Motor starter help.

[marconi]

http://www.electrojumble.org/DATA/STC_Thermistors_Gen_Info.pdf

Just for information and interest.

(I assumed a 5VA coil (12500 Ohm 0.02A)which when closed mainly inductive with x 10 surge when mainly resistive (1250 Ohm 0.2A). NTC R reduces required initial closing surge current to a 1/3 until hot (0.07A). Warm up time of 2s. Required energy absorption rating 20J (= 2 seconds warm up from ambient x 10W power dissipation during this period). R of NTC at ambient is (250/0.07) - 1250 = 2300 Ohms.)

 

[marconi]

I think I would avoid using a thermal delay - they do get hot and in this application are only taken out of circuit if the contactor auxiliary NO contacts by pass it. Use modern technology.

Here is a suggestion. Use a delay on relay:

RS PRO ON Delay Multi timer, Screw, SPDT, 12 → 230 V ac/dc | RS Components - https://uk.rs-online.com/web/p/products/1026124/

This is a 'cheap' one but there are gucci more expensive makes too. You would wire its A1 to RN3 13 and A2 to RN1 A1. You then use the NO contacts - delay On so they don't close until the delay has elapsed - to connect across RN3 13 and 14. You then set up the required delay on time - a few seconds and carefully position the relay inside the enclosure. On the side of the relay I would write with a permanent pen the purpose of this timer and the delay time.

 

[Scott_fd2r]

It seems that what you are seeing as a 1M resistor is actually the NTC thermistor (aka Brimistor which was a trademark of STC). Its function is to slightly delay the operation of RN to ensure a full open transition. Bypassing it, as suggested in note 1 for lower power motors, simply causes RN to operate immediately. If the starter works with it bypassed, the Brimistor itself is probably faulty.



OK, you asked.

Before we start:

a) Series-parallel starting refers only to the connection of the run / main winding. It is the equivalent of star-delta starting but for single-phase, in that it lowers the voltage across each winding to reduce the starting current until up to speed, without the use of resistors or transformers. The start winding configuration and capacitor arrangement is a separate consideration.

b) There are two aspects to the start-run transition; switching the two run windings A1-A2 and A3-A4 from series to parallel, and disconnecting the start capacitor.

c) There are two possible capacitor configurations; capacitor-start induction-run, in which the capacitor winding is completely disconnected in run, and capacitor-start capacitor-run, in which the winding is disconnected from the start capacitor but remains in circuit via the run capacitor.

d) There are two possible centrifugal switch configurations; either it switches the start capacitor directly (in which case the starter timer is only responsible for the series-parallel transition) or it controls the ST contactor, in which case that contactor controls both the series-parallel connection and the start capacitor.

e) ST4 and RN2 are mutual interlocks that prevent ST and RN operating at once, which would short the main circuit L-N.

Pre-conditions for starting:
a) C2, RN2 and TM2 are all closed, i.e. the starter is not already in either the starting or running state and the timer is reset.
b) If the centrifugal switch is in the control circuit, it must be closed, i.e. the motor is not at speed.

START BUTTON PRESSED
Start button energises ST and TM

ST OPERATES. TM BEGINS TIMING
ST2 prepares a holding circuit for ST and TM, ready for when C2 opens
ST3 energises C
ST4 opens to prevent RN operating
ST main contacts 3-4 and 5-6 connect run winding terminals A2-A3 for series starting
ST main contact 1-2 connects start capacitor circuit (if controlled by starter and not directly by centrifugal switch)

C OPERATES
C2 opens to leave ST held only on ST2
C3 prepares a holding circuit for C, ready for when ST3 opens
C main contacts connect motor to mains

MOTOR RUNS UP TO SPEED
Motor run windings are in series, capacitor winding is in series with start capacitor (if CSIR) or start and run capacitors in parallel (if CSCR)]

TM TIMES OUT (OR CENTRIFUGAL SWITCH OPENS IF IN CONTROL CIRCUIT) WHICHEVER IS FIRST
TM2 or centrifugal switch disconnects ST

ST RELEASES
ST2 opens ST's holding circuit and disconnects TM.
ST3 opens, leaving C held only on C3
ST4 closes to energise RN via Brimistor.
ST main contacts disconnect run winding series connection and start capacitor.

