I have a pluggable power supply. It converts 120VAC to 12VDC @10A. This will be used to power actuators on an industrial machine. I will provide an outlet for the power supply to plug in to. Here are my questions that I would appreciate some guidance with. How should I fuse this power supply? Would I fuse the line or load side of it? Would I just fuse the conductor feeding my outlet? I would think that a 120W output would also mean a 120W input, so the input should only be 1A. If these power supplies use rectifiers instead of transformers then this logic would not hold, right? Does this seem correct? Also, should I consider using a GFCI outlet? It will not be in an industrial location, so there could be moisture.
Pluggable Power Supply
- Thread starter fifty60
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gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
130722-1626 EDT
Yes fuse the input. Use the smallest slo-blow that does not blow on worst case inrush current. You can determine this by experiment, somewhat costly.
On a power supply that I build I use a magnetic trip breaker (P&B W67-X2Q12-2, curve 2), and a series thermistor (CL-70 room temp about 16 ohms, around 1 ohm with 1 A). This supply could have a rating of about 180 VA. The combination of these two produced no false trips when starting from room temperature. Turning off and back on within a few seconds would usually cause a trip.
On the output side of the power supply use an appropriate slo-blow for the type of load.
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Yes fuse the input. Use the smallest slo-blow that does not blow on worst case inrush current. You can determine this by experiment, somewhat costly.
On a power supply that I build I use a magnetic trip breaker (P&B W67-X2Q12-2, curve 2), and a series thermistor (CL-70 room temp about 16 ohms, around 1 ohm with 1 A). This supply could have a rating of about 180 VA. The combination of these two produced no false trips when starting from room temperature. Turning off and back on within a few seconds would usually cause a trip.
On the output side of the power supply use an appropriate slo-blow for the type of load.
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Gar, thanks for the information. So fusing the input side is not enough? I am thinking that normally this power supply would be plugged into a wall outlet, where it would be protected by a 15A fuse. The 2 actuators are 5amps and 12VDC. Also, I decided against the GFCI in this situation. GFCI have extremely low SCCR's. The default SCCR for a non GFCI receptacle is 10KA. The SCCR for a GFCI receptacle is 2KA. My receptacle will be supplied from the secondary of a 3KVA control transformer, so I should be able to avoid having to declare such a low SCCR rating. Regardles, I am a little hesitant to ever use a GFCI receptacle. If I use a non GFCI receptacle, and do not physically locate it on my sub panel but still mount it on my machine do I still have to consider the receptacle in my SCCR calculations? It will still be supplied from a control transformer, which will have terminal blocks on the sub panel feeding the receptacle off the panel.
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130722-1926 EDT
With normal fuses or breakers you can not closely provide current limit protection on the input side of a transformer for load side protection.
What I did with the thermistor was to greatly reduce the current rating of the breaker by reducing the inrush current. This meant I could more closely protect the supply from load side overload. Nominally a 2 A breaker at 120 V line would be useful for a load up to about 190 VA steady state. If memory is correct I had to go to a 5 A breaker or larger without the thermistor.
With both of your actuators on at the same time the steady state load is at the power supply rating. You have not defined the characteristics of your actuators. This information could be important. If the power supply is a regulated unit, then there are other considerations. If the actuator load is other than momentary and both are on at the same time I think your power supply is too small.
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With normal fuses or breakers you can not closely provide current limit protection on the input side of a transformer for load side protection.
What I did with the thermistor was to greatly reduce the current rating of the breaker by reducing the inrush current. This meant I could more closely protect the supply from load side overload. Nominally a 2 A breaker at 120 V line would be useful for a load up to about 190 VA steady state. If memory is correct I had to go to a 5 A breaker or larger without the thermistor.
With both of your actuators on at the same time the steady state load is at the power supply rating. You have not defined the characteristics of your actuators. This information could be important. If the power supply is a regulated unit, then there are other considerations. If the actuator load is other than momentary and both are on at the same time I think your power supply is too small.
