Re: 7.5 HP Lathe on a 10 HP idler?

Whoa! Ig, you said, "As you said yourself, reversing leads L1 and L2, on both motors
simultaneously, has no effect. Right? (I believe that as well).

If the motors are in parallel (so to speak) then "line in" terminals A, B on the idler connect to
terminals A, B of the load. It follows if "line in" A and B are swapped (trurned over, reversed,
etc) the direction of rotation of both motors will be unchanged. This is what I tried to say.

You wrote: "1) If you swap two leads L1 and L2 going to the idler, and at the same
exact moment swap two leads L1 and L2 going to the load, then nothing
will happen, right? They will both happily continue to spin in the
same direction as they did."

That is exactly what is done when the "line in" leads are swapped in a RPC. You will reverse the
idler in as much as the line terminals in a RPC connect from idler A to load A and from idler B to
load B. The "line in" is not independently connected to load terminals A and B. It connects first
to the idler, then to the load. In a RPC the line is connected parallel, A to A, B to B. Therefore
if A and B are turned over between idler and load, it is tantamount to a plug reversal and the load
will change direction.

Looking back on it, I think Jim's fairy tale case was about an independent parallel connection, that
is "line in" to idler and "line in" to load, not as connected in a RPC. I believe he was trying to
give us a lesson in understanding rather than the specifics of RPCs. Hopefully he will get back to
us with another lesson.

Bob Swinney


"Ignoramus24574" <ignoramus24574@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:m6ydnU_0Ep0_NozXnZ2dnUVZ_sudnZ2d@xxxxxxxxxxxxxxx
On 2009-05-18, Robert Swinney <judybob@xxxxxxxxx> wrote:
Thanks Iggy.

No I really meant to say a swap of any 2 leads going to the load would reverse the load. My bad!

I thought so too.

Bob, think about this. You seem to have a distinction that only the
motor whose leads are being reversed, may change rotation. Let me try
to sow some doubt.

I will continue calling one motor "idler", and the other motor "load",
just to keep using the same terminology as we did when we started this
thread. As a matter of fact, there is little distinction between them,
once both are running.



2) Now, very quickly after this, swap again, this time only the
leads going to the "idler".

Note that by "very quickly", I mean within one or two AC cycles.

According to your presumption, now the "idler", whose leads were
reversed, will want to reverse. Right?

3) Now, very quickly thereafter, swap the leads again, on both the
idler, as well as the load. That again would have no effect and,
according to your thinking, if I understand it right, the idler motor
will continue reversing itself.

After steps 1-3, what you end up with, is the reversed idler and load
continuing to run in the same direction.

However, steps 1-3 are equivalent to reversing leads on the load only,
and yet, the result is the opposite to what would happen in accordance
with your assumption, if only the leads on the idler were reversed.

This is a logical contradiction. Two equivalent processes lead to
opposite results.

Therefore, the assumption that the it is necessarily the motor whose
leads are reversed that changes rotation, is not a correct one.

i




Perhaps Jim will get back to us on some questions posed in an earlier post on this subject.

Bob Swinney
"Ignoramus24574" <ignoramus24574@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:E7mdnfRfI7gIBozXnZ2dnUVZ_hZi4p2d@xxxxxxxxxxxxxxx
On 2009-05-18, Robert Swinney <judybob@xxxxxxxxx> wrote:
Lloyd,

That's the way I read it too. In a perfectly balanced system, as
Jim depicted, both motors would stall. Of course, that is as Jim
sez, a fairy tale system. In the stark world of actuality, even a
slight imbalance would eventually reverse the idler.

Did you really mean to say "reverse the idler"?

i

Bob Swinney
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message
news:Xns9C0F81F29BB1Dlloydspmindspringcom@xxxxxxxxxxxxxxx
"Robert Swinney" <judybob@xxxxxxxxx> fired this volley in
news:wKednbICp8shE4zXnZ2dnUVZ_uadnZ2d@xxxxxxxxxxxx:

Jim, my confusion arises in that AFAIK if we were to "plug reverse"
only the load motor, the connections would be single-phase line to
A,
B of the idler, A of idler to B of load, and B of idler to A of
load,
With C terminals together. It seems to me this connectivity would
reverse only the load motor, not both motors.

Please explain if this is not the case.

My read on this is that, in the absence of start or run capacitors,
the motors could be spun up in either direction. When the attempt is
made to plug-reverse the load motor, it won't reverse the idler
(alone) What it's actually trying to do is reverse BOTH of them, and
it'll simply stall both in the effort.

In this perfect parallel connection, there's nothing to distinguish
the idler from the load motor except where it's physically located.

LLoyd



.

Relevant Pages

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