3 Phase Saw Assistance

[jsjwilson]

Dear uk workshop friends,

I am seeking some advice on getting my saw up and running. Its a TA450 Sedgwick 3 phase saw which was seen working before purchase. After transport, it has sat in the workshop for a few months awaiting rewiring of the old 3 phase wiring (which needed replaced as it was unchanged from a previous large saw mill saw from the 1950s/60s). Rewired, all 3 phases are present with a new isolator which is working, and there is a new 3 phase board in place too. The first time I tried the saw, the blade turned a revolution, then clicked and stopped, and has not worked since. Now, when trying to start the saw I get a click and then a hum, but no blade movement. I can move the blade mechanically, though it feels as though you are pulling through some notable resistance of a ?magnetic field, which I presume is how it should feel. I've tried swapping one phase for another, which didn't work, but produced the same click and hum. I have opened the starter/brake, which I confess I didn't think to do on purchase as the saw appeared to be working. There is some water damage on the left hands side on the contactor/overload side, but the brake PCB on the right looks pristine. I'm struggling to find a local maintenance sparky. There is one listed in my area, but I can't get ahold by phone or email. The guy who did the 3 phase rewiring said he could have a look, but then said it was beyond his ability to run a diagnostic, but pointed out what he thought was water damage on the left hand side. I spoke to Crompton who have said the contactor and overload are not replaceable, and advised if these are the issue I will need an entire new starter/brake quoting me >£800, which is more than the cost of the saw. I have also had through facebook marketplace an offer for me to courrier the starter/brake to get looked at and repaired. However, I am unsure about this and it has concentrated the mind, and I am wondering whether I should try and work this out myself (though my electric skills are confident DIY level, or those from school >25yrs ago.

I've read a few threads where others have faced similar issues, though mostly this has been around replacing a motor, or converting to single phase. I would really appreciate any help that could be offered on running a diagnostic and how to work through to getting this saw up and running again. I can post pictures as required. Any assistance appreciated.

 

[Chrispy]

How long have you left it powered up?
The hum and resistance sounds to me like the electric brake, this will engage when first powering up the saw, it should cancel out after 20 or 30 seconds then you should be able to start the saw.

 

[Spectric]

The first thing you will need is a full circuit diagram of the machine which will itself guide you through the fault finding but 400 volt three phase is not something you want to be working on unless you are competant and can proceed safetly as it can be lethal. What you need to do when fault finding is to only have one hand / probe in the machine and the other with no contact as this will prevent a hand to hand shock which must be avoided.

So with the electrical diagram fault finding could start, and have you gone through this

 

[Spectric]

Is this the controls and wiring ?

 

[jsjwilson]

This is the circuit diagram, which was tucked inside the starter, on the left hand side, between the inside of the casing and the Contactor and Overload. I am not sure if the burn marks on the diagram might offer any clues?!

 

[Sideways]

A generic contactor + thermal overload can be bought new for under £40.
A DC injection brake is typically several hundred pounds, (or £250 for a good used one such as I sold on ebay a year or so back).
Just so that you understand where the value lies.
It would grieve me to swap out a potentially good, high value device for the sake of a couple of commodity parts.

It sounds to me also as if the configuration of the brake is the issue here.
With all the caveats about 415v 3 phase being dangerous to meddle with if you lack the experience, tools and test gear, the way I would be inclined to fault find is
1. Turn off and unplug the saw.
2. Photograph all connections, sketch out and confirm that the wiring is in accordance with the diagram (hasn't been meddled with).
3. Educate yourself on how a DC injection brake works, get the details of the one in your saw and understand how to set up the timers and currents.
4. If this insight doesn't let you identify what is the problem, I would disconnect the brake completely from the circuit and just prove that the saw is OK working with a simple DOL starter circuit, even if you have to spend £40 and buy a new one to wire in temporarily.
Fault find the brake afterwards.

If this is outside your comfort zone, don't meddle with it.
3 phase voltages will kill you without warning or remorse and your loved ones will have to live with it.
Find an industrial electrician.

 

[Spectric]

If this insight doesn't let you identify what is the problem, I would disconnect the brake completely from the circuit and just prove that the saw is OK working with a simple DOL starter circuit, even if you have to spend £40 and buy a new one to wire in temporarily.
Fault find the brake afterwards.

