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Forum 60. Cable Management & Wiring Mains power wiring - for discussion

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Thread Last Poster Posts Pages Last Post Archive through March 02, 2007 Mike Richards 25  1  03-02-07  06:43 am   Closed: New threads not accepted on this page

Author Message   Gerald_D Registered Username: Gerald_d Post Number: 1079 Registered: 11-2005 Posted on Friday, March 02, 2007 - 07:19 am:        My thinking is that a woodwork spindle, normally under the control of a computer, should have a mechanical disconnect switch for the guy changing the cutter, even if it may damage the VFD. An PE55-like switch should be sitting directly above the cutter (say within 0.5m [2ft] and in view of the operator while the cutter is changed). The only chance of this switch damaging the VFD is if the switch is turned off while the spindle is under load, which would be very unlikely. There is also a chance that the switch is turned on while the VFD is already on, but then you have probably saved a finger. With a local mechanical switch, the guarded fan can stay running.   reza forushani Registered Username: Reza Post Number: 105 Registered: 01-2007 Posted on Sunday, March 04, 2007 - 04:34 am:        Can somebody explain the function of the contactor and how it works., I just got mine and need some help. thanks   Gerald_D Registered Username: Gerald_d Post Number: 1096 Registered: 11-2005 Posted on Sunday, March 04, 2007 - 05:42 am:        A contactor is simply a big relay. Does the sketch at the top of this thread help you at all? What relay did you get (photo or name&number)?   Mike Richards Registered Username: Richards Post Number: 78 Registered: 05-2006 Posted on Wednesday, March 07, 2007 - 07:31 pm:        This post was first made in this thread Here's a little circuit that shows James's circuit schematically as well as the reasoning behind using a bleeder resistor - even with stepper motors. The schematic posted here previously has been deleted as per Mike's request lower down in this thread (Friday, March 09, 2007 - 02:28 am) This schematic has replaced it. In the middle of the schematic is the 70VDC power supply. The + side of the supply connects to the DIN rail terminal blocks through the 'A' contacts on the Contactor. At the bottom of the schematic are the limit switches, 2 per axis. These are true limit switches in that they will remove power to the G202 modules if any one of them is opened. Notice the Limit Override Switch on the bottom right of the schematic. Its use is to temporarily 'override' a limit switch. It is turned on to supply power to the G202 modules, even if a limit switch is open. The purpose for the override circuit is to let the operator jog the axis that hit a limit switch back to the working area. The Limit Override Switch is a 2-pole switch. One pole bypasses the limit switches which allows power to be fed to the coil of the contactor. The other pole turns on a warning light (probably red) to warn the operator that the Limit Override Switch has been turned on. (Edited: When the Limit Switches are part of the Coil circuit, they only have to handle a small current, so they can be physically smaller than if they had to handle all of the power required by the controller.) Just above the Limit Switches is the latching circuit that will turn on the Contactor. Two power supply lines, labeled Latch + and Latch - feed power to the coil of the Contactor. Depending on the voltage requirements of the Contactor's coil, the voltage might be 12VDC, 24VDC, 120VAC or 220VAC. Personally, I like to use the lowest possible voltage to avoid running high voltage through switches that are in close proximity to the metal frame of the machine - but that is just my personal preference. In this particular latching circuit, when the Enable Push Button is pressed, the Contactor's coil is turned on. When the Contactor's coil is turned on, all of the contacts close, including the 'S' contacts. The 'S' contacts act as a bypass circuit that will furnish power to the coil when the Enable Push Button is released - which is why we call it a latching circuit. Once the coil is turned on, it will stay on until either a limit switch is opened or until the control circuit that furnishes the latching voltage is turned off. (As a side note, I always add a 'Stop' push button to every circuit that has an 'Enable' push button. The Stop push button, which would be a normally closed momentary switch, would function exactly as a 7th limit switch.) After all of that background, we finally