Mark VII motor starting switch (not inside the motor)

ryansm7 · Post by **ryansm7** » Sun Jan 02, 2011 5:10 pm

Hi JPG,
Well, I’m going to take a shot at what I think is going on. I may just be sniffin' the wrong kind of glue but here goes...

I think the “black box” consist of a high impedance coil (with low dc resistance) and a set of normally closed contacts. The coil is wired between terminals 2 and 5, with the contacts between terminals 1 and 2. When power is applied the start capacitor provides a phase shift for starting torque.

The “black box” works by an increase in back-electro-motive force (back-EMF), a voltage that is generated across the start winding as the motor increases in speed. The motor’s rotor turning at high speeds near the motor windings (start and running) has a voltage-generating effect; back-EMF.

The generated back-EMF opposes the line voltage and is measured across the start winding or across the relay coil inside the “black box” at terminals 2 and 5. The back-EMF is a higher voltage (266VAC) than the line voltage (122VAC).

The back-EMF voltage generated across the start winding causes a small current to flow in the start winding and the “black box” relay coil, because they are in the same circuit. When the back-EMF has built up to the pick-up voltage, the contacts between terminals 1 and 2 will open. This will take the start capacitor out of the circuit.

The start winding is still in the back-EMF circuit, keeping the “black box” relay coil energized while the motor is running at full speed.

When the power is turned off; the motor’s rotor decreases in speed. Then, the back-EMF generated across the start winding decreases in magnitude. The “black box” relay coil now sees a lower back-EMF and de-energizes. The contacts return to their normally closed position by spring power (and gravity) as the motor coasts to a stop. (The “black box” has a label on the side marked “this side up.” The arrow is pointing toward the pins.)

While taking measurements, I noticed that there were sparks (arc) near pin 1.

At first I thought it was a loose terminal connection. After tightening the contact pins, the arc was still there. I’m guessing the arc is coming from the contacts closing at powering down. So there is a possibility that sawdust is in the contacts. Maybe an air compressor can blow out any debris.

[ATTACH]11347[/ATTACH]

If the continous coil voltage is 300VAC and the nominal pick-up is 266VAC, then maybe the MARS 551 is a better choice.

What do think; am I all wet?

JPG · Post by **JPG** » Sun Jan 02, 2011 6:32 pm

ryansm7 wrote:Hi JPG,

I could not get a clear pic of the motor name plate without completely removing the motor. Here are the specs for the motor. The following is exactly stamped into the name plate.

MODEL C48L2A7
HP 1-1/8
RPM 3450
CY 60
PH 1
SF 1.0
VOLTS 115
AMPS 12.6
SF AMPS
CODE H
TYPE CS
SER 163
FR 48
RISE 50
CONT DUTY

All measurements were taken with a digital multi-meter.

POWER ON MEASUREMENTS:Motor running???????
Pins 1 to 5.... 122VAC
Pins 1 to 2.... 300VAC
Pins 5 to 2.... 266VAC

POWER OFF MEASUREMENTS:
Pins 1 to 5.... 0VAC
Pins 1 to 2.... 0VAC
Pins 5 to 2.... 0VAC

The relay was electrically disconnected from the motor and capacitor for these measurements.

POWER OFF MEASUREMENTS:
Pins 1 to 5.... 3.2 Ohms
Pins 1 to 2.... 0.0 Ohms
Pins 5 to 2.... 3.2 Ohms

Previous assumptions may be invalid(this is not adding up!)

The 300V across 1,2 that was 0 ohms indicates a n/c contact.

The 3.2 ohm is unexpectedly high.

The 551 is a definite no!

At this point I would look for a competent motor repair house and seek their input.

I(moi) would be taking the relay apart(carefully so as to NOT alter its operating and examine the contact for possible 'fixing'.

What is needed to determine equivalent brand x is the specs on what you do have(old rbm data).

Your diagrams above 1)Only include 2 windings 2) assume internal common connection 3)There are three windings

A.O.Smith is no help today(they are in the midst of selling motor products division to Regal Beloit).

ryansm7 · Post by **ryansm7** » Sun Jan 02, 2011 7:26 pm

I'll double check the measurements and get back with you.

I don't have an amp meter right now to check the current in the "black box" relay coil.

Thanks for sticking with this for me.

JPG · Post by **JPG** » Sun Jan 02, 2011 8:32 pm

ryansm7 wrote:I'll double check the measurements and get back with you.

I don't have an amp meter right now to check the current in the "black box" relay coil.