That is how I would proceed to confirm the saw functions and then look at setting up the DC brake later which will mean less to look at.

 

[Billy_wizz]

Is it wired the right way? As I've had issues with machines wired backwards!

 

[jsjwilson]

Th

A generic contactor + thermal overload can be bought new for under £40.
A DC injection brake is typically several hundred pounds, (or £250 for a good used one such as I sold on ebay a year or so back).
Just so that you understand where the value lies.
It would grieve me to swap out a potentially good, high value device for the sake of a couple of commodity parts.

It sounds to me also as if the configuration of the brake is the issue here.
With all the caveats about 415v 3 phase being dangerous to meddle with if you lack the experience, tools and test gear, the way I would be inclined to fault find is
1. Turn off and unplug the saw.
2. Photograph all connections, sketch out and confirm that the wiring is in accordance with the diagram (hasn't been meddled with).
3. Educate yourself on how a DC injection brake works, get the details of the one in your saw and understand how to set up the timers and currents.
4. If this insight doesn't let you identify what is the problem, I would disconnect the brake completely from the circuit and just prove that the saw is OK working with a simple DOL starter circuit, even if you have to spend £40 and buy a new one to wire in temporarily.
Fault find the brake afterwards.

If this is outside your comfort zone, don't meddle with it.
3 phase voltages will kill you without warning or remorse and your loved ones will have to live with it.
Find an industrial electrician.

Thanks for all your comments. Thanks too for the concern for safety. I appreciate this as I have had 2 mains shocks and I wouldn't want anything worse! One not my fault, working on a building job as a 17yo removing an old built in bookshelf which I'd lifted heaved up, and slapped my hand round the back of to get purchase unwittingly slapping a naked live wire with my sweaty hand, a wire in which there was a ft of bare copper. The second entirely my fault, losing track when working on a power amp rebuild in my early 20s. I definitely do not want to risk a 3 phase shock. I am struggling to find a maintenance/industrial electrician, but will keep persevering with that. It was the possibility of disconnecting the starter and sending it away that made me think, is there some basic testing assessment I can do before sending this away. However, if your gut is that the brake card may be the issue, I will need to find someone who can come and assess this.

 

[Ollie78]

Is it wired the right way? As I've had issues with machines wired backwards!

This happenned when our 3 phase saw was installed, quite scary when we tried to put the first test bit through !!

 

[Sideways]

Be aware, there may not be anything wrong with the DC brake. They are a device that have to be configured for the specific motor and application. This may have been done wrongly or inadvertently changed.
Don't assume it is defective until you have identified it, obtained the datasheet and understood how it works and consequently how it should be set up in the TA450.

 

[Sideways]

Here is an explanation of the principle behind DC injection braking

https://electrical-engineering-portal.com/methods-braking-motor

The key concept is that a dc voltage that is much lower than mains voltage is connected across any two of the three motor wires and this creates the braking action.
In general terms a brake module needs to
1. create this dc supply (so it effectively contains a dc power supply)
2. let this be adjusted (braking voltage is adjustable - upto 20 or 30 volts perhaps) with higher voltage giving more braking force so for larger motors and faster deceleration. You have to set this.
3. provide one or two timers - you have to set these too or turn them off.
4. provide control logic - the module must ensure that the DC braking voltage isn't connected at the same time as the 3 phase supply and is connected when it is wanted.
Brakes are general purpose devices used on all sorts of machines. Not specific to a Startrite saw. In some applications you want a brake to be applied before the motor starts - to hold the motor and machine stationary say for loading (vehicles, lifts, conveyors...). The brake then has to release, the motor to run, the supply to be switched off and the braking voltage connected instead. The brake maybe applied for a presettable time - a burst of 5 or 10 seconds only or many seconds allowing the motor to fully stop and then remain locked stationary for a period of unloading or disembarkation.

From the symptoms described, the brake may be holding the motor stationary before starting which is unnecessary in a table saw. It may be set too strong. It may be set to hold the saw stationary after stopping - again unnecessary in a table saw - instead of just being applied for just the 10 sec that a table saw is required to stop within, and only braking as hard as needed to bring the blade to firm stop inside that 10 sec, not trying to crash stop it within a couple of seconds, stressing the electronics, the machine and unscrewing the blade off the arbor due to inertia !