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It is actually 12VDC @12Amps. It is provided by the manufacturer of the actuators. The power supply is intended to be plugged into the wall, that is why I thought the 15A class CC fuse would suffice. To be honest, I am not sure that I have to fuse it at all since it is fed from the secondary of a transformer that has a primary fused at below 167%.
My other concern is integrating this power supply with my industrial machine. My declared SCCR is 5KA, but I have done my own analysis on the chamber and believe it is much higher than that. I am uncertain what adding the receptacle will do to my SCCR rating. I am not sure if it is not actually on the panel, but is being fed from conductors attached to terminal blocks on the panel, then it would even have to be included in the SCCR calculations.
Would it be better to not use a receptacle at all, but cut the plug off the power supply and splice the cable directly to terminal blocks on the sub panel?
My other concern is integrating this power supply with my industrial machine. My declared SCCR is 5KA, but I have done my own analysis on the chamber and believe it is much higher than that. I am uncertain what adding the receptacle will do to my SCCR rating. I am not sure if it is not actually on the panel, but is being fed from conductors attached to terminal blocks on the panel, then it would even have to be included in the SCCR calculations.
Would it be better to not use a receptacle at all, but cut the plug off the power supply and splice the cable directly to terminal blocks on the sub panel?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130722-2109 EDT
What degree do you have and from where, or are you working on a degree? What kind of basic courses in circuits, fields (electric and magnetic), materials, and power systems have you completed? This would help us guide you in your problem.
I don't know what your 167% is. If this a fuse of the next higher value relative to a current rating 1.67 times the primary current to the control transformer at full load, then I expect you will experience blown fuses from time to time resulting from inrush current to the control transformer loaded or unloaded.
Circuit protection devices are used to protect something. So what you choose to do depends upon on value. costs, and safety. You might not use any fuse protection if the load might burnup and not be a safety or cost problem. For example on a Haas CNC machine the RS232 inputs and outputs have series 1/4 W 100 ohm resistors, and I believe internally a transient limiter.
I have tested a similar circuit and applied 120 V to it. The resistor burns out, the Transorb does not. Essentially the resistor was the fuse, and no explicit fuse was used or needed.
If you want to prevent burnout of the actuator on mechanical overload, or burnout of the components in the power supply, then appropriate protective devices may be required. If these are expendable items, then possibly no protection except at the input to the control transformer.
AC solenoids will burnout at nominal voltage if the plunger can not move from its open position because of some mechanical problem. The solenoid probably needs protection, especially on an automotive assembly line. It is probably less costly to be down for the time to fix the mechanical bind, than the likely longer time to replace the solenoid. Whole plants down are possibly $600,000 an hour, smaller lines possibly $1000 per hour.
I can not help on your SCCR question.
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What degree do you have and from where, or are you working on a degree? What kind of basic courses in circuits, fields (electric and magnetic), materials, and power systems have you completed? This would help us guide you in your problem.
I don't know what your 167% is. If this a fuse of the next higher value relative to a current rating 1.67 times the primary current to the control transformer at full load, then I expect you will experience blown fuses from time to time resulting from inrush current to the control transformer loaded or unloaded.
Circuit protection devices are used to protect something. So what you choose to do depends upon on value. costs, and safety. You might not use any fuse protection if the load might burnup and not be a safety or cost problem. For example on a Haas CNC machine the RS232 inputs and outputs have series 1/4 W 100 ohm resistors, and I believe internally a transient limiter.
I have tested a similar circuit and applied 120 V to it. The resistor burns out, the Transorb does not. Essentially the resistor was the fuse, and no explicit fuse was used or needed.
If you want to prevent burnout of the actuator on mechanical overload, or burnout of the components in the power supply, then appropriate protective devices may be required. If these are expendable items, then possibly no protection except at the input to the control transformer.
AC solenoids will burnout at nominal voltage if the plunger can not move from its open position because of some mechanical problem. The solenoid probably needs protection, especially on an automotive assembly line. It is probably less costly to be down for the time to fix the mechanical bind, than the likely longer time to replace the solenoid. Whole plants down are possibly $600,000 an hour, smaller lines possibly $1000 per hour.
I can not help on your SCCR question.
