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G

gorilla

Hi Guys

Needing some help here, I am possibly going to need to source a three phase starter in the very near future. Only problem is the machine that the starter is attached to is ancient.

To give you the scope of the issue, my dad has a old table saw in his work shop and it has a three phase motor to power it. When we try to start it the hold on contact doesn't hold so it stays on.

Now I have two main theories and one of them is the contactors/starter is knackered and needs replaced, the other is there is a issue with one of the phases, now I have had a quick look and see to see if I can spot any potential causes initially I thought it was needing a clean out due to sawdust build up, so I done that as well as made sure all connections were tightened and the contactor was moving freely and all was fine. No signs of any damage to any parts everythign looks good.

That is where I decided to stop and put everything back together, I am not messing around with 3 phase when I don't know much about it, I can do most of the theory and that but in practise I prefer to have a qualified electrician with me when I need to do these sort of things.

I don't have any model numbers as of yet as I couldn't get any. I will try and get some in the next few days, don't think it matters much really as with Christmas being next week I doubt we will need to use it and also doubt we will get our spark up of his backside to have a look as he is now off for Christmas he has strictly stated that if anyone bothers him this Christmas he won't be happy.

Also what other issues could cause the contactor not to hold on? I kind of thought the cold could play a part but in the past years we have been colder and it has worked, really for this time of year the workshop is warm.
 
Sounds like a faulty contactor to me, if it has an overload then that could be at fault. Obviously being an old machine it's hard to say what additional safety mechanisms may be fitted, modern ones have switches to ensure the guards are in place.
It could also be an issue with an emergency stop button (if fitted) a loose connection in this will cause the symptom you describe, possibly a return spring not functioning?
 
Sounds like a faulty contactor to me, if it has an overload then that could be at fault. Obviously being an old machine it's hard to say what additional safety mechanisms may be fitted, modern ones have switches to ensure the guards are in place.
It could also be an issue with an emergency stop button (if fitted) a loose connection in this will cause the symptom you describe, possibly a return spring not functioning?

No emergency stops, no fancy electronics or switches for guards. Proper old school gear that usually never fails. To me it has got to be the contactors I can't see it being anything else.
 
The contactor shoud have an auxilliary set of normally open contacts that are wired in parallel with the start button to work as follows:
1) When the start button is pressed the contactor energises
2) When the contactor energises the auxilliary contacts close
3) The auxilliary contacts then provide a path past the start button to hold the contactor on untill the stop button is pressed.

Might be worth checking the auxilliary contacts to make sure they close when the contactor is energised.
 
The contactor shoud have an auxilliary set of normally open contacts that are wired in parallel with the start button to work as follows:
1) When the start button is pressed the contactor energises
2) When the contactor energises the auxilliary contacts close
3) The auxilliary contacts then provide a path past the start button to hold the contactor on untill the stop button is pressed.

Might be worth checking the auxilliary contacts to make sure they close when the contactor is energised.

Didn't see a auxiliary set, had a good look at it and all I could see was the 3 phase contactor set.

Just a bit more info on the age of the machine just so you get more of an idea of what we may have. It is around the 40 to 50 year old mark and it is still the best table saw we have used, usually no issues with it. Unlike our friends modern electronic machine, he has had a good few issues with it and only had it about 4 or 5 years. This is the first major electrical issue we have had with it since we have owned the business and that has been about 15 years, maybe longer, and from what it looks like it is still the original starter panel and contactor set.
 
If there is just the one contactor then it's DOL (direct on line) and if there is no transformer in the enclosure the contactor coil will be either 380/440v off two phases or 220/240v off a single phase and neutral. If 220/230 check the continuity of the neutral to one side of the coil and live to the other. If the contactor has a cover with start/stop buttons on it, take the cover off and try pushing the contactor in with a stick, and see if the saw spins up as it should. If not then it might be a phase down either in the saw motor or a fuse. Also while you have the cover off, see what the buttons push and try pushing them with the stick to see what happens. It is possible that it is just the contactor coil that is fried but given the age of the starter you might need to replace the whole contactor. Prices don't need to be frightening, I have both new and used enclosed contactors at very silly prices. PM me if you need more info on them..
 
If there is just the one contactor then it's DOL (direct on line) and if there is no transformer in the enclosure the contactor coil will be either 380/440v off two phases or 220/240v off a single phase and neutral. If 220/230 check the continuity of the neutral to one side of the coil and live to the other. If the contactor has a cover with start/stop buttons on it, take the cover off and try pushing the contactor in with a stick, and see if the saw spins up as it should. If not then it might be a phase down either in the saw motor or a fuse. Also while you have the cover off, see what the buttons push and try pushing them with the stick to see what happens. It is possible that it is just the contactor coil that is fried but given the age of the starter you might need to replace the whole contactor. Prices don't need to be frightening, I have both new and used enclosed contactors at very silly prices. PM me if you need more info on them..

