Rope starting a 3 phase 7 1/2HP motor. Tips and tricks?

Guys,

I hope to soon get back to my primitive bare bones RPC project.

I have a 7 1/2HP low speed (1155RPM) 3 phase motor currently fitted with new bearings and reconfigured to 230V.

I am modestly self-confident with single phase residential wiring but have no real experience with three phase.

For the moment I just want to see the motor run. I am aware that there are three motor power inputs and that these are labeled T1, T2, and T3.

As far as I know the motor is designed to run clockwise looking at the motor shaft end. I am aware that a 3 phase motor, when powered by 3 phase, can be made to spin in either direction by simply transposing any two of the motor feeds.

But what about when you power it from single phase?

Is there a "standard" or "proper" way to make the connection? In other words, should one single phase hot go to T1, the other to T2? or T3? Or whatever? And another related question: Between T1, T2, and T3, is there a "standard" or "proper" or "best" (unsupplied) line to use as the wild leg?

If I spin the motor with a rope and then hit it with 230V at the appropriate amperage (I'm gonna start with a 50 amp single phase breaker) AND it's wired right my understanding is that it will spin on up and run.

But what happens if the rope start spins the motor in the wrong direction from which it's wired? Will it quickly stop? Keep spinning anyway? Go up in smoke?

I hope to use the motor to test run an old Gorton tracer mill. If everything starts and runs I hope to then build a more sophisticated 20HP unit.

Thanks for any help.

V

It starts and runs , happily, the way you spin it.

If its hooked up to a shop full of machines starting it the "wrong" way will make every three phase motor it powers also back up.

If you had a spare single phase motor, a spare pair of pulleys, a spare belt, a spare contactor and spare momentary switch, etc...

You could set up a pony motor to get the converter spinning (in the same direction, in a remote location, etc.)

As far as matching the speed, that isn't a deal-breaker; just get it rotating (right?).

Good Luck,
Steve

Vernon Tuck said:

Guys,

Is there a "standard" or "proper" way to make the connection? In other words, should one single phase hot go to T1, the other to T2? or T3? Or whatever? And another related question: Between T1, T2, and T3, is there a "standard" or "proper" or "best" (unsupplied) line to use as the wild leg?

>> It does not matter what two connections the single phase is connect to. But most
>> will use T1 and T2. T3 then is the generated leg.

If I spin the motor with a rope and then hit it with 230V at the appropriate amperage (I'm gonna start with a 50 amp single phase breaker) AND it's wired right my understanding is that it will spin on up and run.
>> That is the way the old-timers did it. Your understanding is correct.

But what happens if the rope start spins the motor in the wrong direction from which it's wired? Will it quickly stop? Keep spinning anyway? Go up in smoke?
>> The motor will quickly reverse and you will know that. It will not burn up. People
>> practice field reversal to quickly change the direction. One little experiment by you
>> wil do no harm.

Click to expand...

You may even try using tennis shoes to spin it. Ever see the term "kick start".

I rope-started my 5HP for a couple weeks before hooking up a pony motor.

Tip #1 - Make sure your rope is well clear of the motor pulley before throwing power to it. You sure don't want the pulley to catch the rope when you are holding it.

Tip #2 - Make sure there is nothing nearby to clobber with your elbow when you jerk the rope - like your 1/4" steel topped welding table.

Tip #3 - Like Steve said, you don't need to get it fully up to speed, but the faster you get it going the less starting current.

Tom

And another related question: Between T1, T2, and T3, is there a "standard" or "proper" or "best" (unsupplied) line to use as the wild leg?

Click to expand...

The standard nomenclature for RPC's is that T3 will always be the generated (wild) leg out of an RPC.

Just for testing it, a 20 amp circuit would be fine I suspect. My 5 hp idler starts
and runs my load motors, off a 15 amp circuit. As mentioned, does not matter
which motor leads you send to the utility power. And it will run the direction you
start it.

And, be sure the motor doesn't spin or walk while it's running or starting, and yank
the wires. If you screw it to a rough frame, that gives you a place to mount a smaller
motor to do the dirty work of starting it.

Totally awesome. John, your answer made me snicker. I can see a shop full of machines running backwards because I could never master the "righty tighty rule".

On a slightly tangential but still related subject...

Tonight I went window shopping on craigslist for some kind of 3 phase breaker box. I found a "20 space" 125 amp QO box for less than $100. However, I could not find the catalog number ("QON" or "QOC" 420 - the picture was terrible) after extensive googling. This led me to wonder if it might be a 30 or 40 year old obsolete box.

Although at one level, and because everything is now made in china anyway, I tend to think that brand loyalty is for suckers. Nevertheless, I can hardly bring myself to consider anything but Square D QO boxes and equipment. Alright, so I'm a sucker. But I'm a loyal sucker...

Seriously, regardless of brand, I would be very grateful for some help as to what I should be shopping for -- not only in terms of brand, but whether I should be looking for a box rated for 600 volts or if a 120 - 240v box is good enough for my purposes.

"My purposes" are: To get a 20 or 25hp idler motor going to run the shop. I don't care how primitive it is or isn't provided that it is safe as I can make it. A couple of months ago, I bought a 7 1/2HP motor. Soon afterward I bought two motor motors, a 20HP and a 25HP, from an ebay seller through "best offer". The seller advertised the motors as being "identical Dayton 20HP motors" having recently having been taken out of compressor service. When I bought them ($300 for the two) and picked 'em up they were stretch wrapped to a pallet. Hence I did not see the motors up close until about 10 days ago when I picked them up from my motor shop after he looked 'em over and test ran 'em. He also reconfigured them for 230V.

