3 Phase Saw Assistance
- Thread starter jsjwilson
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Maybe the easiest option is to fit a new DOL starter as sideways has mentioned which will come with the overload, just needs setting to suit your motor and this will resolve all your issues rather than looking to just replace the contactor itself.
HOJ
Established Member
Sure, but, I think Sideways suggested this as a method of getting the saw working allowing fault finding with the brake, thay being where he suspected the fault may be. Fitting a new DOL would get the saw working, but would leave the saw without a brake, which isn't ideal, which the industrial electrician I have now sourced was quick to remind me. What I am struggling to do is marry the view that contactors, coils etc are generic readily available parts with the view of crompton and now the electrician that these are not available for this saw.
HOJ
Established Member
Did the Sparky get it running by disconnecting the brake electrics?, (I can't tell you on here, but other test methods are available, sparks should know how)
At the moment the saw is not working and therefore the brake cannot work, with the saw working then you check to see if the brake is working. The brake operates when there is no power to the motor by injecting Dc into the motor and there is the possibility that there is nothing wrong with the brake.
OK. So the DOL components won't fit in the old box, so you are talking about a new box. So do you mean running wires to and from the new to the old box to connect up the brake?
Looking at your diagram the main contacts are C with the overload on the motor supply, the 400 volt coil for this main contactor is C1 with one end connected to L1 . When you push the start button the other end of C1 will connect to L2 via the RESET contact, the N/C STOP button and the Brake control card on that Red wire via pins 3 & 2/4. This pulls in the main contactor C and auxilary contacts C2 & C3. C2 shorts out the Start button to maintain the circuit when the Start button is released. C3 is telling the brake control card that C1 is energised and the machine is working. When the STOP is operated C1 loses power and the main contactor C opens to stop the machine, at this point C3 opens and the brake control card loses power on pin 7 and knows the machine has been stopped so will now power the brake contactor coil BC1 via pin 1 which brings in the brake contactor BC . This connects the power card to 400 volts from L1 / L2 and injects a Dc voltage into the motor on L1 / L2 . With a three phase supply the motor has a rotating magnetic field that causes the motor to rotate, with a Dc input it creates a fixed magnetic field that will stop rotation and the amount of Dc injection will determine the rate of motor deceleration.
So it is possible to replace C with a new DOL starter that would be external to the existing enclosure and wire into the brake control card but you need to confirm that C is the root cause of your problem. Now if this was my machine this is how I would proceed.
1) Disconnect the grey wire from terminal 13 of the power card to disable the brake.
2) Is the main contactor C pulling in when you hold the START button in ?
If Not
3) Now with a decent DVM and test leads, set to measure Ac connect between A1 & A2 of C1 coil.
4) Operate the Start button and you should see 400 volts present which shows that C1 is powered.
5) ISOLATE the supply to the machine and measure the coil impedance between A1 & A2 of C1, if open circuit replace.
If C is pulling in but as suggested not all three contacts then again replace, but also are the auxilary contacts C2 & C3 pulling in ?
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