BRIMISTOR HEATS UP
Brimistor resistance falls in a second or so, to the point where it is low enough for RN to operate.

RN OPERATES
RN2 opens to lock out ST
RN3 closes to bypass Brimistor
RN main contacts reconnect run windings in parallel

IF CENTRIFUGAL SWITCH IN MAIN CIRCUIT, IT OPENS
Start capacitor disconnected

Motor is now in running state.

No TL;DR option here. Either you follow it or you don't!
[automerge]1575457796[/automerge]
Re. your specific motor, it's hard to tell from the pics. What I think I am seeing is that the two capacitors are in parallel, making it CSIR, and that there is no centrifugal switch. Therefore, the start winding is controlled by ST and disconnected under timer control at the same time as the series-parallel transition. The maximum timer setting is limited by the start capacitor duty cycle as noted in the instructions.

hi,

I am new to the forum, apologies for replying on an old topic.
I have been searching for info on series parallel single phase motor starting,

I have a job of replacing a 10hp single phase motor on a grain mill. the old motor had been removed and the new one (new one is also an antique) put in place but with no markings on any cables. there were 5 wires into the terminal box. after alot of faffing about i have got the motor connected up how I believe to be correct, run windings linked in series through the contactors on start up changing to parallel when the timer changes the contactors over. as well as linking the windings in series the start contactor also puts a neutral to the motor which i have connected onto the z terminal. (brown wire) reason for this is I found a drawing of an old manual change over switch and that's how it showed the connections.

the starter is a brook series 3000. with the 3 contactors, to the best of my knowledge the motor is a capacitor start induction run motor with 2 start capacitors wired in series which appear to be through a centrifugal switch.

the issue I'm having is it seems like the motor struggles to reach a speed to throw the centrifugal switch. on start up the mill wheels are apart so it is only turning 1 wheel, the motor speeds up slowly but it seems like if it doesn't reach quite a high enough speed when the contactors change over it simply stalls and hums. i have adjusted the timer to give it more time to speed up but it gets to a stage where i hear the motor begin to slow again before the changeover. if the mill is spun by hand then the motor started it starts fine changes over and runs perfectly. i assume this is because of the extra rpm is has achieved.

there is no connection diagram in the motor lid or plate. any help would be greatly appreciated. i will attempt to put some pictures of the terminal box on.

scott

 

[Scott_fd2r]

hi,

I am new to the forum, apologies for replying on an old topic.
I have been searching for info on series parallel single phase motor starting,

I have a job of replacing a 10hp single phase motor on a grain mill. the old motor had been removed and the new one (new one is also an antique) put in place but with no markings on any cables. there were 5 wires into the terminal box. after alot of faffing about i have got the motor connected up how I believe to be correct, run windings linked in series through the contactors on start up changing to parallel when the timer changes the contactors over. as well as linking the windings in series the start contactor also puts a neutral to the motor which i have connected onto the z terminal. (brown wire) reason for this is I found a drawing of an old manual change over switch and that's how it showed the connections.

the starter is a brook series 3000. with the 3 contactors, to the best of my knowledge the motor is a capacitor start induction run motor with 2 start capacitors wired in series which appear to be through a centrifugal switch.

the issue I'm having is it seems like the motor struggles to reach a speed to throw the centrifugal switch. on start up the mill wheels are apart so it is only turning 1 wheel, the motor speeds up slowly but it seems like if it doesn't reach quite a high enough speed when the contactors change over it simply stalls and hums. i have adjusted the timer to give it more time to speed up but it gets to a stage where i hear the motor begin to slow again before the changeover. if the mill is spun by hand then the motor started it starts fine changes over and runs perfectly. i assume this is because of the extra rpm is has achieved.

there is no connection diagram in the motor lid or plate. any help would be greatly appreciated. i will attempt to put some pictures of the terminal box on.

scott

just to put everyone's mind at ease this was all very temporary and i have rewired from the starter to the motor alot better than what is shown. the motor defiantly worked last year on a single phase supply, and has since sat in a shed.

 

[Lucien Nunes]

Hello and welcome! So, you are lacking starting torque but OK for running torque. If you are fairly confident about the wiring, the single most likely fault is the start capacitors, which go bad both with age and with disuse. If they were on their way out and then sat around, they may have failed in the meantime. If I had no other information to go on, I would say change them to begin with at least as a precaution. There is probably a 4-digit date code near the bottom of the print on the can that would give an indication of how likely they are to be life-expired.

