Newbie question about testing voltage with a DVA!

[Grumpy Bear]

Below is what the CDI troubleshooting manual says I need to do to test ignition voltage on my 1974 Mercury 500 50hp. I made my own DVA to connect to my multimeter. However, as any good noob, I have questions!

(1) What setting should I put my multimeter on? DC 200? More? Less?
(2) So I have 2 leads, obviously, a black (-) and a red (+). When is says in the picture, for example, "WIRE: RED, READ TO: WHITE" What lead am I touching where? Are the wires all still connected to the switchbox or not?
(3) Finally, should the motor be started or should this be done while cranking only?

Thank you!

 

[gm280]

Grumpy Bear, when you are reading AC voltage it doesn't matter which test lead goes where. And that is because it is Alternating Current (AC) . In other words the current flows both ways very fast, so there is no polarity for AC. What your DVA adapter is doing is allowing the capacitor to hold the voltage there for enough time for the meter to actually read it. Otherwise the readings would be totally different. So it doesn't matter if you use the red lead or black lead on either wire when reading. Now the doesn't hold true for some resistances or DC voltage readings...

 

[Grumpy Bear]

Grumpy Bear, when you are reading AC voltage it doesn't matter which test lead goes where. And that is because it is Alternating Current (AC) . In other words the current flows both ways very fast, so there is no polarity for AC. What your DVA adapter is doing is allowing the capacitor to hold the voltage there for enough time for the meter to actually read it. Otherwise the readings would be totally different. So it doesn't matter if you use the red lead or black lead on either wire when reading. Now the doesn't hold true for some resistances or DC voltage readings...

Thank you for your response! I did notice when I hooked it up to both wires, the readings were fluctuating all over the place and faster than I could tell. Oddly enough, the capacitor works fine when I connect to the wall outlet. I'm not seeing it hold the charges from the wires/switchbox but maybe I'm not keeping it on there long enough...??

 

[Grumpy Bear]

bump

 

[enginepower]

What size capacitor and resistor did you use to make your DVA? Either your capacitor is too small or your resistor is too low of a value. Also, is your capacitor rated for at least 400V? Too early to think right now but I think if you put the diode in backwards, it wouldn't read at all. Average reading for a stator output is probably 200-250 volts.