On Sunday, August 28, 2016 at 9:26:38 PM UTC-4, Tony944 wrote:


Agree with your other points, but not this one. When you put a cap
in a DC circuit on the power input to an amplifier, it does act as
a reservoir. It's fully charged during light or normal loads, when
the amp has a sudden increase in power needed, that cap can supply
some of it and being close to the destination, it can do so without
the impedance effects of many feet of wire.

However, I don't think a hard start kit works that way. If it did,
it could only be effective for 1/120 of a second, because that's
all the initial charge that's there prior to starting will last.
After that the AC voltage has reversed, the cap is drained, there
is no reserervoir and it's being charged in the opposite direction.
Current is needed through the AC supply to go into the cap and to
supply the motor which is trying to start. So, unless the motor
gets over it's starting difficulty in 1/120 of a second, I don't
see how the cap can be helping by being a reservoir like it is in
a DC circuit. I think the hard start kit probably works by
creating more phase shift to the start winding, which will go on
as long as the cap is in the circuit.

*** I am sorry but you need little more knowledge about Capacitors
And how are used. In his application capacitor is always drained


It's true that it's mostly drained, which is exactly what I posted,
but like any capacitor, when voltage is applied to it,
it does start to charge for the first half of the first AC cycle it sees. That is what I described and stated that isn't how it works because the
small amount of energy stored at that point is obviously insignificant.




and it
is use for two reasons to limit current and keep compressor running in
"right direction" in AC systems.

Does it do that by poking the rotor with a stick? It does it by providing
a phase shift, which is what I stated.


In DC system are used as surge or spiking
Limiters and yes it could be use as instantaneous supply like in Cameras
are even car start up but they always must be connected to source
before it can be used that is why you need to wait to charge before your
flash on camera will work and if capacitor start to leak you lose both.
This Capacitors are call (ELECTROLYTIC) they are not consider Caps.



It's true that caps on DC circuit boards will help limit surges or spiking,
but that is not their main function. MOVs are used primarily for that
purpose an you will find them there together with a cap where power comes
on to a board. The main function of the cap is to provide a close by
current reservoir to accomodate the fast changing power requirements
of that circuit board. If you have a circuit that is switching on
and off, the current needed changes in nano seconds. IF that current
has to come through a length of wire that goes to the power supply,
that wire has impedance and it will limit how fast the current can
ramp up. The local cap doesn't have that limitation and can supply
the increased current immediately. Without the cap, the voltage
would spike downward and that spike would be seen not only by the
components on this board, but other nearby boards in the system.
So, in that sense it limits surges, but it does it by serving as
a near instantaneous supply of current.