Watt to use to measure peak voltage

 (sic)

testing ignition system on 2000 XR80R requires:

Peak Voltage Tester
or
Peak Voltage adapter for a suitable multimeter
or
an oscilloscope

I have always wanted to appear smart enough to need an oscilloscope,
so there's that.

however...

I found this for making the adapter, but seems underspec fo rmeasuring
100 Vpp  (whatever the F pp is). Maybe just up the capacitor specs?
from:
http://www.hondashadow.net/forum/72-technical-discussion/63106-peak-voltage-adaptor.html

Can't say that I've ever used one, but if you can't live without it,
It sure would be simple to make one.

What kinds of peak voltages are we talking about? 20V peaks, or
ignition output (thousands of volts) peaks? If it's under 20 volts,
this is easy.

Get a red alligator clip, and a black one, each with about 12" of wire
on them. Get a 1N4002 diode, and solder it to the red alligator clip
wire with the stripe facing away from the clip. Solder the stripe side
of the diode to the positive pin on a 220uF 50V capacitor, and solder
the other pin on the capacitor to the black clip wire.

Connect the two clips to what you want to measure, watching for
polarity. Connect your volt meter to the capacitor. The diode allows
the capacitor to charge, but doesn't let it discharge. This lets the
capacitor charge to the highest voltage that is input without draining
back down when there's less voltage. That capacitor's voltage will be
the highest voltage that is applied. Add 0.7 volts to whatever your
volt meter displays, since the diode will drop any voltage by that
amount. (Just the way they are.)

That capacitor will hold that voltage for a long time, so to make
another reading, touch the two pins of the capacitor together with e a
screwdriver.

If you want to make it elegant, connect the two pins of the capacitor
together through a momentary contact push-button switch and a 100 ohm
resistor. Press the button for 5 seconds to discharge the capacitor in
style.

--Justin
__________________
1986 Shadow 700
1986 Honda Trail 110 (Postie Bike)
***end quote***

TIA for any insight or advice.

-Dean
currently challenged by electronics.

 I do like your title, being a nerd and all...

I'm not exactly sure what parts of the post are yours, and which are
copies, but BTAIM:

100V p-p is 100 volts peak-to-peak, or a waveform that is +/-50V about
a reference (in your case probably chassis ground).  If you use a
diode/capacitor that is tied to ground (peak detector), you'll end up
with ~50V on the cap for a 100Vp-p signal.  If you use a full-wave
rectifier arrangement w/ peak detector (which adds both halves),
you'll end up with closer to 100V.

Oscilloscopes are graph-displaying devices - they draw a graph of an
electrical signal. In most applications, the graph shows how signals
change over time: the vertical (Y) axis represents voltage and the
horizontal (X) axis represents time.  Don't have to be smart to read
them, but setting them up can be frustrating, especially those new
digital ones with the nested menus and f'n Windows operating systems.
I'm a knob and clickie button guy...

http://www.play-hookey.com/ac_theory/ps_rectifiers.html

At any rate, the circuit described in the previous post isn't really
any good.  The cap is way too big, and I'd put some degree of current
limiting into it just in case the ignition could be damaged by an
overload.  Connect the ignition output to one terminal of a 1K
resistor - connect the other to the end of a D1N4148 diode without the
black stripe.  Connect the diode striped end to the positive terminal
of a 1uF 100V electrolytic cap, with the negative terminal connected
to chassis ground [negative terminal will be marked (-)].  You should
be able to purchase all of these components for about a quarter.
Measure the DC voltage across the capacitor (from the capacitor
positive terminal to chassis ground).  You should get ~50V if the
output is 100V p-p.

JFTR, I bought my analog sillyscope on ebay for <$50 delivered (100MHz
Tektronix 465 copy).

JayC

 
I couldn't resist.


Yeah, I think I want knobs and clicky buttons too.


That seems advanced enough that I'd be second guessing my results even
if I did it right. I'll slog through that link later. I really need to
up my game in the electronics arena.


Cool. Did you have to modify it in any way? LOL
I'm flashing back to the 6 ton press.
;-)


Thanks.   -Dean

 
Nope - just plug in and go.

Incidentally, I'm not sure if 1N4148 diodes can avalanche w/o damage,
and you're on the cusp of specified breakdown at 100V, so I decided
that you'd be better off with two in series.  So, resistor, diode,
diode, cap.

JayC

 
You are correct there. I love an excuse to buy a new tool.

And in most cases, one finds other uses for these special tools. There
is a special joy experienced when you face a funky problem and think
"hey, I have that widget reverser from the submersible diesel
trebuchet project over there..."

-Dean
I left my flux capacitor in a disco