Voltage Step up question.

[keithturtle]

Thanks, POPEYE!

Now to get a 100X probe fer the scope to see those kV spikes!

BTW, can y'all cipher out what resistor to use with regular scope leads?

I don't know much about scopes, but am trying to learn.

Turtle

[kentoot]

Hi Turtle,

Yes, you can use resistors to step down the voltage. Actually the resistor value will pretty much depends on your oscilloscope input impedance, but if you want to try things first, you could try with very high ohmic value first (like 1M to 10M ohm). Probe a known voltage source (say, a 12v dc power source) and try to measure with and without the resistor, you will know the effect of the resistor. You can use higher resistance for more step down measurement.

But i'd like to point out another important matter, that's the oscilloscope isolation.
In many Stan's replication cases, I saw people measuring floating (not grounded) high voltage points with a grounded probe, this a big no-no.
If your oscilloscope is not isolated, I think you will need to isolate the probe first with a differential high voltage probe, like these :

http://www.tek.com/site/ps/0,,51-11195-INTRO_EN,00.html
http://www.powertekuk.com/dp9030.htm

Isolation is even more important if you're probing, at the same time, the primary and the secondary side of a transformer. You will also need channel to channel isolation, not just an isolated oscilloscope. That means each channel is totally isolated from each other, the probe ground leads are not connected together to a common ground.
If your oscilloscope don't have channel to channel isolation, you will need to isolate each channel with some sort of an isolated differential voltage probe (see above link).

So personally I would suggest to buy an oscilloscope with channel to channel isolation :

http://www.tiepie.com/uk/products/External_Instruments/USB_Oscilloscope/Handyscope_HS4-DIFF.html
http://www.tek.com/site/ps/0,,3M-10566-INTRO_EN,00.html

and personally I can't afford any of them .

[keithturtle]

Thanks, Kentoot;

Both scopes are older tektronix solid state, one is 2 and the other 4 channel- rather elaborate, but I ain't sure about isolation.  Two of four channels have ground switches.

I'm about as ignorant as a turtle's carapace when it comes to scopes, and I don't wanna trash either one.   I really gotta spend the time to learn their proper use.  I downloaded a training pdf from tek that is geared more to the newer stuff, but can glean some basic operating understanding from it.

My head hurts.  Back to the basking lamp.

Turtle