Jon: Yes, I did misinterpret what you were saying-it sounded to me like the specs that were quoted from the MPJA catalog were saying that you couldn't use the full current rating of the transformer, and that you were agreeing with that. Or maybe you are thinking that the transformer is rated at 10A only IF you use the center tap for building a power supply?
Sorry about the misunderstanding. I still want to see that cartalog page; I swear it sounds like the numbers quoted awere related to SIZING of the cap or coil, and NOT the actual output current capability. I may have to dig up my MPJA catalog...... Andy Wander Verrex Corporation -----Original Message----- From: Jon Elson [mailto:[EMAIL PROTECTED] Sent: Monday, October 25, 2004 1:17 PM To: [EMAIL PROTECTED] Subject: Re: [CAD_CAM_EDM_DRO] current rating of transformers Andy Wander wrote: >Yeah, but.... > >I still say that the thing that limits the secondary current is the wire >gauge used for the secondary winding. > >I don't think many transformers are built using wire that's a lot heavier >than needing fro rated output current. Therefore, dropping the primary >voltage(thereby dropping the secondary voltage) doesn't mean you can now >pump more current through it to "get back" up to the VA rating. > > Yes, that is absolutely true. You may have misinterpreted what I was saying in an earlier message. On transformers with 2 seperate secondary windings, you can parallel the winding for double current, or put it in series for double voltage. But, on a transformer with a center-tapped winding, you have a similar option. Take an example of a transformer with a 17 VAC winding with a center tap. If you connect a full-wave bridge rectifier to the end terminals, and don't connect the center tap, you will get 24 VDC into a capacitor-input filter. (17 * 1.414) Let's say this transformer is rated for 10 A in this configuration. If you connect the center tap to the minus side of the cap, and connect two diodes with the cathode to the + term of the cap and the anodes to the transformer winding ends, you will get 12 V DC at 18-20 A DC. That is because each half of the transformer winding now is only required to conduct for half of the power line cycle. With the full-wave bridge, the full winding carries its full current EVERY half cycle. Wire size is a major factor in secondary current rating. But, the depth of the winding affects the heat removal from the most interior parts, where the "hot spot" invariably is. Insulation class and the fill of transformer varnish that helps conduct heat away are all part of the equation. Also, the design of the iron to reduce eddy lossed in both the iron and the copper are significant. Jon Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
