Yes, I understand that.
Yeah, I’m going to pull the contactor out this weekend and inspect it, look for where it is damaged.
It has 115V AC coils, so I’ll energize each side and see how each side works.
I am using the interlocking contactor to reverse the flow through my 30KVA transformer, as a soft start mechanism for spinning up my 25HP motor.
I use a 3 position switch: (start/off/run) which is used yo energize the different sides of the contactor.
Once spun up, I switch from start through off and over to run.
My notion is to use 6 SSRs, 3 switched on for starting, switch those off and then 3 for running.
As to the control circuit: Keep my simple 3 position switch? PIC chip with timing? Potential relay?
SSR's are done in arrays often enough, but the wrong goods for this tasking as 'raw' devices.
The issue is twofold:
Starting inrush.
In more complex circuits, the
controls can command a slow-ramp, just as a VFD or DC Drive can do. That's as much to the benefit of their own "pass elements", be they SCR's or IGBT's that need to stay alive, as it is for the load being started.
Power interruption:
OK, the SSR itself cuts-off at a no-energy-flowing zero-cross. Or not. They make them as "randomized" ON and OFF also.
But a massive rotating inductor doesn't give a shit. Transformers? They ARE "inductors", yah? See Old Skewl spark ignition coils.
A rotating motor or a transformer's suddenly de-energized fields "collapsing" can still fling back kinetic energy as electricity AFTER that time-gate has passed.
With Dinosaur Current, our motors are really GOOD DC generators. We expect roughly FIVE times the Voltage excursion as the running Voltage at time of disconnect. Worse? There can be rather serious amounts of energy "under the curve", welding-grade arcs, not just teaser spikes. DC contactors have to be FAR more rugged than AC. They ARE the "zero cross".
"Four-Quadrant" DC Drives or VFD's, neither of which even USE contactors at all, survive and thrive because they
ramp the power UP..and back DOWN to Zero, typically over a full two-seconds, each direction.
Neither tribe has to deal with an abrupt start OR termination of power..
Cheating, y'say? Dambetcha!
Works well, and lasts a long time, too!
Buuuuuuttt. it needs some "smarts" controlling those ramp UP/DOWN behaviour patterns.
Now.. a "mechanical" contactor, either of hard metal or Mercury, is inherently a "binary" device. Full ON. Or full OFF. No Fine Way it can "sneak up" on a damned thing.
BFBI. Brute Force and Bloody ignorance. Not as "ignorant" as first appears, either.
Arcs are going to happen? They simply plan for them. See "Arc chutes", "blowout coils", etc. All old stuff for waaay over a hundred years already.
All
you really have to know is enough to select a stock contactor rated for what you will ask it to do.
Other folk have already earned their wage making sure it happens.
And by the tens of millions, world wide, if that part matters... Asea Brown-Boveri (ABB), Eaton Cutler-Hammer, Schneider Telemechanique? Old. Big. Still here.
Trust those big, Old Line, major makers. They got to BE big, old, and major, typically over a hundred years and more in THEIR game.... because their shit
Just
Faithfully
Works.
If you want to INVENT sumthin'? Don't waste yer time on commodity contactors. Just buy them. Plenty of good ones NOS surplus.
Now .... that faster-than-light spaceship warp-drive?
That puppy.. I could use some help with... How much money d'you have spare?