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Cost to change to VFD?
- Thread starter taltexan
- Start date
- Replies 11
- Views 1,541
thermite
Diamond
- Joined
- Sep 21, 2011
Early AVS used a DC motor with a DC Drive for power.
Later AVS used an AC motor and a VFD for power.
If you already have the AC motor, AND genuine 3-P power?
Your choice of VFD will be any major-maker modern 480 VAC, 3-Phase-only capable one that does not have over-age-in-grade components. One of the good ones could be a Yaskawa, "industrial grade", with a bit higher, NOT lower nor same-as, HP rating as the motor. All the rest as to how to connect it should be right in the VFD maker's manual. Download and review more than just the one manual BEFORE you make your final choice. The manuals are free. Poor choices are not free.
USED and/or old, even if NEVER used, VFD are a bad gamble. Best to buy NEW. With Warranty.
If you have the Dee Cee motor, same again. Dead-easy to select a 3-Phase-only DC Drive. Parker and all the other major-maker have them from 10 HP to 14,000 HP. MAKE SURE you get tacho/resolver input for good feedback speed/load regulation AND the "Field REGULATOR" option! Same again, "RTFM" first.
USED DC Drives are not as big a gamble as used VFD. No significant capacitor complement to degrade. Also not much of a saving to buy used. NEW, with warranty, is still the safer bet.
DC only gets gnarly when all yah have is single-phase AND NOT wound for 90 or 180 VDC dirt-common DC Drives - usually much LESS than a 10 HP motor.
See 3 HP & 5 HP Monarch 10EE. the hard part is there are not as many DC Drives for 230 VDC and above SO a boost transformer is needed as well as a drive that can stand the higher Voltage. Parker-SSD is one of the few "affordable" ones, long-years proven, but also still in brand-new production, and good for nearly 500 VAC input with the boost transformer. Still, "two pulse" plus a bit of jiggery-pokery, it needs a big, fat inductor choke, AKA "ripple filter" lest the motor growl and the switching spikes mess with aged insulation.
A 3-phase-fed DC Drive's output is "six pulse", two per each phase, can be "24 pulse" with some electronics-foo (the patent is online), so is both smoother, and already "naturally" outputting right close to 230 VDC off 240 VAC, input, whereas a 1-P DC drive ony gets 180 VDC out. Boost transformer not required for a 3-Phase DC Drive. EVEN SO..Thyristor-class DC drives put NASTY switching artifacts back onto the INCOMING LINE side. A 1:1 "Drive-isolation" transformer is a Very Good Idea as it keeps most of that noise from messing with yer stereo , WiFi, 'puters, and such.
A 480 to 240 step-down does the same. So long as it is a "full-isolation" transformer. Buck/Boost "autotransformers" don't much block noise. They just pass it right around themselves instead of choking it in the coils.
A modest ripple-filter choke is more than just "nice to have" - Reliance calls for them on ANY motor wound for more than 180 VDC, even if the motor was purpose-built for "Rectified" power (RPM family, lamination-frame design). Filter may not be as obviously essential, but remains a "Very Good Idea", even on 24-Pulse 3-Phase. Most especially if the motor is OLD and pre-dates the "RPM" (Rectified Power Motor) concept.
Same again a dv/dt or "Sine Guard" filter on the output of a VFD. Those protect the 3-P AC load-motor, even IF it is "rectifier duty" or "inverter duty" rated.
FWIW? IF you have a Dee Cee motor? Look up the price of NEW ones before being too hasty to swap it out for AC! They can be seriously sweet creatures when well-fed!
Priced accordingly! A 5 HP Reliance RPM III is right close to twelve thousand US dollars, "MSRP". Ten percent of that - twelve HUNDRED bucks - will get yah a right sweet 3-P AC motor. brand-new. Or even two or three of them.
For machine-tool use, migrating from variable-speed DC to variable-speed AC needs 1.5 to 2.0 times higher AC nameplate HP rating than DC was rated for. That's a torque and smoothness thing. Not hard. AC motors are typically much smaller than DC in that motor type, and waaaay cheaper.
If yah LIKE "smaller and cheaper" yer probably more of a "beancounter" than a machinist. I actually WAS a "beancounter" of sorts, and for waaaay longer than ever I had been a Machinashitist.
But now I'm retired. I get to play with Dinosaur Current and grin again!
Last edited:
Early AVS used a DC motor with a DC Drive for power.
Later AVS used an AC motor and a VFD for power.
If you already have the AC motor, AND genuine 3-P power?
Your choice of VFD will be any major-maker modern 480 VAC, 3-Phase-only capable one that does not have over-age-in-grade components. One of the good ones could be a Yaskawa, "industrial grade", with a bit higher, NOT lower nor same-as, HP rating as the motor. All the rest as to how to connect it should be right in the VFD maker's manual. Download and review more than just the one manual BEFORE you make your final choice. The manuals are free. Poor choices are not free.
USED and/or old, even if NEVER used, VFD are a bad gamble. Best to buy NEW. With Warranty.
If you have the Dee Cee motor, same again. Dead-easy to select a 3-Phase-only DC Drive. Parker and all the other major-maker have them from 10 HP to 14,000 HP. MAKE SURE you get tacho/resolver input for good feedback speed/load regulation AND the "Field REGULATOR" option! Same again, "RTFM" first.
USED DC Drives are not as big a gamble as used VFD. No significant capacitor complement to degrade. Also not much of a saving to buy used. NEW, with warranty, is still the safer bet.
DC only gets gnarly when all yah have is single-phase AND NOT wound for 90 or 180 VDC dirt-common DC Drives - usually much LESS than a 10 HP motor.
