Chris, Yup, that's all I did. Use the line to keep the batteries charging, and when the line goes down, the battery or batteries just keep on supplying the system. Mine wasn't a sine wave though, but a modified square wave, however it worked like a charm.
I got the idea from a website, and modified it to my taste, but it really didn't cost much with all the surplus transformers available, and there is a huge number available with high power ratings. I used a bank of NPN switching transistors, and I forget what they were, but they had slightly higher ratings than a 2N3055. There was a driver circuit between them and the chip. I can't remember if Maxim, or another, made the IC, as I would have to try to find my info on the supply, because I sold it about two years after I finished it. One could try to find an older sine wave UPS, and modify it, but it would need to be a 60Hz output supply, because the transformer would be sized incorrectly, with a higher frequency rating, when dropping it down to 60 Hz. As John mentioned earlier, the el-cheapo inverters are pretty much junk, and run as high as 1 kHz, if I recall. They were made to run small TV's, etc, that don't require a fixed line frequency, since they all have hot chassis now that don't use isolation transformers. Best, Will *********** REPLY SEPARATOR *********** On 6/25/2011 at 11:55 AM Chris Albertson wrote: >> The reason for using 12 Vdc, is that you can pick them up, and 24 Vac CT >> transformer, on the cheap > >That's a good point. So use two of them. One to power a high >current amp that produces a 12V AC signal from a high precision 60Hz >input. Then the other to convert the 12V to 120V. This avoids the >need for a high voltage DC power supply. Likely cuts the total cost >in half at least. So just use use 12V supply to the amp and then a >cheap 12V transformer connected "backwards" to step up to the desired >voltage. > >The second advantage of this design is that you can connect a lead >acid gell cell battery in parallel to the 12V DC supply and if the AC >fails the battery will power the amp for a while. This way there is >no switching so the 60Hz wave remains continuously even if AC mains >fails. > >This is something most UPS don't do but for this application you don't >want the 60Hz sine wave to be broken. > >As long as the load is only a few milliamps of AC this should not be >hard to do. > > >-- > >Chris Albertson >Redondo Beach, California > >__________ Information from ESET Smart Security, version of virus signature database 5851 (20110206) __________ > >The message was checked by ESET Smart Security. > >http://www.eset.com _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