come to the purpose of having a Bleeder Resistor (R1) in the circuit. The whole purpose of having the limit switch/contactor circuit is to cut power immediately (20mS or less) when a limit switch is opened. No gradual power down is allowed - which could be the case with a large power supply and a single active motor. When the coil of the contactor looses power, all of the contacts are opened and all power to the G202 modules is cut off. With power cut off between the output side of the power supply and the G202 modules, the stepper motors cannot drain the power from the capacitors. (Remember, when power to the Contactor's coil is turned off, the G202 modules will be isolated from the power supply. That's a condition that will happen every time the controller is turned off.) However, with a bleeder resistor in the circuit, power will be drained from the capacitors. The time it takes to drain the capacitors depends on the resistance of the resistor. A low resistance will drain the capacitors more quickly than a high resistance. In this particular circuit, as Gerald suggested, a 22,000 ohm resistor would be a good compromise between too much heat and too slow bleeding; however, even though the math specifies 1/4-watt, I would use a 1-watt wire-wound resistor. A 1-watt resistor will still get hot, but not nearly as hot as a 1/4-watt resistor.   Gerald_D Registered Username: Gerald_d Post Number: 1124 Registered: 11-2005 Posted on Wednesday, March 07, 2007 - 08:05 pm:        Mike, I thought it was bad practice to diconnect a G202's power supply while the motor is moving? (the motor needs a place to dump its energy?) Have you seen anyone else put a contactor/relay between the gecko and its supply?   Mike Richards Registered Username: Richards Post Number: 79 Registered: 05-2006 Posted on Wednesday, March 07, 2007 - 08:51 pm:        Gerald, that's an interesting question and a question for which I don't have a definitive answer. It is generally bad practice to manually turn a motor by hand (or manually move an axis) when the power if off, because, in that condition, the motor becomes a generator and generates power. It is also a fact that a gantry will 'coast' to a stop, hopefully in a fraction of an inch, but that could represent hundreds or even thousands of steps. I believe that the G202 is well protected against the voltage spike that shutting off the power would cause. The G203 is supposed to be 'unkillable'; so I believe that the G203 would not be damaged in any way. On the yahoo groups Gecko forum, there is a paper that makes me think that nothing would be harmed. Here is the link to that paper. (Non-members of that group may not be allowed to access the PDF file. I know that you're a member, but some readers of this post may not be.) I will forward the schematic to Mariss and ask for his advice.   Gerald_D Registered Username: Gerald_d Post Number: 1125 Registered: 11-2005 Posted on Wednesday, March 07, 2007 - 09:37 pm:        My approach with E-stops is to use a pair of NC contacts under each E-stop button. One contact unlatches the main power contactor, cutting the input to the Gecko's supply...still leaving the issue of the capacitor being charged.. But, the second contact is wired to the PMDX-122 and its function is to stop the pulse stream instantly.   Mike Richards Registered Username: Richards Post Number: 80 Registered: 05-2006 Posted on Thursday, March 08, 2007 - 05:36 am:        Gerald, your approach with the E-stops is elegant. It would solve the problem as long as the sensor/switch/input latched itself like an E-stop does. A properly designed limit switch should act that way. The ramp or cam or obstruction should continue to hold the N/C switch open until the condition has been corrected. My concern is that too many people don't realize that a switch that 'blips' OFF/ON/OFF or ON/OFF/ON momentarily, won't work without additional circuitry. That's the theory behind a latched relay or contactor. Anything that causes the coil to drop the contacts, will, by definition, keep the contacts from closing again until someone or something pushes a switch to re-latch the relay or contactor. It's relatively easy to design a micro-controller or logic circuit to act as a latch, but, I get the feeling that most CNC operators would rather not get involved with adding their own computer or logic circuitry to their controllers. Running the power supply connections to the PMDX board through the contactor might be the best way to stop the steppers from stepping without damaging the circuitry. My philosophy about how a circuit should work often gets