Speaking of Motor Controls...

Holy shit, sounds like Kalamazoo, with their $900 cutoff switches for their
horizontal bandsaws....
Even the guy on the phone was speechless....


You could proly make contact, no?  c-bore some copper for the mounting
screw?

I've made decent bussbar out of copper plumbing pipe, hammer it flat.  Not
electrical grade copper, but surely a whole lot better than aluminum!!
--
EA

On 8/16/2012 1:10 PM, Existential Angst wrote:
...


Switching contacts for inductive loads are a whole different animal than
static conduction.  (Which is why I've cautioned you on just switches if
your motor controllers are on anything of any size...)

The contact material is bonded to a copper substrate--typical relatively
small motor contacts like these are a Ag/Cd amalgam--I think these are
10% Cd.

The one really bad one has lost the contact substrate off the functional
backing plate entirely.  The others were fairly deeply pitted but able
to clean them up reasonably well they'll last quite a while.

For this starter there are actually four contacts designed in parallel
for larger single-phase motors that are are demanding because the single
phase means higher currents.  For a smaller motor could easily just use
two and even have a spare...which is likely what I'd do if were to put
this one into service somewhere.

Way back when, being limited to single-phase on the farm had a couple of
sizable old motors that ran the elevator leg (12.5 hp which I've not
seen a single phase that large even available any longer--it is about
3-ft in diameter and must weigh 500-lb if an ounce, now mean feat
hoisting it to the top of the elevator and getting enough structure to
hold it up) and a large hammer mill for grinding grain for feed (7.5 hp
iirc).  Now one would go to phase converters but that wasn't such an
option in those way-back days shortly after REA did finally arrive.
That has been a while now but was recently enough I do remember before
anything but the old Delco 32 VDC WindCharger system for lights in the
house and a few applicances and the barest of bulbs in barn.

Interestingly enough, in rural Saskatchewan when was doing coal
analyzers eng'g support in a previous life the Co-op stores in Weyburn
and other regional rural shopping centers still had those appliances on
the showroom floor...that's not been but about 20 yr now and I suspect
they're still there now.

--

You know, they make relatively high current solid state relays now, with
"coils" that operate at ANY voltage from proly below 120 to over 220-240.
No more contacts!
Some fuses, breakers, heaters, whatever in series, and wala, motor starter!
with mebbe a li'l latching/cutout relay in series with the coil -- which
could actually be just another solid state relay, with the coil powered by
the contacts, instead of the line.

HVAC houses carry these, and I'm sure many other places do, at much lower
prices than these ripoff hvac suppliers.
--
EA

On 8/16/2012 4:50 PM, Existential Angst wrote:
...


Indeed, I've done some looking into that -- there's some fairly
important engineering to be done that I've not opted to take on,
particularly as long as I've got old pieces-parts to scrounge up for
play-toy applications.  If it comes to real gear for actual farm
revenue-generation, then all rules change, of course.

The section I've read on general principles in selecting SSRs for motor
applications says in part--


All in all, it says you don't just look at a (say) 10 hp motor drawing a
nominal 50A and just buy a 50A SSR and go on assuming everything is just
hunky-dory...


Any specific parts you know of firsthand for a given/known motor for
comparison purposes?  For 240V need either two or a 3P integrated even
though only need two of the three for load.  Perhaps there are some but
I've not seen any w/ the auxiliary control contact(s) needed for a
starter circuit so that's another or (I presume) w/ the 3P you could use
the third load contact assuming it'll switch the small coil load
satisfactorily.

The Newark catalog ones of minimal size (10A that I'm sure don't meet
any of the above-discussed conditions for even a 1 hp motor what more 2
or 3 or 5) are about $25 for a single pole.  The hp-rated by
manufacturer 2-pole 40A mechanicals were $8+/ea so that seems a
no-brainer on cost.  They require another $8 or so control relay but
still that's pretty inexpensive comparably.

But, I'm still open for going forward at some point...

BTW, I got the old Moeller starter going this afternoon!  :)  No smoke
was harmed in the connecting...I did have to clean up a bunch of
terminals to get a good connection thru the start circuit but I'm about
ready to put it on the DC.  If I can figure out a way to squeeze the
motor start capacitor that's in the present switchbox, I could replace
it entirely and eliminate the piggyback power feed...there's _almost_
enough room; I'm going to see if I can manage to make just enough more
by a rearrangement or removal of the third pole power feed that don't
need for the purpose.  That would "neaten up" things significantly...

--

On 8/16/2012 4:50 PM, Existential Angst wrote:
...


Well, the HVAC reference got me to searching w/ that and variants as
keyword --

So far, I've found some from TEMCO that are 3PH/AC up to 40A (iirc) at
about $25-$35/ea and one 70A.  _BUT_, it appears they also need
heatsinks and very good motor protection because their LRA tolerance is
_very_ short (like 10s of msecs).

Found some SS motor controllers of course but they're $hundreds complete
so don't see (yet anyways) there's any great simple savings to be had...

Still, if you do have a specific part for a given app and have any info
on what is in one of these applications besides just the SSR I'd be
interested in seeing it.  I'm thinking probably there, too, the aux gear
in the field is significant.  For low level stuff we used them all the
time in data collection, etc., and for that I'll agree they're the cat's
meow over mechanical...

--

I think you've pretty well covered it, but I'd add one more warning:
SSRs' failure mode. They quite often fail on. I've used many SSRs in
automation controls to power devices like single-phase sub-fractional
HP motors that don't pose a safety hazard.

SSRs are common in place of the once-standard mercury relays in heater
control circuits. But, depending on the danger posed by a full-on
heater, redundancy is good practice.

This page covers the issues to consider with SSRs. The overview page
gives an idea what's required for heat sinks to utilize the full
capacity of an SSR. If you're putting them in an enclosure you also
need to figure the heat dissipated.
http://www.hbcontrols.com/ssr-controller-assemblies-technical.asp
http://www.hbcontrols.com /

Re the cost, I bet a 3-phase SSR with proper heat sink as a motor
control would be more expensive than a VFD. In fact, the price
difference between a mechanical motor starter and a VFD is not that
great these days. I'm working on design right now that has 10 motors
totalling about 40HP. We decided the other day not to bother with
starters for any of them -- VFDs all the way thru.

BTW, a good value for contactors and overloads are the Fujis from
Automation Direct.

--
Ned Simmons

On 8/18/2012 11:09 AM, Ned Simmons wrote:
...

Good point--the applications I'm familiar with are all just control
(Opto-22, mostly) and no loading to speak of so the thermal problem is
nonexistant.  If one has to design in the redundancy that certainly
pretty much defeats the whole point to begin with as well as definitely
going to up the price point...


OK, thanks; I'll keep them in mind.  At present there's nothing new
going on that's "for real"; this is as much entertainment w/ an end
objective of adding the convenience of a remote control station to the
DC in the woodshop.  Since I have bunches of old stuff laying around I
can rig up pieces and put them together...I've got this one working w/
the exception of rearranging the couple of connections to add the remote
pushbutton and waiting for the paint on the covers to dry to make it
look a little prettier in its new life.  I've also refurbished/cleaned
up several others of various sizes and configurations and figured out
what parts were in the piles of stuff for the most part...who knows when
will dream up a use for some of it?  At least half the fun is in simply
being able to reuse the stuff.  :)


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