Is there a motor starter on the market (or third party add-on module) that will require an off-to-on transition of the motor start button before starting a motor? We have a problem (dirty process) with start buttons sticking. This causes the motors to start unexpectedly when power is restored after maintenance.

 

Responding to Fluoronator's 05-Nov-08 (11:08) query:

See Control List thread #1026215647. It describes the electrically-trip-free or X-Y scheme, or anti-pumping circuit frequently used for control of circuit breakers.

Regards, Phil Corso ([email protected])

 

Most variable speed drives behave as you describe. If this is an important feature for you and a VSD will work in your application it is worth considering a drive over a motor starter.

-James Ingraham
Sage Automation, Inc.

 

James, your answers are usually level headed. So, I am puzzled about your suggestion to use a VSD, when a trip-free circuit can be implemented using two auxiliary relays.

Regards, Phil

 

I think there are safety relays which address this application directly. They look for an off-to-on transition from the push button. You will want to look at how much re-wiring this involves though, as the safety relay voltages may not be directly compatible with the existing installation without some changes.

A major advantage of this approach is that if this is a safety concern, this solution uses certified components. If that is not a concern for you, then as Mr Corso has mentioned, you can also construct a similar circuit from conventional (non-safety) relays.

Of course being unfamiliar with your application or the laws and regulations in your country, I can't recommend a particular course of action. However, the above are a couple of approaches you may wish to evaluate.

 

Phil: "James, your answers are usually level headed."

Thanks!

Phil: "So, I am puzzled about your suggestion to use a VSD, when a trip-free circuit can be implemented using two auxiliary relays."

I generally prefer VSDs to motor starters. I also find there isn't much of a price difference. I also don't like having relay logic; this is perhaps a result of my coming from a computer background rather than electrical. Last, but not least, adding relays means changing documentation, i.e. updating the electrical schematics.

So for me, the question is design work, extra relays, and hard-wired logic vs. just throw a drive in their for about the same price. And then I pick up the advantages of drives; ramp up / ramp down, lower in-rush current, no need for an overload on the output side, etc.

Having said all that, I may not have been exceptionally level-headed in this case. If you already have a complete working system, pulling out a motor started and putting in a drive is probably more work than adding two relays. Plus, there are all the disadvantages of drives; they have to be set up, they introduce noise -- in their wiring, in the cabinet, and back onto the incoming power lines -- they are far more likely to fail than a motor starter, and while they offer some help when troubleshooting the motor starer wouldn't have NEEDED any troubleshooting.

I should probably have some conclusion here, but the Texas Tech v Oklahoma game is about to start.

-James Ingraham
Sage Automation, Inc.

 

Well, not so fast..... I happen to agree with your first assessment.
with the cost of doing _anything_ going up, and the reliability of
relays going down, (Their golden age is past) and the cost of
quality relays properly applied. It isn't much of a stretch to put
in a drive even if all you do is reverse with stuck button detect.

If you do or would like to do _anything_ else, the drive would
provide much more flexibility. You could easily change speeds
or have forward and reverse at different speeds or actually
regulate speed or add a jog function. You could also limit torque,
detect phase loss, provide dynamic braking, detect ground faults,
and perhaps even speed up the process. (management likes that
one) and lots of other things that the relay setup won't do.

Not to mention you can provide feedback that your motor is
actually running rather than just that the relays are closed.
Some drives, (e.g. Yaskawa V1000) will actually save energy
as well. It's a lot of bang for your buck. We replace a lot of
starters and overloads and everything but the simplest
application warrants consideration for the flexible solution.
I see it as a golden opportunity to improve.


Regards
cww