Leitmotif

What is your definition of BMS Dan Bentler

All circuits should (must) have overcurrent protection. Components should have it but there comes a point at which not cost effective ie you dont fuse individual lite bulbs. If you are in a warm and dry office settiing I see no reason for ground fault protection. Over current protection will protect against ground fault BUT at current levels much higher that ground fault protectors (GFCI) will. GFI are designed to protect people not the circuit. I suppose you can get units that will do both. Dan Bentler

THe nice thing with PLC controllling a VFD is that you have complete separation between the power (3 phase) and contrl circuits which are low current or low voltage such as 4 20 mA and 0 to 10 volt. Standalone the VFD can do all motor control start stop speed control reversal and protection ie motor overload. Normal applicatins require a branch circuit with proper over current protection sized IAW with VFD ratings. So you do not need relays between PLC and VFD. In your case I would recommend a 3 pole switch to act as E stop in case you make a mistake - if you are not making mistakes you are not learning. You may need only two pole if you are feeding VFD with single phase. Do NOT put a relay between VFD and motor. Read both the VFD and PLC manusals to see how to get the PLC to control the VFD. Dan Bentler

I do not see any comment about how much material is dumped into the shredder in proportion to either time or conveyer speed. I think this is what really needs to be controlled and is the challenge. SO how is volume or weight controllled is it placed manually and can vary from one inch to six inches thick? If that is the case then infeed speed control will not handle this variable. If so I agree with Bernie the speed on infeed conveyer will vary by quite a bit - that just may be the way it is and may be acceptible. The good side of it is infeed is slowed stopped to let shredder handle an overload. Dan Bentler

One little key thing here What kind of motor are you using series shunt or permanent magnet. Look at torque vs RPM curve for series motor. With little torque speed is high - exactly what you are seeing when going down ie overhauling load. You willl have to cut line voltage quite severly to control speed in down direction. If you have varying load I think you are going to have difficulty controlling a series motor in both directions. IF you can have separate field control a shunt may be better choice. IF not I think I would look at perm magnet. Dan Bentler

Since I am into electric vehicles - desire to convert 56 Chev pickup to AC 3 phase drive - I have some thoughts. I would assume speed to be about 3 to 5 mph and drive more than likely DC. Since this is in high traffic - I assume worst case ie pedestrian - area. Also am assuming rubber tire drive AC would be nice but a little hard to get VFD and motor at 72 or so volts. With off shelf VFD battery voltage would need to be around 160 if using single phase sorce VFD and passing DC thru the rectifiers. For 230 battery voltage is bout 325. Detection and stopping are of paramount concern. Given that then the total load must be considered to enable rapid stopping ALSO again - worst case - crash stop when headed downhill - MUST KNOW THE SLOPES if any. Ice snow and wet pavement are also concerns. Crash stop would be right now probably involving mechanical brake. Any other stop could be done by dynamic braking possibly hooked up to charge battery (regenerative braking). In addition to prox sensors sensitive to building components (wall chairs etc etc) AND people I would have hand (or bump) actuated door type panic bars. Proxes could stop within 6" and panic bar would give crash stop. I would think laser sensing would require line of sight. Loss of laser signal wouold require a stop and a mayday call for service OR a manual operation. Floor sensors would be a good operation maybe but do require maintenance. I do not think having crash stop is worth a darn if cargo can slip off and hurt someone (had conduit slide off truck rack in a panic stop - EMBARRASING) I would definitely have some method of manual operation if for no other reason to clear the highway until maint can get there. Batteries - quick change would be best. No point in equipment idle when charging battery especially so if multi shift operation. Dan Bentler

I decided to spend a day gutting the old wiring, removing not needed components, and rewiring. While I was waiting for some parts, I did write the majority of the PLC and HMI programs. Well, yesterday I was caught off guard when the supervising engineer came by to talk about the project. He was concerned that I missed the scope of work… I didn’t understand what he was referring to, so I asked for clarification. He brought up the fact that I was spending time rewiring the panel. I explained my case on how I was simplifying the design and cleaning things up. I assured him that the PLC and HMI portion was ready, etc… His comeback is what really stuck with me. ‘This panel was working prior… you should have only needed to hook up a few wires… we should have seen motors turning by now…’ Again, I plead my case... He really didn't seem thrilled with my answers. I am I overacting by seeing ‘Red Flags’? I pride myself in a job well done. Being called on the carpet within the first month has never happened to me. Furthermore, the reason I was hired was because I brought to the table, well exactly what I’m doing – documenting, standardizing, simplifying, etc. When I was the managing guy, I wanted my group to give the same detail as I do… Your opinion is appreciated! What do you mean you wanted to take the time to do it right? Just continue on with what worked before. The audacity of forgetting the Production God. Been in that fix also. Seems to me if you wanted his job you would have stayed where you were. They tell you what they want then when you do it,,,,,,,, Dan Bentler

