Motor starter 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