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Jeff Wisnia Jeff Wisnia is offline
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Default Run versus Start Capacitors - How to tell


On Apr 19, 12:09 am, Richard J Kinch wrote:

Jeff Wisnia writes:

there really isn't any difference between a
"run" and a "start" capacitor, the term comes from the application, not
the design.

No, these are "different same" items.

Both are typically electrolytics which are compact but lossy. The start
type is rated for a low duty cycle so they can be made very compact and
very lossy (i.e., cheap). The run type must be physically bigger and more
expensive for the same capacitance to make it less lossy, so that it
doesn't overheat in a 100 percent duty cycle.

Weren't they past the phlogiston and ether theory when you studied EE?
Start vs run types vary in the real component of their impedance, which is
reflected in the resistive component of the lumped element model. This is
usually explained in dumbed-down terms of "ripple" for the non-engineer.

You sound like a hack. Lossy is an audio or compression term. Maybe
you are after...lousy?

No, I don't think Richard is a hack. He was right to pounce on me over
that mistake.

I stand corrected. I either never learned or never thought about the
operating requirement differences for "start" and "run" capacitors, but
it now seems obvious, especially since supply houses list them for one
or the other purpose.

Though, if push came to shove I'm sure one could use a run capacitor of
the correct capacitance rating to do a start capacitor's job, but not
the other way around, huh?

Jeff (Looking forward to attending his 50th MIT class reunion in less
than two weeks. G)

Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.