160 volt 3-8 amp power supply?

Yes, absolutely! :-)

If you've never designed a switcher before, don't start now! Either buy one and be done with it, or:

Depending on how picky your motors are about waveform. If you use current drivers, then you shouldn't need very smooth DC at all. I used to repair pinball machines, and they run all the lights and solenoids off of half-wave rectified pulsating DC, and they use SCRs for switches. I don't know how applicable that is here - I did do a motor driver with a current sink once, which didn't care what the input voltage was, as long as it was more than about 18V.

The isolation transformer (see above) will keep the whole system isolated; as far as isolation between the control circuitry and the mongo current, just use your own discretion. ;-)

BTW, what's a "magnetic pulse isolator?"

Have Fun! Rich

Seems you swapped the currents there? Unless they're smart motors ;)

Nah, more of a 'don't touch' voltage. 160V -> that's close to rectified mains peak over there? Maybe an isolated drive to bridge rectified mains?

You want to reverse the motors (full bridge)?

Something like that, depends how fine a control you're after. There's an H-bridge topology that has the direction switches around the motor, then a separate current controlled switching MOSFET in the negative lead of the H.

But, you'll have to search for the thing, I forgot where I saw it. Common.

Then you get to decide whether that's the way to go, or separately control the output voltage to the H bridge. For a one-off, I wouldn't try merging speed control into the H bridge unless you find an IC that does it all and shows you how in the application notes.

Grant.

...

Fun stuff, particularly the older ones. I attended the Bally seminar when the new 6800 based machines came out -- new rules like no contact file on the gold plated sensor contacts...

Well, since OP talks of 160V, that's a big servo probably run with the old style rectify mains then SCR for speed control.

Possibly a pulse transformer to for the SCR gates, less common for MOSFET gate drive.

Grant.

Like an opto-isolator, but they use magnetic coupling to isolate instead of light. Much faster switching times.

example:

Based on a PDF for a similar motor (same company and base part number, but not 3-phase). If you lock the rotor, it can withstand 2.5 amps continuously. For short-duration pulses, it can withstand up to 7.4 amps. At least that's how I interpret the specs...

I'm still iffy about the actual drive voltage. I based it on hooking the motor to my drill press and getting 27 VAC out of the windings at

1000 RPM, then estimating the voltage needed to get it powered at full speed with usable torque. I also compared the measurable specs with the PDF and the motor they matched was a 160v motor.

That's kinda the whole point of servo motors. These are three-phase BLDC motors, not R/C servos. So, three high/low pairs per motor.

The MCUs I'm going to use have tons of motor control app notes, *that* part isn't the problem. I just don't want to let the magic smoke out before it's time...

As for the bridge itself, there are plenty of smart chips and high-v mosfets at digikey, I don't expect that part to be too complicated.

Cool! :-)

Thanks! Rich

I don't know about big servos, but I have an industrial 1/3 HP DC motor and controller, and the heart of the controller schematic looks an awful lot like a typical lamp dimmer. No isolation. YMMV.

Best regards,

Bob Masta DAQARTA v5.10 Data AcQuisition And Real-Time Analysis

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The point that they are three phase should have been in the original post. Servo motors can mean a lot of things including AC, DC, stepper or amplidyne systems.

Three phase from zero RPM?

My guess was no one was thinking RC servo.

BLDC?

Don't use mosfets, use IGBTs

Don't control voltage, control current (ie. torque).

Power supply doesn't need regulation, just rectify and use a substantial reservoir capacitor.

Don't forget that decelerating (braking) motors makes them regenerate. The inertial energy has to go somewhere, like back into the DC supply.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

They had to *tell* you that?

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Probably permanent magnet rotor.

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Have you ever seen a RC servo that runs on 160 volts?

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Not yet.

I wonder what voltage the larger military RC airplanes use?

Servo has several definitions. I think of electrical signal to movement with feedback, but encountered its use in speed control for things like capstan and tape reel drives too, so I didn't immediately assume he meant it has to work from zero rpm.

The audio fringe element has something called servo feedback where the output from a speaker (actual movement or with a microphone) is compared to the input signal and corrected.

The drones?

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Talking about brakes...

Today, while setting basic parms in a Baldor VS1MD drive, I found a unique problem when using the DC brake in STOP mode. When you open the run circuit, the DC brake operation engages like it should how ever, while it's doing it's 6 sec applied brake of 100% current to the motor for quick stops, in case the load is moving out of control speed and if you vary the PID feed back reference from 0..10 or 10..0 volts, which comes from a POT, the drive putts itself back into run mode with run mode LED on and not flashing like it does when DC braking is being applied. The interesting point here is, the RUN circuit is in the OFF state as far as the external terminals are concerned and this drive is now in a normal on state doing what it does with things are normally does, but with the RUN REVERSE terminal (P8) not even on.. And the only way to clear the problem is a drive repower..

This clearly looks like a firmware problem while DC braking is in operation. Some bit must of gotten toggled on during that operation when it saw a feed back reference error of that extreme.. Cycling the RUN terminals does not clear the problem..

Oh well, so much for QC with the firmware..

Probably any of these:

From the size of them, it looks like a lot of them would use the standard

120V, 400~ 3-phase and 28VDC.

But I wouldn't be surprised to find that the really small ones use something similar to the Futaba hobby RC stuff.

So, essentially, I'm guessing. ;-)

Cheers! Rich

That changes the power supply design? I can manage the control side of this, it's the 1000 Watt power supply I'm worried about, or if I'm way off in my power estimates.

Well, these have 1000-step quadrature encoders on them, I suppose with enough finesse you could control the position down to a dead stop. The guy who picked them was thinking CNC.

:)

Brushless DC. Wired like a three-phase AC motor, but designed to be driven by a phase-controlled DC signal with a feedback loop from some sort of shaft-position-sensor. Magnets in the rotor, coils fixed in the stator.