Tricky motor wiring question.

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Old 07-12-07, 07:17 PM
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Tricky motor wiring question.

hello.i'm building an automated stone polisher(fancy name for contraption that carries a 4 1/2" wet angle grinder back & forth 36").i want to use a 1/2 hp cont duty1800 rpm 120v reversible motor to drive a 1" n.f.threaded rod(4:1 speed reduction via v-belt).firstly,what kind of electrical equipment do i need to allow automatic reversal after hitting set limits?and possibly a simple line drawing to help me wire them up?my electrical ability is basic & limited.thirdly,would there be any detrimental effects on motor to continuously & instantaneously reverse directions(every 30 sec. to a min.)thanks in advance for any information you might have to offer.
 
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Old 07-12-07, 09:53 PM
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If you are wanting to use this device in your home it will be rather complicated and probably not too reliable.

It is quite easy to instantly reverse a 3 phase motor but to do it on a single phase motor will require some surgery on the motor. Instant reversing is going to be hard on all the mechanical parts of your device.

You will need to have some limit switches that can be activated by the carriage. Adjustment of these limit switches may be critical if you do not (or cannot) allow for overtravel in the carriage.

If you could alter your design to allow for a momentary stop of the carriage motor at each end of its travel (it doesn't need to be a complete stop of the motor, just not instantaneous reversal) it would be far easier on the motor and mechanical components.
 
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Old 07-12-07, 10:51 PM
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yes. i was designing this at home for home use,single phase 120/240.i was told to go with a 3 ph motor & vfd.ultimately i would like to have top of the line drive for this but can't afford to spent 1000's on it. i don't know much on the costs of things but phase converters,vfd's & such can't be cheap... let alone wiring every thing up to work properly.not to mention having no idea as to what particular spec. requirements i need to source out such a drive.if money were no object how would you set up this drive?
 
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Old 07-13-07, 12:04 PM
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well, with the 3 phase motor and VFd, you are already over $1k.

If you slam that thing in reverse, you are going to have some problems. Most motors are not intended to do an immediate about face.

If money were no object; I would use a linear motor. They can be programmed via their controllers for various speeds and distances.


If you do not need to alter the distance travelled, I would consider some sort or drive such as chain or belt and attach a pull that would simply pull the grinder along withit. As it reached the end aand went around the pulley/sprocket, it would go the other way.

You would need the polisher to be on a track of some sort and a linkage that would allow it to reach the chain/belt at all times but that isn;t to big of a deal.

If you are creative, you could use a pneumatic or hydraulic actuator as well.
 
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Old 07-13-07, 12:21 PM
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You will have to extend , from the internal motor wiring, two leads from the "Start winding, "S1" & "S2" , and two leads from the 'Run" winding, "R1" & "R2".

These 4 leads will connect to the terminals of two 4-pole contactors, and "F" ( Forward) contactor, and an "R" (Reverse) contactor.

With "L1" as the Black wire of the 2-wire ,120 volt Line circuit, and "L2" as the White wire of the Line-circuit, the "F" contactor is wired so that "L1" is switched to "S1" & "R1", and "L2" is switched to "S2" & "R2".

The "R" contactor is wired so that "L1" is switched to S1" & "R2" and "L2" is switched to "S2 & R1". Note the "reverse" in the "R" contactor wiring--- "L1" to "R2", and "L2 to R1".

If you use contactors with 24 volts coils, you will have a lo-voltage, lo-current control-circuit, ideal for wiring the control devices.
 
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Old 07-13-07, 02:43 PM
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There are several ways that this could be accomplished. I really cannot comment on the "if money were no object" theme because money is ALWAYS an object than needs to be considered.

PATTBAA has the beginngs of a control circuit. Nap also has good suggestions, especially the use of a pneumatic drive for the carriage travel. It would require a compressed air source but it could be implemented a bit easier than an electrical drive and it would also be easier to adjust the speed of travel.

I would consider a permanent magnet DC motor with a brake for the carriage drive if you could allow for an overtravel beyond whatever the grinding head is polishing. Limit switches become more critical (and expensive) the closer a tolerance you need to maintain.
 
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Old 07-13-07, 10:40 PM
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For what you're attempting you'd be much better off with a servo or stepper type motor. Both of these types of motor are designed to reverse almost instantly (smaller versions run the print heads back and forth and move the rollers in most types of printers, larger ones drive the wheels on some types of motorized chairs. Various robotics magazines have articles on how to build drive electronics for these motors. Since the motors often have circuitry to count how many times they turn it's possible to build a controller that doesn't need limit switches (you'd need safety overrun switches regardless). Fairly large motors and controllers that will control speed and direction are often available at surplus companies that advertise in the robotics and most electronics magazines.

Using single phase motors to instantly reverse is going to be very problematic. The function of the start winding is strictly to impart motion to the rotor of the motor. Reversing the motor when stopped is a matter of reversing the start winding connections. If the start winding is removed from the circuit before power is supplied you can start the motor spinning either direction by wrapping a string around the shaft and pulling the string. Reversing the power to the motor while it is spinning won't reverse the motor. Applying power to the start winding while the motor is in motion, especially if in reverse to the direction is running, will most often just slow the motor and not stop or reverse it as the run windings have much more torque. The most likely outcome is letting the high pressure black smoke out of the start and possibly run windings and/or the capacitor in the start circuit will explode. Even if this somehow managed to reverse the motor it wouldn't be instantaneous nor would the point of reverse be repeatable with any accuracy.