Not as easy as that though, the contactor set is attached to the face plate for the start/stop buttons. I thought of that but decided against it. I haven't done any live testing yet and don't plan to until I have our electrician there, as I said theory on the operation of them I can do easily but putting that in to practice is a little bit different.
 
You can still check your continuity with the power off and manually pushing the contactor.
You still need to establish that all phases are live going to the contactor and that the neutral is connected if the coil is 220/240v.
By your description it's time the contactor was retired and replaced anyway. What sort of HP/Kw are we talking about.

3 phase starter/contactors {filename} | ElectriciansForums.net
example -- Allan West starter/Isolator 230v coil. £20.00 + P&P
 
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You can still check your continuity with the power off and manually pushing the contactor.
You still need to establish that all phases are live going to the contactor and that the neutral is connected if the coil is 220/240v.
By your description it's time the contactor was retired and replaced anyway. What sort of HP/Kw are we talking about.

3 phase starter/contactors {filename} | ElectriciansForums.net
example -- Allan West starter/Isolator 230v coil. £20.00 + P&P

I was just thinking of doing the replacement route, saves hassle in the long run really. I haven't had a chance to get a look at the ratings plate yet. Will try and get that soon though. Just know we have a 3 phase motor that is on the large sort of size, (12" Diameter) with a knackered starter/contactor set.

Is it a manual motor starter you have see link below, not seen many contactors fiitted straight to a faceplate

http://www.electrika.com/products/m/man-0170/pdfcat/c-07-183.pdf

if it is you may have a faulty under voltage release if fitted or a faulty starter

Nothing like them and none of them will do by the looks of it. Basically we have the start and stop push buttons on a face plate on the machine case. Attached to the rear of the face plate we have the contactor set. Don't think I can take the contactor set off the face plate easily.

I was thinking under voltage issue but I doubt that as we do get the motor kicking in and sometimes the contactor will hold on for a minute or so before throwing off. Still could be under-voltage issue but I doubt it. Just a nice little issue to test me.

I will get some pics up soonish
 
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Sounds like your problem is an overload problem bot to replace the starter wouldn't be a big job you could even leave the original front plate on just disconnect the wiring to the motor and take to the new starter as in the Alan West starter
 
Sounds like your problem is an overload problem bot to replace the starter wouldn't be a big job you could even leave the original front plate on just disconnect the wiring to the motor and take to the new starter as in the Alan West starter

Problem with most of these old starters was that there was no overloads fitted so they just stayed connected until you switched them off,or a fuse or fuses blew, usually when the smoke from the motor was blinding you.

The motor and starter would obviously still need to be checked for shorts/broken windings/connections etc. before any new kit was fitted.
 
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Just thought I would update this, problem has been diagnosed by our spark, and it was nothing serious just that the starter's contactors are needing replaced. The actual motor is in good working order for its age, just now it is working as the contactors have been cleaned up and things set so that it will work but that will only last until our spark returns from his job offshore where he will probably be nicking someone's contactors and leaving them wondering what is wrong.
 
Sorry to come in so late.
Don't think you have an electrical fault.
The contactor seems like the Allen West type with hydraulic damper dashpots. Little cups under cutout coils. Unscrew cups and check piston and plunger. Should be clean and have approx 1/4" light oil in cup.
If cup is empty or oil is low, over current lifts piston and the plunger unlatches 'hold' mechanics. Contactor won't hold.
3 phase machines have three cups. Depth of oil (or travel of piston) sets the over current trigger point. Adjusting the height of cup sets the point. Don't overfill. Fill to height of 'sleeve' with piston in place.
Regards.
 
Problem with most of these old starters was that there was no overloads fitted so they just stayed connected until you switched them off,or a fuse or fuses blew, usually when the smoke from the motor was blinding you.

The motor and starter would obviously still need to be checked for shorts/broken windings/connections etc. before any new kit was fitted.

This may be an old post, but i have to say, i've been around in this industry for a long time now, and i've never once seen a motor starter without some form of O/L protection, be they Oil Dash pot or the Bi Metal variety... (Well tell a lie, Electrical Em fire pumps, that have designed to run to destruction won't have any such protection ) What would be the point of a motor starter without a means of an adjustable O/L ?? You may as well run the motor directly off the old fuses. But then, the O/L's would have protected the motor to some degree, (depending on the close setting of the O/L's) against single phasing, when one fuse had blown...
 

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