Small Electric Motors - Any Hope?

[hman]

@Bi11Hudson - Good point about the lowest scale on an Amprobe. I get around this limitation when necessary with a homemade "gizmo." It's some solid copper wire (I think 14 or 16 gauge) taken from Romex and a couple of cord caps. One conductor is formed into a single loop, the other is looped around10 times. And if nothing else, the gizmo lets me measure current without having to open up the DUT and separate out the conductors.

 

[Bi11Hudson]

RE the preceding post: Somewhere I have a molded plastic adaptor for the same purpose. It's only 1:1 and 2 wire. From the old days before ground conductors. I like the pictured adaptor, but one should be careful with such a winding. At 50-60 cycles it wouldn't have any effect, but a high speed pulse could cause problems. Like lightening. . .

Sea Story alert. This really isn't relevant except from the perspective of safety. The difference between a fairy tale and a sea story? The fairy tale starts as "Once upon a time", the sea story starts as "This ain't no $#!t. I was there, I saw it"

I was working in an old rolling mill built around 1920(~'86) with a 480 Volt "grounded delta" electrical system(grandfathered) and no cooling in the MCC.(Motor Control Center) Using a "Wiggington" type tester, I read zero(0) volts phase to phase on the buss bars. A rare occasion, I didn't test the Wiggie on a known good circuit. In a rush, the mill was freezing. . . My Wiggie had a broken lead. It was summer, the MCC was hot, I was sweaty. I grabbed the frame (C phase) and leaned in to reach between the buss bars. My right hand between the A Phase and B Phase buss bars, my left hand at ground, the C Phase. On normal "Wye" connected systems, Phase to Ground is 277 volts. On a grounded Delta system, Ground is the third phase. So I got 480 Volts Phase to Phase across the chest. (Across the heart) That knocked me back, into a live front 900 volts DC switchboard. I wasn't hung up, fell free. But still have the burn scars on my shoulder. And best of all, I'm still alive to tell about it. The "B" rate with me was scared I was dead. When I woke up, he was stark white and had thrown up.

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[hman]

You're absolutely right about the hazards of jury-rigged gizmos. I ALWAYS check to see that the insulation around all the conductors is intact. And as you can see, it's ONLY mean for 115 volts. I've never had to deal with anything above 230VAC ... and damned happy about that. Very happy to know that you survived, and are here to tell about it!

 

[Bi11Hudson]

Thank you, Sir. Just another sea story, of which there are many over my lifespan. Get me wound up about "pre-OSHA" electrical systems, 2300 volts, 7200 volts, and 4160 volts where a motor is driven across the line. 480 was "low" voltage in those days. God is keeping me alive for His purposes. I don't worry about it too much.

You can thank Tommy Edison for the low voltages used for domestic systems. A 240 (220, 230, etc) volt system is only 120 volts to ground. It only becomes 240 when one gets across the two lines. Rare, but it can happen. That's why a ground conductor is so important. Even truck batteries, at 12 volts, can be dangerous. And 12 volt systems are well below OSHA standards. I had an uncle lost a finger when his wedding ring got across a battery. 120 volts is considered high voltage when the circumstances warrant. 120 volts can kill just as dead as 4160. A good point to keep in mind.

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[TomKro]

Those sure are exciting work stories. Glad you're still here too.

My work hazards were limited to paper cuts and occasionally losing a big spreadsheet file. Recently retired, so now I can tinker with old electric motors.

Since Thomas Edison was mentioned, I have some pics of a very old GE motor for forum amusement. This one I actually purchased without knowing the cast feet had been cut up. It runs smooth, but unfortunately another hot case. No obvious problems with the power cords, so maybe just insulation issues from moisture and time.

Here's the nameplate:



When I opened it up, the only broken component was a small thrust washer. In the pic you can see the cast foot that was chopped up for some remounting/repurpose.



The windings in the frame cleaned up pretty easy. Note the knot in the power line for strain relief.



The rotor was interesting. The tapered contacts on the left slide along the motor shaft (interior to the rotor windings) with some sort of weight disk on the right. Not clear as to what provided the lateral forces to make/break the contacts. Also, the case bolts were 1/4-20 with brass acorn nut ends. Pretty heavy duty for a 1/4 HP motor. I had to add a jam nut to back out one of the short case bolts that dead ended in the case.



On one end cap was some sort of spring loaded brush control rocker plate. Not clear to me if just for assembly, or if the sliding component on the rotor also backed off these brushes.




Are there any antique motor repair folks out in H-M land?

I doubt the feed wiring is causing the hot case. Maybe someone could use some vintage parts?

Hope you all enjoyed the historical hardware pics.

TomKro

 

[Bi11Hudson]

Another Sea Story for y'all. I've been up all night, couldn't sleep and just wanted to recount some of my experiences.

Background: the same mill as noted above. The furnaces (2) used 115KV to the plant, where it was reduced to 44KV. The 44KV crossed the plant to another transformer where the power was reduced to ~300 volts for the electrodes. I'm not real sure about the electrode voltage, that just sounds right. We're talking over 30 years ago. FWIW, I am not, and never have been a "High Voltage Lineman".

To put the arc furnaces in perspective, picture in your mind a Lincoln "Buzz Box" welder, a farm welder. Three of them, since it was 3 phase. The arc is adjusted by making arc length for each phase longer or shorter. Now picture the "rods", the electrodes as 14 inches diameter. They were toward the small end, USSteel used 18 inch electrodes. Bigger ladles. . .

I will admit up front the failure was my fault. I made a mistake and cost the company several days down time. In my defense, I had been working 84 hour weeks for a while. 7 -12s, no break, no relaxing time, get up, go to work, go home sleep, get up again. When the boss told me to open the switch, I opened the switch. High voltage, 115KV, uses an Oil Circuit Breaker where the contacts are covered with oil to prevent flash over. The disconnect is just that, not a control device, just a way to ensure the circuit is dead. The OCB is supposed to handle loading and unloading the circuit. The disconnect just isolates.

There had been a miscommunication between my boss and the production foreman. Both of the furnaces were running flat out, called a "flat bath" where the ladle was melted and temperature was being brought up. Boss told me to open the switch, I opened the "disconnect" without opening the OCB. Those 84 hour weeks caught up with me. At near full load, when the jacks opened, they arced across. And continued to arc for nearly a minute. At the time, it felt more like 2 hours. The jacks were originally some seven feet long. By the time the arc cut out, they were only about three feet. All I could do was hunker down and pull my collar up to prevent the sparks from getting in my clothes. Shut down the plant for 3-4 days while the power company repaired the switch. Me? I was just numb. There was no disciplinary action taken, I didn't even get chewed out.
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