0
\$\begingroup\$

I have two Magnum 400 10/20 drivers running two stepper motors. Peak power consumption is about 2 kW.

In the event of a power failure on the 3-phase supply, I'd like to trigger a controlled emergency stop. Sudden uncontrolled stop could be fatal to the worm drive in the equipment, due to inertia on the other end.

But that means I have to supply power for an additional two seconds or so to control the motors during deceleration ramp.

How can I do that? Is there some sort of 3-phase UPS or generator that can kick in and do the job?

\$\endgroup\$
3
\$\begingroup\$

There are various companies which sell 3-phase UPSs. Unfortunately, they provide a whole lot of power (a small one is 10 KVA) - and cost a whole lot of money.

Have you considered a large single-phase UPS driving a phase converter? You'd need a relatively high peak power capability but minimal backup duration.

\$\endgroup\$
  • \$\begingroup\$ My problem exactly. I thought about putting in two inverters (to keep the load balanced), but it's not very elegant. Still it's the only solution I could think of on my own. \$\endgroup\$ – frnhr May 11 '14 at 10:57
3
\$\begingroup\$

This is the sort of thing a motor-generator with a decent-sized flywheel is good at. You basically have an electric motor and a generator that share a common shaft. You run the equipment off of the generator all of the time, and if the power input to the motor fails, you still get several seconds of useful output from the generator before it loses too much momentum.

These used to be used in mainframe computer installations so that the equipment could "ride through" short power glitches and perform a controlled shutdown (e.g., park the disk drive heads) in the event of total failure.

\$\endgroup\$
  • \$\begingroup\$ Yeah, I think this is it! Only I with those motors were less noisy :) \$\endgroup\$ – frnhr May 11 '14 at 10:58
  • \$\begingroup\$ Are they noisy these days? Back in the 1970s, I worked in an IBM shop, and we had the MG units right near the operator's consoles, and they really weren't any noisier than the cooling fans in any of the rest of the equipment. \$\endgroup\$ – Dave Tweed May 11 '14 at 11:06
2
\$\begingroup\$

It's worth asking if you can bypass the motor-generator in Dave's answer and put the flywheel directly on the shaft, as a purely mechanical energy store. Given they are stepper motors you would need to isolate them from the supply in the event of failure so they can "freewheel" to a stop.

The load of the flywheel would also affect startup and any speed changes during normal operation; only you have the bigger picture to determine if this is a viable solution.

\$\endgroup\$
  • \$\begingroup\$ Interesting idea! Not doable in my case, I'm afraid, but still interesting, thanks! \$\endgroup\$ – frnhr May 11 '14 at 10:54
  • \$\begingroup\$ You might want to rethink this idea. He specifically needs to perform an emergency stop in about two seconds. He said nothing about letting things coast to a stop. (If he could,, he wouldn't need an emergency stop.) A large flywheel is obviously going to be hard to stop quickly. \$\endgroup\$ – WhatRoughBeast May 11 '14 at 11:54
  • \$\begingroup\$ @ WhatRoughBeast : I didn't say a large flywheel : I meant a flywheel appropriately sized to stop in the desired time (2s). And coasting the motor (disconnecting low impedance "brakes") allows you to reduce the flywheel mass needed for a given rundown time. \$\endgroup\$ – Brian Drummond May 11 '14 at 13:07
  • \$\begingroup\$ The inertia of the system is constant, so that should be good for a flywheel solution. The problem is I don't think I'll have the space to put the flywheel in. \$\endgroup\$ – frnhr May 11 '14 at 20:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.