See 3 HP & 5 HP Monarch 10EE. the hard part is there are not as many DC Drives for 230 VDC and above SO a boost transformer is needed as well as a drive that can stand the higher Voltage. Parker-SSD is one of the few "affordable" ones, long-years proven, but also still in brand-new production, and good for nearly 500 VAC input with the boost transformer. Still, "two pulse" plus a bit of jiggery-pokery, it needs a big, fat inductor choke, AKA "ripple filter" lest the motor growl and the switching spikes mess with aged insulation.
A 3-phase-fed DC Drive's output is "six pulse", two per each phase, can be "24 pulse" with some electronics-foo (the patent is online), so is both smoother, and already "naturally" outputting right close to 230 VDC off 240 VAC, input, whereas a 1-P DC drive ony gets 180 VDC out. Boost transformer not required for a 3-Phase DC Drive. EVEN SO..Thyristor-class DC drives put NASTY switching artifacts back onto the INCOMING LINE side. A 1:1 "Drive-isolation" transformer is a Very Good Idea as it keeps most of that noise from messing with yer stereo , WiFi, 'puters, and such.
A 480 to 240 step-down does the same. So long as it is a "full-isolation" transformer. Buck/Boost "autotransformers" don't much block noise. They just pass it right around themselves instead of choking it in the coils.
A modest ripple-filter choke is more than just "nice to have" - Reliance calls for them on ANY motor wound for more than 180 VDC, even if the motor was purpose-built for "Rectified" power (RPM family, lamination-frame design). Filter may not be as obviously essential, but remains a "Very Good Idea", even on 24-Pulse 3-Phase. Most especially if the motor is OLD and pre-dates the "RPM" (Rectified Power Motor) concept.
Same again a dv/dt or "Sine Guard" filter on the output of a VFD. Those protect the 3-P AC load-motor, even IF it is "rectifier duty" or "inverter duty" rated.
FWIW? IF you have a Dee Cee motor? Look up the price of NEW ones before being too hasty to swap it out for AC! They can be seriously sweet creatures when well-fed!
Priced accordingly! A 5 HP Reliance RPM III is right close to twelve thousand US dollars, "MSRP". Ten percent of that - twelve HUNDRED bucks - will get yah a right sweet 3-P AC motor. brand-new. Or even two or three of them.
For machine-tool use, migrating from variable-speed DC to variable-speed AC needs 1.5 to 2.0 times higher AC nameplate HP rating than DC was rated for. That's a torque and smoothness thing. Not hard. AC motors are typically much smaller than DC in that motor type, and waaaay cheaper.
If yah LIKE "smaller and cheaper" yer probably more of a "beancounter" than a machinist. I actually WAS a "beancounter" of sorts, and for waaaay longer than ever I had been a Machinashitist.
But now I'm retired. I get to play with Dinosaur Current and grin again!
I have this motor on hand, will it be ok with a dc drive to run a 20” l&s AVS? What drive would you recommend if it would work?
Attachments
thermite
Diamond
- Joined
- Sep 21, 2011
NO idea how hard you need to work it. A Large & Shapely was built to kick serious chip, and the AVS was in the baby-sized of their trio, even so (Powerturn, Omniturn, Superturn).
But.. 15 Hoss DEE CEE? Annnnd an AVS is still a "geared head" lathe, just fewer ratios than its constant-motor-speed siblings?
Whole diff'rent ball-game than a 3 or 5 HP 10EE with NO gears in the head -just a one-step low-range reduction set at the input side the Dee Cee models hardly ever use unless yah just need really low RPM for not messing up an operator response-time challenging threading operation or the like.
An AC motor to replace 15 HP DC - when either of them are in variable speed/torque service - "should be" about 20-25 HP. That's a lot of Amps outta the wall and a Hell-for-stout VFD!
Modern DC drive is actually not as hard. No capacitor bank dropped onto the line like a dead-short.
But is it 20 - 25 HP?
Or was it downsized by a previous user for lack of enough juice? Say to 15 HP or even a 10 HP?
And is that "good enough" for your present/expected needs?
If LESS than 20 HP AND "good enough" a VFD to add-back some RPM flexibility won't have to break the budget.
Not cheap, even so, as used ones are just a BAD idea.
The "Old Old" big brick-shithouse VFD used different chemistry in their larger capacitors, but even so, they are now way TOO OLD to risk.
Owner doesn’t know, he thinks it’s a 7 to 10 hp ac. I have a 10 HP dc motor on hand. I have a post with a pic of my 10 HP spec plate but it’s not showing up in this thread. Does mods get involved when pics are posted? What would you recommend for a dc drive for my 10hp motor? Make, model ?
thermite
Diamond
- Joined
- Sep 21, 2011
First, use the PM "Send Email to." feature under my logon ID so I can see what TYPE of DC motor that nameplate sez the ten hoss is.
Ten hoss Dee Cee WITH the modest handfull of ratios the AVS still has will make serious bins of chip.
It just ain't what a defense plant would want three shifts a day to go to winning a war with.
No war. No need. BFD.
Even on partial rations, the tough f**ker will still kick the average Asian pretender's ass right up between its shoulder blades and sometime into the middle of next week!
Count on THAT much!
thermite
Diamond
- Joined
- Sep 21, 2011
A smaller picture would help.
Got it arredy. 500 VDC Armature. Shunt wound. dual-voltage field, cont duty rated.
It's only a lowly Baldor, not a Reliance, rather lower "do not exceed" Field-Weakened RPM by comparison, but even so? An AVS still has a handful of geared ratios, too, so "she'll do".
