Re: Static phase converter


"Ignoramus3187" <ignoramus3187@xxxxxxxxxxxxxxxxxxx> wrote in message
news:ZpSdnSLa_JNulxbUnZ2dnUVZ_j6dnZ2d@xxxxxxxxxxxxxxx
Forget the question, I think that I understand now.

Well, mebbe *ahm* missing something.....

Most commercially sold rpcs are themselves static, in a way, in that the
start capacitors just sit there, and are not switched out, giving dreadful
voltage balance, ie, dat wild-assed leg.

What I thought you were *already* doing was this:
If L1-L2 are line, starting the unit with caps at L1-L3, and *then* adding
in balancing caps at L2-L3.

There are a cupla ways to do this, with relays, timers, etc, but the
simplest way I found was the following:

Find the minimum capacitance to start the idler -- mebbe 100-200 uF for 5
hp, at L1-L3.
Leave those connected, and from a separate bank of caps, switch in those to
L2-L3, for the best wildleg voltage.
Which you can almost do by "ear" -- PV's Principle of Least-Hum.

Another way is to have *two* separate banks of caps, each with an array of
caps from, say, 100 to 20 uF, in steps of 20, each cap sep'ly switched.
Switch in what you need to start, then adjust the switches to whatever
loads/idlers you anticipate connecting, for best leg-leg consistency.
Monitor with 3 HF digital VMs.

Anyway you do it, afaiu, you will still just have 2/3 of the rated hp, by
dint of the difference in incoming line power: fundamental physics/laws of
thermo.

However, the more motors you have connected to "the grid", the more
available power you have for any one loaded motor.
Which makes single large hp idlers superfluous.

I suspect a number of smaller idlers will give better voltage regulation, as
well, esp. if there is a mixture of delta and wye motors, but this is just a
hunch. A kind of law of averages. Like parallel processing???

OH ***..... PV's talkin PYOOTER TALK, and he don't unnerstand a fukn thing
bout pyooters!!!!!

--

Mr. PV'd

Mae West (yer fav Congressman) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??








i

On 2009-02-05, Ignoramus3187 <ignoramus3187@xxxxxxxxxxxxxxxxxxx> wrote:
I have a rotary phase converter, the good thing about which is that
it works very well and is 17.5 HP idler capacity.

What bugs me, however, is a question of how I can get full power out
of a 3 phase motor, using some sort of a static phase converter scheme.

As far as I understand, in a static phase converter, there is a
starting circuit using a start capacitor and a relay that gets the
motor started, and then the motor runs at 2/3 of power from single
phase.

What I do not understand is, why is it not possible to permanently
connect a properly rated run capacitor to legs 1-3 (legs 1 and 2 being
connected to single phase input). The start capacitor would still be
relay controlled. I thought this would shift the phase on leg 3 and
allow the motor develop full power during running. There must be
something that I am missing.


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