Need help speed controlling 240v DC brushed FANUC motor
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    Default Need help speed controlling 240v DC brushed FANUC motor

    As the title states, I am interested in a speed controller that will suit the motor, but also not break the bank.

    The motor is freshly wound, brushes and bearings are new, and it's already attached to a machine that is having spindle PCB issues, so would just like to add a pot that can control speed manually. Hoping it's a temporary fix, hence the budget constraints.

    The motor in question is a FANUC A06b-0820-B. 6hp 240v DC with a field winding.

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    Is it really as simple as two rectifiers and variac? Will a 30 amp variac handle the load?

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    Go to fleebay and find a fincor or AB drive, and look at any info you have and see if the old drive had field weaking, there's a lot to know...Phil

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    Quote Originally Posted by Phil in Montana View Post
    Go to fleebay and find a fincor or AB drive, and look at any info you have and see if the old drive had field weaking, there's a lot to know...Phil
    Field matters. Perhaps by a LOT!

    Also what controlled it and whether resolver, AC or DC tachogenerator feedback to the DC Drive was in-use.

    That said, not hard to ID a workalike - so long as you have 3-Phase power for the DC Drive. Plenty of them new and used, current technology or not-so-much.

    Single-phase that can even STAND a boost to ~ 300 VAC in to get 240 VDC out are scarcer, and do not ordinarily have Field Regulator "achitecture", if even they have any regulation on the field at all.

    Surely not meat for an ignorant Variac + FWB for the application it serves.

    "Major Maker" 3-Phase (only) current item with all the requisite features and options, rather.

    THEN yah could look for an older one, used but not abused. If it fails, a same-same new one is a drop-in, all interface and commissioning already in-place.

    "Orphans", OTOH, no matter HOW "well regarded" back in the day, are not a good idea if the machine is meant to earn a crust and continue to do.

    As with Bodine Brother's motors, DC Drives "..do, too fail. They just take longer" ..than VFD's.


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    3ph at the shop, 109 on each leg. Not sure that I will ever need the full 240v as the spindle max is less than the motor max (appears to be a 3:2 pulley ratio on the spindle belts, 5k max spindle).

    Here's some more info on the motor:

    https://www.practicalmachinist.com/v...it-2-paint.jpg

    Form another site where members were helping diagnose the same motor, and used a car battery to make it run:

    100 RPM @12v
    1000 @120vDC
    2000 @240vDC
    and that is with 12vDC on the field. 6v on JK would give twice that speed for voltages above.
    So the field is weakening.

    Motor tag, which is very difficult to see, it's mashed against the Z servo at full height and the Z ways when lower.

    Speed: 1500/4500
    AMP: 26/32
    Volt: 220v
    FLD Widing

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    Actually looking inside the machine itself, it appears it has a max of 200vDC (makes sense, 3ph is technically 208v). There is no outputs anywhere labeled 240vDC, the big transformers in it have 90v, 100v, and 200v outputs labeled, and are accurate according to the DMM.

    From my understanding, the armature voltage is inverse as the motor speeds up. If the field has 0v and power is applied to the armature, it will be at full speed instantly, drawing massive amounts of current.

    So does this mean 90-0v field need to be inverse of motor voltage increase?

    I found some commercially PWM DC motor drivers with field control that won't break the bank, but they max out at 5hp 180v 26amp.

    Based on the above information about volts and speeds, at 180v on armature and 0v on the field, I should be able to obtain a 3000 motor speed which will still reach max (or close) spindle of 5k due to the pulleys.

    I am way out in left field with this?

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    Quote Originally Posted by J.Caraher View Post
    3ph at the shop, 109 on each leg. Not sure that I will ever need the full 240v as the spindle max is less than the motor max (appears to be a 3:2 pulley ratio on the spindle belts, 5k max spindle).

    Here's some more info on the motor:

    https://www.practicalmachinist.com/v...it-2-paint.jpg
    That's a simplified diagram. Take note that ALL the SCR triggers are tied into one "line".. which will physically be at least two, and probably more than two!



    The 'goods are there" to do-up either of a full 4Q drive, or at minimum, an SCR-reversible drive as needs no contactors.