in the way of making the circuit practical. My philosophy about emergency switches and limit switches is to cut the power from that particular circuit quickly and completely and to use fail-safe devices that prevent power from being restored until the operator manually turns the power back on. Probably overkill on my part. That philosophy dates back to my early years as a process control designer when I read horror stories about people being maimed or killed when someone defeated safety circuits. One particularly gruesome story told about a man who cut off an arm because someone had defeated one of the two switches that had to be pressed at-the-same-time for the cutter's blade to operate. Somehow, he had one hand and arm inside the machine pushing the material into position when he either pressed the other Operate button or somehow bumped the Operate button. Another man had both hands totally crushed in a 200-ton press when he personally rewired the machines two Operate buttons - that needed to be pressed at the same time - to a foot switch. He stepped on the foot switch when both hands were positioning some sheet metal. The owner of that shop was one of my best friends. Needless to say, he was overcome with grief when he realized that his employee had destroyed his own hands. He blamed himself for not personally checking the equipment for unauthorized modifications. His employee's reason for modifying the machine was very simple. He said, "I wanted to be a little bit more productive." Every time I change a cutter in my Colombo spindle, the thought goes through my mind that the only thing that keeps that spindle from turning on is a 1.5 volt logic signal on a circuit surrounded by a very noisy 240V line and the latching contactor that is OFF and un-latched (thank goodness for that contactor). Some people don't realize that most TTL and computer circuits consider a voltage of 0 to 0.70 volts to be OFF and a voltage of 2.2 to 5 volts to be ON, so the difference between OFF and ON can be as little as 1.5 volts. That's really scary when you can watch on an oscilloscope voltage spikes on many of the TTL circuits that are many times that voltage. Sometimes I think that designing safe, reliable, simple circuits that work in an industrial environment is impossible.   Gerald_D Registered Username: Gerald_d Post Number: 1126 Registered: 11-2005 Posted on Thursday, March 08, 2007 - 07:27 am:        Regarding mechanical latching of the cams/limits/e-stops, that is actually not essential. Once those NC switches have broken, they unlatch the main contactor (and Mach3). Re-making those switches will not close the contactor again, nor will Mach3 start without a reset at the keyboard. The more I think about changing the cutters, the more I believe we have been amiss in not providing a disconnect switch right at the spindle/router. Whether our VFD is going to like it or not is a secondary issue.   Mike Richards Registered Username: Richards Post Number: 81 Registered: 05-2006 Posted on Friday, March 09, 2007 - 02:28 am:        Gerald, You and Mariss agree that cutting the power to the PMDX is the BEST way to stop a stepper. When I telephoned Gecko support a few minutes ago, Mariss answered the telephone, ran the math, and said that my idea of cutting the power between the power supply and the G202s would create an instantaneous current surge in excess of 400A per drive. In other words - disaster. On the other hand, cutting the power to the PMDX would cause no damage. So, here's an updated schematic that shows the more proper way to stop the steppers when a Limit Switch is opened. This schematic will not allow the coil of the Contactor to be turned on unless ALL of the limit switches are closed OR the Limit Override Switch is turned on (which would also turn on the Warning Lamp as a visual indicator that the Limit Switches were no longer functional). (NOTE: Gerald, if possible, please delete the posting of the other schematic or at least note that the schematic has been replaced with this schematic, so that there will be less confusion to those reading this thread.)   