There are other possibilities of course; faulty windings (unlikely as it was working) faulty starter or wiring error. Some problems, such as the two sections of the run winding being connected out of phase, would make themselves known immediately. A couple of possibilities are more subtle. Since you only have one Z terminal, one end of the start winding or capacitor must be connected to one end of one run winding section. If the two halves of the winding are in-phase but interchanged, the junction of start and run circuits will be in the wrong place causing everything to be out of phase and at the wrong voltage during starting, but OK during running.

Please could you post pics of the motor data plate, capacitors, possibly a sketch of which leads are where in the terminal box (it's hard to trace them in the pic) and anything else useful.

E2A if you want to try something in the meantime, see whether the voltages across the two run winding sections are approximately equal during starting, also the voltages across the caps.

 

[Scott_fd2r]

Hello and welcome! So, you are lacking starting torque but OK for running torque. If you are fairly confident about the wiring, the single most likely fault is the start capacitors, which go bad both with age and with disuse. If they were on their way out and then sat around, they may have failed in the meantime. If I had no other information to go on, I would say change them to begin with at least as a precaution. There is probably a 4-digit date code near the bottom of the print on the can that would give an indication of how likely they are to be life-expired.

There are other possibilities of course; faulty windings (unlikely as it was working) faulty starter or wiring error. Some problems, such as the two sections of the run winding being connected out of phase, would make themselves known immediately. A couple of possibilities are more subtle. Since you only have one Z terminal, one end of the start winding or capacitor must be connected to one end of one run winding section. If the two halves of the winding are in-phase but interchanged, the junction of start and run circuits will be in the wrong place causing everything to be out of phase and at the wrong voltage during starting, but OK during running.

Please could you post pics of the motor data plate, capacitors, possibly a sketch of which leads are where in the terminal box (it's hard to trace them in the pic) and anything else useful.

E2A if you want to try something in the meantime, see whether the voltages across the two run winding sections are approximately equal during starting, also the voltages across the caps.

 

[Scott_fd2r]

thanks for the advice.
i had a very quick look today. i removed both capacitors and tested them, both appear good. they are marked 690-850 uF one is reading 770uF and the other 740uF.
i have made a rough sketch of the cables markings from the terminals going into the motor on the left and on the right i have sketched what is connected to each terminal during starting and then during running. hope this makes sense.
hopefully someone could explain how the capacitors and centrifugal switch are connected during starting. it doesn't look like they can be connected in series with windings?

 

[Scott_fd2r]

i have a terrible picture of the name plate. it appears to show phase-3 with a 1 stamped on top of the 3.

 

[Lucien Nunes]

I agree with you that it does not appear to be connected correctly internally. If the start winding is Z1-Z2 then it is in parallel with one section of the run winding during starting and disconnected during run by the starter removing the neutral from terminal Z. That explains why it has a bit of starting torque - there is a phase shift due to the different R/L of the windings, but the capacitors aren't in play.

What I would do next is disconnect lead Z2 from terminal A3 to segregate the start circuit, and test with a meter to identify the two pairs of leads for the switch and the start winding and confirm there are no internal connections between them. Then it will be possible to connect the windings and caps in series with some confidence.

Since the starter has a contact for the start winding you can optionally use that to disconnect the winding at the same time as the series-parallel transition and use the centrifugal switch as a backup to the timer to trigger the transition (I think this starter allows for this option by changing a link.) Or you can connect the start winding itself via the switch and the winding will disconnect either at speed or when the starter transitions to parallel, whichever happens first.

Then there is one final question, which is whether the start circuit is supposed to have the full 480V line voltage across it, or whether (as presently connected) it is supposed to be auto-fed from the centre-tap of the run winding (A2/A3). I need to read up on this, intuitively the existing connection to the tap is wrong and the Z2 end of the start circuit should be fed from line at A1 during starting. But if I am wrong about this, the smoke would escape very rapidly from the capacitors. Unfortunately, just this weekend I took most of my motor books up to the new museum library and won't be able to check them until Wednesday.

 

[Lister1987]

No idea if this willbe of help to you but we recently covered AC motors on my L3 8202, the attach file talks of capacitive start/run motors, not sure if will be of any help.