k miles and I'm the second owner for the last 26 years).

Because the idle was getting unstable I decided to do the carb dip (all done and the carbs are ready to reinstall). Then I decided I 'miteswell' adjust the valves as the tank was already off (all done and valve cover installed. And my son loaned me his Motion Pro to sync the carbs (but I have to yet make some drain plugs to measure the wet fuel level in the carbs.)

Then I figured I 'miteswell' go over the wiring harness (while everything is accessable) as the voltage to the coils was only around 10.5 volts and the horn was kinda weak and the charge rate was about 13 volts, etc.

Okay. Measuring the resistance from the battery + cable to the hot wire of the horn circuit was 11 ohms. Cleaning connectors and switches I got that down to 2.2 ohms. Is that a decent reading?

Also measured the resistance from the battery + cable to the connectors for the coils. IIRC, that was about 9 ohms, but cleaning the kill switch and the connectors in the headlight bucket ( I couldn't figure out how to get the ignition switch out to clean it, but it only showed .1 ohm resistance accross the switch) the resistance through the coil feed circuit now shows 1.0 ohms. Is that a reasonable reading?

If these are reasonable readings I will progress to measuring the resistance in the ground circuits . . . .

Just a thought,but has anyone thought about building a spread sheet of actual resistance readings for various circuits of the various GS years/models?

Here is a little hint. The value of an acceptable resistance is mainly a function of how much current you are pushing. In that light it is more important to measure voltage drops which take resistance and current into account. The primary consideration of acceptable voltage drop is then related to providing acceptable terminal voltages to the device in question.

[SqDancerLynn1]

You made no mention but the fuse block connections should be cleaned too!!!

[pdqford]

You made no mention but the fuse block connections should be cleaned too!!!

The fuse block connections looked nice and clean after all those years. My DMM read <0.1 ohm accross the fuse clips.

[pdqford]

The primary consideration of acceptable voltage drop is then related to providing acceptable terminal voltages to the device in question.

So with a given battery voltage of 12.6 volts with "Key on/engine off", what is an acceptable voltage drop or acceptable 'terminal voltage' for the horn and for the coils?

[posplayr]

So with a given battery voltage of 12.6 volts with "Key on/engine off", what is an acceptable voltage drop or acceptable 'terminal voltage' for the horn and for the coils?

Can't say about what is acceptable for a 12V horn, loudness is subjective unless you have a way to measure it. If you have a lab supply, you could connect the horn and measure what is loud enough as you vary and find a minimum voltage.

However I do have expereince with the coils; at 10V the coils can cause a hard start. Keep the coils closer to no more than 1V drop (e.g. 11.6v). With a coil relay mod you are probably about 0.5V drop.