On Thu, 28 Feb 2008 16:09:22 -0500, Fred Bloggs
wrote:



legg wrote:
On Thu, 28 Feb 2008 12:51:29 -0500, Fred Bloggs
wrote:



Placing impedance in series with the working solenoid could produce a
reduction in speed/dropout performance in the armature of the relay
switching the main working load. (not shown in the above drawing)

I'm not sure how you modelled the relay coil, but if it used a linear
inductor, it will not likely reflect actual performance. A relay
drive coil is coupled to a mechanically changing magnetic circuit.

As the OP already has a cost-free solution involving programmed timing
adjustments, perhaps it's best to let the issue drop?

RL


He was working with a largely resistive 8KR coil, the 100R has no effect
on pull-in or hold-in. The programmed timing can be dropped, what
happens at line loss, does his controller lock up because things didn't
go exactly as planned, you tell me.


I've asked for this information, but still see only the reference to a
6W AC coil in the relay doing the work. Larger AC working relay coil
current is seldom determined by the DC impedance of the coil. You can
refer to the Leach tutorial on this issue, and their catalog, though
they don't seem to supply relays or contactors with low frequency AC
coils, at present.

For example, a 115V 400Hz coil in a 4W series, is listed as consuming
90mA. This indicates that the DC resistance of the coil must be less
than half an RDC value that would produce the specified current, in
order to keep combined power loss from coil and armature poles to the
value expected.

The losses in AC activated coils is typically 5 times that for DC
rated ones, in simpler commodity forms like OMRON MGN.

http://components.omron.com/components/web/webfiles.nsf$FILES/family.html?ID=CNEN-6TJQPU

But that wasn't always the case.

Older SquareD parts anticipate coil current ratios of more tha 4:1
between closed and open armature, with different values expected for
50 and 60Hz dedicated parts..

http://ecatalog.squared.com/catalog/...6.html#1013844

The same relationship shows up in lower-powered parts:

http://catalog.tycoelectronics.com/T...354,16453&LG=1

RL

I'm aware of that. Generally AC coils with predominantly reactive
impedance are rated in VA and the so-called impedance limited coils with
impedance dominated by coil wire resistance are rated in Watts. The OP
is working with a 6W impedance limited coil.

Sorry, but I don't see a resistance limited coil described in any
correspondence from the OP.

The most common ( old P&B now Tyco ) contactor for high current that
still offers AC coils and a fair description of their impedance and
wattage expectations:

http://tinyurl.com/3845jx

RL