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Topic Title: Adding contactor to inverter three-phase output
Topic Summary: Avoid contactor drop out when reversing direction of rotation
Created On: 10 February 2019 12:12 PM
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 10 February 2019 12:12 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

I bought a large three-phase pillar drill to run in a single phase workshop. Using a single phase to three phase inverter (Yaksawa J1000) it runs nicely.

I'm considering adding a contactor to the 3-phase side. I'd like to be able to open a switch in the emergency stop button or guard interlock safety circuit I'm designing and building and have the contactor open which is relatively easy enough. But I'd also like to be able to reverse rotation using the inverter control circuit but am I right in assuming the contactor will open at the point of rotation reversal when, I again assume, current ceases to flow? if so can this be avoided?

I know I can switch direction using contactors alone, but then the inverter won't know if its rotating forward or in reverse. I'd rather keep control at the inverter and safety function at the contactor separate.

(I'm a registered electrician and currently working as a safety engineer)

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jonathan d
 10 February 2019 01:28 PM
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alancapon

Posts: 7492
Joined: 27 December 2005

Most VSD Manufacturers advise against opening the circuit between the drive and the motor with either fuses or a contactor - I believe in some circumstances it can damage the drive.

The drive has the facility for managing the "reverse" function, I would expect it to be able to handle the emergency stop too. There is a possible input labelled "external fault" which may do what you want. There is also the facility according to the manual to add a "braking resistor" which should make the machine stop faster.

Regards,

Alan.
 10 February 2019 01:39 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

HI Alan,

I saw that input mentioned I'll have another look at it.

I did get a braking resistor in anticipation of needing it, but so far have got the stopping time it set to 0.1s with no sign of the error code which indicates the resistor is needed. I assume there's not enough inertia to need it.
Thanks,
Jonathan

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jonathan d
 10 February 2019 03:55 PM
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paulskyrme

Posts: 1364
Joined: 12 February 2003

Is the drill at home or work?
 10 February 2019 04:51 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

The drill's in my own personal workshop (but can't get there till next weekend now)

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jonathan d
 10 February 2019 05:47 PM
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Dave69

Posts: 789
Joined: 16 July 2011

Why do you need to reversethe motor quickly? Are you tapping out holes.

A contactor for emergency reasons is a good idea and always used to have to be installed, ive not done any panel work for a few years now so things may have changed, a simple digital input to the drive was not allowed for emergency stop. The contactor could simply be wired into the safety circuit in a fail safe way so it is always energised unless an emergency stop button is operated or some other kind of safety switch, I.e. A gaurd switch.

Reversing should be left to the inverter, whats the point of having it and it being able to reverse the motor and then using contactors instead
 10 February 2019 06:36 PM
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paulskyrme

Posts: 1364
Joined: 12 February 2003

Wire your safety circuits to the contactor on the input to the inverter, you only need to kill the power, not the control.
DO NOT put a contactor or isolator in the inverter output, unless it is linked into the feed to the inverter, i.e. the inverter cannot get power unless the output side device is closed.
Many don't like it, and it's worth avoiding it just in case as it's not needed.
If you are going the whole hog, then e-stops are PLc, and guard switches depend on the ISO13849-1 assessment, but this is for your own use not a workplace, so it's up to you if you hurt yourself!
Use the inverter to do the reversing, it's easier in the long run, and that is what the inverter is designed for.
You should also be able to programme the inverter for different stop scenarios depending in whether you use the stop, or e-stop/safety function to stop it.
It's not considered good practice to only have an e-stop as they are defined as having a finite life before they can fail to danger, so fit and use a normal start/stop pair, then put the e-stop where needed for emergency use.
 12 February 2019 07:59 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

Dave69
Why do you need to reversethe motor quickly? Are you tapping out holes.

That's the plan.
a simple digital input to the drive was not allowed for emergency stop

That's the principle I was thinking of when I considered a contactor on the drive output. Also that power sources can contribute to accidents so by opening it under control of my safety module (XPS-TSA) that aspect would be covered. I've a guard switch (XCS-TE) to connect to that.
Reversing should be left to the inverter,

I agree.

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jonathan d
 12 February 2019 08:20 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

Paulskyme
Wire your safety circuits to the contactor on the input to the inverter, you only need to kill the power, not the control.

Input is single-phase to the inverter - both control and output are powered by it, so can't kill just input power.
DO NOT put a contactor or isolator in the inverter output,

This seemed an easy solution to the safety system but recofnise it could mess up the inverter by removing its load.

There's a circuit on page 45 of here Telemecanique safety docs which is close to what I need, but it assumes three phase power which can be removed via a contactor by the safety controller.
so fit and use a normal start/stop pair,

Done that on the inverter controls + forward/reverse. Currently the E-Stop is also connected to inputs on the inverter - but I'm not confident this is allowed for safety purposes. I'' have to check the Inverter documentation on this.

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jonathan d
 12 February 2019 10:47 PM
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paulskyrme

Posts: 1364
Joined: 12 February 2003

If the job is for yourself in your shed, don't worry about being allowed for safety purposes, DIY doesn't come under workplace H&S law.
Some drives will have Safe Torque Off, and Standstill monitoring, so running the e-stop into the drive, might be acceptable, that depends on the drive configuration.
 17 February 2019 01:05 PM
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jgdavies

Posts: 32
Joined: 09 July 2006

Thanks for the comments.
I understand when there's a need for safety protection on this three-phase pillar drill, and do intend to fit some protection. Before putting up this post I had controls: Start, Stop, Forward/Reverst and speed control all working through the single to three phase inverter drive plus an 'Emergency-Stop' button working through the drives 'fast-stop' input "like an emergency stop".

Now, so far, using a guard interlock (on the bench) I've added:
1. The two NO switches in the interlock in series with the Start button - so now the Start function won't operate without the guard shut.
2. Set one of the the inverter drive's multi-function outputs to 'During run' so whilst there's any three-phase output i.e. rotation of the drill, including any deceleration its active. I've then connected this output to the lock in the interlock to prevent the guard being opened when the drill is running.

1 & 2 have been done 'on the test bench' so have yet to be proven on the drill.

I appreciate that bar the interlock this 'safety' all relies upon the correct functioning of the drive inverter. To remove that reliance that's why I asked about a contactor on the drive output - something that isn't advised it seems. So for now, assuming 1 & 2 actually work on the drill, it will be 'safer' than it was.
Jonathan

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jonathan d
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