    A "non trivial exercise" to rev-engineer the details, but it is a sophisticated replacement yah need, not a simplistic one.

    Speed: 1500/4500
    First number, 1500, is the "base" RPM @ rated Voltage, loaded to Full-Load Amps to match HP under load on the data plate. Unloaded spins faster, same Voltage, very little current drawn

    Second number is the sustainable-forever Do Not exceed RPM. That's a physical limit above which (plus a safety margin we are not meant to know even exists!) there is risk of physical damage - the motor's various rotating bits wanting to exit the zone as fast-moving shrapnel.

    You'd need a reasonably full-featured 3-Phase-input ONLY DC Drive, here.

    Even if very few of its sophistications end up fully utilized, they provide the FLEXIBILITY to sort-out which ones MUST be active, and howso, so as to be a "workalike" substitute that altereth-not the overall machine-tool operation.

    The greater part of the integration challenge is insuring that nothing ELSE has to change in the overall control scheme.

    IOW. whatever the master control logic ASKS for, the motor should respond, same as if the OEM controller was still the player carrying the demand message to it.

    Not hard if you have done a lot of it, even to crafting bespoke level-shifters. Just tedious.

    For mass-productuon, you want to use the generation of DC drives that utilize PLA's, NVRAM, keypads with numerical display (same as most VFD do..) so the SAME settings can be preloaded into tens of thousands of same-same identical product.

    For a one-off or different tribe repair, you want the older but still made "analog" logic so "feeling" your way to optimal settings is faster and easier by tweaking several potentiometers with an ignorant screwdriver.

    Not the easiest of projects from a cold start, but "do-able" if one at least has a dual-trace scope and understands control signal methodology.

    The DC drive itself is not hard. It will have been already built by experts!


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    Thanks Thermite.

    Just went ahead and dug into some EE papers about field motors. Not my area of expertise, but am fairly edumakateds.

    So, a field motor can vary speed on both the armature voltage, as well as field. So, in a simplistic way, here is what needs to happen (based on reading).

    Field voltage must be applied first. Increasing inverse of armature volts

    Armature voltage ramps up from 0v to max, this will cause a soft start on the spindle and ~1500rpm.

    If more speed is required, drop voltage on field.

    In this manner we can have at or near full volts at slower speeds. Having been building RC aircraft (mostly helicopters for years), got petty acquainted with speed and servo control, just on the microscopic level compared to this. In the latter days before retiring the hoby (about 6yr ago) brushless AC motors were becoming commonplace and NiMh batteries had been nix'd for LiPo.

    EDIT: Holy cowmoly time flies. it was 11yr since retiring RC flight.

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    Quote Originally Posted by J.Caraher View Post
    EDIT: Holy cowmoly time flies. it was 11yr since retiring RC flight.
    Yah think? I haven't run an Analog Vacuum tube Air Defense computer since September of 1965, nor a Digital Vacuum tube Air battle computer since later, same year. "Flight" were 101-Wonders, 106's mostly. The Air Battle was simulated. Aircraft,' pilots. and TONS of jet fuel burnt were all as real as could be!

    55 years ago, this year.

    Yah. Grab ye SEVERAL of the major maker 3-P only DC Drive tech manuals, not sales brochures, free offline for the storage space of a local download.

    A replacement drive won't be hard to select and swap-in, so long as you already know how to eval the control interface to it, and implement level and/or "protocol" shift to interface the system to the new drive "transparently".

    Better than even chance they'll be compatible right out of the box - 10 VDC min, 24 VDC max, centered of 15 VDC, buffered for-sure, open-collector for several, dual-differential probable for others. Don't expect 5 VDC. Too susceptible to noise spikes.

    At least you have a straight-shunt compound-shunt, or compensated shunt wound-field motor. Drive selection choice gets narrower were it a servo or stepper!

    Be CAREFUL! "Stick and rectumfry-lethal" Dinosaur Current takes NO prisoners!


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    Quote Originally Posted by thermite View Post

    At least you have a straight-shunt compound-shunt, or compensated shunt wound-field motor. Drive selection choice gets narrower were it a servo or stepper!

    Be CAREFUL! "Stick and rectumfry-lethal" Dinosaur Current takes NO prisoners!

