Hey Guys!
This is my first post.

I know this circuit is fairly simple, but I need some help. I need a circuit to put in line with my test leads so that I can filter out the DC signal from a car alternator. I can look at the waveform on my Snap-On scope.

Can anyone help?
Thanks!
Brit

 

All you really need is a small capacitor, perhaps 1uF. If you use an electrolytic, have the + side towards the alternator wiring. A poly cap would be much better. If your scope has extremely high input impedance, you may need a resistor to ground (say, 47k) on the output of the cap.

Capacitors block DC, but allow the effects of AC to pass right through.

See the attached for a simulation of a portion of an alternator, the bridge rectifier, outputs along the way, and the C1/R1 combination I've mentioned. Notice that the simulated O-scope trace from point (E), the green trace is virtually the same as the original output (D), the yellow trace, but is settling down to become centered around 0v; which you need to help diagnose problems with the rectifier bridge or the diode trio/exciter diode.

 

If your o'scope has an AC setting for the vertical input, it is capacitor coupled and will block the DC level.

 

If your o'scope has an AC setting for the vertical input, it is capacitor coupled and will block the DC level.

Unfortunately, this scope does not have that option

 

All you really need is a small capacitor, perhaps 1uF. If you use an electrolytic, have the + side towards the alternator wiring. A poly cap would be much better. If your scope has extremely high input impedance, you may need a resistor to ground (say, 47k) on the output of the cap.

Capacitors block DC, but allow the effects of AC to pass right through.

See the attached for a simulation of a portion of an alternator, the bridge rectifier, outputs along the way, and the C1/R1 combination I've mentioned. Notice that the simulated O-scope trace from point (E), the green trace is virtually the same as the original output (D), the yellow trace, but is settling down to become centered around 0v; which you need to help diagnose problems with the rectifier bridge or the diode trio/exciter diode.

Great info. Thanks!