Thanks for sticking with this for me.

I edited my last post(while you were creating thisun).

Not sure what an ammeter will provide to help.

I really do not think the 550 is correct either.

Wish I could remember what 'rbm' stood for!

ryansm7 · Post by **ryansm7** » Sun Jan 02, 2011 10:36 pm

If there is a small current thru the "black box" relay coil (and start winding), then it will help to determine the voltage drop across both coil/winding. I'm not sure if it will be milliamps or higher. The measured 3.2 Ohms is purely resistive. The coil/winding inductive impedance cannot be measured directly with an Ohm meter.

I did a lot of looking for RBM, but could not find the specific part number.

White Rodgers offers 5 types of relay series: the White Rodgers Type 128000 relay series, the White Rodgers 90-290Q thru 90-295Q WR/RBM type 84 relay series, the White Rodgers 90-3360 thru 90-486 WR/RBM Type 184 relay series, the White Rodgers RBM type 129000 and the White Rodgers RBM Type 129000 AR relay series.

The White Rodgers Type 128000 relay series consists of model 90-63 thru 90-71 and they have a continuous coil voltage that ranges from 170 to 420. The first model, the White Rodgers 128000 90-63 relay has a pick-up of 140 to 155V, whilst the last model, the White Rodgers 90-71 relay has a pick-up rating of 223 to 252V and a drop-out of 150V.

It's a long shot, but I have a call into White Rodgers to see if they can help with the markings on the relay. I'll post the feedback.

JPG · Post by **JPG** » Sun Jan 02, 2011 11:42 pm

ryansm7 wrote:If there is a small current thru the "black box" relay coil (and start winding), then it will help to determine the voltage drop across both coil/winding. I'm not sure if it will be milliamps or higher. The measured 3.2 Ohms is purely resistive. The coil/winding inductive impedance cannot be measured directly with an Ohm meter.

I did a lot of looking for RBM, but could not find the specific part number.

White Rodgers offers 5 types of relay series: the White Rodgers Type 128000 relay series, the White Rodgers 90-290Q thru 90-295Q WR/RBM type 84 relay series, the White Rodgers 90-3360 thru 90-486 WR/RBM Type 184 relay series, the White Rodgers RBM type 129000 and the White Rodgers RBM Type 129000 AR relay series.

The White Rodgers Type 128000 relay series consists of model 90-63 thru 90-71 and they have a continuous coil voltage that ranges from 170 to 420. The first model, the White Rodgers 128000 90-63 relay has a pick-up of 140 to 155V, whilst the last model, the White Rodgers 90-71 relay has a pick-up rating of 223 to 252V and a drop-out of 150V.

It's a long shot, but I have a call into White Rodgers to see if they can help with the markings on the relay. I'll post the feedback.

None of the 128000 series has a coil resistance of 3.2 Ω.

ryansm7 · Post by **ryansm7** » Mon Jan 03, 2011 3:21 pm

JPG40504 wrote: I(moi) would be taking the relay apart(carefully so as to NOT alter its operating and examine the contact for possible 'fixing'.

Hi JPG, well you didn't come right out and say it but looks like my first wack at it left me "all wet".

If this motor was yours ] A.O.Smith is no help.[/QUOTE]

So with out anymore tounge and cheek from me...

I have a second motor from another Mark VII. It's just had a bath and fitted with new bearings. It has a start capacitor and wires - no "black box".

Just to bench test this motor; what wires can I connect to check it for forward operation?

Yes, the power cord has black, white, and green (gnd). What on the motor needs to be connected?

[ATTACH]11357[/ATTACH]

Thanks again for the help and patients with a newbe
..

JPG · Post by **JPG** » Mon Jan 03, 2011 8:46 pm

This help?

[ATTACH]11365[/ATTACH]

And this

[ATTACH]11366[/ATTACH]

See next post for 'bench test' wiring. SECURE before powering up!!!!! It will jump off the bench if not!

JPG · Post by **JPG** » Mon Jan 03, 2011 8:52 pm

wh to power neutral
blk to power hot

red to yellow
redwhite to whiteblk

reverse red/redwhite to reverse direction.

ryansm7 · Post by **ryansm7** » Tue Jan 04, 2011 7:47 am

1/2 cool...

Forward direction works very smooth.

Reverse direction does not rotate, hums loud, and gives off unsavory toasty smell after only being plugged in for 1/2 second.

Just to confirm reverse direction bench test wiring:

wh to power neutral (white)
blk to power hot (black)

red/redwhite
yellow/whiteblk