    You would consider me "young" with appearance, but alas, the vehicle has few years, but many miles put on it. Most of the people I converse with, and work for me are 20yr elders. My best and closest friends are still only in the mid 60's, but then again, so are my parents lol.

    I have been bit by many currents, and the scariest was when we had to do an insurance rip-out of a burned up house. The guys left the dishwasher dedicated circuit so there was 110v for hand power tools, and I was even warned about it. Luckily there was my dad and another worker in the kitchen at the time - completely was chatting about a football game, grabbed the gang box in the left hand, ground-shield whip in the other, and pulled the lead out. My left/right hands completed the 110v circuit and was instantly attached to the wires - started walking backwards to release my hands, and they became stretched straight out, but the hands would NOT let go. The whole area had mirror walls and I watched myself getting fried - eyes the size of grapefruit. Thought "I'm a gonner". Started yelling, and pops looked at me in a laughing/joking way since many times we would startle each other when working on circuits. Finally, he realized it wasn't a joke and used a furring strip to knock the gang box from my hands.

    I also have a vintage Miller Sync 300. Often times due to rapid turn around, and being in the auto industry, there;s water or moisture in adjacent areas when welding (have even submersed parts to avoid warping etc). When the leather gloves get wet and you have 14v @ 300amps, that junk hurts. So does square wave 200amps - and if you forget a ground - boo-ya.

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    After poking around in the machine, found I have 200vdc already if the 3ph pull in relay is activated. This is great news since the relay can be wired in series with the e-stop, so that will remain functional. The spindle drive is FUBAR'D, so just need to control speed to keep working.

    Found a company in Hungary that specializes in DC to DC controllers, so may end up going this route. Either way, will report back with whatever option gone with for future reference. Here is a link to the product: LINK if you use the drop down menu, there's a 200v 45amp with heat sink option. They have sold many of these around the world and have good reviews. They usually deal with transportation, most of that stuff still uses high current DC.

    They suggested using a 200v 45 amp DC to DC circuit. 0-5v potentiometer and/or programmable via Arduino style boards. Then it's a matter of coming up with a logic and/or circuit for the field current control.

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    It will be a little tricky to refit a drive, can be done but there is a lot going on in side the control. Your motor is a stabilized shunt, (it has a weak series field) for speed regulation, but makes rev the motor a little tricky. Also to retain counter emf at high speeds the field can Not go to zero, ( you will need around 20% of full field voltage )to control the speed , and loss of all field power will overload the armature and the smoke will leak out. You might be better off to find a DC man and hire him do do the swap...Phil

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    Thanks Phil. This is not a retrofit, just something to keep the spindle turning at a desired speed for an interim.

    Currently undecided if a true retrofit to AC, or another repair/replacement of the spindle drive mother board this round. It seems no matter how many hours are on them, they fail after some years ('06, 13[or so?], 16 and now 2020). The parts are getting more scarce, used spindle drives were $600, now $3k and another 14yr older... it weren't for fresh windings, bearings and brushes just a couple years ago the motor would have likely been nixed at this point (the 200vAC-DC box was replaced with NOS in '16 when the top board was last repaired).

    The DC to DC driver linked in the above post has logic, feedback, pulse generator detection, hall effect throttle control, and programmable over-load shut down etc. Here's the datasheet with programming parameters: LINK

    Wouldn't a small circuit with logic be able to send a 0-5v signal to the DC/DC driver input case of an overload on the armature (or use the input current draw protection in the software)? The controller is pretty advanced, and is typically used with LiPo batteries which have a much less safety margin than regulated 208vAC/200vDC stable shop service.

    It's amazing when realizing the huge circuit boards of the past have been replaced with tiny bitty things. My Fluke fuse blew and of course didn't have a spare - borrowed the neighbors DMM and it was this little tiny red foreign-built box that couldn't weigh more than a couple ounces, and it got the job done, anyways. Out of curiosity, popped the screws out to look inside, and there was a board the size of a Zippo lighter, and with all the components, maybe 1/8" thick. Shoot, look at tricorders ('err, smartphones). I still have the TripleT in the bottom of the toolbox, it's quite hefty, even for the Fluke.

