3-ton start capacitor

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Beekster

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Jun 30, 2011, 9:05:36 PM6/30/11
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I found a source for the 145-175 MFD. @ 330 VAC START CAPACITOR, but
am confused because the manufacturer has 2 part numbers with this
spec. I'm not sure how I know which one is the right one--if there is
a right one. If anyone can help me with this, I would certainly
appreciate it.

I think this link will let you view the 2 part numbers.

http://bit.ly/k2xgla

Mike

one mad dealer

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Jun 30, 2011, 9:42:25 PM6/30/11
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I'm ordering caps with bleed resistors so I can offer them on my eBay
page. The 3ton I've been testing with a 145 start cap has been
working perfectly.

Gabe

Wolfe 4656

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Jun 30, 2011, 9:44:33 PM6/30/11
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Gabe, what is your ebay page? and about how much do you think they will be?  Dave...

one mad dealer

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Jun 30, 2011, 10:24:59 PM6/30/11
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josephsiaq, but I have no items up for sale at the moment. Price will
depend on the source, so I'm not sure yet.

Gabe

On Jun 30, 9:44 pm, Wolfe 4656 <wolfe4...@gmail.com> wrote:
> Gabe, what is your ebay page? and about how much do you think they will be?
> Dave...
>
> On Thu, Jun 30, 2011 at 9:42 PM, one mad dealer <G...@josephsiaq.com> wrote:
>
>
>
> > I'm ordering caps with bleed resistors so I can offer them on my eBay
> > page.  The 3ton I've been testing with a 145 start cap has been
> > working perfectly.
>
> > Gabe
>
> > On Jun 30, 9:05 pm, Beekster <beekst...@gmail.com> wrote:
> > > I found a source for the 145-175 MFD. @  330 VAC  START CAPACITOR, but
> > > am confused because the manufacturer has 2 part numbers with this
> > > spec. I'm not sure how I know which one is the right one--if there is
> > > a right one. If anyone can help me with this, I would certainly
> > > appreciate it.
>
> > > I think this link will let you view the 2 part numbers.
>
> > >http://bit.ly/k2xgla
>
> > > Mike- Hide quoted text -
>
> - Show quoted text -

Chris

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Jul 4, 2011, 12:17:05 AM7/4/11
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http://stearns.rexnord.com/pdf/Cat_902/18-19.pdf

Brief Operating Description: Longer Motor Life Starts with a Switch
1
For over 75 years, single-phase
motors have utilized a mechanical
centrifugal switch to switch the start
circuit. Inherent characteristics of a
mechanical device have made these
switches prone to various problems,
including tolerances, tolerance buildups,
mechanical fatigue, vibration
and a host of others that can lead to
switch failures and/or performance
inconsistency.
Our challenge was to design a
reliable solid-state switch to replace
the mechanical switch and actuator
mechanism that would duplicate
the function of connecting and
disconnecting the start circuit at
particular speeds with the additional
benefits of a solid-state device. After
considerable research, we decided a
successful electronic motor starting
switch could be created by sensing the
voltages present in the main and start
windings.
Until the rotor of a single-phase motor
begins to rotate, there is no coupling
between its start winding and main
winding. When the rotor begins to turn,
the main winding induces flux in the
rotor, which then induces a voltage
in the start winding. The voltage
induced in the start winding is directly
proportional to motor speed.
In Stearns SINPAC Electronic
Switches, the voltage across a motor’s
main winding and the voltage across
its start winding are sampled and fed
to a comparator. The logic circuitry is
designed so that the electronic switch
interrupts the start circuit current after
the motor has accelerated to the speed
at which cut out voltage is developed,
generally 75 to 80% of synchronous
motor speed. The logic circuitry then
shuts down the switch’s power stage,
which consists of a triac or inverse
parallel SCR’s. This function is referred
to as “cut out.” When the start circuit
is disconnected, the main winding
field then drives the motor’s rotor to its
running speed.
If the motor encounters an overload,
and the motor speed falls to
approximately 50% of its synchronous
speed, the SINPAC Switch
automatically reconnects the motor’s
start circuit. This function is referred
to as “cut in.” Cut in detection circuitry
constantly monitors start winding
voltage. When the motor’s speed falls
to the cut in point, the detection circuit
causes the control logic to energize
the SINPAC Switch’s power output
stage. The motor then goes through its
normal startup procedure, with the start
circuit being switched out at a motor
speed approximately 75 to 80% of
synchronous speed.
SINPAC Switches are potted
and completely sealed, making it
impervious to dust, dirt and moisture.
The unique speed sensing circuit
provides a universal design which
allows a few switches to work on most
standard motor designs regardless of
manufacturer.
Acceptance by Motor
Manufacturers
US and foreign motor manufacturers
have tested and retested the SINPAC
Switch for reliability and quality. Today,
many of these manufacturers have
begun installing SINPAC Switches
on their standard motor lines with
more companies ready to make the
changeover.
UL Recognition
Many SINPAC Switches have already
been recognized under the Component
Program of Underwriters Laboratories,
Inc. (E-71115). In addition, all switches
have internal surge protection which
is tested according to IEEE C62.41 –
1991 Category A3.
CSA Certification LR-6254.

one mad dealer

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Jul 4, 2011, 4:13:36 PM7/4/11
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seems like an interesting product, it senses motor start like a umsr.
I wonder what the price point is and if it could be qualified by
Bristol.

