[Prev][Next][Index][Thread]
Re: cap firing voltage scope measurements question (tests)
In a message dated 99-06-16 20:53:01 EDT, you write:
<<
> Such a high voltage rise seems strange to me but I could belive it in an
> LTR setup with a sync gap. Of course, the scope or probe may have bad
> bandwidth characteristics or your getting noise which may be messing the
> readings up. However, I thought you were using pretty good HV probes and
> such but that would be the first place I would look for a problem... Do
> you have safety gaps? They should be firing like made at 30kV I would
think...
> Terry
>>
Terry, all,
I did some work with the safety gap, it turns out I had it set too wide
from previous work. I was able to reduce the safety gap to 1/4" which
caused it to fire at 21.4kVpeak according to the scope. The safety
gap fired at this voltage whether the TC was running or not. When
the TC was not running (I shut off the rotary and mis-aligned the
elecrodes so it couldn't fire), the variac had to be turned up to 60 to
show 21.4kVpeak on the scope and cause the gap to fire. When
the TC was operating normally, (rotary firing and giving spark output),
the variac only had to be turned up to 44 to cause the safety gap to
fire, the scope still showed 21.4kVpeak. So if the safety gap can be
trusted to fire at the same voltage whether or not the TC is operating,
this then suggests that the scope readings are correct, and that the
cap voltage is actually higher when the TC is operating. This is
perhaps not a definitive test, but it a clue nevertheless. I am not
aware of any cap charging theory that explains this extra voltage
rise I'm seeing when the coil is operating.
I still didn't find my gap spacing vs. voltage chart to see if 1/4" is
reasonable for a 21.4kV safety gap firing voltage. I realize that
the gap firing voltage is dependent on many variables. The two acorn
nuts I'm using as safety gaps are a little different in size; one is
1/4" radius, the other is 9/32" radius.
Cheers,
John Freau