With a 3 phase motor reversing two of the leads actually changes the orientation of the poles in the motor and it has no choice but to reverse. This is hard on all the components in a motor and one not designed to do this will self distruct over not too many cycles. The smallest single phase 120 volt to 240 volt 3 phase VFDs run around $300.00 but usually won't handle the currents involved in instantly reversing the motor.
 
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Old 07-15-07, 04:50 PM
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okay...i've decided that before i spend big bucks on a fancy drive i'm going to do what i can & as cheaply as possible to achieve carriage travel so that i can at least verify proper function.i was originally planning on using a hydraulic drive because this has 36" vertical travel as well as horizontal travel.for the most part though i don't really anticipate needing vertical travel(aside from raising work pieceto a comfortable working height rather than 18" off ground)i can raise & lower hydraulic cylinders pneumatically for now.so what i've done is bought a 50$ square D 2601-ag2 reversing drum switch(instuction bulletin ref.344as).the problem i now face is wiring it.there are 9 different configurations with 3 pertaining to single phase operation.i have to determine whether my motor is a split phase motor,a 4 wire repulsion induction motor or a 3 wire motor.inside my motor is a ceramic terminal block numbered 1 through 6.# 1 has a yellow wire and a spot for incoming line.#2 has no terminal(has a hole for rivit but no terminal is there).#3 has terminal but no wire.#4 has a red wire.#5 has a brown wire & a yellow wire.#6 has a blue wire,a black wire and a spot for incoming line.when i bought this motor as a garage sale it came with a 2 wire non-polarized plug(i'm assuming for demonstration purposes only & yes i will be upgrading to proper grounded plug).of # 1 & #6 which terminal is hot & which is common?i also know that water & electricity don't mix.the polisher has it's own gfci in power cord & i plan to mount a gfci outlet on machine as well as ground machine directly to ground rod.motor & controls will be well away from water source & over spray.anyway... back to motor.to reverse rotation i exchange #5 yellow with #6 blue.not sure of the relevance but # 1 yellow & # 5 brown dissappear to 1 side of terminal block and all other wires dissappear to the other side.i'm suspecting something is going on underneath terminal block otherwise why would #4 red be standing alone?i know this sounds like rather hokey info but maybe i can use multimeter to check for continuity & resistance if more info is needed to determine internal wiring.i'm trying to avoid complete disassembly of motor but i will if i have to.i also have 2 limit switches i want to incorperate to prevent overtravel of carriage.i'm not too concered about having to manually stop & reverse motor since i will only require 1 maybe 2 passes before i turn everything off to change grit sizes(8 in total).thanks again for any useful info you might have to offer.
 
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Old 07-15-07, 11:58 PM
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i've done more research and found a very useful site.http://www.aosmithmotors.com/pdf/brochures/bulletin3100/Acdc.pdf.it would appear that this is a split phase motor as PATTBAA's wiring suggested.tommorrow i'll wire it up & keep u posted.
 
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Old 07-16-07, 12:43 PM
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Possibly a "Forward- Reverse" push-button station.Press the "Forward" button and the motor would operate until a normally-closed limit-switch would open the "Forward" circuit and stop the motor. You then would press the "Reverse" button, and when the direction of travel reverses, the "Forward" limit-switch would return to "normally-closed" , re-closing the "Forward" circuit.

This presumes you are alway pressing the buttons while the motor is operating. If you want "momentary-contact" operation, you will need another contact on the control-contactor.

As to the internal motor-wiring, best if you take the motor to a motor-repair shop for advise and assistance.
 
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Old 08-12-07, 12:04 AM
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Smile

Well i bit the bullet & bought a variable frequency drive & a 3 phase motor.I was under the assumption that to go with 3 phase i would need some type of phase converter.I don't understand the principles behind it but the vfd is the phase converter.I can't quite get my mind around it but i can input only 120v ac & it can run a 230/460v 3 phase motor with variable speed.Not to mention reversing the motor using simple limit switches.Its a very slick operation indeed.However, I ran into the limitations of using a 1"N.F. threaded rod to transfer linear motion very quickly.It took me all of an hour before i realized that galling occurs when using like materials for nut & rod.Also that n.f. thread(& n.c.) are designed strictly for fastener use & not to apply linear motion.I am patiently waiting for delivery of my 1" stainless acme thread rod & self lubing plastic acetal nut(no lubrication because any residual oil leakage would stain the stone)The reason i started with n.f. rod was to slow the linear motion further than just the drive/driven ratio of pulley sizes.The vfd takes care of that nicely.Anyway,I thank you for your input & maybe someday when i get up & running I can sell you a high end indoor fountain.Not meant as a solicitation.
 
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Old 08-12-07, 12:16 AM
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You may want to check the VFD info about useing the single phase input voltage if you want 120 v input you may be restricted to the number of the HP you can use on 3 ph motor side but if you used 240 Volts then the chance is much better you have more slection for motor sizewise.

if you want more info please do post it here we will be glad to help ya.

I been working on alot of VFD from small one to very large one the motor is much bigger than the fullsize car sizewise

as you mention travel rod for limit switch best to used smooth rods but add a threaded end on each one or put a " ring clamp " on the rod and let limit switch it like a cam or something like that


Merci , Marc
 
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Old 08-12-07, 12:46 AM
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Smile

I'm truly impressed (wow) with the knowledge and expertise on all of yours knowledge on motors You all are "True Electricians" I was an appliance repair man for 20 years dealing with lots of reversable motors. I "always" found them very confusing. So yes I am in "awe". Have a great week-end
 
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