Leitmotif

MrPLC Member
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About Leitmotif

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    Sparky
  • Birthday 05/03/48

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  • Gender Male
  • Location Seattle Wa
  • Country United States
  • Interests Waste energy capture and reuse.<br />Conservation<br />Electric Vehicles<br />Interactive multi system design, testing and "make run"

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  1. Any BMS experts out there?

    What is your definition of BMS Dan Bentler
  2. Circuit Protection

    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
  3. Electric Motor Control

    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
  4. Motor Speed Command based on Analog Signals

    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
  5. Vertical Load PID Tuning for a LIFT

    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
  6. Automated Guided Vehicles (AGV)

    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
  7. Potential Red Flag

    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
  8. VFD Regenerative Braking

    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
  9. NTC temperature sensor and CP1H

    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
  10. Flash Mob Christmas Surprise

    Thanks Alaric. Good cheer up after tough day. Dan Bentler
  11. Dielectric Strength Test Procedure

    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
  12. On/Off Switch to turn on light

    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
  13. motor feedback

    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
  14. Servo Motor Advice

    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
  15. Electrical Wiring and Test

    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