The following quick simulations I just did demonstrates this:
The first graph shows the current drawn from each winding for the aforementioned mismatched transformer with a light load and the second graph shows the same supply with a greater load. This shows that the effect if greatest when the load current is low, so although the currents are mismatched they will both be within the rating for a light load. Similarly, the mismatch is smaller when the load is greater, so if the rating of one winding is exceeded it is unlikely to be by enough to cause a problem. Also, there are a lot of other factors besides load current involved here, so the above simulation is by no means comprehensive.
In short it's extremely unlikely for the windings to be mismatched enough for either method to cause problems, so although I'd advise buying a transformer rated for half the voltage so you can put the secondarys in series, if you find one for the right price which has to be wired in parallel I wouldn't worry.
15-08-2013 #72Originally Posted by Rogue
Last edited by Jonathan; 15-08-2013 at 09:25 PM. Reason: Fixed quote formatting
Last edited by Jonathan; 15-08-2013 at 09:23 PM.
Yes it's always better to match current to motor ratings but not go higher. The only margin you want to leave is on the voltage but it's also always better if the drives are not max'd out on current IE max current setting = motor current so the drives not working flat out.!
Last edited by JAZZCNC; 15-08-2013 at 09:32 PM.
I was thinking about this from the point of view of the stepper motors (4.2A) rather than the drivers. Either of the two drivers discussed are rated higher than the stepper (up to 5.2A for the DM856, up to 8.2A for the AM882) so there is plenty of margin. My question was whether it's better to run the steppers at their max or give them a bit of a margin. If your answer still applies (which logic suggests it does) then it seems reasonable to set the drivers for a little under 4.2A.
I'd set the driver current as near as you can to the motor rating without exceeding it. You might be able to go lower, but I think it's better to ensure the machine will not stall by having a good safety margin, rather than worrying about the lifetime of the motors.
Going back to me previous point about the power supply, I just ran the simulation again but this time with both configurations. The first graph is with the windings connected in parallel on the DC side and the second graph has them connected in parallel before the rectifier:
I realise that there's not much point discussing this further, but it's interesting to note that the waveforms do look slightly better for the DC coupled version. There's still not much in it.
Last edited by Jonathan; 15-08-2013 at 10:01 PM.
AM882's are an excellent bit of kit and really are easy to use once you get around the chinese strange way of setting up the software for programing the drives. I use them and they really do make things run very very smoothly. -MichaelLife is Live it
CAD software VIACAD Pro v9 (Beta testing x64) Also Aspire v8
CAM Software Aspire v8, PhotoVCarve, CamBam
Machine: Custom built see build log: http://www.mycncuk.com/threads/3661-...Second-machine
Work with Solid Surfaces, Acrylics, Woods, Foamboard.
By suesi34e in forum Milling Machines, Builds & ConversionsReplies: 1Last Post: 17-11-2013, 10:44 PM
By badgerman in forum Routers, Spindles & ControllersReplies: 12Last Post: 15-09-2013, 08:26 PM
By range3rrr in forum Rails, Guideways & BearingsReplies: 1Last Post: 24-08-2011, 10:44 PM
By Jimmybristol in forum Items For SaleReplies: 11Last Post: 30-05-2011, 10:04 PM
By gorbo in forum Computer HardwareReplies: 5Last Post: 23-01-2011, 02:25 PM