On 11/26/2015 9:18 AM, Tony Hwang wrote:
Ralph Mowery wrote:
wrote in message
...
I put a 75w equivalent CFL on a scope with a current probe, looking at
the wave form.
This is what it looks like

http://gfretwell.com/electrical/CFL%...0a%20scope.jpg

Those spikes are almost 2 amps so this might average 33w but it is not
that simple. I assume this is also a very reactive load so if you
opened a relay at or near peak, it could get pretty ugly

What is the time division on the display?

Should be pretty obvious -- current repeats with a periodicity that
tracks (rectified) line frequency. So, 8.3ms between repetitions...

relay reaction time is in the msecs.

You're not concerned with the actuation/release time (except if you
try to synchronize it with a certain point on the waveform (e.g., to
deliberately avoid these spikes which are roughly coincident with voltage
peak). You're more concerned with how long the contacts bounce
as they make/break -- especially when opening the connection
(cuz current is flowing and will want to maintain an arc across the
widening gap -- contacts melt)

It is safe to say that loads have inductive reactance value causing the spike
like that.

I have the B version of that scope. What are you using for the current
probe ? I may want to look into getting one.