Mill is in a residential garage shop, we're current limited. With across the line start of the main spindle there are some spindle speeds that simply overtax the 240 / 60 / 1 mains and trip the service entrance breakers. Ideally more power, but not possible at this location. And I'd rather not change the motor.
The goal is simply to damp the inrush current slightly
Similar challenge, here. Save that I can have all 200A if I really need it.
But.. since Dominion Power went-over to a "demand" component, even on residential billing? I do not want to "really need it" even once!
"Patience" is cheap in Virginia. So.. my solution is a multi-idler RPC.
Start each/any/all of 3, 7.5, 5-to-7.5 (weird motor) and 10 HP idlers, staggered over time. Once enough electrical and kinetic inertia is motating as the pilot and supplementary idlers? Starting any of my 1.5 HP to ~ 8 HP loads has a far less dramatic effect on the single-phase feed.
From THEIR seats? Bang! Up and away, same as utility mains 3-Phase. They have no need of "soft start" .. nor much of a klew there is any limitation at all. Because they are calling on the resources of a fairly well "funded" mentor, upstream.
"BFBI" method, save that the heaviest idler I'd ever start in a demand time-period is the 10 HP one.. and mostly I don't start that one
at ALL, what with a pair of 7.5 HP. Stagger-start of a 3 HP and a 7.5 HP, or two 7.5 HP, spaced in time realm, and I'm good to go. Once the heavier load-motor is up and running? I may have the option of dropping one of the idlers off the line.
The 3 HP, BTW, is all I need for a couple of sub 2 HP 3-Phase loads, but does double-duty as a "trimmer", for better balance of the heavier "nameplate" loads , which may or may not be loafing or working hard, any given tasking.
The whole rig takes a LOT more SPACE than a VFD. Or even SEVERAL VFD.
Especially as there is a 27 KVA Delta-Wye 1:1 Drive Isolation transformer and a transfer switch to run off a 10 HP Phase-Perfect instead.
Some make chips. I make tests. I didn't want to re-configure this a third time. 28 HP max idler when all are singing and dancing? That will handle anything I am likely to drag home.
There was a chunk of freight involved. I did say HEAVY idlers? - but the net cost isn't all that different from multiple VFD'ing.
Rugged as it all be, it won't mind living sorta "outdoors" in a half-vast shelter with the Diesel gen set, either. Arse-end of the carport for now, so "BFD". Noise is exiled outdoors with it.
Not that a deaf-ass Old Fart much
notices "noise". More a "high value space" vs low-value thing.
Only the 3-P panel, breakers, and controls take up any
shop space
at all, and even then "not really" - where they go weren't "premium" space.
VFD? They work. Kinda neat. Lotta nice features.
That I don't need, give every one of my loads has either a Reeves or cousin vari-drive, the odd-man-out a PIV-Werner-Reimers metallic equivalent.
And ... with 3 of the 4 idlers massive Reliance Duty-Masters and ALL of them new or NOS?
The rig is likely to outlive ME ...even if I clock a hundred years of age.
VFD's aren't near as good at
that part! Nor do they "share" as well as an "RPC Array"
4 idlers worth...
Your shop?
You could be as well-off as you NEED to be with only TWO idlers - primary and supplementary?
Give it a thunk.
Dave Kamp has posted a schematic as to how dead SIMPLE that is. I mean. .... any SIMPLER ....it would have to be a blank sheet of paper!