 

[jsjwilson]

Thanks. Does it matter which phases feed the break card?

 

[Sideways]

I can't speak for your brake so check the datasheet when you track it down.

I imagine it will take any two phases (from L1, L2 and L3) and it won't matter which as they are all equivalent.
It wouldn't make sense for it to require one phase and neutral as the rest of the motor won't need a neutral, but if it did, that's a 240V input and won't be happy being fed with 415v.
It may, for convenience of switching or wiring, draw it's own power from whichever two phases it is going to feed the DC into at the motor, but then again, it might not.

What you are seeing here is :
"I don't know. It may well differ from one model to another. It is prudent to think about how any given brake may work and then check these details for the one you have."

That's the generic stuff.
Now, looking at the circuit diagram you uploaded, there are two circuit boards. One takes power from (probably, it's hidden by the scorch mark) L1 and L2 and makes DC from it. This card has a potentiometer where you need to adjust the DC voltage to match your braking requirements. To start with, I suggest you turn the pot all the way anti clockwise and then turn it back up to 25%. Enough that you should be able to notice some effect.

The second card is the one that does all the control logic. The schematic shows only one timer adjustment on that card, so for testing I would turn it all the way anticlockwise (effectively off). Once you get the motor running you can turn that up a little and apply a few seconds of braking.

Note that there are two contactors. C is the one that connects the 3 supply phases to the motor. The coil for C is shown near the brake control card in the schematic as a box labelled C1 with it's terminals A1 and A2. A second contactor BC, when operated, connect power from L1 and L2 to the brake power card, it also connect the DC out from the card to the corresponding motor terminals. Contactor BC is activated by the brake control card energising it's coil (box labelled BC1 with terminals A1 and A2) for however many seconds you set on it's timer.

Note there are a couple of switches labelled C2 and C3. These will be auxilary contacts of the main contactor C.
C2 is wired in parallel with the start pushbutton and performs the no volt release function. It holds power onto the contactor coil when you let go of the green start button.
C3 is used to ensure that the coil of the BC contactor cannot be energised and DC connected unless the main contactor C has been turned off and the 3 phase supply is no longer connected to the motor. It's a safety interlock function.

Lastly, all the control wire colours are labelled in the diagram. Red (RD) Black (BK) Violet (VT) White (WH) Blue (BU) Grey (GY) etc. That should help you check the wiring wire by wire to ensure that nothing is different from what the schematic says.

Good hunting

 

[Billy_wizz]

This happenned when our 3 phase saw was installed, quite scary when we tried to put the first test bit through !!

Lol that's always fun but they should of checked really! To be fair I was thinking more about some of our newer machines that refuse to do some or all of there actions when wired the wrong way!

 

[Vann]

...Rewired, all 3 phases are present with a new isolator which is working, and there is a new 3 phase board in place too...

When you say all 3 phases are present, have you been able to check that, since you found this fault?

The reason I ask is that I had a similar issue when one of the phases dropped out at my place. Turns out it was a blown pole fuse (I assume you have those in the UK)

However, I don't have electric brakes on any of my old machines.

HTH.

Cheers, Vann.

 

[HOJ]

I had a look in the starter housing, on mine, but it is a newer version, so a different arrangement for the braking, with no circuit boards in the housing, so presume the on the motor itself.



As @Vann has said I would certainly be rechecking to see if you have a phase disconnect.

 

[jsjwilson]

Thanks again for the assistance. I took the advice offered and managed to get an industrial electrician to visit. He identified the fault as the contactor, and one of the phases remaining open. He says he can't source a replacement through his typical suppliers and will need to search the Internet to try and ID one or replace the whole starter.
Will try and find an old contactor if I can. Anyone know where best to search?

 

[HOJ]

He identified the fault as the contactor,

Not teaching here, but, Is he sure its not just the coil? and also, has yours got a remote stop button, mine is a pain as it locks in, big mushroom one, I keep catching it with my foot, you need to turn it to release.

 

[Spectric]

What is the problem sourcing the contactor, they are readily available with a range of coil voltages and auxilary contacts ?