Motor starter help.

[dlt27]

Hi all, thanks again for any input.
I have been asked to look at this starter as motor starts ok, but when switches over to run motor stops and starter just hums.
First of all like I’ve said in previous posts I haven’t had a lot of experience with motors/ starters etc
Am I right in thinking this starter is for a capacitor start - capacitor run motor with no centrifugal switch as it has a timer set to 15 seconds and then 3 contactors?
The motor starts ok and contractor in middle kicks in and contractor on right kicks in but after time delay right contractor drops out, but left one doesn’t kick in.
The part I’m not sure about is that there is a 1M ohm resistor across the 13 and 14 contacts on the left contractor and if I bypass this with some cable it all appears to work fine. I have checked resistor and it reads 1M ohm like it should ( brown, black, green and gold).
Could anybody tell me why the resistor is there in the first place and what it does ( is it to stop a back feed?) and why the starter seems to work fine when I bypass it yet it is reading ok???
Thank you
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Also forgot to mention there is a cable from 14 terminal to A2 of run contractor..

 

[plugsandsparks]

Have you located the cap ? - try testing that first, resistor maybe for safely discharging of cap.

 

[westward10]

Can you show a pic of the motor and it's rating plate. Have you looked at the piece of paper wedged in the back of the enclosure.

 

[davesparks]

Is it definately a single phase starter and motor?
My guess from the picture and description woukd have been that it's a star delta starter.

 

[dlt27]

It’s definitely 240v as no 3 phase on the farm. Capacitor’s are in the motor terminal housing. If it was a dodgy capacitor surely it would be the same even when bypassing the resistor?
I’ve found a drawing now, but struggling to read. If anyone could guide the stages of the starter that would be brilliant. Thank you
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[westward10]

Was going to ask if it was a farm. Sounds like someone has made a two stage starter. What is the motor running is it a heavy load.

 

[dlt27]

Motor plate etc.
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Yes it’s a large motor for the grain. What are the advantages of a 2 stage starter compared to a dol? I presume reduces starting current, but how. Thank you
[automerge]1575311929[/automerge]
Sorry to ask so many questions, but could somebody explain what is the difference between a series parallel motor and a capacitor start/ capacitor run motor as well please? Thank you

 

[Lucien Nunes]

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.

If anyone could guide the stages of the starter that would be brilliant.

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!
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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.

 

[westward10]

Correct me if I am wrong but the motor plate indicates it has always been connected to a two stage starter, the original probably having a manual start to run handle.

 

[Lucien Nunes]

Agreed, Stimmt, D'accord.

 

[Lucien Nunes]

@dlt27 How did you get on? Did you find out anything about the NTC or leave it bypassed?

 

[dlt27]

Where could I find a brimistor to replace the existing one. I’m struggling to find one.
Many Thanks
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This is the what I thought was a 1M ohm resistor that I bypassed. Could it be a brimistor? Thank you
[automerge]1575665726[/automerge]

 

[Lucien Nunes]

That, as you say, is a regular 1MΩ 1W carbon film resistor. But 1MΩ is too high to serve any useful purpose in the starter that I can think of, so I am not sure why it is there. However, looking at where the heat shrink sleeves meet the resistor body, there appear to be solid wires poking out with round flat bits on the end or possibly loops, and traces of a black substance. That would have been the Brimistor, a black rod of NTC material between those two ends. They do sometimes crack apart with age.

First, do you need it? Note 1 on the drawing states it is not needed for units below a certain current rating that I can't read, which probably have different contactors fitted. See whether the present application is above or below that figure.

Next thought, Brook Crompton still exist, I'd give their technical dept a call. They might be able to supply one from stock, or advise a modern equivalent NTC to replace it. Brimistors were just one popular manufacturer's range of NTC's, it doesn't have to be a Brimistor.

NTC's are still available and used in various electronic applications. There are a few dozen standard types, that have different resistances, current ratings etc. Much the same as the Brimistors of old, which were sold in a range of ratings more usually targeted at jobs like limiting inrush in AC/DC valve radios and TVs. If we have to, we can select something suitable ourselves.

 

[dlt27]

Thanks again Lucien Nunes I will hopefully try Brooks Crompton on Monday..

 

[marconi]

I think the 1 MOhm 1W resistor is used to provide mechanical rigidity in the flexible link so that the Brimistor can be placed across it, thereby reducing flexing stress which might damage the fragile end connections of the Brimistor. Without the resistor all the flexing stress is applied to the Brimistor leads. 1MOhm because only a tiny current flows through it so does not change the circuit's operation.

 

[Lucien Nunes]

That sounds reasonable, I have done similar.TBH I had expected the original arrangement to have been a bit more sophisticated like a slice of tagstrip, as the bare ends of the Brimistor can't have been left flapping around. I assumed this was a retro-bodge but perhaps not.

 

[dlt27]

Thanks again. Could anybody send a link for a thermistor/ brimistor that I could use to replace the faulty one..