Gerald_D Registered Username: Gerald_d Post Number: 1128 Registered: 11-2005 Posted on Friday, March 09, 2007 - 07:48 am:        Mike, your focus is "Limit Switches" while my focus is "E-Stops" - we are actually coming from two very different places. I personally don't regard limit switches as a personnel safety device (the mechanical stops prevent the gantry from landing on your toes) and my machines don't even have such switches. The reason that I am mentioning this now, and possibly diverting this thread, is because Mach3 (together with PMDX) treat these switches differently to E-stops. These switches will stop motion "instantly", while Mach3 does not lose the calibration, and gives a facility to safely jog off the limit and carry on. There is another facility in Mach3 to treat the same switches as "homing" switches for calibration - when in this mode, the operator does not have to do a "reset" when the switch is hit. In short: - while in normal cutting mode, the switches stop motion, the operator has to manually reset at the keyboard and jog away from the limit. The machine has not lost its calibration. - while in homing/calibration mode, the switches act like our familiar z-zero plate, the machine does its little dance against the switch, backs off and waits. The machine is freshly calibrated. The concept of limit/homing switches is well ingrained into the Mach3 software, literature, and videos. With respect, I think you are confusing the readers by coupling these as part of a power safety circuit.   Mike Richards Registered Username: Richards Post Number: 82 Registered: 05-2006 Posted on Friday, March 09, 2007 - 08:20 am:        Gerald, I agree that Mach 3 has provisions that make limit switches unnecessary. And, because my only experience with Mach 3 is on my test bench where I've never had a 'communications error' or a 'hiccup', maybe I'm just expecting unexplained errors to happen (like I've had with my Alpha). On more than one occasion, the Alpha has 'hiccuped', lost position, and then slammed into the stops before I could waddle over and hit the E-stop. Admittedly, these 'hiccups' are few and far between, but they have happened too often during the last (almost) three years. That is why I keep coming up with this particular type of circuit. I also agree that when a limit switch is opened in the circuits that I've designed, that position will be lost and that the machine will have to go through a homing routine. For that, I prefer to use proximity switches that are totally separate from the limit switches. In my mind, the limit switch is the last resort to keep an axis from slamming into its stop, while a proximity switch could be placed at some convenient position to act as a homing switch. As long as the distance between the proximity switch and the true home position is know, offsets will take care of the rest. Even though I prefer 'safety switches' for peace of mind, there's a Shopbot just across the street at the local High School where the students just plop down a piece of material, jog the axes to a corner of the material, give a Z2 command and start their cut. It's simple and effective and it doesn't require expensive and fragile circuits. The main difference between the High School shop and my shop is that at the High School, they don't allow the Shopbot to run unless a student is holding the E-stop in his hand to keep the unexpected from causing damage. In my shop, I nurse the machine the first few times a new design is run, but after those initial test runs, I do other work while the Shopbot does its work - and that's when the 'hiccups' happen.   Gerald_D Registered Username: Gerald_d Post Number: 1130 Registered: 11-2005 Posted on Friday, March 09, 2007 - 08:57 am:        Don't get me wrong, I am not recommending that guys work without limit switches. The only thing that stops me from adding switches to my machines and to the drawings, is to find a commonly available, reliable, dust-proof system. (The drawings make provisons for 12mm proximity switches - but they can't be simply strung together in series) - this is a whole other thread by itself. (The homing switch is a red herring here in this discussion because Mach allows the homing switch to be either the self-same switch as the limit switch, or the homing switch can be separate on its own input (movable or z-zero plate))   Gerald_D Registered Username: Gerald_d Post Number: 1143 Registered: 11-2005 Posted on Tuesday, March 13, 2007 - 06:51 am:        When a USA-man-in-the-street buys a 220V appliance, takes it home, opens the box, finds that the power cord has 4 conductors (green, white, black, red) (maybe only 3, green/black/red?) without a plug at the end....what does he typically do? Is there a standard plug he can get from the hardware store? Are 220V plug outlets commonly fitted in the garage/basement/kitchen? In case these sounds like stupid questions, over here all appliances for the man-in-the-street (except a stove) are 3 wire, plugs (from any store) are a DIY fit, and outlets are standard throughout a house or building. (Stoves are sold without a cord, and with a note: "to be installed by electrician....." The main reason I ask about this is because I am dispatching a 220V motor to Atlanta tomorrow and I need to "plug it in" when I get there....   