What I'd like to do is mount a 3 phase service panel near the machines and feed the panel from the output of first the 7 1/2HP motor. Later, I will substitute the 20 or the 25, once I get them properly wired and mounted. I also have a decision to make as to which one to use. If I use the 25HP motor as the idler I assume that a 125 amp 3 phase, 230V panel will be big enough for either? I think the 20HP motor outputs about 53 full load amps. So the 25HP unit would be... what? 65 amps? The motors are outside in our van and it's dark and rainy and I'm warm and dry so that detail will have to wait.

But if one of y'all would recommend an appropriate distribution box that will be hugely helpful - especially if you can quote the catalog number. I simply cannot afford to spend $300 - $500 for a 3 phase panel. So that means I will need to take my shopping list and buy on craigslist or ebay. The unit I saw on c/l supposedly will take QO, QO-T, or Q1 3 pole circuit breakers. I'm still trying to figure out if:

a) such a box will do or,

b) if it's obsolete, and

c) even if it is, if circuit breakers are still available for it.

Thanks yet again.

Vernon

not exactly answering your question but..
there is alot of this stuff out there

LOT OF 4 FUJI EARTH LEAKAGE ELECTRIC CIRCUIT BREAKERS 3 EG53B AND 1 EG33B | eBay

not as handy as an actual load center but these installed in an ordinary steel enclosure with jumpers across the top side is how virtually all machine tools are set up for all the multiple motors.
then something like this

http://www.ebay.com/itm/Allen-Bradl...677?pt=LH_DefaultDomain_0&hash=item2310d266bd

and your spittin' in tall cotton

I was able to rope start my 7.5 hp with great effort. When I hooked up a 1/2 hp to start it was easy. Some may kick start mine ' NO WAY'. ---Trevor

Rope started a 10hp when I went to look at and test my latest Van Norman, a 1-R3. Funny part was that we dug it out of the guy's scrap heap. Should have seen his face when it lit off and I started running everything on the VN as if we had three phase service. Lower rpm motors rope start more easily (duh... lol). A 3600rpm 10hp would probably be a royal PITA to rope start, but a 5 or 10hp 1750rpm should wick right off, 1100rpm, even easier.

What size Gorton mill is this that you are powering up, Vernon? Unless it is a real monster and you are going to run it at full load all the time (like a 7-10hp mill swinging a 48 tooth pie plate size facemill buried 1/2" deep) you may very well find the 7 1/2hp to be all you will ever need. I was going to build a 20hp converter when I first started out, but decided to go with a 5hp. It'll run my bridge mill with a 3hp spindle motor, 1/2 and 3/4hp feed motors all day long without anything getting hot. It'll also start and run my big old 5hp lathe, but it is a clutched spindle, so no load inrush on start except the motor itself. I have a home built cap start, cap balanced RPC.

I've had no luck "kick starting" my idler, and no luck using an electric pony motor either. Don't laugh -- I use a 5 hp gas engine from a IR construction compressor(two tank model) that sits in front of the first 10hp idler. With this set up zero starting issues. I have a 7.5hp and another 10 hp in parallel for a total of 27.5hp. I found an ITE three phase panel for $20 with breakers.

My 7.5hp RPC self-starts, so I was able to avoid this issue... but it seems that some sort of wood cone on the motor shaft, spun by a section of rubber radiator hose on a hand drill, would be easier and safer than the rope.

I went with the QO 3-phase box, too. Box was cheap. Breakers, not so cheap.

Chip

"I went with the QO 3-phase box, too. Box was cheap. Breakers, not so cheap."

True enough.

For whatever reason, Square D chooses to price single-pole (120 volt) breakers at around $8 retail ($8 per pole), two-pole (240 volt) breakers at around $16 retail (also $8 per pole) and three-pole breakers (240 volt) at around $90 retail ($30 per pole).

Go figure!

Here is a photo of a pony motor start 20 hp idler using a 3/4 hp pony motor. Both motors are 3450 rpm. It is noisy but does a great job of converting. I only need 120 mf of capacitance on each converted phase. It is operating a 15 hp, 24" Powermatic wood planer. Voltages were 245, 258 and 262 at idle and were within 3 volts of each other when running the planer but not passing any wood through the planer.

http://s686.photobucket.com/albums/vv225/toolnut_photos/Pony Motor Start Rotary Phase Converter/

7.5 HP Zip Starter

This is a R.P.C. I built about a year or two ago.I mounted a pull starter and it's driving dog, salvaged from an old lawn mower, on a 7.5 HP 4 pole (in Australia it is 1420 RPM 50 hertz) motor. Very easy to pull start the motor, always starts in the same direction.The back cable is the single phase input and the cover being held in my hand, has a 3 phase socket outlet mounted and is the RPC output.

Jim

I have a 30 hp 1160 rpm idler as a phase generator. It is outside in a steel enclosure. After a freezing rain event, the starting capacitor contactor was frozen. I gave the shaft a twist with my hand and pushed the start button. I was surprised how little rotation it took to have the motor come to speed.

Check out HGR Industrial (search for it in goggle) They have piles of stuff from motors, Transformers, disconnects, lathes, mills and just about everything else. They bring it in, list it with price and as time goes on if it don't sell the price keeps going down. They are in Euclid, Ohio, offer free pizza on Wednesdays and often have ook-outs on Saturdays when the weather warms up but will ship items if your too far away. I've seen 3 phase disconnects and motor starters being offered from time to time on their Markdown Madness page for $25.

Wow. Thanks!

Vernon

One interesting item I have run into, I have 3 hp low rotor mass motor for the RPC driving a 3 hp old design motor with a large rotor mass. When I tried to plug reverse the lathe, the lathe motor over took the RPC and reversed its rotation.

Tom