On Thu, Dec 29, 2011, at 11:36 AM, Clint Washburn wrote: > I am in the process of building a power supply for my lathe and need > a big transformer for for the powersupply. My main question is given > the type of transformer I was not sure how the transformer performs > with two hot legs as opposed to one hot and one neutral. I am having > a hard time finding a refrence to explain it to me.
OK, that sheds a little light on things. I assume you are going to rectify and filter the output to make DC for your servo (or stepper) drivers. 100 to 110 volts AC when rectified and filtered will make between 140 and 155 volts DC. More at light load (since most transformers spec the output voltage at full load, it will go up unloaded), and less at full load (as the DC filter caps droop between cycles). I assume that is the DC range your drives need. Since you probably want isolation, the buck-transformer approach isn't a good idea, even if you have a neutral and thus have 120V. So you might as well get a 240 to 100V transformer. Many standard transformers are not intended to feed a rectifier load. The rectifier draws current in pulses, which cause additional heating of the transformer compared to a plain AC load. If you find something that is described as a "rectifier transformer" you are good to go, otherwise you probably need to oversize the transformer a bit. For more than you ever wanted to know (probably), see http://www.toroid.com/custom_transformers/technical_bulletin_1.htm Transformer sizing for a CNC is tricky anyway. How often are all three axes of your machine going to be running at full torque and full speed at the same time? And for how long? Only a few seconds probably. That is the peak load, but transformers have lots of mass and can handle large overloads for short periods of time. It is a lot harder to calculate the average load - it will depend on the size of the parts you are making, the nature of your g-code programs, etc. A decent rule of thumb might be to size the transformer for about 1/3 to 2/3 of the peak load. The one-third end of the scale is for lightly used machines where you need to save money and space. Two-thirds will be more robust. Sizing it for 100% of the peak load is just wasting money. -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a complex infrastructure or vast IT resources to deliver seamless, secure access to virtual desktops. With this all-in-one solution, easily deploy virtual desktops for less than the cost of PCs and save 60% on VDI infrastructure costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