Mike Richards Registered Username: Richards Post Number: 85 Registered: 05-2006 Posted on Tuesday, March 13, 2007 - 03:32 pm:        The only 'standard' 220V-240V plugs that I've seen pre-installed are the receptacles for plugs that are found on electric clothes dryers and electric cooking ranges. There are many other configurations that are available. Most Home Depot sized stores carry a variety of plugs and receptacles. Here's a link to a Hubbell reference chart. Many of the stores carry the Hubbell brand.   Gerald_D Registered Username: Gerald_d Post Number: 1145 Registered: 11-2005 Posted on Tuesday, March 13, 2007 - 06:39 pm:        The variety of pin configurations on that Hubbell chart had me gasping for air! And your Home Depot lets the DIY bloke loose among all these choices?....I am beginning to understand why fire-trucks feature in so many of your movies! When ShopBot sells you a PRTAlpha for router duty, they imply that you have a DIY installation because they only insist on a licensed electrician for spindles. Does the average handyman really know how to handle those 4 wires?   Mike Richards Registered Username: Richards Post Number: 86 Registered: 05-2006 Posted on Tuesday, March 13, 2007 - 07:29 pm:        The chart makes everything look complicated, but it really isn't too bad. If we stay with two voltages 120V and 240V (although the chart says 125V and 250V), you'll note that the plugs/receptacles are sorted by their current rating and whether they are a standard plug/receptacle or a twistlock receptacle. So, a 240V/20A receptacle can receive either a 15A plug or a 20A plug (which is how I've wired my planner, my dust collector and my air compressor). A few minutes at the hardware store looking at the various plugs and receptacles takes most of the mystery out of everything.   Gerald_D Registered Username: Gerald_d Post Number: 1146 Registered: 11-2005 Posted on Tuesday, March 13, 2007 - 08:50 pm:        Okay, I have ordered a Hubbell HBL5666C plug for the 230V 11.5Amp Single Phase motor going to Atlanta. Let's hope the organisers can provide a suitable receptacle - I'll check with them tomorrow. Price of that plug out here: $25 - high because of rarity....   David Rosenbleeth Registered Username: Dave_r Post Number: 22 Registered: 07-2006 Posted on Thursday, March 15, 2007 - 12:11 am:        Gerald: Just ask the guys where you are planning to plug it in what amp receptacle, how many leads, and whether their receptacle is twist lock or not and then you can be sure to have the right one. Odds are a Home Depot is close to them (They are everywhere around Atlanta) and you could even make sure you have the right one by checking it out once you are there. The right amp plug will, of course, be determined by the circuit, not the motor. Most light industrial outlets here are 20 amp unless there is a dedicated reason to go higher. Of course the key word is "most". By the way: I'm about a 10 Hour drive from Atlanta-Comne on down while you're here.   Gerald_D Registered Username: Gerald_d Post Number: 1148 Registered: 11-2005 Posted on Thursday, March 15, 2007 - 06:54 am:        10 hour drive - sure! The plug I ordered here is the only "American" 230V plug that I could find stocked in South Africa. But at least I have a reference point to tell the exhibition organisers what I am bringing. They must have catered for stuff from Europe before, so I am not too worried about it.   Hugo Carradini Registered Username: Hugotel Post Number: 57 Registered: 11-2006 Posted on Thursday, April 26, 2007 - 12:53 am:        Hello Gerald and forum friends. I moved to a new shop and that was a lot of work that keep me very busy for the last couple month. Now I am ready to keep working on my project. I got all my electronics except the cables (I will use normal cables for my "kitchen project" and the G203 "vampire drives that I hope arrive this week. I all ready got the PK296A1ASG7.2 motors, Piltron transformer 300 VA 2x25 VAC 6amp, PMDX-135 Module, PMDX-122 card, ENSTO Rotary Load Break Disconnect Switch, 3 Pole, 600V, 40ª, and TECO IEC Contactor - 16A, 120VAC / 60Hz Coil, 3 Pole 600V, 1 N.O. Aux and the micelaneas in the list. The question I have right now is how to install the contactor. I think many people is going to use the TECO IEC Contactor because is in the list you suggested and would be nice to know how to install it to the basic package. As soon I get my office strait out I will post the assemble process of the electronics so it can be cheeked out. Thanks for your help. Hugo Carradini PD. My Web site is working now www.vitrales.com.ve   Gerald_D Registered Username: Gerald_d Post Number: 1292 Registered: 11-2005 Posted on Thursday, April 26, 2007 - 12:19 pm:        Welcome back! From the spec sheet: What is the supply voltage in your country? Single phase? Split phase? Three phase? Normally 1, 3, 5 is used for incoming mains. 