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What degree do you have and from where, or are you working on a degree? What kind of basic courses in circuits, fields (electric and magnetic), materials, and power systems have you completed? This would help us guide you in your problem
Electrical Engineering Technology degree from an ABET accredited University (sorry, clinging to the shield of anonymity here). Course work, in brief, was basically Co-op's and preparation for the PE exam. I have just completed my first full year of full time work, so I am still officially an Engineer in Training. I am not as green as I once was, but still pretty green. I hope to take the PE exam after 3 full years of working.
I don't know what your 167% is. If this a fuse of the next higher value relative to a current rating 1.67 times the primary current to the control transformer at full load, then I expect you will experience blown fuses from time to time resulting from inrush current to the control transformer loaded or unloaded.
I cannot find the exact NEC reference (somewhere in 450.3) but I believe that if the available current on the primary is less than 9A, then I take 1.67 times the available primary current and round down to the nearest time delay fuse, this eliminates the need for secondary fusing. I always fuse the ungrounded secondary conductor, but I think that fusing the primary this way takes away the need to.
AC solenoids will burnout at nominal voltage if the plunger can not move from its open position because of some mechanical problem. The solenoid probably needs protection, especially on an automotive assembly line. It is probably less costly to be down for the time to fix the mechanical bind, than the likely longer time to replace the solenoid. Whole plants down are possibly $600,000 an hour, smaller lines possibly $1000 per hour
These are DC solenoids. I definitely want to fuse them. Using time delay fuses (class CC), what is a good approach for sizing fuses for individual actuators and solenoids that operate on DC voltage? 125% times rated load? I am worried about the actuators opening half way and getting stuck, as you described fusing them would be a way to detect and protect against this. So if the actuators do get stuck trying to open or close, the fuse will open?
I can not help on your SCCR question.
I mainly need help determining the available fault current of a transformer. Then I can determine whether or not a panel mounted receptacle impacts my SCCR. From what I am reading, I can determine the available fault current of a control transformer without knowing the customer's utility information (which I do not know). I do not like integrating this plug in power adapter with my industrial machine. I want to do it in a way that is not going to create a safety hazard. I am trying to find out all of the implications of adding a receptacle to my machine, powered from the secondary of my 3KVA control transformer.
Electrical Engineering Technology degree from an ABET accredited University (sorry, clinging to the shield of anonymity here). Course work, in brief, was basically Co-op's and preparation for the PE exam. I have just completed my first full year of full time work, so I am still officially an Engineer in Training. I am not as green as I once was, but still pretty green. I hope to take the PE exam after 3 full years of working.
I don't know what your 167% is. If this a fuse of the next higher value relative to a current rating 1.67 times the primary current to the control transformer at full load, then I expect you will experience blown fuses from time to time resulting from inrush current to the control transformer loaded or unloaded.
I cannot find the exact NEC reference (somewhere in 450.3) but I believe that if the available current on the primary is less than 9A, then I take 1.67 times the available primary current and round down to the nearest time delay fuse, this eliminates the need for secondary fusing. I always fuse the ungrounded secondary conductor, but I think that fusing the primary this way takes away the need to.
AC solenoids will burnout at nominal voltage if the plunger can not move from its open position because of some mechanical problem. The solenoid probably needs protection, especially on an automotive assembly line. It is probably less costly to be down for the time to fix the mechanical bind, than the likely longer time to replace the solenoid. Whole plants down are possibly $600,000 an hour, smaller lines possibly $1000 per hour
These are DC solenoids. I definitely want to fuse them. Using time delay fuses (class CC), what is a good approach for sizing fuses for individual actuators and solenoids that operate on DC voltage? 125% times rated load? I am worried about the actuators opening half way and getting stuck, as you described fusing them would be a way to detect and protect against this. So if the actuators do get stuck trying to open or close, the fuse will open?
I can not help on your SCCR question.
I mainly need help determining the available fault current of a transformer. Then I can determine whether or not a panel mounted receptacle impacts my SCCR. From what I am reading, I can determine the available fault current of a control transformer without knowing the customer's utility information (which I do not know). I do not like integrating this plug in power adapter with my industrial machine. I want to do it in a way that is not going to create a safety hazard. I am trying to find out all of the implications of adding a receptacle to my machine, powered from the secondary of my 3KVA control transformer.
