Motor starter help.

[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

 

[marconi]

The guru on old electrical equipment is Lucien not me. I just like the odd electrical problem to mull over to keep the grey cells firing. I've probably stood on his toes on this one - sorry to him.

EF folk may be interested these links on Newman electric motors:

http://vintagemachinery.org/mfgindex/detail.aspx?id=9415

https://www.gracesguide.co.uk/Newman_Industries

https://www.yateandsodburyvoice.co.uk/the-history-of-newman-industries-of-yate

 

[Scott_fd2r]

hello again.

today I was back at the motor,
the voltage is only around 220v at the starter. during starting this can drop to around 212v, during running its is around 218v.

everything has been ok since i was last there, but i am told the mill/bruiser throughput is less than with the previous motor. i did some load tests. the motor draws around 36A at startup and quickly settles to around 11A. as the grain flow is increased the load rises to around 15A. at this flow the operator says it will run constantly with no problem. if the flow is increased further the load can rise to around 20A but at this rate the current is very unsettled jumping from 18-22A the voltage remains steady at 218v. if the flow is increased by just a fraction more the load jumps to 30+ amps and the motor stalls and sits humming until it is stopped or trips.
the rpm never alters much from 1400 just drops immediately as the current shoots up and the motor stalls

i checked the current on both windings at each stage and the windings appear well balanced with the currents exactly the same at each stage. (half of the total load drawn).

they are happy to leave it like this for now and run with a reduced flow rate until the other motor is rewound and refitted. just posted this info incase anyone was interested

 

[Pete999]

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
[automerge]1575303628[/automerge]
Also forgot to mention there is a cable from 14 terminal to A2 of run contractor..

Is this a SP OR TP Motor?

 

[Lucien Nunes]

Its single-phase, but it turned out to be a 480V motor that had been installed second-hand as a replacememt by mistake on a 230V supply and also incorrectly wired internally at the time the OP first encountered it. The behaviour is consistent with the voltage mismatch, as at 1400 rpm it's running below rated full load speed even at moderate load. Unfortunately an earler measurement of the speed in post #41 indicated it was reaching 1490 rpm off load which suggested the voltage was correct.

Thanks for the update @Scott_fd2r, it's good to hear the original motor is being rewound.

E2A Pete that first post was actually about a different motor from last year

 

[marconi]

Re:
today I was back at the motor. the voltage is only around 220v at the starter. during starting this can drop to around 212v, during running its is around 218v.

The off-load supply voltage at the starter is somewhat low at 220V. Is this the voltage at the input terminals of the main switch for the building? Does the building have a high current demand from permanently energised loads which is causing a significant voltage drop? What voltage does the incoming supply rise to when the building's main switch is opened?

As a simple rule of thumb the power of a motor is proportional to Vsquared so a motor wound for 240V would produce about (220/240)squared = 80% of its rated power output. Is the motor powering the machine often required to operate at rated power? Could this be a factor in why the previous motor burnt out? Some thought then into what voltage to rewind the motor to operate at.

And an investigation as to whether the incoming supply is 'weak' because of some external high resistance connection. What for example are the line-neutral voltages in neighbouring buildings using the same DNO distribution cables - could you measure these?

 

[Farmspark]

Evening, I have a similar issue with a grain mill where farmer has given me a 5hp motor and this starter box. Connections to A1,A2,A3 and A4 seemed straight forward but the 2 capacitors in series that go through the first stage contactor on left (red and white wire in con block) I am unsure of terminals to attach to on motor. Any help please? They come out of connection on second stage after a 4 second timer.
Stage 1 main contactor (with O/L) and left contactor go in, controlled by timer on left. Stage 2 middle contactor and main contactor go in.
thanks in advance

 

[marconi]

Evening, I have a similar issue with a grain mill where farmer has given me a 5hp motor and this starter box. Connections to A1,A2,A3 and A4 seemed straight forward but the 2 capacitors in series that go through the first stage contactor on left (red and white wire in con block) I am unsure of terminals to attach to on motor. Any help please? They come out of connection on second stage after a 4 second timer.
Stage 1 main contactor (with O/L) and left contactor go in, controlled by timer on left. Stage 2 middle contactor and main contactor go in.
thanks in advance

Do you still want help with this or have you fathomed it out already?