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.

 

[marconi]

Scott_fd2r - A quick contribution - you don't specifically mention it so:

1. Are you providing a single phase supply to this single phase motor? ie: Is the supply derived from a split phase transformer L1-N-L2 (viz 240-0-240V) or are you using L1, L2 and N from a three phase 4 wire 415V supply?

2. What is the supply voltage at the Brook starter L1-L2, L1-N and L2-N before starting, during starting and when running?

 

[Scott_fd2r]

thanks for the advice, the supply is just single phase live and neutral on a TT earth 230v and neutral. this motor did run last year at a neighbouring farm on a single phase live/neutral supply. i know this for a fact as i connected the supply into the pre wired starter motor setup early last year.

i did find some info on another forum which appears to show the same motor connected in the same way as this one.

lucien nunes, how would you think the motor should be connected internally to achieve a true series start? i have tried to draw how to connect it but keep talking myself out of it. i don't have much experience with single phase motors to be honest. I will hopefully get back to it in the next day or 2 for some more testing.

 

[Lucien Nunes]

Hang on, 230V?

The plate doesn't make it out to be a dual-voltage motor - it only states 480V - therefore surely it is supposed to start in series and run in parallel on 480V but not at all on 230V. (As opposed to running in series on 480V and in parallel on 240V, with DOL starting, in which case the blank areas on the plate would be stamped 240V 48A). If this is the case, then it is significantly overpowered for the job if it can drive the load at half nameplate voltage, but the speed will be low which if you can confirm with a tacho will be the giveaway.

Re. winding configuration, I would use a low range on a meter to confirm that the start winding is connected between Z1 and Z2 and the centrifugal switch between SW and Z, and that none of those four leads connects to anything else. If so, interchanging the leads SW and Z1 from within the motor will put the start winding in series with the switch, the capacitors and the starter's controlled start-winding output. But the voltage anomaly remains.

 

[marconi]

thanks for the advice, the supply is just single phase live and neutral on a TT earth 230v and neutral. this motor did run last year at a neighbouring farm on a single phase live/neutral supply. i know this for a fact as i connected the supply into the pre wired starter motor setup early last year.

i did find some info on another forum which appears to show the same motor connected in the same way as this one.

lucien nunes, how would you think the motor should be connected internally to achieve a true series start? i have tried to draw how to connect it but keep talking myself out of it. i don't have much experience with single phase motors to be honest. I will hopefully get back to it in the next day or 2 for some more testing.

Scott_fd2r - A quick contribution - you don't specifically mention it so:

1. Are you providing a single phase supply to this single phase motor? ie: Is the supply derived from a split phase transformer L1-N-L2 (viz 240-0-240V) or are you using L1, L2 and N from a three phase 4 wire 415V supply?

2. What is the supply voltage at the Brook starter L1-L2, L1-N and L2-N before starting, during starting and when running?

Scott_fd2r: Good evening from rainy London

For clarity could you consider my question again please? What electricity supply is available at the location and what lines and neutrals are provided at the Brook motor starter with their line-neutral voltages please?

Also - is the current motor identical to the one that is being replaced? Just a caution to you that grain mills are a fire and explosion risk so the motor needs to be suited to this application eg flame and spark proof.

 

[marconi]

I think there are some hints:

1. Working voltage of each capacitor is 120-150Vrms and they are in series so as a combination 240/300V which lower than the motor's operating voltage of 480V - thus the start winding energisation voltage is derived from the mid-point of the identical series connected armature windings. And the Z terminal, one end of the start winding, has a neutral connected to it which is switched in the starter. The motor is therefore a capacitor start type not a capacitor start/capacitor run one.

2. This is an antique motor which I believe would have used one of the old-fashioned manually operated handle start and run changeover switches. There is no centrifugal switch internal to the motor which suits it being used in a flameproof/ sparkless application as in a grain miller.

3. 480V supply for the day's when farms only had single phase supplies and sometimes split-phase 240-0-240V thus 480V.