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
many power supplies are self protected and thus do not require secondary protect. some also have primary protection.
I would suggest that a "pluggable" type power supply is generally not appropriate for any true industrial machine.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130723-0647 EDT
fifty60:
If a DC solenoid is designed for continuous energization, then it can be stuck full open with no damage for any period of time. The current drawn by a DC solenoid follows an exponential curve defined by the LR time constant of the series LR circuit. This is a great advantage of a DC solenoid. The maximum current in a DC solenoid occurs at steady state and is the applied voltage divided by the coil resistance. The disadvantage of a DC solenoid is that it lacks the initial force capability of a similar size AC solenoid. The current to a DC solenoid will not tell you the position of the plunger. Fusing a DC solenoid won't protect the solenoid, unless somehow an overvoltage is applied.
In an AC solenoid the inductance and therefore the impedance of the coil varies greatly with plunger position.
The 180 VA transformer I previously referenced has a peak inrush current of about 40 A and a full load steady state RMS current of about 1.5 A. The series thermistor I used probably reduced the peak inrush to about 10 A. Off hand I don't know if a 2.5 A slo-blow without the thermistor could tolerate the 40 A peak inrush. But 2.5 A is not going to protect the diodes in the DC power supply unless they are considerably oversized.
You need to know what is inside the DC power supply to make a judgement on whether it is suitable for the application, and what external protection is needed.
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fifty60:
If a DC solenoid is designed for continuous energization, then it can be stuck full open with no damage for any period of time. The current drawn by a DC solenoid follows an exponential curve defined by the LR time constant of the series LR circuit. This is a great advantage of a DC solenoid. The maximum current in a DC solenoid occurs at steady state and is the applied voltage divided by the coil resistance. The disadvantage of a DC solenoid is that it lacks the initial force capability of a similar size AC solenoid. The current to a DC solenoid will not tell you the position of the plunger. Fusing a DC solenoid won't protect the solenoid, unless somehow an overvoltage is applied.
In an AC solenoid the inductance and therefore the impedance of the coil varies greatly with plunger position.
The 180 VA transformer I previously referenced has a peak inrush current of about 40 A and a full load steady state RMS current of about 1.5 A. The series thermistor I used probably reduced the peak inrush to about 10 A. Off hand I don't know if a 2.5 A slo-blow without the thermistor could tolerate the 40 A peak inrush. But 2.5 A is not going to protect the diodes in the DC power supply unless they are considerably oversized.
You need to know what is inside the DC power supply to make a judgement on whether it is suitable for the application, and what external protection is needed.
.
Thanks for the information on DC actuators and Power supplies. I now have a clearer understanding of the technical side of this circuit. I would rather not use the Plug-in power adapter but finding a DC power supply that is 115VAC to 12VDC @12A that is not $400 is not going well.
mgookin
Senior Member
- Location
- Fort Myers, FL
Digikey, Mouser & Avnet have wide selections of power supplies. Good stuff and good prices. Digikey has the best parametric search but not always the best prices. Not sure if you're buying 1 or 1k pcs.
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I have a din rail mountable phoenix contact receptacle that meet UL498 and IEC 83. What do these standards really tell me about the receptacle? There is not an SCCR for the receptacle (I have requested that information) and from the conflicting results I have found for the default SCCR I am not sure if it defaults to 2KA or 10KA when not marked.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Generally, I would suggest that at least under the UL508a supplement that deals with determining the SCCR of an ICP, that what you have is a control circuit and not a power circuit, and thus is not required to have an SCCR.
When I first read the supplement that was my take on it. Later my boss determined I was wrong and she ordered that control circuits had to be considered as well. I went to a lot of work to convince her that she was wrong, and eventually she came around.
In any case, I suggest you buy the UL508a standard if you are trying to determine the SCCR of an assembly, and use the SCCR supplement found in it. It is not as simple as just working off a chart of SCCR values. Some of it is that simple though. At least that way you have a consistent methodology from a recognized source to support your SCCR conclusions.
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