ASSUMING you have "standard" VFD where incoming 3 phase is rectified to obtain DC for DC bus: 1. You cannot pass power back thru the rectifiers to the AC line 2. You CAN tie the DC buses of two VFDs together such that when one is regen and other motoring the regen will generate power to the motoring VFD DC bus. 3. With some tinkering and calculation you could in theory use regen braking resistor to provide heat to something else ie office air or hot water or (??) Dan Bentler

From what I have read either thermocouple TC or Resistance Temp Detecter (positive temp coefficient) are preferable to thermister (negative temp coefficient) 1. Both RTD and TC are built to a standard. Regardless of manufacturer a type K TC will be nearly same as another built by someone else. Same can be said for RTDs ie PT 100 is basically same regardless of source. This is not the case with thermisters - they are NOT built to a standard - so there is variation between manufacturers and who knows maybe even a particular production run. The moral here is it may be difficult getting a replacement thermister. 2. Thermisters are accurate (maybe better term would be proportional with predictabiltiy ??) only in a much tighter temperature band compared to the accuracy vs temp bands for TC and RTD. Dan Bentler

Thanks Alaric. Good cheer up after tough day. Dan Bentler

1. Never megger yourself 2. Never meggere solid state components A lot of your decisions will be made based on what the voltage of your equipment is. I would check with Biddle http://www.biddlemegger.com/ They should be able to give you the relevant standards appropriate to your installation. Dan Bentler

Now that you are progessing and getting into newer and bigger you have to watch out for current demand by load to avoid burning out you PLC power supply. The pump may do just that. It is time to learn about interposing relay where PLC output energizes a relay coil and the relay contracts energize the pump motor from a separate power supply. Also you may as well learn about the collapsing field of the relay and install MOV (metal oxide resistor) or a diode across relay coil that conducts to reduce collapsing field voltage. Dan Bentler

Regardless of the terms used in stuff you read I think the important thing is to understand what you want the machine to do and design based on your "you do this" cirteria. From simple to complicated MOTOR RUN can be done with a contact on main starter relay. In case of VFD this would be a contact in the VFD - MOTOR TRIP (fault) can be done with contact on sensor ie overload, winding temp switch etc. In case of VFD you can use a contact there. EXCEPTION - where multiple motors are powered from one VFD - in that case each motor has individual relays with overload protection so this should be monitored by PLC in my mind. MOTOR RUN and it is actally doing something - ie the pump is actually pumping water - use flow switch flow sensor or pressure switch. MOTOR SPEED can get complicated depending on what you are doing. can be done by tach generator or encoder MOTOR (or load) position can be done by encoder for very fine positioning or limit switches if you have a wider tolerance on position. MOTOR DIRECTION can be gotten from the contactors (simple) to reversal of tach generator output voltage to using encoder. Dan Bentler

I do not think your problem will be in the motor but in the sensing. What is your tolerance for teh 0 and 180 positions? Does the motor have to hold that position - any drift allowed? In other words how precisely must you stop the motor at a position? If you tolerance was say + - 10 degrees then you could possibly do it with off shelf VFD motor and encoder?? Dan Bentler

Seems to me this looks an awful lot like homework. IF that is the case just say so AND tell us what you think and WHY. Even if wrong it will still be a good learning experience. Dan Bentler

400 is approx 87% of 460. Bit outside of normal + - 10% on equipment but just gotta ask the question. What is voltage tolerance of the European equipment. Is it possible it may be OK on 460? Dan Bentler

I have tried "contact us" 3 times. Does not appear to work. I give up. Why do I ahve a warn status? What does it mean? Dan Bentler

Ron What is your fallback position if everything sinks? Have you been talking with Social Security and can you survive on that ie fuel roof and food. Social Security has classes in my area and I think they are very good. Check with your local senior organization of local bank or credit union. I just read in paper where it reported many large industry are taking the hire incentive money only for cheap money and banking it. They are not using the money to hire or so the media says. IF true it seems this is hedging their bets and sorta supports "wait until elections". Do you have free space at home for developing and testing? If so then in theory you could get by on renting classroom space. Seems to me local high school or community college would have teh support (audio visual, computer etc etc) and may be willing to rent. Last choice in my mind is a hotel or motel - if only because it seems cheap to me (have seen some with good audio visual support though). I have looked at a few of your videos and like the "hands on", practical, and the little gotchas that are not in the manual. I think you have a very good product which should be in demand once management opens the money gates. Dan Bentler