4. Standard nomenclature would make the armature windings start-ends as A1-A2 and A3-A4. So for correct magnetic polarization current flows A1 to A2 and A3 to A4. This explains the connection via the starter of A3 start to A2 end - (note I believe the OP made a mistake when he writes that A1-A3 are connected together via the starter during 'start' phase on the diagram he sketched - he meant A2 and A3.).

So, my attached diagram may be along the right lines. Or something close to this. Ignore first attachment which has a small mistake - look at second one.

 

[marconi]

To help confirm the winding connections to the 6 terminals could you disconnect the wires from the starter at the motor and remove one spade connector from one of the capacitors to take them out of circuit. Then please take an Ohmmeter on 0-100 Ohms range say and measure:

1. A1-A2 (should be about the same reading as A3-A4)
2. A3-A4
3. Z1-Z2(tens of Ohms)
4. A1-A3(Open circuit O/C)
5. A2-A4(O/C)
6. A1-Z1(O/C)
7. A3-Z1(O/C)
8. A2-Z2(O/C)
9. A4-Z2(O/C)

what I expect shown in brackets.

 

[Lucien Nunes]

We've taken CSIR as a given, there's no run cap present, but there does seem to be a centrifugal switch. Pending confirmation from the OP, that would appear to be between Z and SW. But all this is immaterial if he has only 230V and a 480V motor. The only salvation would be if the data plate was shoddily stamped and it is actually a 240/480V motor intended for DOL starting on 480V, that can be series-parallel started on 240. Then it would be a certainty that the start winding end should not be on the centre tap but across L & N. I would connect in series across 230V and check the speed. If it is not above nameplate speed at less than full load, it's a 480V motor.

 

[marconi]

Another small error corrected - see attached diagram below - Z connects to L2 during start phase where L1-N-L2 is =+/-240, 0, -/+240V.

I reckon someone has tinkered with the motor terminals to wire the start coil Z between A3 and Z1(Z) instead of between Z1(Z) and Z2; and wired the start capacitor between Z1(Z) and Z2 instead of between A3 and Z2. (Direction of rotation normally reversed by swapping over connections at Z1(Z) and Z2 terminals).

I don't think the internal centrifugal switch - if there is one - is used because the Brooks motor starter mentioned by the OP provides a switched Z line to de-energise the start coil when changeover to run (and armature windings from series to parallel) occur.

There is low torque at start up because of these wiring errors - during start there is next to no current through the start coil and what current that flows is not phase shifted. The motor requires a 480V two wire supply but the starter may need 3 wire for a neutral for the contactor coils and timer - can't say for sure.

It'll struggle too during start phase on 240V two wire because in start phase armature coils only have 120V across them which rises to 240V during run.

Or something along these lines.

 

[Lucien Nunes]

I gathered that the starter was existing at the mill but that the motor is being replaced, i.e. the two were not previously used together. The centrifugal switch is not needed with this starter but might have been in use when the motor was in its original installation. My reasoning on the leadouts was based on lead Z having a push-on receptacle connected directly to the capacitor, whereas the others have forks / rings for the terminal studs, making it less likely that the connection between the capacitor and Z had been altered.

But we may be flogging a horse of the wrong voltage here. We need to clarify the motor's run voltage. There are a couple of ways to do this including measuring the magnetising VARs, but at half voltage the slip will be very high and the speed well below rated. What do other people think about the data on the plate and the significance of the start capacitor voltage / connection to the run winding midpoint? I had overlooked the cap voltage until Marconi pointed it out.

 

[marconi]

Scott_fd2r: Turning attention to the starter, you might find the attached wiring diagram for the Brook Crompton Single Phase Series Parallel motor starter 3SP1CHS useful.

I obtained it from Brook Crompton Technical Services.

See page 8 of this link for further details should you need to order a new one or spares for it:

https://www.yumpu.com/en/document/read/55037547/this-is-crompton-controls