Gabe

David Friedman

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Jul 4, 2011, 5:50:07 PM7/4/11
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Note that the part is not easy to mount and it is only rated to 220 so would not work in our app.  I wonder if it vilates Andy Katah's patent,  or if it fails to look at slope and only looks at motor voltage in which case it is a sophisticated electronic replacement for the earlier KSTS retroseal parts used on the T-89.
 
David Friedman

Chris

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Jul 5, 2011, 11:47:26 PM7/5/11
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Here is the umsr's patent.


http://www.wikipatents.com/US-Patent-4486700/universal-single-phase-motor-starting-control-apparatus

A starting circuit for single phase electric motors including both
split-phase and capacitor start motors includes a gate controlled
solid state switch serially connected to the start winding of the
motor. Rectified reference pulses from a pulse transformer are
generated to turn on a first transistor to provide gating current for
the solid state switch. Initially, when the motor is energized at zero
rpm, the pulses are received at the switch after the start winding
current passes through the zero current level to gate the switch to
conduct each half cycle and energize the start winding however as the
motor speeds up, the pulses are received earlier and earlier relative
to the start winding current zero cross over until at a selected speed
the pulses are received at the switch prior to the start winding
current zero cross over with the result that the switch is no longer
gated conductive. When this occurs the voltage across the switch goes
high. This voltage is rectified and received at the base of a second
transistor adapted to shunt the pulses from the pulse transformer away
from the first transistor to lock out the switch with the start
winding deenergized. In a first embodiment the pulse transformer is
energized by the main winding current to directly employ the phase
difference between main winding current and start winding current
while in a second embodiment the pulse transformer is energized by
line current to directly employ the phase difference between line
current and start winding current.

Chris

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Jul 6, 2011, 12:07:46 AM7/6/11
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Here is Rexnord's patent. They claim ac wave synchronization between
start and run capacitors is critical. Maybe this is the cause of the
potential relay arcing. Rexnord says it is vital to time the ac wave
to the caps before connecting. I think the umsr's method is to drain
the start cap before connecting. These are around $90, a little more,
might it be worth it?

http://www.everypatent.com/comp/pat5017853.html

A capacitor-start capacitor-run single phase AC induction motor
control starting circuit is provided which minimizes first cycle
current spiking magnitude, and also minimizes cycle to cycle current
spiking magnitude, without a choke or inductor in the loop containing
the run capacitor, start capacitor and start switch. The first cycle
current spiking problem is solved by controlling when the start switch
may be turned on at initiation of the starting mode in relation to the
AC cycle, to permit turn-on of the start switch only within a known or
predictable range of voltage differential between the run and start
capacitors. The cycle to cycle current spiking problem is solved by
proper phasing of gate current, and supplying gate current to the
start switch in phase with the voltage across the run capacitor and
out of phase with the current through the series connected start
switch and start capacitor.


Chris

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Jul 6, 2011, 12:10:15 AM7/6/11
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These are shaped and sized similar to the start caps. It could be
easily bundled with them, you wouldn't even need to mess with a screw.
,

David Friedman

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Jul 6, 2011, 6:47:39 AM7/6/11
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Clearly USMR senses actual motor speed condition and is superior to any other motor start system I have seen
 
This helps confirm the reason why the USMR is teh correct choice.
 
Thanks
 
David Friedman

Chris

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Jul 5, 2011, 11:20:00 PM7/5/11
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Here is Rexnord's patent. It seems they are saying that timing of the
ac wave is critical when connecting the start and run capacitors, this
is what their product does. Perhaps this is what causes the arc in
the potential relay, voltage differential between the start and run
caps. I don't know if the umsr does this, it is still a mechanical
relay and I don't know if it could be controlled accurately enough to
time the ac wave. I have yet to find as detailed an explanation of
the umsr's operation so it's hard to say.

http://www.everypatent.com/comp/pat5017853.html

A capacitor-start capacitor-run single phase AC induction motor is
subject to a phenomenon known as "first cycle current spiking", and to
another phenomenon known as "cycle to cycle current spiking". The
first cycle current spiking is experienced in both mechanical and
solid state disconnect switches.

The present invention addresses and solves the first cycle current
spiking problem, and also addresses and solves the cycle to cycle
current spiking problem.

As is known in the prior art, a single phase AC induction motor has a
main winding and an auxiliary winding both connectable to an AC power
source. A start capacitor provides a phase shifted field for starting
torque. A semiconductor power switch automatically connects and
disconnects the start capacitor to and from the AC source in starting
and running modes, respectively. The gate current for the
semiconductor power switch is derived through a resistor, such as
resistor 72 in the above noted Bossi et al patent, connected to a node
common to the start capacitor and a main terminal of the power switch.
This circuitry performs admirably on capacitor start or split phase
motors. However, when applied to capacitor-start capacitor-run motors,
a gate circuit of this type is subject to the above noted first cycle
current spiking and cycle to cycle current spiking.

