14 Replies Latest reply on Aug 18, 2011 1:49 AM by electrical.engineer

    VeSys simulation shortcomings

    ian.cox

      Hello,

      I have noticed a few shortcomings in the VeSys electrical simulation function, in order of importance they are:

       

      Inability to simulate a latching circuit

      Inability to calculate circuit characteristics where more than one battery is present

       

      Would it be possible to evolve the simulation application so that when a simulation is live it could be "nudged" through a series of states?  An example would be a latching relay where step 1 would be for the trigger event to occur, step 2 relay closing, step 3 trigger removed and so-on...

       

      A similar process could be used with the multiple-battery system problem...

       

      Perhaps a state-machine function in a similar manner to "named circuit states" could be used?

       

      This is a refinement that I think would be useful as it is only an extension of the ability to evaluate the suitability of an electrical system.

       

      Matt Roberts

        • 1. Re: VeSys simulation shortcomings
          Joel_Pointon

          Hi Ian,

           

          I agree that a latching relay would be useful.

           

          I can understand you want to visually see that multiple batteries are placed in series but in practise one 24V battery will electrically be the same as two 12V in series, the only problem this would cause is if you wanted to tap off some 12V feeds from inbetween the two batteries.  What most customers do in this case is graphically show two 12V batteries but only have one 24V battery electrically connected.  I'm not sure how hard this would be to change in the simulation engine but the issue that prevents batteries being placed in series is that each battery requires an earth on each negative terminal and as VeSys 2.0 is now available it is unlikley there will be any changes to simulation in VeSys Classic.

           

          Unfortunately your only option is to use the switch states as you've described and manually nudge them through the states.

          • 2. Re: VeSys simulation shortcomings
            Nigel

            There is some good news here. VeSys 2.0 includes enhanced simulation capabilities, specifically providing state-machine driven simulation models (which you can now create yourself) and support for multiple batteries (it is a configuration option, but once turned on, it's on).

             

            Regads,

             

            Nigel

            • 3. Re: VeSys simulation shortcomings
              electrical.engineer

              Further to the original question on this subject I have encountered another  problem as follows: If there is a motor rated at 12 amps and the fuse protecting it is only rated at 10 Amps should the fuse blow?  Logically I don't think it should because VeSys doesn't appear to be able to simulate inrush current or other transients.  This worries me as I am basing documents to be submitted to a notified body on data validated by VeSys.

               

              I wondered whether there was more subtlety involved regarding volt drops which I have missed.

               

              Improved functionality on VeSys 2 does not really address some of the shortcomings with "original" VeSys which I find as there appear to be errors which have not been rectified by subsequent service packs.

              • 4. Re: VeSys simulation shortcomings
                Muhammad_Askar

                Hi electrical.engineer

                 

                I had recently answered a similar question on an email thread, and I am just wondering if that is the one you're referring to. VeSys 2.0 offers logical and numeric simulation. The numeric simulation is done in DC mode which means things such as in rush current are not modeled. A 12 Amp rating for a motor would then mean that its DC current can be 12 Amp at maximum, there's no notion of time.

                 

                This means that if you had a model at which the motor fails at 12 Amps of current, and a fuse which fails at 10, since both are working in DC notions, then te fuse would blow before the motor reaches its maximum. Does that make sense to you?

                 

                On the other hand, Capital, which is VeSys 2.0's sister product, does offer transient simulation in a number of methods/formats which I can point you to in case that is what your question is about.

                 

                Please let me know if this answer does not satisfy your query.

                 

                Thanks

                Muhammad

                • 5. Re: VeSys simulation shortcomings
                  Joel_Pointon

                  You are correct that the fuse would not blow, assuming the wire length to the motor is sufficiently long.  This is a replication of what should happen in real life unless as you mentioned the inrush was enough to cause the fuse to blow.

                   

                  Assuming you are referring to the modelling of inrush currents as one of the short comings of VeSys Classic it might help to explain why it works the way it does.  VeSys Classic (and its simulation) was designed to be as quick and easy to use as possible, modelling of transients would not only have had a large impact on the simulation performance but on the level of user data required (much more complex than defining the voltage and current) and useability to the point where it may have been unuseable.  That said there were still a few nice features that could have been added to provide more feedback which wouldn't have had any negative impact.

                   

                  VeSys is a tool to aid engineers in the design process and so is not a complete replacement for real world tests.  To illustrate this the major Automotive companies perform vehicle crash analysis in the 3D environment but they will still perform real life crash tests, the analysis tools they have used helped them optimse their designs.

                   

                  I have tried recreating the scenario you described and it ended up as quite an extreme model, I had 33 metres of 2.0mm wire in order for the fuse not to blow.  Unfortunately if you have extreme cases like this it still relies on the judgement of the engineer to determine what should/shouln't be done.  If you could supply a copy of your particular design or a little more detail I'll take a look at it.

