On Tuesday 20 November 2012 14:15:44 Viesturs Lācis did opine: > 2012/11/20 andy pugh <bodge...@gmail.com>: > > On 20 November 2012 11:23, <kqt4a...@gmail.com> wrote: > >> I see a great many lower priced switching supplies > > > > Possibly because a motor power supply contains too few components to > > bother selling as a unit. > > A transformer, rectifier and capacitor is all that is needed. And the > > transformer may be optional. > > For my last 3 machines I used ~1kW transformer with 220VAC input and > 20VAC output, which gives ~28 VDC after rectification. My current > build has 800W transformer with 20VAC output, that machine has 2 7i39 > drives, 10A for each motor is 40A total. That is what transformer > rated for, but I am now curious to find out, if capacitors, when they > will be charged, will not actually draw a lot more current. What do > others think about it? How can I calculate that? > Back of the envelope stuff would tell me the caps, delivering a 10 amp load, would be getting 100 amps during the top 10% of the voltage waveform. This is why the emphasis on power factor correction in the newer and better designed switchers. That load only on the waveform peaks puts a heck of a hit on the supply lines power factor, which is by default designed to supply a purely resistive load.
> BTW those are custom-made for me torroidal transformers by a company > in Poland. The 1kW transformer cost me 200EUR, including shipping, the > 800W was 150EUR. I managed to burn down 50A rectifier bridge (despite > the heatsink), but I was not able to feel by hand that transformer had > warmed even a little. They work really great. > If anyone ever needs, let me know, I can pass their contacts. I might be interested in a 34volt or so, 12 amp rated out, 127 in for my lathe, the surplus E core laminated in there now will do an excellent job of keeping ones coffee too hot to drink. Toroid would be nice, but locally such a beast is priced accordingly, custom wound, from the price, by hand by the president of the company. A center tap would be nice, to tap off some fan power from. Unforch, in a box falling off the UPS truck here, shipping would be half of it from your 'neck of the woods'. :( But in the event I do stumble over something like that at a price I can afford, I will probably burn up the card machines head swiping it to get 2 or 3 of them. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! In buying horses and taking a wife shut your eyes tight and commend yourself to God. ------------------------------------------------------------------------------ Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