One solution to current spiking known in the prior art is to provide a
choke for the run capacitor, such as a large inductance or coil
connected in series with the run capacitor or an extended winding. The
choke is undesirable because it is massive and expensive. Furthermore,
the choke does not solve the first cycle current spiking problem. The
choke does reduce the current spike, but not enough to be
satisfactory. Another disadvantage of the choke is that it requires
the insertion of an element in series with the run capacitor, which is
costly from a manufacturing standpoint. Another disadvantage of the
choke is that it is in the circuit continuously.

The present invention provides a solution which is particularly simple
and effective, and eliminates the need for a separate series connected
choke.

The present invention solves the first cycle current spiking problem
by controlling when, in relation to the AC cycle, the power switch is
allowed to turn on, rather than just allowing the power switch to turn
on at random during any point in the AC cycle upon initiation of the
starting mode. Instead, the start switch may be turned on only within
a known or predictable range of voltage differential between the run
and start capacitors.

The present invention solves the cycle to cycle current spiking
problem by controlling phasing of gate current to the start switch to
be in phase with the voltage across the run capacitor and out of phase

Chris

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Jul 5, 2011, 10:49:00 PM7/5/11
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Here is Rexnord's patent description of how these things work. It
seems they are saying with both a start and run capacitor that timing
of ac wave is critical between the 2 caps. These seem to synchronize
the caps to the ac wave before connecting them for starting. This may
explain some of the arcing across the potential relay. I wonder if
the umsr works the same way, or do they use a voltage differential
only as they describe?


http://www.everypatent.com/comp/pat5017853.html

David Friedman

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Jul 6, 2011, 6:52:25 AM7/6/11
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Chris
 
You miss the point.  The reason that Bristol specified the dual start/dual relay circuit is due to the assymetrical coils of the TS motor which makes the motor start up very very different for the two directions - hence the need inteh Bristol circuit for two potential relays and the need for a selection contact which has beenthe failure mechanism.
 
The USMR senses the state of the motor and can tell when it is up to spped and needs the start cap disconnected so hence it needs only the one smart relay.
 
The more expensive part is both not rated for the voltage required for our app - and won't work.
 
David

David Friedman

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Jul 9, 2011, 4:44:29 PM7/9/11
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This discussion is a bit academic for two more fundametal reasons, The device you guys are looking at is not able to deal with the different start voltage curves of the TS in its two modes,  and is not rated for the 300 plus votage R to S that our compressor motor sees.
 
The reason I think that the 50 amp contact in the USMR (or the old potential relays) held up was that at the end of the run cycle with the start cap at zero volts - the only stored energy "short circuit discharge" seen is the voltage across the run cap which is quite small and thus stores much less energy than a charged start cap.  The contact used is rated to handle this energy for the rated number of operations which is huge.
 
My observation at the time my unit failed was that the primary one potential contact was very clean but that the primary two - which had a failed L2 contact and was leaving the huge start cap current in the circuit and trying to disconnect that load - was very dirty.
 
The compressor failures have not been caused by "dirty" potential relays,  and when the start cap has a bleed resistor so that the larger cap (the start) is disharged and only absorbs the stored energy of the run cap (50 uf or so) there has been no reported welded contacts.
 
So - I think that the USMR will last as specified (and as will be seen in our testing) which is longer than the life of other components,  and will not limit Acadia life.
 
 
 
David Friedman

David Friedman

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Jul 9, 2011, 5:01:02 PM7/9/11
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Now I get it
 
They are talking about start systems using electronic switches which don't like and fail when subject to high current spikes.  The electronic switch in question must make a connection between the run and start caps which are in parallel.  In an electronic switch like the one described - they worry that when startup occurs the switch shorts the two caps together with the start cap inititally discharged,  but with the run cap at any old voltage. When two caps with different voltages are connected in parallel - a large spike occurs.  Note that in our USMR the contact in the device is normally closed paralleling the two caps at start so the intial "spike" is non existant.  However - at the end of the run cycle - the power contactor opens and the USMR contact goes back to closed shorting a running votage charged run cap (but small value) into the discharged start cap.  There is a spike but the 50 amp contact can handle it for its rated life.
 
Much more important than phasing control to eliminate spikes destructive to electronic switches (which the USMR apparently doesn't use - is that the USMR looks at phase differance between applied power and current thru the start winding and is able to figure out if the motor is up to speed - IN BOTH DIRECTIONS OF SPIN.  This causes the single USMR relay to in effect act as if it were two relays of different voltage as required by the Bristol specification for the dual relay/dual contactor circuit.  It was invented and patented for that purpose and after two years of testing was rejected with no explanation by Bristol who accoring to inside private information trid to steal the patent but was stopped by ICM.
 
David Friedman
 
David Friedman
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