IIRC, the guy who had the 30" 10EE WRECK write up I believe had 2 10EE's side by side, one with original DC and one that had been converted to AC, and claimed there was no noticeable difference in performance. From what I recall...
Read it again. Harry didn't use a boost transformer for the DC drive. At 180 VDC out instead of 260 VDC, he was running it at about 60 percent of normal performance, and he said so. Tried to boost it, blew the used drive he was messing with, quit and did a VFD.
Surely it compared well. With a cripple.
Those spurious "VFD is just as good" claims gave been around for Donkey's Years.
Why "spurious"?
Too few folks bother to provide the voltage the Monarch DC motors used. Nominal 230 VDC on the nameplate, actual around 260 VDC in real life. They'll STAND 300 VDC armature and 140 VDC field (greater torque, low and slow, faster stopping and reversing.) .
Bump a 1Q Beel/BICL D510 to 300-340 VAC input to get 260 VDC out, fry the SCR bridge on the spikes. It has a peak rating not much above the SSD's all-day, every-day
working rating.
What JFW? DC Drives that SHIPPED ready for 480 VAC in, 380 VDC out. As used in Europe.
Eurotherm/Parker-SSD 514C-16 for 3 HP, stretched at 5 HP, where a 514C-32 is 'proper', but but works.
Use full-isolation boost transformers to 320-350 VAC input side, 20 Milli-not-micro Henry Choke, output side. Do NOT omit either one.
It is all right there in the SSD manual.
IF... you have genuine 3-Phase power? Utility mains or a stout Phase-Perfect?
THEN you can have near-as-dammit "Plug and Play" with a 3-Phase-only DC Drive.
- No boost transformer needed.
- Many more drives available.
- Even the ripple filter is not essential.
You want to MATCH that with a VFD?
First you need 8 poles and 7.5 HP or six poles and 10 HP. And a good VFD, not an El Cheapo.
Then you have the machining to do to mate the gearbox, 'coz a VFD will STILL NEED it.
SSD-Drive + ripple filter choke, and DC motor, not so much.
Why do they no longer ship NEW DC motored machine-tools in general?
Conventional DC motors of the type Monarch once used are 11 or 12 THOUSAND USD, new.
Servos can be had for less money. There are five or so 10EE out there that have been converted to servos, too.
That's righteous enough.