Operate servo motor off of DC battery?

deerefanatic · Mar 11, 2021

Hello,

I'm in the process of moving a CNC boring mill that has a dead control. I need to be able to jog the head/spindle up so that the counterweight can be rested on a steel support bar for the lift and move. The mill has 150 VDC brushed servo motors on it. I wondered if a guy could use 2 12v car batteries, 24V in total to drive the motor slowly to accomplish this.. Or, would I be better off to just support the head with a come-along, remove the motor and move it that way? My understanding is that ballscrews will freewheel.

CarbideBob · Mar 11, 2021

Maybe better if you want to move slowly is only one car battery.
Yes this works if DC brushed.
Bob

Guest · Mar 11, 2021

Can you get to the ball screw and turn it by hand?

Comatose · Mar 11, 2021

Adjustable power supplies are pretty cheap, cheaper than a car battery, and may be useful to you anyway when you start resurrecting the control. The big advantage is they current limit if something is bound up or shorted, whereas a car battery could smoke something.

Something like this. I don't have any experience with this specific one. DC Bench Power Supply, 30V/10A Dr.meter Variable 4-Digital LED Display Power Supply, Multifuncitonal (White): Amazon.com: Industrial & Scientific

thermite · Mar 11, 2021

deerefanatic said:
Hello,

I'm in the process of moving a CNC boring mill that has a dead control. I need to be able to jog the head/spindle up so that the counterweight can be rested on a steel support bar for the lift and move. The mill has 150 VDC brushed servo motors on it. I wondered if a guy could use 2 12v car batteries, 24V in total to drive the motor slowly to accomplish this.. Or, would I be better off to just support the head with a come-along, remove the motor and move it that way? My understanding is that ballscrews will freewheel.

Best power source for a "servo" motor is a counterpart to the one - or "class-of" - it was meant to be matched to. They tend to diverge a tad or three from plain vanilla Dee Cee motors.

Straight battery-sourced Dee Cee works a treat for nominal 230 VDC 10EE 3 HP straight-shunt and wound-field DC lathe motors where "slow" is good and their ain't voltage enuf to overheat nuthin'.

Motors in general need fairly deep pockets of Amperage to come off rest, under load most of all - even at Voltages too low to push much total power onct they DO commence to motating...and CEMF'ing.

"Starting" class IC engine market batteries and Marine/RV dual use HAVE that low resistance for the initial oomph. Deep-discharge and such may not, always.

More precise - regulated, and current limited - lab supplies are not EVEN as likely to make it happen. More likely to go immediately into "foldback current limit", what with the motor at-rest doing a fair job of pretending to be near-as-dammit a dead-short at initial power ON but not-only. Can't get THERE from HERE syndrome?

Ballscrews are reversible only if meant to be.. or on certain early truck and farm tractor Saginaw gear applications? Surprise arm-breakers out of ignorance when one wheel took a severe hit that either of worm and sector or cam and follower had already been engineered to block or absorb. Mostly, that HAD to be given a better balance ...and was.

So I would NOT count on them being reversible on a(ny) servo'ed machine tool ... unless they SAY they are or you have already seen that it works that way.

CarbideBob · Mar 11, 2021

I know for a fact that one can power the axis servos on this machine with a car battery and jumper cables.
BTDT in a situation similar to the OPs.
Perm mag brush dc. Do any DC brush axis servos on any machine tool have a field? Spindles of course yes but axis drives?

Up/down axis motors often have a brake which will be a problem and makes turning the screw by hand just about impossible unless power is applied to the brake to release it.
Good news is that if equipped with a brake the axis screw will not backdrive in transport.
Bob

Phil in Montana · Mar 11, 2021

if its a brushed servo, a battery charge will move it...Phil

Ziggy2 · Mar 11, 2021

CarbideBob said:
Do any DC brush axis servos on any machine tool have a field? Spindles of course yes but axis drives?

Up/down axis motors often have a brake which will be a problem and makes turning the screw by hand just about impossible unless power is applied to the brake to release it.

I think some of the large old NC machines used DC servo motors with fields but these would be 3hp to 15hp sized motors.

I think Thermite was trying to make the point that the smaller lab power supplies will probably not supply enough current to get the servo motor to start to move before they go into overload.

The OP never mentioned how big of a CNC this is so the servo motor size and associated load are at best a guess with what we consider average.

A battery charger with appropriate circuit breaker would likely be more appropriate or else the batteries as you suggested.

thermite · Mar 12, 2021

Ziggy2 said:
..Thermite was trying to make the point that the smaller lab power supplies will probably not supply enough current to get the servo motor to start to move before they go into overload.

Nor will LARGE ones. Lab bench supplies are meant to preserve the lab and other gear on the bench. Not act as welders, missile squibs, nor rail guns.

So they have appropriate and sensitive solid-state sensors to reduce or prevent "drama".

CarbideBob nailed it. Same machine. Jumper cables JF worked.

"Brake" needs I know not, that needs checked.

One of my "NOS" 180 VDC Dinosaur-Current RPM III motors has an auto-engaged brake. But the "release" coil isn't meant for DC at all. Data plate calls for 120 V AC to hold-off braking.

In THIS case one may TRY it @ 12 V, but not be surprised if some OTHER source is needed if brakes there be.

Brakes generally prefer ON/OFF within a narrower operating range than the variable-voltage motors are good with.

See above - the RPM III, and "not-only". MOST electric brakes on a(ny) variable service will need independent powering for useful predictability.