                  • 6. Re: VeSys simulation shortcomings
                    Joel_Pointon

                    Hi Muhammad,

                     

                    Excessive voltage drop in the wires would mean that the 12A Motor could draw a much lower current i.e. 9A, this would mean that a 10A fuse should never blow.  If the wires were shorter or the CSA increased then the motor would draw more current.

                     

                    Regards

                    Joel

                    • 7. Re: VeSys simulation shortcomings
                      Muhammad_Askar

                      Yes, sorry, my assumption was that the circuit was created in such a way to allow 10 Amps or more to flow through both the fuse and the motor, then the the fuse would fail (at 10 Amps) before the motor does.

                      But you're right, if the wires are long enough in the circuit they can significantly drop the voltage down and hence current in motor and fuse would be less than blowing either.

                       

                      Thanks

                      Muhammad

                      • 8. Re: VeSys simulation shortcomings
                        electrical.engineer

                        It is probably easier if I log peculiarities of VeSys simulation as I find them.  I understand that it is intended as a design guide and that circuits should be validated on a prototype installation but I have very little confidence in the design guide when I find problems with things such as bus bars and very small (milli) Volt drops resulting in whole volts "going missing"...a specific example here is:

                         

                        Bus bar - I thought that these had "infinite" current capacity and hence zero Volt drop so why do I have a bus bar which is rated at 50 Amps in the schematic?

                        I tried removing the bus bar and putting a new one in but the fault remains.

                         

                         

                        As far as the cumulative millivolt drop is concerned I will follow the circuit and record each volt drop as I find it but I am fairly certain that there are not four volt's worth of millivolt losses.

                        • 9. Re: VeSys simulation shortcomings
                          Joel_Pointon

                          As in the real world the Busbar the Busbars in VeSys have some resistance along with a current rating (default of 50A), if you want it to be higher than this you can create a Busbar in the component database as a wire.  Its a little bit of a workaround but you then use that wires in your schematic and convert it to a Busbar, it should retain the rating from the "Wire" that was previously defined.  If you want almost zero resistance connectivity you should use a Virtual Wire, I think its not a true zero value because the simulation models don't like zero values (it ends up being 0.00001 ohms or something so it shouldn't have any impact on your simulation.)

                          • 10. Re: VeSys simulation shortcomings
                            Joel_Pointon

                            Sorry I should have also commented that 4 volts does seem very excessive and shouldn't be caused by Busbars unless you had hundreds of them involved.

                            • 11. Re: VeSys simulation shortcomings
                              Joel_Pointon

                              If possible can you either post a copy of the circuit/schematic or e-mail it me (joel.pointon@eds-design.co.uk) and I'll check out why you have a 4V drop.

                              • 12. Re: VeSys simulation shortcomings
                                electrical.engineer

                                thank you for all the responses to this problem, I believe that today I have unintentionally identified the cause of the problems I have been experiencing:

                                 

                                Any wires used in the schematic MUST be present in the components database and with exactly the same parameters.

                                 

                                Because a lot of our product is based upon legacy design the VeSys loop of schematic - harness - import DSI was not followed so there was no validation that wires are in the database hence the discrepancies in either CSA, material or wire colour leading to incorrect voltage drops.

                                 

                                No alerts are given by the VeSys schematic or simulation unless you check each wire for unusual voltage drops.

                                • 13. Re: VeSys simulation shortcomings
                                  Joel_Pointon

                                  If you go to the "Electrical" tab from the Design Tools -> Design Options menu and select "Check and Update Wire Ratings..." VeSys will report any wires in the schematic that aren't in the database, it will also update the resistance/current ratings of all wires in the Schematic.

                                   

                                  As you have pointed out for simulation to work correctly you need to be selecting wires that are in the database as this is the only place you can define the resistance and current ratings for the wires.

                                   

                                  Once you have placed a wire into the schematic its properties are then remembered unless you edit the wire or click "Check and Update Wire Ratings...", there are two reasons for this:

                                   

                                  1. To enable users to e-mail the schematic to others without having to send the database.

                                  2. Guarantee's that any simulation performed today will be the same in 5 years time even if someone has updated the database.

                                   

                                  Hope this helps.

                                  • 14. Re: VeSys simulation shortcomings
                                    electrical.engineer

                                    Hi Joel,

                                    thank you for the tip, I did wonder what that "check and update" button did, once I tried it and expected it to change all the wire sizes on the schematic to suit...no joy!

                                     

                                    As an addition to my previous post I also found a problem in custom component logic links where I was getting Voltage drops of the order of 1.9 Volts but I soon resolved this.  Happily the simulation ties up with what we measured on the installation in the yacht.

                                     

                                    thanks again...

                                     

                                    Matt