On Tuesday, August 30, 2016 at 6:03:52 PM UTC-4, Diesel wrote:
trader_4
Tue, 30
Aug 2016 15:08:14 GMT in alt.home.repair, wrote:

Neither am I. The above is specific to either a run cap or a
start cap. Neither has any charge on it prior to throwing the
switch to apply power to the motor. The point is there is no
energy there prior to that, no reservoir, to
aid in starting the motor. You compared it to a cap at an
amplifier in a car. That is very different, because there it's a
DC circuit and the cap is fully charged and available to supply
instantaneous current needs instead of it all having to come from
the battery which is located many feet away, through the impedance
of that wire.

I agree, bad comparison on my part. When using AC it's phase
shifting. When using DC, it's holding and dumping it's charge. For
simplicty sake, I just say it boosts them and don't go further into
the specific details. One (DC) actually does boost and the other
assists it with a phase shift (so not technically a boost, but, it
does cause less of a startup drain on the panel and the motor comes
up to speed quickly)

I also clearly messed up the explanation when I said the start cap
holds a charge (I was confusing it for the DC type which is what I
have more hands one experience with) and dumps it into the AC motor.
My apologies. That's what I get for playing on usenet on little
sleep. [g]

The AC compressor is an AC motor and it uses the phase shift
that a cap provides to help create the proper rotating magnetic
field. The two uses are very different. That is all that I'm
saying.

Understood.

You specifically compared it to a cap in a car amplifier, which is
a DC circuit. The function of the cap there is completely
different than how it works in an AC motor.

I agree. it was a **** poor comparison on my part. And I should have
been much more specific. I should also have started that when used in
the AC start method, it's phase shifting; so, you're right, not
technically a 'boost', but essentially in laymens terms, it is. The
motor comes up to speed quickly and doesn't draw down an excessive
amount of amps to do it, with the start caps help.

You might want to review what phase shift is. These videos are
targeted at someone who wants to buy a start cap and put it in.
They don't describe the physics involved, they just use vague
terms like the cap assists the motor in starting.

I know what phase shifting is, thanks. And, I was completely off base
with the comparison as I said, several times now. It wasn't the best
comparison I could have used for the purpose, but the idea behind the
selected comparison is this: Your mains (battery for car example) or
panel for your house isn't being taxed hard to supply the required
startup power when a start cap is put into play. That's really all I
intended to convey with the poorly chosen example.

It's actually giving it a phase shift to provide the correct
rotating field. It's not really what I'd call a "boost".

Fair enough. Is it easier to just say it gives it a boost, or try to
explain what it's actually doing to a lay person? By lay person, I
mean someone who can't even find the travelers on a 3way switch
without wiring it up several different ways, several times.



Excellent, glad to see we're all in agreement.