 

[marconi]

I did some rough calculations which indicate you need a brimstor or ntc thermistor with a cold resistance of about 2500 Ohms. I struggled to find a surge current limiter that might substitute because the max cold resistance I have found so far is 120 Ohms. It would be clumsy to put 20 of these in series. maybe my sums, oiled by half a bottle of Muscadet are wrong.

I did find some old brimistors for sale with a resistance of 3000 ohms.
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Brimistor CZ1 3000 Ohm 20°C STC Thermistor (Rare) | eBay - https://www.ebay.co.uk/itm/Brimistor-CZ1-3000-Ohm-20-C-STC-Thermistor-Rare-/112790433533

THis one drops its R to circa 300 Ohms or lower when hot. Of course it is eventually short circuited but one should not assume that.

 

[dlt27]

Thank you marconi

 

[Lucien Nunes]

My hunch is that the delay on a CZ1 will be too long. I'm not near my STC data book but I think they were popular for 100mA series heater chains, in which they give a gentle 10-20 second warmup. The original part in the starter looks like it had much lower thermal mass, so if the resistance and hence dissipation on 230V is similar, the delay would have been much shorter.

My other hunch is that when a call to Brook Crompton will either get one in the post for a few bob or they'll say 'we always tell people to bypass them, they were never really needed.'

@dlt27, were you able to confirm the motor FLC as per note 1?

 

[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

 

[Scott_fd2r]

Evening guys. I had replied last night but cant see my post anywhere. Dont know whither it went on or not.
Just for info this starter and motor were used together it started and ran without issue. Since then they were disconnected and not marked so i thought the problem to be a wiring mixup but i cant see how else is could be connected using 5 wires. It was definitely connected to a single phase line neutral 230v supply before. It could be that the load was less so this issue didn't show up? The motor and starter are now on a different mill, but it looks very similar in size with pulleys the same size.

today i started the motor by spinning the mill slightly first then starting it. When it is up and running it is doing 1490rpm with the mill running. So pretty much spot on what it should be.
I removed the belts and started the motor to prove the centrifugal switch. I tested between bottom right terminal and A3. Which is closed circuit at startup then open circuit when it reaches speed. I can actually hear the switch open.
This could be useless info but the cables disappearing into the motor are in sleeves cables z2+sw go in the same sleeve an head towards the fan end of the motor. A2+A4+z1 go in a sleeve towards the front of the motor. The rest appear to go in another sleeve.
i did the resistance tests with the supply cables disconnect but have left the paper in my jacket pocket. I will post these readings later.
hope that makes some sort of sense.

 

[Lucien Nunes]

Well it sounds like you are in luck with the voltage, as I can't believe it would slip only 10rpm at half voltage even off load. But it's daft for the plate not to give 240 / 480V options with the two different currents as is normal on a reconfigurable motor. Obviously series/parallel starting is available at 240V but at the nameplate 480V it would have to be DOL as the windings would already be hard-wired in series for running.

So just fix the start winding connections so that the cap and winding are in series, optionally bypass the switch if you trust the starter, and personally I think the start circuit should be across full 230V mains, not connected to the main winding midpoint. Marconi (& anybody else out there) what say you?

 

[marconi]

Scott_fd2r: I have now studied the blueprint for the Brook Crompton Series Parallel starter and arrived at the following advice:

(see attached diagram here and the B_C blueprint in my last message).

1. The motor is CSIR with an integral centrifugal switch - this switch is to be used as it is the reliable way to de-energise the start winding Z at the appropriate speed - so we DO NOT use the starter to switch in/out the Z winding. The connection from the motor Z terminal to the starter is INCORRECT and should be removed.

2. The motor is wired for series-start and parallel run. I will come on to the 480V question at the end. Wire the motor terminals as in the attachment below.

3. The motor is connected to the starter by 4 conductors viz A1, A2, A3 and A4. These connect to starter as A1 to U1, A2 to U2, A3 to U5 and A4 to U6. Top right wiring diagram on blueprint refers CSIR Series 1.

4. Now study the note numbered 6 on the blueprint - read it very carefully and make the connections as in para 3 above, and CONNECT a link between 62 and 54 on Run(RN) contactor - or check that one is there already - this link is required because the motor is using its centrifugal switch.

5. Now study wiring schematic of blueprint above the notes and make sure that at the overload the wiring is done in accordance with the note - 'or cap start/Ind run disconnecvt from 2 and connected to 4.

6. Make sure incoming L and N go to 1 and 5 on contactor C.

7. Check/adjust timer delay so that changeover from series to paralle occurs BEFORE centrifugal switch opens.

8. Energised by a 240V 2 wire supply the motor in the run state will produce less mechanical power than on a 480V 2 wire supply. I'd estimate 25 per cent less so about 2.5kW output. Power being proportional to Vsquared or Isquared. You can calculate it roughly by the product of supply voltage and motor current times a nominal power factor of say 0.8.