I think I am qualified to comment, graduate of US Navy Nuclear Power, AA, BS MS and two quarters of PLC and a dash of VFD therein. SO I have been thru a few schools and have seen my share of dropouts and completers. I think your class title "Industrial Controls" is dead on. The PLC cannot do anything without sensors and output devices. Those are most of the trouble calls anyway. I think a quality program is 25% material, 30% instructor and balance student. Good (motivated?) student can overcome bad instructor. When I took PLC it was because I was trying to learn at home. I decided I had a lousy instructor (me) and I had better find a qualified one. So I did. As it worked out I "wrote" my curriculum and decided what to learn and when or in what step I should do it. Instructor approved or modified as needed. Started out with how to configure NO and NC switches and what happened with each configuration, at the end (after several projects) I had a stepper motor and VFD setup controlled by PLC (that project was a simulated automated drill press). It was alll AB PLCs. Am now teaching also - class oriented to Electric Vehicle teaching principles of AC 3 phase motor and VFD to drive a car. After 5 sessions I have a 90% satisfaction grade from students. Next session Sat 10/23. Dan Bentler

A lot has been written here and in other places referring to E stops. This is not an easy question and there can be different answers adn opinions. The purpose of an E stop is to completely shut down a machine in emergency and is intended to protect PEOPLE not the machine. All parts of the machine should go to zero potential mechanical state. In some cases components must be allowed to move to aquire zero mechanical state. Yes you are correct they are open contact (in pushed in position ie E stop activate) and normally closed when pulled out ie OK to run. I prefer to use two contacts in series to ensure activation - same as I do on the STOP switch. I care twice about being able to STOP the machine than abilty to start it. I noted with Cutler Hammer you can remove the contact body from the actuator and if this were done on a machine the E stop will not activate no matter how many times you push the red button. Reactivating an E stop should (must??) NOT start the machine by itself. This is quite common in my experience and I believe can be dangerous especially on machines with multiple E stops in multiple locations. In general an E stop (MUST ??) should kill all contol power to deactivate all relays thus shutting down all motors etc. You can wire the E stop into the PLC (configure it in same method as the stop button) - HOWEVER - the average PLC cannot be relied on to shut down machne components - that is why you kill control power. You can get PLCs that are safety related and are designed and tested to provide personnel protection. To conclude When designing you have to evaluate the risk and degree of hazard to people the machie imposes THEN decide on control mechanisms algorythms to achieve this protection. I woud recommend you 1. come up with the evaluation of risk 2. Come up with preliminary design of controls 3. Have someone check the design (we all make errors, do not think of everything etc) 4. IF machine is a high risk machine ie punch press etc have an independent agency review and approve. Dan Bentler

Re your statement I still plan on completely my electrical engineering degree, I just don't want to walk into the engineering department monday and not know what the hell I'm doing. This is a kind of internship job. The company is paying for my EE degree. I think you would be best off walking in Monday tell them you studied your head off and are still quite ignorant. They will appreciate the honesty and truth up front instead of finding the truth in a week or so and they WILL -- THEN the question for you is will you be able to overcome the black mark?? Dan Bentler

What I think Jeff is getting to is Is your problem in the PLC or in the press? What if the machine itself cannot go any faster? The mechanism has to have enough time to do its work - speeding up the PLC will not improve this. Dan Bentler

Does anyone know of a good start with basic and get to advanced reading material on brushless DC motors. Why I ask I need to learn more. Have a in wheel hub motor off a scooter that we wanted to test and see if would rotate. Phase to phase reads approx 0.3 ohm phase to ground 1M or better. rotates freely. -- So motor looks OK so far. Tried running for one or two second on 1. AB non vector VFD no luck although it was harder to turn tire when energized 2. Old six step inverter motor would turn approx 1/8 turn 3. Applied DC to two of 3 phase leads motor would turn approx 1/8 turn did on all three pairs and turned each time SO we conclude the motor is OK it will turn when energized move on to the controller and replace both capacitors - one is blown out. try controller and see if can make run IF that fails students decide to either scrap project buy new controller From another source we see the pulse shape may be special for this not a PWM and not a full six step. So we do not know what wave form a controller must have to make motor run. Scooter is 1. owned by a group of EV enthusiasts 2. Donated by an electric vehicle shop who gave up on it and is a basket case 3 We are doing this project as Inependent Study in association with high school students and is THEIR project all I do is mentor and advise they make own decisions 4. complete mystery no markings not even a serial number anywhere on scooter. Students were able to track down US representative who is helpful but gave wrong manual - working on that issue 5. This is a great lesson to students on reality of working in industry with equipment ie "do we have a manual" etc etc. 6. These are good hard working high achieving kids who are worthy of your help. Any help study info on what the waveform may be would be great. Dan Bentler

Thanks Peter Evaluating and learning. Sure hope you do not want book report on all. Dan