Re: motor starting relay


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:506qr251akt2st9rk7p4429thg7mf5ahin@xxxxxxxxxx
On Sun, 28 Jan 2007 14:13:56 -0600, "Maxwell" <luv2fly99@xxxxxxx>
wrote:


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:92epr2dco468v2q9fm11fsh9a77j0sm65h@xxxxxxxxxx
On Sun, 28 Jan 2007 02:17:42 GMT, "Homer J Simpson"
<nobody@xxxxxxxxxxx> wrote:


"Maxwell" <luv2fly99@xxxxxxx> wrote in message
news:JwTuh.18131$8U4.9385@xxxxxxxxxxxxxxx

Well now, it does have a 5 hp contactor that works off a pressure
switch
now. On at 150 psi, off at 175 psi. That contactor makes connection of
the
two 120v legs that supply power. But it also has a spring loaded
switch
that switches out the starting capacitors at about 1400 rpm or so,
it's
a
17XX rpm motor. The 5 hp contactor and power leads to the motor are
something different.

The relay I want to ad would switch on the starting capacitors
immediately
when the power is switched on by the existing 5 hp contactor, and
break
that connection about 1.5 seconds later. So although I know the main
contactor has to be rated for switching a 5 hp single phase motor,
that
normally draws 23 amps ( nd has a lock rotor rating of much much
more),
I
don't know how much amperage is being supplied through, and has to be
broken, by the capacitor circuit. Now that I think about it, it's only
about a 14 or 16 gage wire, so it would have to be a lot less aperage
than
the power legs though the 5 hp contactor. The contactor closes a 30
amp
circuit wired with #10 copper.

For sure you don't want the contacts to weld together however it may be
that
the starting current through the cap start circuit is quite reasonable
once
the motor gets up to speed.

---
"Quite reasonable"??? It goes to zero, you fucking moron, once the
motor gets up to a certain speed and the centrifugal switch opens,
disconnecting the caps from the starting winding. So you don't know
anything about motors, either? What a surprise.
---

So any half way reasonable contactor should
do the job OK - inc. a pre owned one!

---
"Half way reasonable"? What the hell is that goddam gobbledygook
supposed to mean?

Plus, the OP doesn't need a contactor, he needs a relay that
connects the capacitors to the starting winding when power is
connected to the motor via the 5HP contactor he's using now. Then
1.5 seconds or so later, he wants the relay to drop out and
disconnect the caps from the starting winding. He's stated that
very clearly, I think, so either you can't read worth a *** or your
reading comprehension is very, very poor. The turn-off delay
function is easily achievable, so the only thing that's up in the
air is how much current the relay contacts have to be able to
handle.

To the OP:

If you can measure the current in the starting winding and post what
you find then any number of us (except Homer) can help you pick a
suitable relay.



I'm not sure how accurate it is, but my meter was indicating about 28 amps
at startup, and 5 amps during run on the capacitor circuit, and about 120
amps at start up, and 23 amps during run on the line voltage.

I couldn't find a size on the wires in the capacitor circuit, but it
appears
to be about a #14, it only measures .116" on the outside of the
insulation.

---
I'm confused.

I would have thought that after the centrifugal switch disconnected
the capacitor circuit the current in that circuit would have gone
to zero. Maybe there's more to this than meets the eye?

Do you have a manufacturer and part number for the motor?


Confused me too John, but now that I think about it, I think it is probably
a cap start, cap run motor. It has both a large pair and small pair of caps.
I was probably measuring the cap run circuit when I made that observation.
But every circuit in the cap box ran either 28 or 23 on start up. Oddly
enough, I checked a 2 hp disk sander I have been having the same problem
with, and it showed 20 amps on start up. But it's only a singe cap motor. It
has a single cap about the same size as the two small caps on the 5 hp.



.