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#21
November 24th 05, 01:04 AM
posted to sci.electronics.design,rec.crafts.metalworking,rec.radio.amateur.homebrew,sci.engr.joining.welding
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Uses for Old UPSes
Ignoramus22022 wrote:
On Wed, 23 Nov 2005 23:21:02 GMT, Bruce L Bergman wrote: On Wed, 23 Nov 2005 16:22:24 GMT, Ignoramus22022 wrote: On Wed, 23 Nov 2005 16:13:58 GMT, Bruce L Bergman wrote: On Wed, 23 Nov 2005 wrote: On Tue, 22 Nov 2005 12:55:29 -0800, "Bob Headrick" wrote: "Highland Ham" wrote: Bob , Interesting info ; can you confirm that the 18 pcs 12V battery were in fact 9 strings of 2 batts in series (each string having a fuse ) providing 24 V ? or were all the 18 batts in parallel ? Actually they were all in series, making it a bit nerve-wracking to replace a battery in the string. 216 volt battery pack??? I don't think so. No, quite possible and makes some design sense - they would not need a heavy output transformer in the unit boosting the voltage of a 36V or 48V battery string after converting it to a sine wave AC, as 216V would be right around the sine wave peak voltage of 120VAC. Just run the battery DC through two sets of power transistors to let through a reconstituted sine wave - one for the positive half of the output waveform, the other negative. And it cuts the current the transistors have to pass. Bruce, this also sounds like a simple approach to generating 3 phase out of DC. Without the noise and weight of rotary phase converters. What are your thoughts on that? Quite Plausible, but when you add the caveat of reproducing 3-Phase power the engineering just got really complicated, and more than likely rather expensive. And I'm NOT a high-powered electronics drive wonk by any means, the best I could do for fixing them is look for the obviously crispy components and swap out the blown boards - or swap the crispy parts and diodes that fail a VOM test and see if that does it. With a single phase inverter, they're just doing a push-pull on one 240V lead, relative to the center tapped neutral. Right. As you know, I recently made a DC - AC inverter myself. When you try 3-phase, there's going to be constant voltage, current and capacitance interaction between all three sets of "hot AC" switching transistors (or Triacs, or whatever). And the load's resistive, inductive and capacitive components are all going to come into play. Yep. The resulting inverter would need to be built rather robust, and be able to overcome drive issues with brute force where finesse won't do. Compared to that, RPC's are the KISS method. And RPC's aren't a bad way to go, if they are well balanced and have cooling air you can tuck them away in a closet. You are right. I am going to redo my RPC into a 17.5 HP RPC. (two motors, 10 and 7.5 HP). Right now I have a 10 HP RPC. Someone offered me a Semikron 6 IGBT drive, with which I could make a 3 phase inverter. That sort of made me interested. i Get your hands on a large, like 30kw or better, used as in "please take it out of here", three phase, online UPS from a computer room installation. As long as you can supply adequate power to the DC bus the inverter portion will happily generate your three phase power with no issues with designing and inverter or trying to synchronize three inverters or duty cycle problems. It's a DC - 3 phase AC continuous duty inverter, ready-to-go. Pete C. |
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