    Am I in left field trying this? Theoretically, it wouldn't take much firmware to actually integrate this DC/DC drive into the System 6 NC, but would rather do a full AC conversion - again this is a temporary "band-aid". Found someone parting a working (wore out ways) machine a few years newer that will almost be "plug-and-play", but all the wiring has already been cut, and uses newer connectors (lots and lots of patch wiring, ugh).

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    Quote Originally Posted by J.Caraher View Post
    Thanks Phil. This is not a retrofit, just something to keep the spindle turning at a desired speed for an interim.

    Currently undecided if a true retrofit to AC, or another repair/replacement of the spindle drive mother board this round. It seems no matter how many hours are on them, they fail after some years ('06, 13[or so?], 16 and now 2020). The parts are getting more scarce, used spindle drives were $600, now $3k and another 14yr older... it weren't for fresh windings, bearings and brushes just a couple years ago the motor would have likely been nixed at this point (the 200vAC-DC box was replaced with NOS in '16 when the top board was last repaired).

    The DC to DC driver linked in the above post has logic, feedback, pulse generator detection, hall effect throttle control, and programmable over-load shut down etc. Here's the datasheet with programming parameters: LINK

    Wouldn't a small circuit with logic be able to send a 0-5v signal to the DC/DC driver input case of an overload on the armature (or use the input current draw protection in the software)? The controller is pretty advanced, and is typically used with LiPo batteries which have a much less safety margin than regulated 208vAC/200vDC stable shop service.

    It's amazing when realizing the huge circuit boards of the past have been replaced with tiny bitty things. My Fluke fuse blew and of course didn't have a spare - borrowed the neighbors DMM and it was this little tiny red foreign-built box that couldn't weigh more than a couple ounces, and it got the job done, anyways. Out of curiosity, popped the screws out to look inside, and there was a board the size of a Zippo lighter, and with all the components, maybe 1/8" thick. Shoot, look at tricorders ('err, smartphones). I still have the TripleT in the bottom of the toolbox, it's quite hefty, even for the Fluke.

    Am I in left field trying this? Theoretically, it wouldn't take much firmware to actually integrate this DC/DC drive into the System 6 NC, but would rather do a full AC conversion - again this is a temporary "band-aid". Found someone parting a working (wore out ways) machine a few years newer that will almost be "plug-and-play", but all the wiring has already been cut, and uses newer connectors (lots and lots of patch wiring, ugh).
    Thing is, all that Arduous-in-you-yo-yo-ing and "small controller" stuff is re-inventing ADJUSTABLE "logic" that is already sitting there, right on the PCB of any decent (read "and seldom 180 VDC") DC Drive - the 3-Phase-input-only ones most of all.

    The need has been around for a long time. So have the drives that serve it.

    The majority either have the Field Regulator option on an area of the main board - or a connector for one on an option card plug-in.

    Moreover, their manuals have the needful "commissioning" steps and tests and/or a plug-in "configuration tool".

    Better - and end-fo-the-day CHEAPER - to have features already "there' that you may not need, and can "park", set agnostic/neutral, or bypass to not utilize, than the reverse and have to build them, DIY as they catch you up.

    WHEN you are planning to mass-produce several thousand, you head for minimizing unit cost.

    WHEN you have a marginally documented "one off" to simply repair? You grab the "over-qualified" toolset and use only what you need out of its general-purpose, wide-market, "universal donor" blood-type.

    That sort of "store bought" box it is itself independently re-purposable to some other challenge, later. Your kitchen-table kludge may or may not be, even if it works well for this application.

    And it might not- not only not "right out of the box", but even after weeks of experimenting, later.

    A Control Techniques, or a (John) Shackleton Systems Drives (1974 founding thru Eurotherm-era, and since 2005, part of Parker-Hannefin) "SSD" 4Q DC Drive might be "overkill", but each of those - and a few other "major-maker" drives - have just about EVERYTHING you could possibly need.

    Already. They are no longer virgins at this stuff. Not by a lot of years:

    Annnnd... their DC drives have been mass-produced and "in the market" for as much as a score of years, can be found NOS or used-but-good for very affordable prices.


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