Comatose · Mar 12, 2021

thermite said:
Nor will LARGE ones. Lab bench supplies are meant to preserve the lab and other gear on the bench. Not act as welders, missile squibs, nor rail guns.

So they have appropriate and sensitive solid-state sensors to reduce or prevent "drama".

Please. It'll fold back to the limit current, which is exactly what you want. A brushed DC servo on an old machine is gonna be what, 500W at 150V? Maybe a kilowatt? The full torque current, even in operation, is gonna be less than 10A. There meaningfully weren't high current dc axis drives back in the day. No IGBTs to support it.

But hey, feel free to Tim the Toolman Taylor it with jumper cables.

thermite · Mar 12, 2021

Comatose said:
There meaningfully weren't high current dc axis drives back in the day. No IGBTs to support it.

ROFL! Youngsters!!! "Nothing happened before we arrived?" is it?

"spew alert" before you make another funny of that class, wilyah?

Tip of a VERY large "iceberg", "pre IGBT" wise?

Gears of war: When mechanical analog computers ruled the waves | Ars Technica

HWElecRepair · Mar 12, 2021

CarbideBob said:
Up/down axis motors often have a brake which will be a problem and makes turning the screw by hand just about impossible unless power is applied to the brake to release it.
Good news is that if equipped with a brake the axis screw will not backdrive in transport.
Bob

+1 to this.

DDoug · Mar 12, 2021

On larger d.c motors, a stick welder has been used.

NOT a MIG welder.

I've seen it done with the old Lincoln variable shunt models, start low, and bring up
the current as needed.

deerefanatic · Mar 12, 2021

Sorry to not speak back up sooner..

These are BIG servos. The amps are 150VDC Allen Bradley 1388's, rated at 40 AMPS (3KW). These are on a Wotan Rapid 1 Horizontal Boring mill. I'm gonna guess the spindle head is over 1000 lbs (but counterweighted). I'm going to have to do some digging to see what the voltage for the brake is. The servo motor is about 13ft up in the air on top of the column. It attaches to a gearbox, which then drives the ballscrew.

thermite · Mar 12, 2021

deerefanatic said:
Sorry to not speak back up sooner..

These are BIG servos. The amps are 150VDC Allen Bradley 1388's, rated at 40 AMPS (3KW). These are on a Wotan Rapid 1 Horizontal Boring mill. I'm gonna guess the spindle head is over 1000 lbs (but counterweighted). I'm going to have to do some digging to see what the voltage for the brake is. The servo motor is about 13ft up in the air on top of the column. It attaches to a gearbox, which then drives the ballscrew.

Welll... it the brake is ON it, then "Plan B" would be to separate it and drive the gearbox input (or out-put-side ballscrew) "directly" with whatever you can get at it. A heavy "corded" reduction-gear drill motor, maybe?

An air impact wrench is rudely insulting to precision ballscrews, so I wouldn't.

Not "fun" but a 4-way lug wrench welded to a coupling, used windlass style, and two men if not one could lift 'er far enough on muscle to get dunnage under, then set 'er back down on it. Prolly closer to 3,000 lbs and a bit than 1,000, but we have all changed a flat on a far heavier truck, and the counterweight is intact, yah?

vmipacman · Mar 12, 2021

If it’s a big vertical axis there will be a brake on that motor. Too much cowboy electronics for me. I wouldn’t do it that way. My opinion is do your second option. Support the head with bottle jack, loose the motor mount and timing belt, let if slip over the timing gear teeth until at the desired height and retighten Mount. Last time I did this was moving a machine from a busy plant and everyone is a critic. Hot wiring the motor would have looked bad. Just a thought

thermite · Mar 12, 2021

vmipacman said:
If it’s a big vertical axis there will be a brake on that motor. Too much cowboy electronics for me. I wouldn’t do it that way. My opinion is do your second option. Support the head with bottle jack, loose the motor mount and timing belt, let if slip over the timing gear teeth until at the desired height and retighten Mount. Last time I did this was moving a machine from a busy plant and everyone is a critic. Hot wiring the motor would have looked bad. Just a thought

I think this one is hard-down and needs to come UP and inch or several, but no more than that, so yaz. Wrench rather than cables.

More intuitive, better understood risks, easier to coordinate between players, "etc."

Ziggy2 · Mar 12, 2021

vmipacman said:
If it’s a big vertical axis there will be a brake on that motor. Too much cowboy electronics for me. I wouldn’t do it that way. My opinion is do your second option. Support the head with bottle jack, loose the motor mount and timing belt, let if slip over the timing gear teeth until at the desired height and retighten Mount. Last time I did this was moving a machine from a busy plant and everyone is a critic. Hot wiring the motor would have looked bad. Just a thought

There will also be gib locks on the head that might be locked or on locked. You will not be able to move the head even with the servo motor disconnected and the motor brake off unless the gib locks are in the unlocked position.

Phil in Montana · Mar 12, 2021

Just need a little bigger charger, the 40 amps is at full speed, at 12 volts the amps will be down to less than 1/2 and it will move...Phil

deerefanatic · Mar 12, 2021

Does this machine for sure have Gib Locks? I talked with a gentleman that used to service this machine at the plant it was in for years and he said there aren't any brakes/locks other than the one in the servo itself..

As for the timing belt, there is none. The servo is mounted directly to the y axis ballscrew gearbox.

Operate servo motor off of DC battery?

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