2,4,6 go out. Terminals A1 and A2 are lower down (normally under 13 and 14).   Hugo Carradini Registered Username: Hugotel Post Number: 58 Registered: 11-2006 Posted on Thursday, April 26, 2007 - 05:13 pm:        Hello Gereald. We work with 110 and 220 volts 110 uses a hot line and a neutral line and the 220 uses 2 hot lines and a neutral line. I am planing in base of 110 volts system .   Gerald_D Registered Username: Gerald_d Post Number: 1303 Registered: 11-2005 Posted on Thursday, April 26, 2007 - 05:32 pm:        So Hugo, you can follow the drawing right at the top of this thread. Here are your contactor connections:   Mike Richards Registered Username: Richards Post Number: 110 Registered: 05-2006 Posted on Thursday, April 26, 2007 - 09:10 pm:        Gerald, After looking at your schematic, I think that pushing the N/O pushbutton is going to be an exercise in futility. If Contactor connector 3 is the connection for the incoming Neutral (as stated above), shouldn't the N/C pushbutton be connected between Contactor connector 3 and the Coil connection A1? That way, when the N/O pushbutton is closed, the coil will receive power from L1 and the coil will also have a complete circuit through the N/C switch to neutal. Also, when the N/O pushbutton is closed, switch terminals 13 and 14 will close and the Contactor will be self-latching. The Contactor will remain turned on until the N/C pushbutton is opened or until the disconnect/breaker feeding power to L1 is opened.   Gerald_D Registered Username: Gerald_d Post Number: 1305 Registered: 11-2005 Posted on Thursday, April 26, 2007 - 09:36 pm:        Mike, after re-visiting the circuit, yes, you are right, pushing the NO will not do anything because the Neutral is broken. But, I'll have to think harder about your suggested solution, because the neutral won't be isolated anymore - it will continue deeper into the circuit via the coil. I have a funny feeling that we are using a double-pole NO pushbutton to start the circuit? (Right now I am packing for 5 days away, 4 days back and then 10 days away again - need to chew on this one carefully....) PS. I have purchased vBulletin software and will be converting this board so that the start of threads don't go so deep into the archives.   Gerald_D Registered Username: Gerald_d Post Number: 1306 Registered: 11-2005 Posted on Thursday, April 26, 2007 - 09:37 pm:        As the first post shows (the faulty diagram):   Mike Richards Registered Username: Richards Post Number: 111 Registered: 05-2006 Posted on Thursday, April 26, 2007 - 10:46 pm:        Gerald, You're right. A 2-pole, 1-throw N/O Pushbutton could be used to activate the relay. Once the Contactor's coil was activated, the coil would be held in the active state by switch contacts 13 and 14. Good luck on your trip(s).   Hugo Carradini Registered Username: Hugotel Post Number: 59 Registered: 11-2006 Posted on Friday, April 27, 2007 - 01:08 am:        Thanks Gerald. I will be posting photos soon.   Gerald_D Registered Username: Gerald_d Post Number: 1308 Registered: 11-2005 Posted on Friday, April 27, 2007 - 06:06 am:        Thanks Mike. Off to Oudtshoorn in an hour's time for a little break before the Atlanta visit.   Gerald_D Registered Username: Gerald_d Post Number: 1309 Registered: 11-2005 Posted on Tuesday, May 01, 2007 - 08:05 pm:        The long drive cleared the head. The Neutral going "permanently" to the coil of the contactor is no problem - there is a big multipole "disconnect" just to the left of the contactor. Follow Mike's "shouldn't the N/C pushbutton be connected between Contactor connector 3 and the Coil connection A1? That way, when the N/O pushbutton is closed, the coil will receive power from L1 and the coil will also have a complete circuit through the N/C switch to neutal. Also, when the N/O pushbutton is closed, switch terminals 13 and 14 will close and the Contactor will be self-latching. The Contactor will remain turned on until the N/C pushbutton is opened or until the disconnect/breaker feeding power to L1 is opened." until I can fix that drawing. Sorry for the slip.