9. Caution - the capacitors may need replacing.

 

[Scott_fd2r]

Marconi.
Today i rearranged the cables almost identical to your drawing. However i ended up using the starter to switch the neutral as cables i have coming from the motor didn't allow for exactly what you have drawn.
the cable Z goes from the capacitor and straight into the motor. I have attached a picture or how i have it connected now and it seems to be working as it should start up torque is far better. Timer is set at about 3 or 4 seconds which gives a smooth changeover. Is there any reason why i shouldnt be using the starter to switch out the neutral?

On start up its drawing about 38 amps and settles to around 15 when running on load.

if the rollers are squeezed together too quickly After it reaches full speed the contactors drop out. It doesnt trip the overload they just stop. I never actually checked the voltage to see if it is causing a voltage drop to de energies the coil i doubt that is the case though. Its not an issue as the rollers can be squeezed together slowly giving the idle roller time to get upto speed. I just wondered if there was an obvious reason for this?

 

[Scott_fd2r]

 

[marconi]

Scott - good evening. I'll think on your last post tonight and reply tomorrow - I get up early.

Could you describe/draw how the motor is actually now connected to the B-C starter by reference to the motor terminals (my As1-4 and Zs1-2) and the starter terminals (Us1-4 and Z)? If wiring has been done as I advised then A4 is a permanent N so Z2 can be connected to it - and thus no need for a fifth wire from Z2 back to the starter to connect to N.

I would appreciate it if you could take some voltage measurements at the input to the starter as I mentioned for the stop, start and run phases.

 

[Scott_fd2r]

Thats actually makes perfect sense. Dont know why i never just put a link onto the a4 terminal. Will reply with more info later.
thanks.

 

[marconi]

Good morning. As numbered points:

1. We don't need to use the starter to switch out the N for the Z coil because its N can be obtained from A4 and the centrifugal switch will de-energise the coil when the motor is close-enough to normal running speed for induction only motoring. Being a centrifugal switch it will actually operate at a speed - using the starter would switch based on a time delay.

2. Starting current of 38A and running current of 15A; you can see why series parallel is used to start the motor. The initial starting current would be much higher if both A windings were in parallel abd connected DOL - quite a 'shock' to the sub-main to the motor starter and the supply in general.

3. 15A running - 230 x 15 x 0.8 = 2.8kW electrical power so about 2.5kW mechanical power.

4. That the contactors drop out indicates to me the supply voltage at the starter input terminals is sagging far too much when the motor running current is higher than the normal operating current. This will happen anyway as the motor slows down under load and be made worse still if the centrifugal switch switch closes again. I wondered in one of my earlier posts if the mains supply and the sub-main to the motor starter were 'weak'. Those voltage/current measurements during stop, start and run and then under normal grinding load will provide information on the voltage drop. Could you also estimate the length of the sub-main run and determine its conductor size? We can then do a volt-drop calculation.

5. Could you tell me and perhaps post some photos of the mill machine and tell us what it used for and how it is operated ie: short burst milling or prolonged milling of a batch of grain. I want to consider the adequacy of this motor (I still believe it to be a 480V two wire circa 10HP being operated at 240V now so 2.5kW output. It may well be under-powered for the work to be done unless there is some other problem with the mechanical drive chain, gearbox(?) and mill wheels/rollers necessitating the motor to work harder than it should do.

6. I reckon - in other words what I would do if I was you - that the machine and its wiring and starter needs a thorough checking over including connections, safety interlocks, trip settings, earthing and bonding, bearings, roundness of rollers and wheels - to ensure it is fit and safe for purpose. I recommend you let the client know and secure his approval and funding for these checks.

7. Only 'cos I am curious and it adds to the interest could you tell me where you are in Ayrshire?

8. REMEMBER and USE ALL YOUR TRAINING ABOUT WORKING SAFELY ON ELECTRICAL AND MECHANICAL EQUIPMENT.

 

[marconi]

Today I asked B-C technical department about the release voltage of the contactors used in the starter.

As a rule of thumb the release voltage is between 50-70% of rated operating voltage. Release or drop out is when the contactor coil's holding force no longer exceed the spring pressure designed to open the contacts quickly.

During contactor closure, the reluctance decreases rapidly which aids the rapid rise in the force of closure. But during voltage dips the force of separation may rapidly exceed the force of holding - which opens the magnetic circuit a little - which causes an increase in reluctance which causes a further decrease in holding force - so the spring pressure becomes more dominant.........so the opening widens further.....so the reluctance increases .......

Imagine bringing to bar magnets together N to S and then separating them.

 

[Scott_fd2r]

hello again. yes that all makes sense.

i have added the the contactor connections to my drawing of how the motor is connected just now.
I'm back at work today (at my real job) for 5 days so I wont be back at the motor until next week. i will get some accurate voltage readings at stop, start and run then.

i have no real evidence yet, but i would doubt if the voltage is dropping as much as 30-50% as i would have expected the lights to dim or flicker if that was the case. i have seen that happen in the past when big single phase motors start. i will know better next week after some voltage tests.

i am from a village called Ballantrae in South Ayrshire.

i want to thank Marconi and lucien nunes for all you help and advice. the whole thing could have been flung in the skip by now if it wasn't for you input