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Re: DC-> AC Power Switching

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx> To: <tesla@xxxxxxxxxx> Sent: Tuesday, March 29, 2005 8:06 PM Subject: DC-> AC Power Switching

> Original poster: Davetracer@xxxxxxx > > Hi, ><SNIP> > > > Inverters are expensive and the transformers and sheer iron are > terribly expensive. Again, "cheap tech". He came up with the idea of > patterning a sine wave, from 0 to 120 volts and on down to 0, by connecting > an increasing number of batteries in series with medium speed, computer > driven, semiconductor switches (probably transistors). I mean, at 60 times > per sec, I don't think relays are going to keep up, but probably someone > will mention how wrong I am (grin). > > Thus at (+)0, nothing is connected; at the first point in the sine > wave, as it approaches +12, the first battery connects, as it approaches > +24, the second battery connects, and so forth, up to 120V, then back > down. Yes, I know a true AC sine wave goes up past 120V, but this is more > of a "does this approach stand a chance" versus "nailing it on the dot" > question. We'll definitely be outputting sinewave data much faster than Mr. > Nyquist requires; 60 Hz is not a big challenge to even a slow 8 bit > microprocessor. <SNIP>

That can work, BUT think about the amp-hour drain for each battery.  The
first battery will be discharging almost continuously, and the last one will
discharge for just a brief moment near the top of the stepped sinewave.
Thus the first battery will "poop out" much sooner than the others, and you
will not get nearly the total amp-hours out that the batteries are capable
of producing.

I think you should use a converter instead.  I would think you can scrounge
some DC-AC converters, such as Uninterruptable Power Supplies that were
junked because the batteries went bad.

You can get a rough idea of how efficient a lead-acid battery is by
measuring it's temperature rise as you charge or discharge it.  Then use a
small direct contact heater to cause the same temperature rise in the
battery and measure the energy consumed by the heater.

Sounds like a winning project!

--Steve Y.