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Hukshawn
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In Europe we used induction motors in our walk behind lawnmowers and they had to meet stopping time requirements with shut off. To the best of my remembrance they were very simple friction brakes, but sigh can't remember all the details.
David
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Hukshawn
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I've heard that 3 ph motors are more power than single phase. What would be the 3 phase comparator to a single phase 2hp?
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This came from a really old timer in the mid-70s. He was nearing retirement then so probably isn't even alive now. I haven't had need for this information since so cannot guarantee it would work like you would think. But I did see it work then, although it wasn't me that did the work. I was the hey you go-getter in those days.....
For a single phase motor, take one half of the line voltage and rectify it. No need for filters, just a full wave bridge. i.e. 120 V line, use 60 V source. For 240 V line, use 120 V source.
Set up an interlocking contactor so when the main drops out, the brake runs for several seconds into the T1 and T2 leads to the motor. Be sure the interlock works properly, mechanical being preferable. Start with three seconds then adjust up or down as needed. Do not exceed ten seconds. Well. you can, but do so at your own risk.
We used a 480/240 control transformer wired so the 480 was the motor feed and the 240 was the DC to the motor. Best I remember it was on the 240 side of the plant, it may have been the 220 side. In any case, the 120 volt motor got 60 volts more or less for braking.
This is known as dynamic braking so is not an absolute locked rotor stop. It tapers off as the motor speed decreases. While not a safety shutdown, it does dramaticaly reduce the motor speed. You mentioned some gearing overhead. Between the two it should stop pretty quick.
The application was on an internal pipe grinder of 19 ft reach and 4+ inch diameter. It significantly cut down the maintenance on the rotary grinding head. It may do what you want..... Presumably the same technique would work with three phase motors and a poly-phase rectifier.
As an aside;
I've heard that 3 ph motors are more power than single phase. What would be the 3 phase comparator to a single phase 2hp?
A three phase motor is much more efficient than a single phase motor. However, when spec'ing the motor, a horsepower is a horsepower. It's calculated in during the making. Think of the square root of two. That's the conversion factor between single and three phase.
For a single phase motor, take one half of the line voltage and rectify it. No need for filters, just a full wave bridge. i.e. 120 V line, use 60 V source. For 240 V line, use 120 V source.
Set up an interlocking contactor so when the main drops out, the brake runs for several seconds into the T1 and T2 leads to the motor. Be sure the interlock works properly, mechanical being preferable. Start with three seconds then adjust up or down as needed. Do not exceed ten seconds. Well. you can, but do so at your own risk.
We used a 480/240 control transformer wired so the 480 was the motor feed and the 240 was the DC to the motor. Best I remember it was on the 240 side of the plant, it may have been the 220 side. In any case, the 120 volt motor got 60 volts more or less for braking.
This is known as dynamic braking so is not an absolute locked rotor stop. It tapers off as the motor speed decreases. While not a safety shutdown, it does dramaticaly reduce the motor speed. You mentioned some gearing overhead. Between the two it should stop pretty quick.
The application was on an internal pipe grinder of 19 ft reach and 4+ inch diameter. It significantly cut down the maintenance on the rotary grinding head. It may do what you want..... Presumably the same technique would work with three phase motors and a poly-phase rectifier.
As an aside;
I've heard that 3 ph motors are more power than single phase. What would be the 3 phase comparator to a single phase 2hp?
A three phase motor is much more efficient than a single phase motor. However, when spec'ing the motor, a horsepower is a horsepower. It's calculated in during the making. Think of the square root of two. That's the conversion factor between single and three phase.
Bill Hudson
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