Tom Senior Milling machine running problems

[Paul RadfordParticipant @paulradford79614]

Hello again! I’m relatively new to this after getting a Tom Senior M1 milling machine this year. About a month ago it stopped running and thought it was the starter switch. Had an electrician out who said the Transwave converter was faulty. I bought a new static converter and had a new starter switch fitted. It ran for 10 mins then burnt the starter switch out. I swapped the converter for a rotary one as was told they’re more reliable. Had another starter switch fitted. It ran for about an hour and burnt the starter switch again! It’s got a 1hp motor (1.6amp) and the rotary converter is 2.2. The thermal overload in the starter has been changed to 1.6-2.5 amps. Any ideas what’s going on here please? The electrician has said we could fit a rotary isolator to see if this helps. I’m cautious with electrics because it’s not something I know much about and obviously want a machine that runs but safely too! Thanks Paul

[Chris CrewParticipant @chriscrew66644]

If the first Transwave was suspect you maybe should have contacted the manufacturer in Birmingham who, when I had an issue with one of their products, was extremely helpful and it was resolved. I can’t offer any ‘technical’ advice on the electrics because I am not qualified or knowledgeable enough but when I have a problem I try to apply logic and common sense. So, if the problem is common to both your new static and rotary converters I would suspect the motor as the common denominator. I am certain other more knowledgeable people on here will tell you how to check the windings properly but as a quick check I would just put an AVO across each coil just to make sure there is continuity and the readings across all three are pretty much the same, it might just provide a clue, or you could take it to a local rewinder for a proper diagnosis. Transwave statics are robust and reliable, IMO, I have used three of them for over 25 years with no real problems. Given that you have spent a considerable amount of money on a new static and a rotary converter I might consider changing the motor for a single phase and selling the converters to cover the cost.

[Dave HalfordParticipant @davehalford22513]

Sounds like your electrician is playing poke and hope with your money.

The motor will pull what it needs, in this case possibly more than it should.

Please post photos of the starter and the internal wiring.

[Dave WoottonParticipant @davewootton]

By starter switch I’m assuming you mean a no volt release contactor type, is it the switch contacts that are burning out or the operating coil or overload? The more information you can give will make it easier for someone on here to help diagnose the fault remotely. As an initial check if you can get hold of a multimeter is as Chris says above continuity of the windings, that they are correctly connected in star for 415V , the contactor coil is the correct voltage rating, and all other connections in the whole machine are sound. When the motor runs does it run quietly and at an apparrenly normal speed? just thinking it could be two phasing. Sorry if this seems to have more questions than answers but it might help reach a diagnosis. Like Chris I’ve run machines on static converters for years with no problems, and yours should run perfectly on a rotary one. Perhaps if you have one in your area you could remove the motor and take it to a rewinders for checking out, good luck. Is your electrician conversant with motors and controls? agree with Dave above it does sound a bit poke and hope.

Dave

Might help if you put your approximate location you might find someone knowledgeable nearby.

 

[SillyOldDufferModerator @sillyoldduffer]

I don’t like the news that starters are burning out.   What make and model were they?  Their purpose is to protect the motor against high current during the start-up phase, and I would expect the thermal cut-outs to operate without drama if the problem were simple.

First thing to check is that the mill turns freely.  If a bearing is binding, or some other drive train fault is loading the machine heavily before it starts, then maybe the motor is already horribly overloaded before being asked to cut metal.   Also, how hard was the mill being driven, and for how long?  As a 1HP mill isn’t a metal muncher, the operator has to drive it with TLC, and a learner might not recognise a difficult material or blunt cutter etc etc.

When the motor was running, did it turning smoothly, without odd noises or getting hot?

I fear the motor has one or more shorted windings, and this is overloading the electrics and doing nasty things to the converter.  I’m not sure what happens to a converter when one phase draws excess current.  Maybe that phase’s thermal cut-out operates leaving the motor running on only two phases, which is bad news.   I imagine a static converter would misbehave badly with an unbalanced load, and so would a rotary, depending on which phase had failed.

Chris’s suggestion that the resistance of the 3 windings be measured is a good one.   With the motor disconnected, all three windings should have the same resistance.  A DC resistance check may not be conclusive though, because the short might be quite small, only causing havoc when AC is applied.

