"Bruce L. Bergman (munged human readable)" wrote in message
...

On Thu, 13 Oct 2011 02:41:52 -0500, "RogerN"
wrote:

It may be helpful to go to ab.com and look in their literature library,
it's
great to get instructions (for those who use instructions) on older
equipment.

We have an indexing festoon at work that cycles every few seconds 24/7, the
contactor welded itself closed, made a bit of a mess but out of 17 such
indexing festoons, we don't replace contactors very often. This was an AB
100 series IIRC.

You've got a different problem - with that kind of short-cycling
service, the machines really should have been designed with a second
fail-safe contactor to kill incoming power to the whole machine if
this happens. Safety contactor, or a Shunt Trip Breaker.

The trick would be sensing the problem before the machine totally
crashes and self-destructs. Is there a hard stop or an indexing pin
at the station stop? Perhaps change it from a hard stop point (like
an adjustable bolt on a solenoid drop-pawl) to a really stiff spring
and the micro-switch to sense when it keeps pushing.

One other (far simpler) solution would be to change them out to an
electronic starter - Soft Start or a full on Variable Speed Drive.
Probably have to go way oversize on it because of the short-cycling
heating issues.

The VSD should have a sanity check built in that drops out the safety
contactor if the transistors(*) short - "Hey, I turned off but there's
still power on the Load. Something's Wrong Here..."

-- Bruce --

(* Transistors, SCR, SCS, Diac, Triac, etc. - whatever the hell they
used. There are several ways to do it.)



This uses a motor with brake and a prox switch to detect the index position.
I have a timer in the program that if it doesn't complete the index in time,
it alarms and shuts off the contactor, but that doesn't help when contacts
are stuck. I agree we should have a contactor that kills the 460V AC to the
starters when either the control detects a problem or when the E-Stop is
pressed. We do have a disconnect between the starter and motor so things
can be locked out.

I wouldn't have designed it the way it is but that's what the company has
used for years and hasn't had enough failures for them to decide to change
the circuit. Some of the new lines have VFD's for the festoon indexing, and
power is killed to the drives on E-Stop conditions.

RogerN