The electrician may be on a steep learning curve himself.   Not many domestic sparkies have to debug 3-phase motors, and not many industrial sparkies run 3-phase motors off static or rotary converters!

Dave

[Paul RadfordParticipant @paulradford79614]

Thanks for your replies! I’m based in Lichfield Staffs. It’s so frustrating because I’m new to this and desperate to get going! I’ll attach photos of the starter switch and motor after as it keeps deleting the post! 🤷🏻‍♂️ I think the machine may not have had much use recently as the gentlemen I purchased it off wasn’t well. I cleaned it up to the best of my ability and it ran well initially for about a month. The motor runs quietly and I’m careful not to force the machine. The transwave that came with it was looked at by a local company who said it wasn’t viable to repair and quoted £2500 to repair!! Thanks again Paul

[Paul RadfordParticipant @paulradford79614]

[Paul RadfordParticipant @paulradford79614]

[Paul RadfordParticipant @paulradford79614]

[Chris CrewParticipant @chriscrew66644]

“The transwave that came with it was looked at by a local company who said it wasn’t viable to repair and quoted £2500 to repair!!”

Some companies quote ludicrous prices because they simply don’t want the work, or don’t know what they are talking about, but won’t say so directly. Transwave statics are very simple devices, they simply place a capacitance across one winding of a three-phase motor and temporarily increase it to gain sufficient starting torque. I have configured a circuit like this myself on an ex-school Boxford shaper simply by following the information contained in the Workshop Practice book ‘Electric Motors’.

If you are in Lichfield you are not a million miles from Tyseley where Power Capacitors are based. They are the first port of call for all things Transwave. My understanding is that static and rotary converters are now old hat. The way to go is with an inverter with a 3-phase motor, but what do I know? It took me 3 hours to set up our new smart TV this afternoon!

That being said, if you have a little more confidence in your own judgement and common sense you will find that you know more than you ever thought you did, trust me!

[duncan webster 1Participant @duncanwebster1]

I suspect a Transwave static converter has an auto transformer to produce 415v and both start and run capacitors in a sort of Steinmetz arrangement for the third phase. Then you don’t need to rewire the motor to delta.

I’d just fit a new motor and VFD. You can get a prewired package that you just bolt on, no electrical knowledge needed.

 

[noel shelleyParticipant @noelshelley55608]

DID it work on the transwave when you bought it ? DID YOUR ELECTRICIAN UNDERSTAND 3pHASE ? Is the motor wired star or Delta eg 240v or 415v Get an electrician to check the resistance of the 3 coils and put a insulation (megger ) tester on the motor. If that is sound and there is no excessive load be it bearings gone or the machine working to hard then The motor should be good. The whole point of the overload cuttout is to drop out at the right setting – in this case 1.65A Not 2.5A. wiring 240v ac to transwave, then the starter then the motor. IF it has laid about unused and got damp moisture could have taken out the windings ?. Will come back to this later ! Noel.

[duncan webster 1Participant @duncanwebster1]

1.65 A is full load current, cut out must be higher surely or the motor wouldn’t develop full power.

If the switch is on the mains side could it be drawing even more current?

[Martin Johnson 1Participant @martinjohnson1]

From what is described, it is drawing too much current and so frying the switchgear.  I would be checking that you have 3 phase power.  Given that you seem to have burnt out two converters, I would certainly be checking for continuity on all 3 phases of the motor, plus all the wiring.

Does it run a bit rough and have trouble starting?

Martin

 

[noel shelleyParticipant @noelshelley55608]

For those who do not know how an overload device works it is a thermal device that will take the start current for a few seconds, enough to spin the motor up to speed ! If the start current doesn;t drop or there is an overload situation then again it will drop. and may need to be reset before another go can be had ! It sounds to me that either A the motor is faulty or things are wired up or set wrong. On some motors the start current can be 1200% above running current so it is obvious that a fuse is a waste of time, hence the overload device ! Noel.

Duncan is right about transwave statics, a bank of capacitors, an autotransformer and a boosting device to help the start up..

[Paul RadfordParticipant @paulradford79614]

Thank you for all your responses! The issues since the new converter was fitted was due to the wrong size starter switch being fitted as a 240v starter was used instead of a 415v! Fingers crossed all is well now! Thanks again! Paul

[Author]

Posts